Search

Genomic resources have yielded unprecedented insights into ecological and evolutionary processes, not to mention their importance in economic and conservation management of specific organisms. However, the field of macroalgal genomics is hampered by difficulties in the isolation of suitable DNA. Even when DNA that appears high quality by standard metrics has been isolated, such samples may not perform well during the sequencing process. We here have compared Oxford Nanopore long‐read sequencing results for three species of macroalgae to those of nonmacroalgal species and determined that when using macroalgal samples, sequencing activity declined rapidly, resulting in reduced sequencing yield. Chemical analysis of macroalgal DNA that would be considered suitable for sequencing revealed that DNA derived from dried macroalgae was enriched for polyphenol–DNA adducts (DNA with large polyphenols chemically attached to it), which may have led to sequencing inhibition. Of note, we observed the strongest evidence of sequencing inhibition and reduced sequence output when using samples dried using silica gel—suggesting that such storage approaches may not be appropriate for samples destined for Oxford Nanopore sequencing. Our findings have wide‐ranging implications for the generation of genomic resources from macroalgae and suggest a need to develop new storage methods that are more amenable to Oxford Nanopore sequencing or to use fresh flash‐frozen tissue wherever possible for genome sequencing. [ABSTRACT FROM AUTHOR]

Macroalgae influence local and global biogeochemical cycles through their production of dissolved organic carbon (DOC). Yet, data remain scarce and annualized estimates are typically based on high growth periods without considering seasonal variability. Although the mechanisms of active exudation and passive leakage need clarifying, ecophysiological stress is known to enhance DOC release. Therefore, DOC leakage from seasonally senescent macroalgae may be overlooked. This study focuses on the annual kelp Saccharina japonica var. religiosa (class Phaeophyceae) from Oshoro Bay, Hokkaido, Japan. Three years (2020–2022) of seasonal data were collected and analyzed, with least squares mean DOC release rates established for kelp (n = 88) across 16 incubation experiments (t ≥ 4 d, DOC samples ≥1 · d−1) under different photosynthetically active radiation (PAR) treatments (200, 400, 1200, or 1500 μmol photons · m−2 · s−1). Differences in PAR, dry weight biomass (g DW), sea surface temperature, or salinity could not explain DOC release‐rate variability, which was high between individual kelp. Instead, there were significant intra‐annual differences, with mean DOC release rates (mg C · g−1 DW · d−1 ± standard error between n kelp) higher during the autumn "late decay" period (0.71 ± 0.10, n = 27) compared to the winter "early growth" period (0.14 ± 0.025, n = 10) and summer "early decay" period (0.25 ± 0.050, n = 24). This relationship between seasonal senescence and macroalgal DOC release is further evidence that long‐term, place‐based studies of DOC dynamics are essential and that global extrapolations are premature. [ABSTRACT FROM AUTHOR]

Seaweeds play a strong ecological and economical role along the world's coastlines, where they support industries (e.g., aquaculture, bioproducts) and essential ecosystem services (e.g., biodiversity, fisheries, carbon capture). Evidence from wild and cultured seaweeds suggests that microorganisms play crucial roles in their health and functioning, prompting the need for considering seaweeds and their microbiome as a coherent entity or "holobiont." Here we show that the number of studies investigating seaweed hosts and their microbiome have increased in the last two decades. This likely reflects the increase in the appreciation of the importance of microbiomes for eukaryotic hosts, improved molecular approaches used to characterize their interactions, and increasing interest in commercial use of seaweeds. However, although increasing, most studies of seaweed holobionts have focused on (i) a few seaweed species of ecological or commercial significance, (ii) interactions involving only bacteria, and (iii) descriptive rather than experimental approaches. The relatively few experimental studies have mostly focused on manipulating abiotic factors to examine responses of seaweeds and their microbiome. Of the few studies that directly manipulated microorganisms to investigate their effects on seaweeds, most were done in laboratory or aquaria. We emphasize the need to move beyond the descriptions of patterns to experimental approaches for understanding causation and mechanisms. We argue that such experimental approaches are necessary for a better understanding of seaweed holobionts, for management actions for wild and cultivated seaweeds, and to better integrate studies of seaweed holobionts with the broader fields of seaweed ecology and biology, which are strongly experimental. [ABSTRACT FROM AUTHOR]

Environmental changes associated with rapid climate change in the Arctic, such as the increased rates of sedimentation from climatic or anthropogenic sources, can enhance the impact of abiotic stressors on coastal ecosystems. High sedimentation rates can be detrimental to nearshore kelp abundance and distribution, possibly due to increased mortality at the spore settlement stage. Spore settlement and viability of the Arctic kelp Laminaria solidungula were examined through a series of lab‐based sedimentation experiments. Spores were exposed to increasing sediment loads in three experimental designs simulating different sedimentation scenarios: sediment deposition above settled spores, settlement of spores on sediment‐covered substrate, and simultaneous suspension of spores and sediments during settlement. Spore settlement was recorded upon completion of each experiment, and gametophyte abundance was assessed following a growth period with sediments removed to examine short‐term spore viability via a gametophyte‐to‐settled‐spore ratio. In all three types of sediment exposure, the addition of sediments caused a 30%–40% reduction in spore settlement relative to a no‐sediment control. Spore settlement decreased significantly between the low and high sediment treatments when spores were settled onto sediment‐covered substrates. In all experiments, increasing amounts of sediment had no significant effect on spore viability, indicating that spores that had settled under different short‐term sediment conditions were viable. Our results indicate that depending on spore‐sediment interaction type, higher rates of sedimentation resulting from increased sediment loading could affect L. solidungula spore settlement success with potential impacts on the long‐term persistence of a diverse and productive benthic habitat. [ABSTRACT FROM AUTHOR]

Kelp forests are among the most valuable ecosystems on Earth, but they are increasingly being degraded and lost due to a range of human‐related stressors, leading to recent calls for their improved management and conservation. One of the primary tools to conserve marine species and biodiversity is the establishment of marine protected areas (MPAs). International commitments to protect 30% of the world's ecosystems are gaining momentum, offering a promising avenue to secure kelp forests into the Anthropocene. However, a clear understanding of the efficacy of MPAs for conserving kelp forests in a changing ocean is lacking. In this perspective, we question whether strengthened global protection will create meaningful conservation outcomes for kelp forests. We explore the benefits of MPAs for kelp conservation under a suite of different stressors, focusing on empirical evidence from protected kelp forests. We show that MPAs can be effective against some drivers of kelp loss (e.g., overgrazing, kelp harvesting), particularly when they are maintained in the long‐term and enforced as no‐take areas. There is also some evidence that MPAs can reduce impacts of climate change through building resilience in multi‐stressor situations. However, MPAs also often fail to provide protection against ocean warming, marine heatwaves, coastal darkening, and pollution, which have emerged as dominant drivers of kelp forest loss globally. Although well‐enforced MPAs should remain an important tool to protect kelp forests, successful kelp conservation will require implementing an additional suite of management solutions that target these accelerating threats. [ABSTRACT FROM AUTHOR]

Brown algal male gametes show chemotaxis to the sex pheromone that is released from female gametes. The chemotactic behavior of the male gametes is controlled by the changes in the beating of two flagella known as the anterior and posterior flagellum. Our previous study using Mutimo cylindricus showed that the sex pheromone induced an increment in both the deflection angle of the anterior flagellum and sustained unilateral bend of the posterior flagellum, but the mechanisms regulating these two flagellar waveforms were not fully revealed. In this study, we analyzed the changes in swimming path and flagellar waveforms with a high‐speed recording system under different calcium conditions. The extracellular Ca2+ concentration at 10−3 M caused an increment in the deflection angle of the anterior flagellum only when ionomycin was absent. No sustained unilateral bend of the posterior flagellum was induced either in the absence or presence of ionomycin in extracellular Ca2+ concentrations below 10−2 M. Real‐time Ca2+ imaging revealed that there is a spot near the basal part of anterior flagellum showing higher Ca2+ than in the other parts of the cell. The intensity of the spot slightly decreased when male gametes were treated with the sex pheromone. These results suggest that Ca2+‐dependent changes in the anterior and posterior flagellum are regulated by distinct mechanisms and that the increase in the anterior flagellar deflection angle and sustained unilateral bend of the posterior flagellum may not be primarily induced by the Ca2+ concentration. [ABSTRACT FROM AUTHOR]

