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Despite growing interest in edible seaweeds, there is limited information on seaweed chemical contaminant levels in the Salish Sea. Without this knowledge, health-based consumption advisories can not be determined for consumers that include Tribes and First Nations, Asian and Pacific Islander community members, and recreational harvesters. We measured contaminant concentrations in edible seaweeds (Fucus distichus, F. spiralis, and Nereocystis luetkeana) from 43 locations in the Salish Sea. Metals were analyzed in all samples, and 94 persistent organic pollutants (POPs) (i.e. 40 PCBs, 15 PBDEs, 17 PCDD/Fs, and 22 organochlorine pesticides) and 51 PAHs were analyzed in Fucus spp. We compared concentrations of contaminants to human health-based screening levels calculated from the USEPA and to international limits. We then worked with six focal contaminants that either exceeded screening levels or international limits (Cd, total Hg, Pb, benzo[a]pyrene [BaP], and PCBs) or are of regional interest (total As). USEPA cancer-based screening levels were exceeded in 30 samples for the PCBs and two samples for BaP. Cadmium concentrations did not exceed the USEPA noncancer-based screening level but did exceed international limits at all sites. Lead exceeded international limits at three sites. Because there are no screening levels for total Hg and total As, and to be conservative, we made comparisons to methyl Hg and inorganic As screening levels. All samples were below the methyl Hg and above the inorganic As screening levels. Without knowledge of the As speciation, we cannot assess the health risk associated with the As. While seaweed was the focus, we did not consider contaminant exposure from consuming other foods. Other chemicals, such as contaminants of emerging concern (e.g., PFAS, pharmaceuticals and personal care products), should also be considered. Additionally, although we focused on toxicological aspects, there are cultural and health benefits of seaweed use that may affect consumer choice.

Ulva lactuca and Ulvaria obscura are seaweeds that form green tides on Salish Sea shores. They have similar macroscopic morphologies but differ in their biochemistries and physiological responses. To understand how they are affected by changes in environmental conditions, a factorial experiment was conducted in which algae were grown in artificial seawater with either low (10 μM) or high (160 μM) nitrate (NO3−) concentrations at high (29 mol photons·m−2.day−1) and low (4 mol photons·m−2.day−1) light levels. Light and NO3− affected algal responses, but always independently. After two weeks, U. lactuca grown in high light were larger, had lower maximum quantum yields (MQYs), and lower nitrogen (N), carbon (C), pigment, and dimethylsulfoniopropionate (DMSP) concentrations, respectively, relative to algae in low light. In contrast, U. obscura growth was unaffected by light. Like U. lactuca, U. obscura grown in high light had lower MQYs, and N, pigment, and DMSP concentrations. In high light, U. obscura also had 89% higher dopamine concentrations and a tendency to fragment. Both U. lactuca and U. obscura grown in 160 μM NO3− were larger, had higher MQYs, and higher N, pigment, and DMSP concentrations, respectively, than algae in 10 μM NO3−. Also, when U. obscura was grown in the 160 μM NO3− medium, it significantly increased its surface area/mass ratio. Although both species grew faster in high NO3−, high light only promoted the growth of Ulva, which may explain the dominance of Ulva in summer months. High light was physiologically stressful to both species and caused increases in photoprotective mechanisms, such as the production of dopamine, a melanin precursor, in Ulvaria, and DMSP lysis in Ulva to generate antioxidants. Growing in 10 μM NO3- produced responses that were consistent with nitrogen limitation and had greater impacts on Ulvaria than Ulva, suggesting that Ulvaria responds more strongly to eutrophication.