Species interactions can influence key ecological processes that support community assembly and composition. For example, coralline algae encompass extensive diversity and may play a major role in regime shifts from kelp forests to urchin‐dominated barrens through their role in inducing invertebrate larval metamorphosis and influencing kelp spore settlement. In a series of laboratory experiments, we tested the hypothesis that different coralline communities facilitate the maintenance of either ecosystem state by either promoting or inhibiting early recruitment of kelps or urchins. Coralline algae significantly increased red urchin metamorphosis compared with a control, while they had varying effects on kelp settlement. Urchin metamorphosis and density of juvenile canopy kelps did not differ significantly across coralline species abundant in both kelp forests and urchin barrens, suggesting that recruitment of urchin and canopy kelps does not depend on specific corallines. Non‐calcified fleshy red algal crusts promoted the highest mean urchin metamorphosis percentage and showed some of the lowest canopy kelp settlement. In contrast, settlement of one subcanopy kelp species was reduced on crustose corallines, but elevated on articulated corallines, suggesting that articulated corallines, typically absent in urchin barrens, may need to recover before this subcanopy kelp could return. Coralline species differed in surface bacterial microbiome composition; however, urchin metamorphosis was not significantly different when microbiomes were removed with antibiotics. Our results clarify the role played by coralline algal species in kelp forest community assembly and could have important implications for kelp forest recovery. [ABSTRACT FROM AUTHOR]

Culturing kelps for commercial, conservation, and scientific purposes is becoming increasingly widespread. However, kelp aquaculture methods are typically designed for ocean‐based farms, and these methods may not be applicable for smaller scale cultivation efforts common in research and restoration. Growing kelps in closed, recirculating culture systems may address many of these constraints, yet closed system approaches have remained largely undescribed. Extensive declines of the bull kelp (Nereocystis luetkeana), an ecologically important canopy species in the Northeast Pacific, have received widespread attention and prompted numerous research and conservation initiatives. Here, we detail two approaches for cultivating N. luetkeana sporophytes in closed recirculating systems. Nereocystis luetkeana were reared as attached thalli in custom seaweed growth flumes and also free‐floating in tumble culture tanks. Careful control of stocking density, water motion, aeration, and nutrient levels allowed for rapid growth and normal morphogenesis of laboratory‐grown kelp. Culture systems reached up to 3 kg · m−3, and individual thalli attained lengths of up to 6 m before the trials were terminated. Our results demonstrate the potential of recirculating, closed culture systems to overcome limitations associated with traditional culture methods. Recirculating systems enable the precise control of culture conditions, improving biosecurity and facilitating cultivar development and other research. Kelps can be grown away from the ocean or outside their native ranges, and seasonal or annual species can be produced year‐round without seasonal constraints. [ABSTRACT FROM AUTHOR]

Kelp are important primary producers that are colonized by diverse microbes that can have both positive and negative effects on their hosts. The kelp microbiome could support the burgeoning kelp cultivation sector by improving host growth, stress tolerance, and resistance to disease. Fundamental questions about the cultivated kelp microbiome still need to be addressed before microbiome‐based approaches can be developed. A critical knowledge gap is how cultivated kelp microbiomes change as hosts grow, particularly following outplanting to sites that vary in abiotic conditions and microbial source pools. In this study we assessed if microbes that colonize kelp in the nursery stage persist after outplanting. We characterized microbiome succession over time on two species of kelp, Alaria marginata and Saccharina latissima, outplanted to open ocean cultivation sites in multiple geographic locations. We tested for host‐species specificity of the microbiome and the effect of different abiotic conditions and microbial source pools on kelp microbiome stability during the cultivation process. We found the microbiome of kelp in the nursery is distinct from that of outplanted kelp. Few bacteria persisted on kelp following outplanting. Instead, we identified significant microbiome differences correlated with host species and microbial source pools at each cultivation site. Microbiome variation related to sampling month also indicates that seasonality in host and/or abiotic factors may influence temporal succession and microbiome turnover in cultivated kelps. This study provides a baseline understanding of microbiome dynamics during kelp cultivation and highlights research needs for applying microbiome manipulation to kelp cultivation. [ABSTRACT FROM AUTHOR]

Foundation seaweed species are experiencing widespread declines and localized extinctions due to increased instability of sea surface temperature. Characterizing temperature thresholds are useful for predicting patterns of change and identifying species most vulnerable to extremes. Existing methods for characterizing seaweed thermal tolerance produce diverse metrics and are often time‐consuming, making comparisons between species and techniques difficult, hindering insight into global patterns of change. Using three kelp species, we adapted a high‐throughput method – previously used in terrestrial plant thermal biology – for use on kelps. This method employs temperature‐dependent fluorescence (T–F0) curves under heating or cooling regimes to determine the critical temperature (Tcrit) of photosystem II (PSII), i.e., the breakpoint between slow and fast rise fluorescence response to changing temperature, enabling rapid assays of photosynthetic thermal tolerance using a standardized metric. This method enables characterization of Tcrit for up to 48 samples per two‐hour assay, demonstrating the capacity of T–F0 curves for high‐throughput assays of thermal tolerance. Temperature‐dependent fluorescence curves and their derived metric, Tcrit, may offer a timely and powerful new method for the field of phycology, enabling characterization and comparison of photosynthetic thermal tolerance of seaweeds across many populations, species, and biomes. [ABSTRACT FROM AUTHOR]

Coral reefs are shifting from coral to algal‐dominated ecosystems worldwide. Recently, Turbinaria ornata, a marine alga native to coral reefs of the South Pacific, has spread in both range and habitat usage. Given dense stands of T. ornata can function as an alternative stable state on coral reefs, it is imperative to understand the factors that underlie its success. We tested the hypothesis that T. ornata demonstrates ontogenetic variation in allocation to anti‐herbivore defense, specifically that blade toughness varied nonlinearly with thallus size. We quantified the relationship between T. ornata blade toughness and thallus size for individual thalli within algal stands (N = 345) on seven fringing reefs along the north shore of Moorea, French Polynesia. We found that blade toughness was greatest at intermediate sizes that typically form canopies, with overall reduced toughness in both smaller individuals that refuge within the understory and older reproductive individuals that ultimately detach and form floating rafts. We posit this variation in blade toughness reduces herbivory on the thalli that are most exposed to herbivores and may facilitate reproduction in dispersing stages, both of which may aid the proliferation of T. ornata. [ABSTRACT FROM AUTHOR]

Host‐related microbiota are critically important for the adaptation/acclimation of hosts to changing environments, but how environmental factors and host characteristics shape the microbial communities remains largely unknown. We investigated the effects of temperature on habitat‐forming macroalgae and their associated bacterial communities. Three Sargassum species (S. horneri, S. fusiforme, and S. thunbergii) and seawater samples were sampled in Gouqi Island, China, and these macroalgal samples were incubated at different temperatures (10, 20, and 27°C) for 7 d. Bacterial communities were identified from the 16S rRNA gene V3–V4 regions. The algae‐associated bacterial communities of the field samples were significantly different from seawater, implying host specificity. During laboratory incubation, decreased physiological status (photosynthetic rate and oxidative stress response) was detected for all the species at 10°C, especially with regard to S. horneri and S. fusiforme. For each host, associated bacterial communities at 20 and 27°C clustered closely, and these were separated from samples at 10°C based on constrained PCoA analyses. Permutational multivariate analysis of variance revealed that algae‐associated bacterial communities were more affected by host species (23.3%) than by temperature (2.48%) during laboratory incubation. The changes in bacterial community composition may be influenced by algae metabolites, which should be tested in a future study. These results further contribute to our understanding of algal microbiome changes in response to environmental changes. [ABSTRACT FROM AUTHOR]

Macroalgae, particularly commercially grown seaweed, substantially contribute to CO2 removal and carbon storage. However, knowledge regarding the CO2 concentrating mechanism (CCM) of macroalgae is limited. Carbonic anhydrase (CA), a key component of the biophysical CCM, plays important roles in many physiological reactions in various organisms. Few characteristics of CA in Neopyropia yezoensis are known, particularly its intracellular location and responses to different concentrations of Ci. We identified, amplified, and characterized 11 putative genes encoding N. yezoensis CA. The predicted corresponding proteins clustered into three subfamilies: α‐, β‐, and γ‐type. The intracellular localization of seven CA isoforms—one in the chloroplasts, three in the cytoplasm, and three in the mitochondria—was elucidated with fusion proteins. Higher NyCA expression, particularly of certain chloroplastic, cytosolic, and mitochondrial CAs, is observed more often during the foliose stage, thus suggesting that CAs play important roles in development in N. yezoensis. [ABSTRACT FROM AUTHOR]

Nereocystis luetkeana is a large, canopy‐forming kelp that is commonly found in nearshore waters between Alaska and California. Despite regularly reaching lengths in excess of 30 m, this alga demonstrates a remarkable ability to endure hydrodynamically stressful environments without being dislodged by waves or currents. While morphological aspects of this kelp, including its long flexible stipe, have been shown to reduce drag, blade clustering has never been directly tested. In this study, we examined how the distinctive multi‐bladed morphology of Nereocystis thalli limits drag in flow. We measured drag on whole kelps in a large recirculating flume and quantified how drag was affected by serial removal of blades. We then compared measured drag with predictions of "additive drag", which we defined as the sum of the drag that each blade experiences in isolation. We found that, on average, intact thalli experience only 37% of the predicted additive drag when subjected to a flow rate of 0.40–0.50 m · s−1. Our results indicate that the subdivision of the photosynthetic area into multiple blades has a drag‐reducing effect on Nereocystis thalli. We found drag increases less than proportionally with the cumulative area, meaning the contribution of individual blades to overall drag decreases with increasing blade number. That is, as thalli develop, each additional blade incurs a reduced hydrodynamic cost, perhaps lending insight into how thalli can grow so large. [ABSTRACT FROM AUTHOR]

The role of marine primary producers in capturing atmospheric CO2 has received increased attention in the global mission to mitigate climate change. Yet, our understanding of carbon sequestration performed by macroalgae has been limited to a relatively small number of studies that have estimated the ultimate fate of macroalgal‐derived carbon. This systematic review was conducted to provide a timely synthesis of the methods used to determine the fate of macroalgal carbon in this rapidly expanding research area. It also aimed to provide suggestions for more effective future research. We found that the most common methods to estimate the fate of macroalgal carbon can be categorized into groups based on those that quantify: (i) export of macroalgal carbon to other environments—known as horizontal transport; (ii) sequestration of macroalgal carbon into deep‐sea sediments—known as vertical transport; (iii) burial of macroalgal carbon directly beneath a benthic community; (iv) the loss of macroalgal carbon as particulate carbon or dissolved carbon to the water column; (v) the loss of macroalgal carbon to primary consumers; and finally (vi) those studies that combined multiple methods in one location. Based on this review, several recommendations for future research were formulated, which require the combination of multiple methods in a whole system analysis approach. [ABSTRACT FROM AUTHOR]

The UN Decade of Ecosystem Restoration is a response to the urgent need to substantially accelerate and upscale ecological restoration to secure Earth's sustainable future. Globally, restoration commitments have focused overwhelmingly on terrestrial forests. In contrast, despite a strong value proposition, efforts to restore seaweed forests lag far behind other major ecosystems and continue to be dominated by small‐scale, short‐term academic experiments. However, seaweed forest restoration can match the scale of damage and threat if moved from academia into the hands of community groups, industry, and restoration practitioners. Connecting two rapidly growing sectors in the Blue Economy—seaweed cultivation and the restoration industry—can transform marine forest restoration into a commercial‐scale enterprise that can make a significant contribution to global restoration efforts. [ABSTRACT FROM AUTHOR]

Marine heatwaves (MHWs), discrete periods of extreme warm water temperatures superimposed onto persistent ocean warming, have increased in frequency and significantly disrupted marine ecosystems. While field observations on the ecological consequences of MHWs are growing, a mechanistic understanding of their direct effects is rare. We conducted an outdoor tank experiment testing how different thermal stressor profiles impacted the ecophysiological performance of three dominant forest‐forming seaweeds. Four thermal scenarios were tested: contemporary summer temperature (22°C), low persistent warming (24°C), a discrete MHW (22–27°C), and temperature variability followed by a MHW (22–24°C, 22–27°C). The physiological performance of seaweeds was strongly related to thermal profile and varied among species, with the highest temperature not always having the strongest effect. MHWs were highly detrimental for the fucoid Phyllospora comosa, whereas the laminarian kelp Ecklonia radiata showed sensitivity to extended thermal stress and demonstrated a cumulative temperature threshold. The fucoid Sargassum linearifolium showed resilience, albeit with signs of decline with bleached and degraded fronds, under all conditions, with stronger decline under stable control and warming conditions. The varying responses of these three co‐occurring forest‐forming seaweeds under different temperature scenarios suggests that the impact of ocean warming on near shore ecosystems may be complex and will depend on the specific thermal profile of rising water temperatures relative to the vulnerability of different species. [ABSTRACT FROM AUTHOR]

Genera and species of the tribes Rhipileae and Rhipiliopsideae are abundant in most coral reef ecosystems worldwide. However, the group has been largely overlooked, and very little genetic data is available to accurately assess its diversity, phylogenetic relationships, and geographic distribution. Our study provided an in‐depth reassessment of tribes Rhipileae and Rhipiliopsideae based on a species‐rich dataset and the combination of molecular species delimitation, multilocus phylogenetic analyses (tufA, rbcL, and 18S rDNA), and morpho‐anatomic observations. Our results revealed an unexpected diversity of 38 morphologically validated species hypotheses, including 20 new species, two of which are described in this paper and one resurrected species (Rhipilia diaphana). Based on our phylogenetic results we proposed to redefine the genera Rhipilia and Rhipiliopsis and described two new genera, Kraftalia gen. nov. (Rhipileae) and Rhipiliospina gen. nov. (Rhipiliopsideae). Finally, we validated Rhipiliella Kraft and included it in the tribe Rhipileae. Although Rhipilia and Rhipiliopsis have a pantropical distribution, none of the species studied here appeared cosmopolitan; instead, they have restricted distributions. [ABSTRACT FROM AUTHOR]

Understanding the forces that shape species distributions is increasingly important in a fast‐changing world. Although major disturbance events can adversely affect natural populations, they can also present new opportunities, for example by opening up habitat for colonization by other lineages. Following extensive geographic sampling, we use genomic data to infer a range extension following disturbance for an ecologically important intertidal macroalgal species. Specifically, we genotyped 288 southern bull kelp (Durvillaea) plants from 28 localities across central New Zealand. All specimens from the North Island were expected to be D. antarctica, but unexpectedly 10 samples from four sites were identified as D. poha. Extensive sampling from the northern South Island (105 samples at five locations) confirmed the absence of D. poha north of the Kaikōura Peninsula. The North Island specimens of D. poha therefore reveal a biogeographic disjunction, some 150 km northeast of the nearest (South Island) population of this species. Based on strong geographic correspondence between these North Island samples and historic disturbance, we infer that tectonic upheaval, particularly earthquake‐generated landslides, likely extirpated local D. antarctica and created an opportunity for a northward range expansion event by D. poha. Close phylogenomic relationships between this new North Island population and South Island samples support a geologically recent northward expansion, rather than a deeper evolutionary origin. These findings indicate the potential of large‐scale disturbances to facilitate sudden biogeographic range expansions, and they emphasize the ability of genomic analyses with fine‐scale sampling to reveal long‐lasting signatures of past disturbance, dispersal, and colonization. [ABSTRACT FROM AUTHOR]