Climate change is affecting the health and physiology of marine organisms and altering species interactions. Ocean acidification (OA) threatens calcifying organisms such as the Pacific oyster, Crassostrea gigas. In contrast, seagrasses, such as the eelgrass Zostera marina, can benefit from the increase in available carbon for photosynthesis found at a lower seawater pH. Seagrasses can remove dissolved inorganic carbon from OA environments, creating local daytime pH refugia. Pacific oysters may improve the health of eelgrass by filtering out pathogens such as Labyrinthula zosterae (LZ), which causes eelgrass wasting disease (EWD). We examined how co-culture of eelgrass ramets and juvenile oysters affected the health and growth of eelgrass and the mass of oysters under different pCO2 exposures. In Phase I, each species was cultured alone or in co-culture at 12°C across ambient, medium, and high pCO2 conditions, (656, 1,158 and 1,606 μatm pCO2 , respectively). Under high pCO2 , eelgrass grew faster and had less severe EWD (contracted in the field prior to the experiment). Co-culture with oysters also reduced the severity of EWD. While the presence of eelgrass decreased daytime pCO2 , this reduction was not substantial enough to ameliorate the negative impact of high pCO2 on oyster mass. In Phase II, eelgrass alone or oysters and eelgrass in co-culture were held at 15°C under ambient and high pCO2 conditions, (488 and 2,013 μatm pCO2 , respectively). Half of the replicates were challenged with cultured LZ. Concentrations of defensive compounds in eelgrass (total phenolics and tannins), were altered by LZ exposure and pCO2 treatments. Greater pathogen loads and increased EWD severity were detected in LZ exposed eelgrass ramets; EWD severity was reduced at high relative to low pCO2 . Oyster presence did not influence pathogen load or EWD severity; high LZ concentrations in experimental treatments may have masked the effect of this treatment. Collectively, these results indicate that, when exposed to natural concentrations of LZ under high pCO2 conditions, eelgrass can benefit from co-culture with oysters. Further experimentation is necessary to quantify how oysters may benefit from co-culture with eelgrass, examine these interactions in the field and quantify context-dependency.

For autogenic ecosystem engineers, body size is an aspect of individual performance that has direct connections to community structure; yet the complex morphology of these species can make it difficult to draw clear connections between the environment and performance. We combined laboratory experiments and field surveys to test the hypothesis that individual body size was determined by disparate localized physiological responses to environmental conditions across the complex thallus of the intertidal kelp Hedophyllum sessile, a canopy-forming physical ecosystem engineer. We documented substantial (> 40%) declines in whole-thallus photosynthetic potential (as Maximum Quantum Yield, MQY) as a consequence of emersion, which were related to greater than 10-fold increases in intra-thallus MQY variability (as Coefficient of Variation). In laboratory experiments, desiccation and high light levels during emersion led to lasting impairment of photosynthetic potential and an immediate > 25% reduction in area due to tissue contraction, which was followed by complete loss of structural integrity after three days of submersion. Tissue exposed to desiccation and high light during emersion had higher nitrogen concentrations and lower phlorotannin concentrations than tissue in control treatments (on average 1.36 and 0.1x controls, respectively), suggesting that conditions during emersion have the potential to affect food quality for consumers. Our data indicate that the complex thallus morphology of H. sessile may be critical to this kelp's ability to persist in the intertidal zone despite the physiological challenges of emersion and encourage a more nuanced view of the concept of "sub-lethal stress" on the scale of the whole individual.

Algae are a phylogenetically diverse assemblage of organisms ranging from single-celled plankton to giant kelps. They are common in both marine and freshwater habitats. The common animal neurotransmitters acetylcholine, dopamine, histamine, phenethylamine, and serotonin occur within members of the algal Phyla Charophyta, Chlorophyta, Ochrophyta, and Rhodophyta, but not all compounds are found in all phyla. Because there are relatively few reports of these compounds in algae, discerning distributional patterns among the major algal taxa is not currently possible. The functions of neurotransmitters in algae are diverse and often unknown. In charophytes, they may be involved in the transmission of electrical signals (however, the putative transmitter, acetylcholine, has not yet been shown to occur in these algae), alleviating oxidative stresses and regulating growth. In the chlorophyte Ulvaria obscura, dopamine is synthesized in the thylakoid membranes of chloroplasts and stored in acidic vesicles. It’s only identified function is herbivore deterrence. Dopamine can also be released from U. obscura into the surrounding seawater where it may be toxic or allelopathic toward other organisms.