Sublethal biomass loss has been found to have a variety of effects on marine macroalgae, from decreasing reproductive output to increasing individual survival and frond density. The ability of an individual to recover and persist through herbivore and wave damage is facilitated by the location of several meristematic growth regions throughout an individual. In kelps (Order Laminariales), meristems are found basally at the holdfast, at the base of each blade, and/or apically on each frond. In the intertidal kelp Egregia menziesii, fronds are thought to have an intercalary meristem at a transition zone between the main frond's midrib and a small terminal lamina. This study examined the effect of removing the terminal blade and transition zone on the elongation of the frond and found no significant difference in growth, contrary to expectations. Elongation occurred in the 30 cm of midrib at the apical end of fronds and was not isolated at the base of the terminal lamina as was previously thought. These results indicate the presence of a diffuse meristematic growth region that has not been reported in other kelps and may be an advantage for this intertidal species. [ABSTRACT FROM AUTHOR]

Canopy‐forming macroalgae form the basis of diverse coastal ecosystems globally. The fucoid Hormosira banksii is often the dominant canopy‐forming macroalga in the temperate intertidal of southern Australia and New Zealand, where it is commonly associated with an understory of coralline turf. Hormosira banksii is susceptible to both natural and anthropogenic disturbance and despite its abundance, few studies have examined the demography of this important species. This study determined the demographic response of H. banksii to different gradients of disturbance to both its canopy and to the understory coralline turf. We established plots in which the density of H. banksii and/or understory coralline turf was manipulated in a pulse perturbation to simulate a disturbance event. The manipulated plots contained eight treatments ranging from 100% removal of H. banksii to 100% removal of the understory coralline turf. We then measured recruitment and followed individual recruits for up to 18 months to determine growth and survivorship. We found that H. banksii recruitment was seasonally variable throughout the experiment and highest over summer, survivorship of recruits was generally high, and the species was slow‐growing and long‐lived. Moreover, the level of disturbance did not seem to affect recruitment, growth, or survivorship and post‐recruitment mortality was independent of H. banksii density. In this system, it appears that H. banksii is a relatively long‐lived perennial species whose demography is density‐independent which appears to allow recovery from disturbance. [ABSTRACT FROM AUTHOR]

Dimethylsulfoniopropionate (DMSP) plays many important physiological and ecological roles in macroalgae. The most common method to measure DMSP is by gas chromatography analysis of the dimethylsulfide (DMS) produced after NaOH hydrolysis (pH > 12). Storage of DMS, however, is not recommended for more than a week. We investigated if acidification can be a suitable method to preserve DMSP in macroalgal samples over three months of storage, compared to widely used protocols such as drying and freezing at −20°C. The DMSP content of green (Ulva sp. and Ulva compressa), red (Chondrus crispus), and brown (Bifurcaria bifurcata) macroalgae were analyzed: 24 h after NaOH addition (control values); and after acidification (0.2 mol · L HCl−1) for 24 h of fresh material, followed by NaOH addition for 24 h. These values were compared to measurements after 3‐month storage of samples that had been either dried in a heater (60°C for a night, and storage at room temperature), or frozen at −20°C, or kept in 0.2 mol · L HCl−1. There was no significant difference between DMSP measurements on freshly collected material and after acidification of the samples, whether 24 h later or after 3 months of storage. This was in contrast to 3‐month storage protocols involving overnight drying at 60°C (75‐98% DMSP loss), and to a lesser degree freezing at −20°C (37‐80% DMSP loss). We thus advise to acidify macroalgal samples for preservation over long periods of time rather than drying or freezing, when assaying DMSP content. [ABSTRACT FROM AUTHOR]

Foliose Ulva spp. have become increasingly important worldwide for their environmental and financial impacts. A large number of such Ulva species have rapid reproduction and proliferation habits, which explains why they are responsible for Ulva blooms, known as "green tides", having dramatic negative effects on coastal ecosystems, but also making them attractive for aquaculture applications. Despite the increasing interest in the genus Ulva, particularly on the larger foliose species for aquaculture, their inter‐ and intra‐specific genetic diversity is still poorly described. We compared the cytoplasmic genome (chloroplast and mitochondrion) of 110 strains of large distromatic foliose Ulva from Ireland, Brittany (France), the Netherlands and Portugal. We found six different species, with high levels of inter‐specific genetic diversity, despite highly similar or overlapping morphologies. Genetic variation was as high as 82 SNPs/kb between Ulva pseudorotundata and U. laetevirens, indicating considerable genetic diversity. On the other hand, intra‐specific genetic diversity was relatively low, with only 36 variant sites (0.03 SNPs/kb) in the mitochondrial genome of the 29 Ulva rigida individuals found in this study, despite different geographical origins. The use of next‐generation sequencing allowed for the detection of a single inter‐species hybrid between two genetically closely related species, U. laetevirens, and U. rigida, among the 110 strains analyzed in this study. Altogether, this study represents an important advance in our understanding of Ulva biology and provides genetic information for genomic selection of large foliose strains in aquaculture. [ABSTRACT FROM AUTHOR]

Studies of quantitative trait loci based on genetic linkage maps require the establishment of a mapping population. Permanent mapping populations are more ideal than temporary ones because they can be used repeatedly. However, there has been no reported permanent sporophyte population of economically important kelp species. Based on the characteristics of the kelp life cycle, we proposed a method to establish, and then constructed experimentally, an "immortalized F2" (IF2) population of Undaria pinnatifida. Doubled‐haploid "female" and "male" sporophytes were obtained through the parthenogenesis of a female gametophyte clone and the selfing of a "monoicous" gametophyte clone (originally male), respectively, and they were used as the parents. The F1 hybrid line was generated by crossing the female and male gametophytes derived from the respective female and male parents. Full‐sibling F2 gametophyte clones, consisting of 260 females and 260 males, were established from an F1 hybrid sporophyte. Thirty‐five females and 35 males were randomly selected and paired to give rise to an IF2 population containing 35 crossing lines. A parentage analysis using 10 microsatellite markers confirmed the accuracy of the IF2 population and indicated the feasibility of this method. This proposed method may be adapted for use in other kelp species, and thus, it will be useful for genetic studies of kelp. [ABSTRACT FROM AUTHOR]

The sensitivity of kelps to elevated temperatures has been linked to recent declines in some kelp populations, with cascading impacts on marine communities. However, it remains unclear how thermal stress affects the ability of kelps to respond to other environmental factors, which could influence their vulnerability to climate change. We investigated the effect of thermal stress on the ability of the bull kelp Nereocystis luetkeana to acclimate to its surrounding hydrodynamic environment through tension‐regulated plasticity in blade morphology. We first determined optimal and stressful temperatures for N. luetkeana by measuring growth over nine temperatures from 5°C to 22°C. We then exposed N. luetkeana blades to a factorial combination of temperature (13°C and 20°C) and tension (0.5 N and 2.0 N) simulating different flow conditions, and measured changes in blade length and width after 7 days. The temperature at which N. luetkeana exhibited maximum growth was estimated to be ~11.9°C, though growth was high over a relatively wide temperature range. When thermally stressed, N. luetkeana maintained morphological responses to simulated high flow, but were inhibited from acclimating to low flow, indicated by an inability of blades to widen. Our results suggest that N. luetkeana in sheltered habitats may be particularly vulnerable to climate warming, where an inability to adjust blade morphology to local hydrodynamic conditions could drive declines at sublethal levels of warming. As ecologically important foundation species, declines in sheltered kelp populations could result in major biodiversity loss and disrupt ecosystem function. [ABSTRACT FROM AUTHOR]