Seagrasses are ecosystem engineers of essential marine habitat. Their populations are rapidly declining worldwide. One potential cause of seagrass population declines is wasting disease, which is caused by opportunistic pathogens in the genus Labyrinthula. While infection with these pathogens is common in seagrasses, theory suggests that disease only occurs when environmental stressors cause immunosuppression of the host. Recent evidence suggests that host factors may also contribute to disease caused by opportunistic pathogens. In order to quantify patterns of disease, identify risk factors, and investigate responses to infection, we surveyed shoot density, shoot length, epiphyte load, production of plant defenses (phenols), and wasting disease prevalence in eelgrass Zostera marina across 11 sites in the central Salish Sea (Washington state, USA), a region where both wasting disease and eelgrass declines have been documented. Wasting disease was diagnosed by the presence of necrotic lesions, and Labyrinthula cells were identified with histology. Disease prevalence among sites varied from 6 to 79%. The probability of a shoot being diseased was higher in longer shoots, in patches of higher shoot density, and in shoots with higher levels of biofouling from epiphytes. Phenolic concentration was higher in diseased leaves. We hypothesize that this results from the induction of phenols during infection. Additional research is needed to evaluate whether phenols are an adaptive defense against Labyrinthula infection. The high site-level variation in disease prevalence emphasizes the potential for wasting disease to be causing some of the observed decline in eelgrass beds.

In Penn Cove, ulvoid green algal mats occur annually. To examine seasonal variation in their causes, nitrogen and carbon were measured in Ulva lactuca in May, July, and September and stable nitrogen and oxygen isotope ratios were quantified in U. lactuca, Penn Cove seawater, upwelled water from Saratoga Passage, water near the Skagit River outflow, and effluents from wastewater treatment facilities. Ulvoid growth was nitrogen limited and the sources of nitrogen used by the algae changed during the growing season. Algal nitrogen concentrations were 0.85-4.55% and were highest in September and at sites where algae were abundant. Upwelled waters were the primary nitrogen source for the algae, but anthropogenic sources also contributed to algal growth towards the end of the growing season. This study suggests that small nitrogen inputs can result in crossing a "tipping point", causing the release of nutrient limitation and localized increases in algal growth.

Climate change is affecting the health and physiology of marine organisms and altering species interactions. Ocean acidification (OA) threatens calcifying organisms such as the Pacific oyster, Crassostrea gigas. In contrast, seagrasses, such as the eelgrass Zostera marina, can benefit from the increase in available carbon for photosynthesis found at a lower seawater pH. Seagrasses can remove dissolved inorganic carbon from OA environments, creating local daytime pH refugia. Pacific oysters may improve the health of eelgrass by filtering out pathogens such as Labyrinthula zosterae (LZ), which causes eelgrass wasting disease (EWD). We examined how co-culture of eelgrass ramets and juvenile oysters affected the health and growth of eelgrass and the mass of oysters under different pCO

Herbivore impacts on macrophyte growth vary with the identity of the herbivores and macrophytes, as well as under different abiotic conditions. This interaction is further complicated by anthropogenic alterations to the environment, such as eutrophication. In this study, we utilized in situ herbivore exclusion experiments and mesocosm feeding preference assays to examine the impacts of different herbivores on the growth of two morphologically similar, co-occurring macroalgal bloom Ulva species in a nutrient-rich environment. We found that herbivory had a measurable impact on Ulva biomass, though the rate of consumption rarely surpassed growth for either Ulva species. We determined that the primary herbivores within the blooms were amphipods and mud crabs, and that their effects varied among study sites and months. Our results also confirmed that, even with a diverse suite of consumers, Ulva blooms are capable of escaping herbivore control, particularly early in the growing season when growth rates peak and herbivore activity is limited. Furthermore, our experiments revealed species-specific feeding preferences among herbivores, as well as differences in growth rates and chemistry between the two Ulva species, which likely influence bloom dynamics.

Herbivores strongly influence macroalgal community structure. Crustacean herbivores may be important in some systems; the Northern Kelp crab (Pugettia producta) is a common sub-tidal species with reported feeding preferences for kelp. In the Salish Sea, standing beds of Macrocystis pyrifera, a highly preferred food of Pugettia in California, do not occur; instead, the dominant canopy-forming kelp is Nereocystis luetkeana. However, drift Macrocystis occasionally washes up following autumn storms. This study used laboratory feeding trials to address whether Pugettia that live where Macrocystis beds do not occur will consume it and how their consumption of this less-familiar kelp compares to their feeding on the locally abundant Nereocystis. We found that Pugettia consumed much greater quantities of drift Nereocystis than drift Macrocystis in both choice and no-choice feeding experiments. Chemical analyses suggest no difference in phlorotannin levels between Nereocystis and Macrocystis, although Nereocystis had a slightly more favorable C:N than Macrocystis. The observed preference for bull kelp exhibited by Pugettia in the Salish Sea may be explained by the fact that only bull kelp is familiar, locally abundant, nutritious, and provides suitable crab habitat.

Accumulations of green macroalgae (green tides) are becoming increasingly common in many coastal habitats and substances released by these blooms may impact other organisms. In the northeastern Pacific, a dominant contributor to green tides is Ulvaria obscura, an alga that produces dopamine which affects a variety of physiological processes and can trigger metamorphosis in marine invertebrates. Eggs, embryos, and larvae of Pacific oysters (Crassostrea gigas) and sand dollars (Dendraster excentricus) were exposed to U. obscura exudates and dopamine to determine how exposure affects fertilization, development, and morphology. Exposing eggs to these compounds had no significant effect on fertilization of C. gigas and limited impact on D. excentricus, relative to unexposed controls. Early embryos exposed to the compounds developed successfully, but the resulting C. gigas veligers had larger shells and the D. excentricus gastrulae had shorter archenterons. When exposed to dopamine, C. gigas veligers had smaller shells, while larval arms of D. excentricus were significantly shorter relative to unexposed controls. Results indicate that compounds released by U. obscura affect development differently between invertebrate species and among developmental stages. The stage-specific responses likely result from changes in structure and metabolic activity at different life history stages, as well as changes in the localization and function of dopamine and dopamine receptors that occur during larval development. The changes in larval morphology and function induced by compounds released by marine macroalgae could ultimately impact the ability of larvae to feed and survive.

Dopamine is produced by Ulvaria obscura, a bloom-forming green alga that occurs from the mid intertidal to the shallow subtidal zones of North Pacific and North Atlantic shores. Its concentrations in the alga are approximately 0.5–1% of the alga's fresh mass. When experimentally desiccated and rehydrated at ecologically realistic densities, Ulvaria releases dopamine, resulting in seawater dopamine concentrations that can exceed 500 μM. Thus, dopamine could be responsible for previous reports of bioactivity by Ulvaria exudates. We tested this hypothesis by measuring the effects of dopamine in seawater on co-occurring macroalgae and crab larvae and juveniles. We ran assays that examined the effects of a range of dopamine concentrations on the growth of the green alga Ulva lactuca, on the germination of zygotes of the brown alga Fucus distichus, and on the survival, time to metamorphosis and time to first molt of crab (Metacarcinus magister and Cancer oregonensis) larvae and juveniles. Dopamine began to inhi...

Macroalgal blooms are occurring in greater size and frequency and many of these blooms are composed of ulvoid green algae. Ulvoid algae can release a variety of allelopathic compounds that include reactive oxygen species (ROS), oxidants that have detrimental effects on other organisms. When algae are subjected to environmental stressors, oxidant production increases and can exceed the scavenging capacity of antioxidants, which can result in the passive diffusion of excess ROS into the extracellular environment. Because macroalgal blooms consist of high biomasses of algae and occur in intertidal or shallow subtidal habitats where they experience large and rapid changes in environmental conditions, there is the potential for significant releases of ROS into waters that contain them. To examine the effects of environmental stressors on the accumulation of oxidants around bloom-forming ulvoid algae, we manipulated emersion times, extracellular dopamine concentrations following emersion, seawater temperatures following emersion, and seawater oxygen concentrations and then measured the accumulation of extracellular oxidants around Ulva lactuca and Ulvaria obscura. In most cases, the accumulations of oxidants were similar among our experimental treatments except that the concentrations of extracellular oxidants resulting from Ulva were significantly lower when algae were exposed to either dopamine or high water temperatures than they were from controls or lower temperatures, respectively. The accumulations of oxidants in water surrounding Ulvaria were higher in unemersed than emersed algae, regardless of emersion time. These differences in concentrations of extracellular oxidants were most likely due to differences in algal photosynthetic rates among treatments, although oxidant decay and the upregulation or activation of antioxidants may also have affected our measurements. Based on the relatively high concentrations of oxidants that we measured and the interspecific and environmentally-driven differences in their accumulations, we hypothesize that accumulations of oxidants in waters near intertidal or shallow subtidal macroalgal beds will be larger in magnitude, more driven by biotic sources, and more seasonally and spatially variable than those measured farther offshore.