The subtidal kelp Nereocystis luetkeana (hereafter Nereocystis) maintains an upright stature by producing a single gas‐filled float (pneumatocyst) that provides buoyancy. The ability of Nereocystis pneumatocysts to inflate with gas underwater is peculiar, and the gas composition of pneumatocysts has been the topic of several studies over the last 100 years. Past studies of pneumatocyst gases only examined large sporophytes, leaving open questions about the origins of these gases and how gas composition may change during development. In this study, we use developmental time as a means to understand the origin and physiological mechanisms that give rise to different gases within Nereocystis pneumatocysts. Total gas composition was measured across a range of pneumatocyst sizes (5–725 mL). Contrary to previous studies that documented pneumatocyst gas concentrations to be similar to air, this study found internal gas levels of CO, CO2, and O2 to be 1.2 ± 0.8%, 0.6 ± 0.2%, and 59.9 ± 13.6%, respectively. Our data suggest that the composition of gases does not change as pneumatocysts grow and that the rate of each gas added is approximately proportional to changes in pneumatocyst volume. Therefore, cells constituting the pneumatocyst wall are likely producing more gas (per surface area) to fill pneumatocysts as they expand, maintaining proportional gas composition and corresponding internal pressure. [ABSTRACT FROM AUTHOR]

The subtidal kelp Nereocystis luetkeana (hereafter Nereocystis) maintains an upright stature by producing a single gas‐filled float (pneumatocyst) that provides buoyancy. The ability of Nereocystis pneumatocysts to inflate with gas underwater is peculiar, and the gas composition of pneumatocysts has been the topic of several studies over the last 100 years. Past studies of pneumatocyst gases only examined large sporophytes, leaving open questions about the origins of these gases and how gas composition may change during development. In this study, we use developmental time as a means to understand the origin and physiological mechanisms that give rise to different gases within Nereocystis pneumatocysts. Total gas composition was measured across a range of pneumatocyst sizes (5–725 mL). Contrary to previous studies that documented pneumatocyst gas concentrations to be similar to air, this study found internal gas levels of CO, CO2, and O2 to be 1.2 ± 0.8%, 0.6 ± 0.2%, and 59.9 ± 13.6%, respectively. Our data suggest that the composition of gases does not change as pneumatocysts grow and that the rate of each gas added is approximately proportional to changes in pneumatocyst volume. Therefore, cells constituting the pneumatocyst wall are likely producing more gas (per surface area) to fill pneumatocysts as they expand, maintaining proportional gas composition and corresponding internal pressure. [ABSTRACT FROM AUTHOR]

This study was designed to understand better if and how juvenile sporophytes of Macrocystis pyrifera can photoacclimate to high‐light conditions when transplanted from 10 to 3 meters over 7 d. Acclimation of adult sporophytes to light regimes in the bathymetric gradient has been extensively documented. It primarily depends on photoacclimation and translocation of resources among blades. Among other physiological differences, juvenile sporophytes of M. pyrifera lack the structural complexity shown by adults. As such, juveniles may primarily depend on their photoacclimation capacities to maintain productivity and even avoid mortality under changing light regimes. However, little is known about how these mechanisms operate in young individuals. The capacity of sporophytes to photoacclimate was assessed by examining changes in their photosynthetic performance, pigment content, and bio‐optical properties of the blade. Sporophytes nutritional status and oxidative damage were also determined. Results showed that juvenile sporophytes transplanted to shallow water were able to regulate light harvesting by reducing pigment concentration, and thus, absorptance and photosynthetic efficiency. Also, shallow‐water sporophytes notably enhanced the dissipation of light energy as heat (NPQ) as a photoprotective mechanism. Generally, these adjustments allowed sporophytes to manage the absorption and utilization of light energy, hence reducing the potential for photo‐oxidative damage. Furthermore, no substantial changes were found in the internal reserves (i.e., soluble carbohydrates and nitrogen) of these sporophytes. To our knowledge, these results are the first to provide robust evidence of photoprotective and photoacclimation strategies in juveniles of M. pyrifera, allowing them to restrict or avoid photodamage during shallow‐water cultivation. [ABSTRACT FROM AUTHOR]

This study was designed to understand better if and how juvenile sporophytes of Macrocystis pyrifera can photoacclimate to high‐light conditions when transplanted from 10 to 3 meters over 7 d. Acclimation of adult sporophytes to light regimes in the bathymetric gradient has been extensively documented. It primarily depends on photoacclimation and translocation of resources among blades. Among other physiological differences, juvenile sporophytes of M. pyrifera lack the structural complexity shown by adults. As such, juveniles may primarily depend on their photoacclimation capacities to maintain productivity and even avoid mortality under changing light regimes. However, little is known about how these mechanisms operate in young individuals. The capacity of sporophytes to photoacclimate was assessed by examining changes in their photosynthetic performance, pigment content, and bio‐optical properties of the blade. Sporophytes nutritional status and oxidative damage were also determined. Results showed that juvenile sporophytes transplanted to shallow water were able to regulate light harvesting by reducing pigment concentration, and thus, absorptance and photosynthetic efficiency. Also, shallow‐water sporophytes notably enhanced the dissipation of light energy as heat (NPQ) as a photoprotective mechanism. Generally, these adjustments allowed sporophytes to manage the absorption and utilization of light energy, hence reducing the potential for photo‐oxidative damage. Furthermore, no substantial changes were found in the internal reserves (i.e., soluble carbohydrates and nitrogen) of these sporophytes. To our knowledge, these results are the first to provide robust evidence of photoprotective and photoacclimation strategies in juveniles of M. pyrifera, allowing them to restrict or avoid photodamage during shallow‐water cultivation. [ABSTRACT FROM AUTHOR]

Water motion in coastal areas can produce hydrodynamic forces that damage or dislodge benthic macroalgae if the tissues of macroalgae are not sufficiently strong. Some macroalgae vary their morphology and strength in response to ambient water motion, but little is known of how morphology and strength of macroalgae change relative to one another across flow regimes. Here, we use Turbinaria ornata, an ecologically important macroalga, to study how both the morphology and strength of macroalgae vary with ambient water motion. Typically, T. ornata exhibits weakening of its stipe when sexually mature, leading to breakage from the substratum and dispersal, which is beneficial for reproduction. Across three flow regimes, adult T. ornata increased its size but decreased its strength as water motion decreased. However, the strength of T. ornata relative to the maximum hydrodynamic forces it is expected to encounter (the environmental safety factor) did not differ between flow regimes. Our results showed that T. ornata can conform to its local flow habitat by varying both size and strength, similar to other macroalgae. Varying multiple traits between flow regimes suggested that T. ornata is capable of surviving a wide range of flow conditions, which may permit more control over the timing of its weakening, breakage from the substratum, and dispersal, even with future increases in flow velocities (e.g., large waves from storms) that are expected to occur frequently with climate change. [ABSTRACT FROM AUTHOR]

Seaweeds are important components of near‐shore ecosystems as primary producers, foundation species, and biogeochemical engineers. Seaweed communities are likely to alter under predicted climate change scenarios. We tested the physiological responses of three perennial, turf‐building, intertidal rhodophytes, Mastocarpus stellatus, Osmundea pinnatifida, and the calcified Ellisolandia elongata, to elevated pCO2 over 6 weeks. Responses varied between these three species. E. elongata was strongly affected by high pCO2, whereas non‐calcified species were not. Elevated pCO2 did not induce consistent responses of photosynthesis and respiration across these three species. While baseline photophysiology differed significantly between species, we found few clear effects of elevated pCO2 on this aspect of macroalgal physiology. We found effects of within‐species variation in elevated pCO2 response in M. stellatus, but not in the other species. Overall, our data confirm the sensitivity of calcified macroalgae to elevated pCO2, but we found no evidence suggesting that elevated pCO2 conditions will have a strong positive or negative impact on photosynthetic parameters in non‐calcified macroalgae. [ABSTRACT FROM AUTHOR]

The kelp Laminaria digitata growing in the low intertidal region along energetic coastlines are exposed to a range of hydrodynamic environments. Macroalgae in the intertidal zone can experience both waves and currents independently, but it is unknown how they influence growth rate. Relative growth rate of the meristematic region and the entire blade of L. digitata were measured to assess the influence of wave and current motion from three hydrodynamic environments: low current and low wave (LCLW), high current and low wave (HCLW), and high wave and low current (HWLC). Alongside hydrodynamic data, seawater nutrient concentrations and temperature were also collected and analyzed. Results suggest that differences in L. digitata relative growth rates were not attributed to the seawater nutrient concentrations or temperature, but attributed to the hydrodynamic environments. At the high current condition, kelp growth rate of the meristematic region was enhanced by 45% compared to the high wave condition. When including the entire blade growth rate, an average increase of 25% was observed between the high current and high wave condition. Potentially, the division in growth rate observed between the wave and current motion is related to the frequency and magnitude at which the hydrodynamic forces act. These findings highlight the complexity of the hydrodynamic environment and that forces associated with waves and currents may have a significant role on the productivity of kelp. [ABSTRACT FROM AUTHOR]

Recognition of the wide diversity of organisms that maintain complex haploid–diploid life cycles has generated interest in understanding the evolution and persistence of such life cycles. We empirically tested the model where complex haploid–diploid life cycles may be maintained by subtle/cryptic differences in the vital rates of isomorphic haploid–diploids, by examining the ecophysiology of haploid tetraspores and diploid carpospores of the isomorphic red alga Chondrus verrucosus. While tetraspores and carpospores of this species did not differ in size or autofluorescence, concentrations of phycobiliproteins of carpospores were greater than that of tetraspores. However, tetraspores were more photosynthetically competent than carpospores over a broader range of photosynthetic photon flux densities (PPFDs) and at PPFDs found at both the depth that C. verrucosus is found at high tide and in surface waters in which planktonic propagules might disperse. These results suggest potential differences in dispersal potential and reproductive success of haploid and diploid spores. Moreover, these cryptic differences in ecological niche partitioning of haploid and diploid spores contribute to our understanding of some of the differences between these ploidy stages that may ultimately lead to the maintenance of the complex haploid–diploid life cycle in this isomorphic red alga. [ABSTRACT FROM AUTHOR]

Recognition of the wide diversity of organisms that maintain complex haploid–diploid life cycles has generated interest in understanding the evolution and persistence of such life cycles. We empirically tested the model where complex haploid–diploid life cycles may be maintained by subtle/cryptic differences in the vital rates of isomorphic haploid–diploids, by examining the ecophysiology of haploid tetraspores and diploid carpospores of the isomorphic red alga Chondrus verrucosus. While tetraspores and carpospores of this species did not differ in size or autofluorescence, concentrations of phycobiliproteins of carpospores were greater than that of tetraspores. However, tetraspores were more photosynthetically competent than carpospores over a broader range of photosynthetic photon flux densities (PPFDs) and at PPFDs found at both the depth that C. verrucosus is found at high tide and in surface waters in which planktonic propagules might disperse. These results suggest potential differences in dispersal potential and reproductive success of haploid and diploid spores. Moreover, these cryptic differences in ecological niche partitioning of haploid and diploid spores contribute to our understanding of some of the differences between these ploidy stages that may ultimately lead to the maintenance of the complex haploid–diploid life cycle in this isomorphic red alga. [ABSTRACT FROM AUTHOR]

The macromolecular composition of macroalgae influences nutrient flow and food quality in aquatic ecosystems and the value of macroalgae species for human consumption, aquaculture, biofuels, and other applications. We used literature data (125 publications, 1,117 observations) and a hierarchal Bayesian statistical model to estimate the average macromolecular composition, protein, lipid, and carbohydrate of macroalgae as a whole and at the phylum level. Our focus was on marine, noncalcified macroalgae sampled from wild‐grown populations in the field. We found that the median macromolecular composition is 9.98% protein, 2.7% lipid, 48.5% carbohydrate, and 31.8% ash as percent dry weight. We compared the median macromolecular content of macroalgae to microalgae and herbaceous plants and test for differences in macromolecular content across macroalgal phyla. Macroalgae were much more enriched in carbohydrate and minerals than the microalgae and lower in protein and lipid than many herbaceous plants. Rhodophyte macroalgae have significantly less lipid and more protein and the Ochrophyte macroalgae have significantly less protein than the average. [ABSTRACT FROM AUTHOR]

The red macroalgae Hydropuntia cornea, Gracilariopsis longissima and Halopithys incurva were cultured for 14 d under laboratory conditions, in enriched seawater with a high nutrient content (N‐NH4+ and P‐PO43−) and two radiation regimes: PAR (400–700 nm) and PAB (280–700 nm). The UV radiation effects under high availability of nutrients on growth, photosynthetic pigments (chlorophyll a, carotenoids and phycobiliproteins), photosynthetic activity and biochemical composition were studied. Maximum quantum yield (Fv/Fm) was not significantly different among the PAR and PAB treatments during the experiment. However, the maximum electronic transport rate (ETRmax) increased over time, showing the highest values in PAR for H. incurva and H. cornea, whereas for G. longissima it was found in PAB. Photosynthetic efficiency (αETR) decreased over time in the first two species, but increased in G. longissima. Saturation irradiance (EkETR) and maximum nonphotochemical quenching (NPQmax) increased in PAB with time up to 80% and 30%, respectively, indicating a photosynthetic acclimatization like that of sun‐type algae. Five MAAs were identified in all species using high performance liquid chromatography (HPLC). The total content of MAAs increased over time, being 30% higher in H. incurva, 40% in G. longissima and 50% in H. cornea in PAB than in the PAR treatment. Finally, the antioxidant activity was also higher in the PAB treatment. All of the species presented an effective mechanism of photoprotection based on the accumulation of photoprotective compounds with antioxidant activity, as well as a high dissipation of excitation energy (high NPQmax). [ABSTRACT FROM AUTHOR]

Light availability is a fundamental factor that controls the productivity and distribution of macroalgae and is highly variable, both spatially and temporally, in subtidal coastal systems. Our comprehension of how macroalgae respond to such variability is a significant knowledge gap that limits our understanding of how light influences the structure and productivity of these environments. Here, we examined the pigment characteristics of individual species, and for the first time the whole community, within one low‐light, and one high‐light kelp‐forest system in southern New Zealand. The aim was to quantify the range of pigmentation seen within the two kelp‐forests which differed in irradiance regime. Light availability was 33% and 64% greater at the high‐light compared to the low‐light site at 2 and 10 m depth, respectively. Results suggested Phaeophyceae species at deeper depths in the low‐light site may be living at the edge of their photosynthetic ability and pigment synthesis appeared significantly restricted. Even with greater investment in the pigment fucoxanthin, biomass of Phaeophyceae species was significantly lower in the low‐light site. Highly pigmented Rhodophyceae species made a greater proportional contribution to community biomass within the low‐light site where they likely possessed a photosynthetic advantage. This work helps explain discrepancies in community structure between the two study sites and explores the complex relationship between irradiance and photoacclimation. The comparison of community pigment concentration holds potential as a tool for assessing the relative degree of photoacclimation occurring between sites and provides a proxy of photosynthetic cost under a specific light regime. [ABSTRACT FROM AUTHOR]