In the NE Pacific, Ulvaria obscura is a common component of "green tide" blooms. It is also the only alga known to produce dopamine, which is released into seawater on sunny days when Ulvaria is emersed and then rehydrated. To better understand the mechanisms associated with dopamine release, we experimentally determined whether light quantity and quality, desiccation, temperature, exudates from conspecifics, and dissolved dopamine caused dopamine release. We also examined the effects of desiccation on Ulvaria's ability to photosynthesize, grow, and survive. Desiccation was the only factor that caused significant amounts of dopamine to be lost from U. obscura tissues. The loss of water from Ulvaria tissues was strongly and positively correlated with the loss of dopamine after rehydration. Only 56% of desiccated algae survived for 1 week, compared to 100% of undesiccated control algae. Desiccated algae lost 77% of their pigmented surface area and grew only 15% as much as undesiccated algae, which remained fully pigmented. The oxygen saturation of water containing Ulvaria that was desiccated and then rehydrated was significantly lower than that of seawater containing undesiccated algae. Thus, desiccation, which is coupled with dopamine release, is associated with the deterioration and death of some, but not all, tissues in Ulvaria. Although dopamine released into seawater can reduce the survival or growth of potential competitors, its release is associated with significant physiological stress and tissue mortality. However, the survival and continued growth of some Ulvaria tissues indicates that a net fitness benefit to release dopamine following desiccation cannot be ruled out.

Phenolic compounds are found in all brown macroalgae and function as cell wall structure, UV protection and as herbivore deterrents. The concentrations of phenolic compounds vary among taxa and between temperate and tropical ecosystems. Australasia has high concentrations of soluble phenolics compared to other regions. Presently, relationships between phenolic concentrations and environmental gradients are unclear. The purpose of this study was to determine the soluble phenolic concentrations of brown seaweeds along temperate and tropical ecosystems of the Western Australia coastline. We tested the hypothesis that phenolic concentrations are related to local and broad-scale abiotic environmental gradients. Strong environmental gradients of coastal Western Australia provided the opportunity to characterize phenolic compounds across one large gradient. Phenolic concentrations of brown seaweeds at seven study locations varied across latitude with higher concentrations found at higher latitudes and were comparable to seaweeds from similar latitudes in Australia. This trend coincided with a negative relationship between photosynthetically active radiation and phenolic compounds, and a positive relationship with salinity. We also found phenolic concentrations were positively related to salinity in tropical Shark Bay but this was dependent on species. Environmental conditions are important in regulating concentrations of phenolic compounds. Multiple factors influence the concentrations of macroalgal phenolic compounds creating unique distributions among geographical regions. This study highlighted the importance of considering multiple factors when studying phenolic ecology and suggests photosynthetically active radiation and salinity as important drivers of phenolic compound distribution in Western Australia.

Ulvaria obscura, a prominent component of green tide blooms in Washington, is unique among macroalgae because it contains dopamine. To examine dopamine release by U. obscura following simulated low tides, we conducted 6 field experiments in which algae were emersed for 75 min and then immersed in filtered seawater (FSW). Dopamine was measured in algal tissues prior to emersion and 3 h after immersion and in seawater for 3 h following immersion. In our experiments, algae released 7–100% of their tissue dopamine, resulting in average seawater concentrations of 3–563 μM. In 5 of 6 experiments, seawater dopamine concentrations were highest immediately after immersion, and then decreased over time. The percentages of dopamine released were not correlated with tissue dopamine concentrations, but were positively correlated with solar radiation during emersion. The release of dopamine, which is both cytotoxic and genotoxic, may explain the negative effects of U. obscura exudates on marine organisms.

Recreational clam harvesters at Northwest Penn Cove leave pools in the sediments that fill with porewater before being inundated by the incoming tide. We hypothesized that this nutrient-rich porewater may affect ulvoid algal growth. To test this, we measured nutrient concentrations in seawater, tidepools, shellfishers' pools, and in porewater from the top 9 cm of the sediment. On average, sediment porewater was 4495% higher in ammonium, 772% higher in nitrite, and 3238% higher in phosphate than nearby seawater; nitrate concentrations in porewater were 35% of the seawater concentrations. Water in shellfishers' pools was 291% higher in ammonium and 122% higher in nitrite than seawater. Nitrate and phosphate concentrations in shellfishers' pools and seawater did not differ significantly. We then transplanted Ulva lactuca around shellfishers' pools, tidepools, and onto the mudflat. Transplanted algae did not differ significantly in tissue carbon, nitrogen, and phosphorus concentrations after 2 days. However, the algae transplanted around shellfishers' pools grew 20% more over two weeks than the algae transplanted around tidepools and onto mud flats. Our results suggest that the nutrient-rich water in shellfishers' pools enhances algal growth near the pools and may contribute to the formation and persistence of the Ulva bloom at this site.