Trace metal or rare earth element (REE) content of marine macroalgae are underexamined and there is a great need for further understanding since macroalgae are used for food and may also be bioindicators of environmental changes. This study, by using high resolution inductive coupled plasma spectrometer in a clean laboratory (class 1000), investigates the trace metal and REE concentrations and composition in the youngest tissue of various species within three algal classes in the Trondheimsfjord, Norway, comprising phaeo‐, chloro‐, and rhodophytes in winter (February) and Spring (May) 2013, with the main focus on phaeophytes. The macroalgae were found in a clear zonation pattern as a function of depth. A significant difference in element concentration and composition was found between the six phaeophyte species along with a significant difference between winter and spring tissue. A zonation depth trend in algal tissue element concentration was also found for the phaeophytes, where the algal species located in both extreme ends (upper vs. lower littoral zone) obtained a lower element concentration than the algae located in the middle part of the littoral zone. This trend seems to result from different algal contact with the metal‐rich sea surface microlayer. The chlorophytes had 5–27 times higher concentration of REE and lead (Pb) than the two other algal classes. Results indicate that the rhodo‐ and chlorophytes are better accumulators than the phaeophytes for several trace metals and REE. [ABSTRACT FROM AUTHOR]

Light availability is a fundamental factor that controls the productivity and distribution of macroalgae and is highly variable, both spatially and temporally, in subtidal coastal systems. Our comprehension of how macroalgae respond to such variability is a significant knowledge gap that limits our understanding of how light influences the structure and productivity of these environments. Here, we examined the pigment characteristics of individual species, and for the first time the whole community, within one low‐light, and one high‐light kelp‐forest system in southern New Zealand. The aim was to quantify the range of pigmentation seen within the two kelp‐forests which differed in irradiance regime. Light availability was 33% and 64% greater at the high‐light compared to the low‐light site at 2 and 10 m depth, respectively. Results suggested Phaeophyceae species at deeper depths in the low‐light site may be living at the edge of their photosynthetic ability and pigment synthesis appeared significantly restricted. Even with greater investment in the pigment fucoxanthin, biomass of Phaeophyceae species was significantly lower in the low‐light site. Highly pigmented Rhodophyceae species made a greater proportional contribution to community biomass within the low‐light site where they likely possessed a photosynthetic advantage. This work helps explain discrepancies in community structure between the two study sites and explores the complex relationship between irradiance and photoacclimation. The comparison of community pigment concentration holds potential as a tool for assessing the relative degree of photoacclimation occurring between sites and provides a proxy of photosynthetic cost under a specific light regime. [ABSTRACT FROM AUTHOR]

Temporal and spatial variations in Sargassum ilicifolium thallus density and length were investigated on equatorial coral reefs in Singapore from November 2011 to October 2012. Thalli density varied little throughout the year, however, we found strong seasonal patterns in thallus length and identified temperature as the significant driver. Sargassum ilicifolium reached maximum length in December (110.39 ± 2.37 cm) during periods of cooler water temperatures, and minimum length in May (9.88 ± 0.48 cm) during periods of warmer water temperatures. Significant spatial variation was also observed for both thallus density and length of S. ilicifolium among reefs. Within reefs, densities of S. ilicifolium were higher on reef flats (20.40 ± 0.40 individuals · 0.25 m−2) compared to upper reef slopes (5.66 ± 0.23 individuals · 0.25 m−2). Our findings highlight that marked seasonality in the growth of canopy‐forming macroalgae can occur within equatorial reef systems where temperature ranges are restricted (<3°C). [ABSTRACT FROM AUTHOR]

Maintaining buoyancy with gas‐filled floats (pneumatocysts) is essential for some subtidal kelps to achieve an upright stature and compete for light . However, as these kelps grow up through the water column, pneumatocysts are exposed to substantial changes in hydrostatic pressure, which could cause complications as internal gases may expand or contract, potentially causing them to rupture, flood, and lose buoyancy. In this study, we investigate how pneumatocysts of Nereocystis luetkeana resist biomechanical stress and maintain buoyancy as they develop across a hydrostatic gradient. We measured internal pressure, material properties, and pneumatocyst geometry across a range of thallus sizes and collection depths to identify strategies used to resist pressure‐induced mechanical failure. Contrary to expectations, all pneumatocysts had internal pressures less than atmospheric pressure, ensuring that thalli are always exposed to a positive pressure gradient and compressional loads, indicating that they are more likely to buckle than rupture at all depths. Small pneumatocysts collected from depths between 1 and 9 m (inner radius = 0.4–1.0 cm) were demonstrated to have elevated wall stresses under high compressive loads and are at greatest risk of buckling. Although small kelps do not adjust pneumatocyst material properties or geometry to reduce wall stress as they grow, they are ~3.4 times stronger than they need to be to resist hydrostatic buckling. When tested, pneumatocysts buckled around 35 m depth, which agrees with previous measures of lower limits due to light attenuation, suggesting that hydrostatic pressure may also define the lower limit of Nereocystis in the field. [ABSTRACT FROM AUTHOR]

Vitronectin (Vn) is a glycoprotein that serves a wide variety of roles in multicellular organisms. It was first identified in multicellular animals but has also been isolated from land plants and some algae, where it appears to serve as an extracellular adhesive molecule. In order to further elucidate presence and localization of a Vn–like protein and its potential role in algae, we surveyed different morphological regions of 24 species of macro‐ and microalgae and three species of cyanobacteria for the presence of a Vn–like protein. Vn–like proteins were not detected in any of the species of cyanobacteria, microalgae or Rhodophyta investigated. They were detected in several species of the Phaeophyceae and Chlorophyta where their localization was limited to the holdfast and rhizoids of these organisms, respectively. Detection of a Vn–like protein (between 0.0125 and 0.097 μg · μL−1 protein extract) was therefore limited to locations associated with substrate attachment. [ABSTRACT FROM AUTHOR]

The biogeochemistry of iodine in temperate coastal ecosystems is largely mediated by macroalgae, which act as a major biological sink and source of iodine. Their capacity to accumulate, retain and release iodine has been associated with abiotic and biotic stressors, but quantitative information is limited. We evaluated the seasonal iodine retention capacity of eleven macroalgal species belonging to different systematic groups, collected from two sites in Ireland. Iodine accumulation and retention were then further quantified in Fucus vesiculosus and Laminaria digitata in relation to I− concentrations in seawater and temperature. In general, iodine contents were ~101–102 μmol · (g dw)−1 for Laminariales, 100–101 μmol · (g dw)−1 for Fucales, 10−1–100 μmol · (g dw)−1 for Rhodophyta, and 10−1 μmol · (g dw)−1 for Chlorophyta. Typically, algal iodine contents were above average in winter and below average in summer. Iodine accumulation in F. vesiculosus and L. digitata depended on I− availability and followed the Michaelis‐Menten kinetic. The ratio of maximum accumulation rate to half accumulation coefficient (ρmax: Kt) was 2.4 times higher for F. vesiculosus than for L. digitata, suggesting that F. vesiculosus was more efficient in iodine accumulation. Both species exhibited a temperature‐dependent net loss of iodine, and only an exposure to sufficient external I− concentrations compensated for this loss. This study revealed that both environmental (e.g., I− in seawater, temperature) and organismal (e.g., the status of the iodine storage pool) variables determine retention and variability in iodine in temperate seaweeds. [ABSTRACT FROM AUTHOR]

Little is known about the bulk hydrogen stable isotope composition (δ2H) of seaweeds. This study investigated the bulk δ2H in several different seaweed species collected from three different beaches in Brazil, Australia, and Argentina. Here, we show that Ulvophyceae (a group of green algae) had lower δ2H values (between −94‰ and −130‰) than red algae (Florideophyceae), brown algae (Phaeophyceae), and species from the class Bryopsidophyceae (another group of green algae). Overall the latter three groups of seaweeds had δ2H values between −50‰ and −90‰. These findings were similar at the three different geographic locations. Observed differences in δ2H values were probably related to differences in hydrogen (H) metabolism among algal groups, also observed in the δ2H values of their lipids. The marked difference between the δ2H values of Ulvophyecae and those of the other groups could be useful to trace the food source of food webs in coastal rocky shores, to assess the impacts of green tides on coastal ecosystems, and to help clarify aspects of their phylogeny. However, reference materials for seaweed δ2H are required before the full potential of using the δ2H of seaweeds for ecological studies can be exploited. [ABSTRACT FROM AUTHOR]

Marine-freshwater and freshwater-marine transitions have been key events in the evolution of life, and most major groups of organisms have independently undergone such events at least once in their history. Here, we first compile an inventory of bidirectional freshwater and marine transitions in multicellular photosynthetic eukaryotes. While green and red algae have mastered multiple transitions in both directions, brown algae have colonized freshwater on a maximum of six known occasions, and angiosperms have made the transition to marine environments only two or three times. Next, we review the early evolutionary events leading to the colonization of current habitats. It is commonly assumed that the conquest of land proceeded in a sequence from marine to freshwater habitats. However, recent evidence suggests that early photosynthetic eukaryotes may have arisen in subaerial or freshwater environments and only later colonized marine environments as hypersaline oceans were diluted to the contemporary level. Although this hypothesis remains speculative, it is important to keep these alternative scenarios in mind when interpreting the current habitat distribution of plants and algae. Finally, we discuss the roles of structural and functional adaptations of the cell wall, reactive oxygen species scavengers, osmoregulation, and reproduction. These are central for acclimatization to freshwater or to marine environments. We observe that successful transitions appear to have occurred more frequently in morphologically simple forms and conclude that, in addition to physiological studies of euryhaline species, comparative studies of closely related species fully adapted to one or the other environment are necessary to better understand the adaptive processes. [ABSTRACT FROM AUTHOR]

Global declines of macroalgal beds in coastal waters have prompted a plethora of studies attempting to understand the drivers of change within dynamic nearshore ecosystems. Photosynthetic measurements are good tools for assessing the consequences of numerous stressors of macroalgae, but there is somewhat of a disconnection between studies that focus on organism-specific ecophysiological responses and those that address causes and consequences of shifts in macroalgal productivity. Our goal is to highlight the applications of two complementary tools for measuring photosynthesis--variable chlorophyll a fluorescence and photorespirometry--and provide guidance for the integration of physiology and ecology to understand the drivers of change in macroalgal communities. Photorespirometry can provide an integrated measure of whole-community metabolism, including an estimate of the physiological costs associated with stressors, while fluorescence-based techniques provide point measures of the efficiency of the photosynthetic apparatus within communities. Variable chlorophyll a fluorescence does not provide an estimate of carbon balance or integrated photosynthesis across either whole plants or whole communities but can be used to estimate the contribution of individual community components in the dynamic subcanopy environment to help us understand the mechanisms underlying observed responses. We highlight the importance of the highly dynamic light environment within macroalgal communities and call for better integration of physiological techniques in an ecological context to enhance our understanding of the responses of whole communities to local and global stressors. [ABSTRACT FROM AUTHOR]

Global climate change is expected to alter the polar bioregions faster than any other marine environment. This study assesses the biodiversity of seaweeds and associated eukaryotic pathogens of an established study site in northern Baffin Island (72° N), providing a baseline inventory for future work assessing impacts of the currently ongoing changes in the Arctic marine environment. A total of 33 Phaeophyceae, 24 Rhodophyceae, 2 Chlorophyceae, 12 Ulvophyceae, 1 Trebouxiophyceae, and 1 Dinophyceae are reported, based on collections of an expedition to the area in 2009, complemented by unpublished records of Robert T. Wilce and the first-ever photographic documentation of the phytobenthos of the American Arctic. Molecular barcoding of isolates raised from incubated substratum samples revealed the presence of 20 species of brown seaweeds, including gametophytes of kelp and of a previously unsequenced Desmarestia closely related to D. viridis, two species of Pylaiella, the kelp endophyte Laminariocolax aecidioides and 11 previously unsequenced species of the Ectocarpales, highlighting the necessity to include molecular techniques for fully unraveling cryptic algal diversity. This study also includes the first records of Eurychasma dicksonii, a eukaryotic pathogen affecting seaweeds, from the American Arctic. Overall, this study provides both the most accurate inventory of seaweed diversity of the northern Baffin Island region to date and can be used as an important basis to understand diversity changes with climate change. [ABSTRACT FROM AUTHOR]

Kelps are a clade of morphologically diverse, ecologically important habitat-forming species. Many kelps live in wave-swept environments and are exposed to chronic flow-induced stress. In order to grow and survive in these harsh environments, kelps can streamline (reducing drag coefficient) to avoid drag or to increase attachment and breakage force to tolerate it. We aimed to quantify the drag tolerance and streamlining strategies of kelps from wave-swept intertidal habitats. We measured drag coefficient and tenacity of populations from eight kelp species over a wide range of sizes to determine whether kelps avoid dislodgement by reducing drag coefficient or by increasing tenacity as they grow, and whether these traits are traded off. We employed phylogenetic comparative methods to rule out potentially confounding effects of species' relatedness. There was a significant negative relationship between drag avoidance and tolerance strategies, even after incorporating phylogeny. Kelps that were more tenacious were less able to reduce drag, resulting in a continuum from 'tolerators' to 'streamliners,' with some species demonstrating intermediate, mixed strategies. Drag and tenacity were correlated with geometric properties (i.e., second moment of area) of the stipe in large kelps. Results presented in this study suggest that kelps are either strong or streamlined, but not both. This continuum is consistent with avoidance and tolerance trade-offs that have been documented in many different biological systems and may have widespread implications for the evolution of large macroalgae, perhaps driving morphological diversity within this group. [ABSTRACT FROM AUTHOR]

The influence of oscillatory versus unidirectional flow on the growth and nitrate-uptake rates of juvenile kelp, Laminaria digitata, was determined seasonally in experimental treatments that simulated as closely as possible natural environmental conditions. In winter, regardless of flow condition (oscillatory and unidirectional) or water velocity, no influence of water motion was observed on the growth rate of L. digitata. In summer, when ambient nitrate concentrations were low, increased water motion enhanced macroalgal growth, which is assumed to be related to an increase in the rate of supply of nutrients to the blade surface. Nitrate-uptake rates were significantly influenced by water motion and season. Lowest nitrate-uptake rates were observed for velocities <5 cm ⋅ s-1 and nitrate-uptake rates increased by 20%-50% under oscillatory motion compared to unidirectional flow at the same average speed. These data further suggested that the diffusion boundary layer played a significant role in influencing nitrate-uptake rates. However, while increased nitrate-uptake in oscillatory flow was clear, this was not reflected in growth rates and further work is required to understand the disconnection of nitrate-uptake and growth by L. digitata in oscillatory flow. The data obtained support those from related field-based studies, which suggest that in summer, when insufficient nitrogen is available in the water to saturate metabolic demand, the growth rate of kelps will be influenced by water motion restricting mass transfer of nitrogen. [ABSTRACT FROM AUTHOR]

Polyamines ( PA) are ubiquitous, small, aliphatic cations found in all living cells. In recent years the importance of these molecules for macroalgae has become evident and a substantial body of knowledge has been accumulated over the last three decades. This review summarizes research on the PAs found in macroalgae, their transport and metabolism, and their biological significance in processes such as cell division, chloroplast development, and reproduction. The involvement of PAs in environmental stress responses in macroalgae is also addressed. The discussion of PAs in this review not only demonstrates that PAs play an important role in physiological processes in macroalgae, but also clearly demonstrates the similarities and differences between PA metabolism in macroalgae and higher plants. Key areas for future research are also discussed. [ABSTRACT FROM AUTHOR]