In this study, we investigated why a littorinid snail, Littorina sitkana, preferentially consumes the ulvoid green algae Ulva lactuca and Ulva linza, even though these algae contain high concentrations of dimethylsulfoniopropionate (DMSP), which has been shown to be the precursor to an activated defense that deters feeding by sea urchins (Strongylocentrotus droebachiensis and S. purpuratus). When urchins consume algae containing DMSP, the DMSP is rapidly cleaved into DMS and acrylic acid, which are feeding deterrents to the urchins. In multiple-choice feeding-preference assays, L. sitkana consumed U. lactuca and U. linza at a greater rate than six other algal species. In experiments to confirm that DMSP was being cleaved by the snails, DMS was generated when snails were fed either U. lactuca or U. linza, but was not present in containers with snails alone or algae alone. In laboratory bioassays, acrylic acid reduced feeding by snails when it was incorporated into agar-based diets at concentrations of 0.25% and 0.50% of the food's fresh mass, demonstrating that the animals are deterred by one of the products of DMSP cleavage. When feeding rates from multiple-choice feeding-preference assay were compared to the carbon to nitrogen ratio (C:N) of the macroalgae, there was a strong negative linear relationship between grazing rates and C:N until a C:N of ~ 8 was reached. Algae with a C:N higher than 8 were avoided by snails. When the snails were offered agar-based diets containing a range of nitrogen concentrations (1.96–6.85% of the dry mass), feeding rates were positively correlated with the diets' nitrogen concentrations and negatively correlated with their C:N. Because L. sitkana forages only during low tides, it may have a limited window of time to obtain sufficient nitrogen. Therefore, it may preferentially select foods with high nitrogen concentrations, even though these foods contain chemical defenses.

The sulphonium compound dimethylsulphoniopropionate (DMSP) is commonly found in temperate green macroalgae. To examine taxonomic and regional and local geographical patterns of DMSP production in Australasian algae, I collected 30 species of green algae from 14 sites in three regions, eastern Australia, Tasmania, Australia, and the North Island of New Zealand. The distribution of DMSP content was similar to that seen from other areas of the world. DMSP was found in high concentrations inUlvaandCodiumspp. It tended to be undetectable or in lower concentrations in other members of the orders Bryopsidales and Cladophorales. There was no evidence for differences in concentrations among the three regions in the generaCodiumandUlva; however, the invasive subspecies ofCodium fragile, C. fragilessp.tomentosoides, had significantly higher concentrations of DMSP than the non-invasivesubspecies.The herbivorous sea slugElysia maoriahad whole body concentrations that were not significantly different from those of its host algaC. fragilessp. tomentosoides. The distribution patterns of DMSP inCodiumspp. do not support the hypothesis that DMSP is used as an antioxidant in this genus. Based on the data collected here and previous reports from the literature, I speculate that one function of DMSP in these algae may be to deter herbivores.

Green macroalgal blooms have substantially altered marine community structure and function, specifically by smothering seagrasses and other primary producers that are critical to commercial fisheries and by creating anoxic conditions in enclosed embayments. Bottom-up factors are viewed as the primary drivers of these blooms, but increasing attention has been paid to biotic controls of species composition. In Washington State, USA, blooms are often dominated by Ulva spp. intertidally and Ulvaria obscura subtidally. Factors that could cause this spatial difference were examined, including competition, grazer preferences, salinity, photoacclimation, nutrient requirements, and responses to nutrient enrichment. Ulva specimens grew faster than Ulvaria in intertidal chambers but not significantly faster in subtidal chambers. Ulva was better able to acclimate to a high-light environment and was more tolerant of low salinity than Ulvaria. Ulvaria had higher tissue N content, chlorophyll, chlorophyll b: chlorophyll a, and protein content than Ulva. These differences suggest that nitrogen availability could affect species composition. A suite of five grazers preferred Ulva to Ulvaria in choice experiments. Thus, bottom-up factors allow Ulva to dominate the intertidal zone while resistance to grazers appears to allow Ulvaria to dominate the subtidal zone. While ulvoid algae are in the same functional-form group, they are not functionally redundant.

In this study, we present evidence that the invasive alga Codium fragile ssp. tomentosoides is chemically defended against grazing by a wound-activated chemical defense involving dimethylsulfoniopropionate (DMSP) and the products of its cleavage, dimethylsulfide (DMS), and acrylic acid (AA). DMSP in C. fragile ssp. tomentosoides was present throughout the year, but concentrations varied seasonally and were highest in the winter. Intra-thallus variation was neither large, nor consistent over time. High DMSP concentrations were uncommon among northwestern Atlantic macrophytes. Of 26 other species tested, only two, Ulva lactuca and Polysiphonia harveyi contained concentrations comparable to, or higher than, those of C. fragile ssp. tomentosoides. DMS and AA, both individually and together, deterred grazing by the green sea urchin Strongylocentrotus droebachiensis at “natural” concentrations. These results suggest that DMS and AA contribute to the avoidance of C. fragile ssp. tomentosoides by S. droebachiensis. As a result, the production of DMSP and its subsequent cleavage, upon injury, may reduce herbivory on C. fragile ssp. tomentosoides and contribute to its success.

The production of dimethylsulfoniopropionate (DMSP) and its cleavage products are well studied in phytoplankton. However, less is known about their sources, distributions, functions, and impacts in other marine organisms. We examined the distribution of DMSP in benthic macroalgae and macroinvertebrates geographically and taxonomically. In macroalgae, concentrations significantly increased from the tropics to the poles in the northern, but not the southern, hemisphere. The increase in the northern hemisphere was due to an increase in concentrations with latitude in the Chlorophyta. This pattern was generated by a relatively high proportion of species in the order Ulvales (median [DMSP]: 145 μmol g-1 dry mass (DM)) at higher latitudes, and a high proportion of species in the orders Caulerpales and Siphonocladales (median [DMSP]: below detection level for both orders) in the tropics. Low DMSP concentrations (< 10 μmol g-1 DM) were reported from all red and brown macroalgae, except Polysiphonia and Halopytis. In macroalgae, some of the reported functions of DMSP and its cleavage products included acting as a compatible solute, an anti-herbivore defense, a reactive oxygen scavenger, and a cryoprotectant. Among macroinvertebrates, DMSP occurred in higher concentrations in cnidarians than in sponges and molluscs. Concentrations in animals harboring endosymbiotic algae were 6.5 times higher than animals without symbionts. This and direct measurements of DMSP from isolated symbionts suggest that endosymbionts are a major source of DMSP for some macroinvertebrates. Diet may be a source of DMSP in animals that lack endosymbionts. The functions and impacts of DMSP in invertebrates are not well known.

We investigated the presence and kinetics of the oxidative stress response in intertidal and subtidal individuals of the ulvoid macroalga Ulva lactuca L. Stress responses, as measured with both enzymatic and fluorescent-based antioxidant assays, differed between individuals collected from a subtidal and an intertidal habitat. Subtidal individuals secreted significantly more hydrogen peroxide (H2O2) than intertidal individuals when subjected to osmotic stress or desiccation. The activity of reactive-oxygen-scavenging enzymes and the ability to scavenge exogenous H2O2 were lower in subtidal than in intertidal individuals, suggesting that subtidal individuals are less stress tolerant. In vitro experimentation demonstrated that millimolar concentrations of dimethylsulfoniopropionate (DMSP) and its breakdown products could efficiently scavenge H2O2, with DMSP being a less-effective scavenger than dimethyl sulfide (DMS), acrylic acid, and acrylate. The addition of H2O2 at concentrations of 2.5 mM or greater induced the cleavage of DMSP into DMS and acrylic acid in subtidal individuals. Intertidal individuals were affected in the same manner with the addition of 5 mM H2O2. There were no differences in the amounts of DMSP cleavage in subtidal and intertidal algae when the algae were subjected to hyposaline conditions. Our data suggest that the oxidative-stress-induced cleavage of DMSP affords products with efficient H2O2-scavenging abilities. In addition, U. lactuca individuals growing in intertidal habitats are better acclimatized to changing environments and thus have a higher threshold for oxidative stress than conspecifics in subtidal habitats.

Green tides are large growths or accumulations of green seaweeds that have been increasing in magnitude and frequency around the world. Because green tides consist of vast biomasses of algae in a limited area and are often seasonal or episodic, they go through periods of rapid growth in which they take up large amounts of nutrients and dissolved gases and generate bioactive natural products that may be stored in the plants, released into the environment, or broken down during decomposition. As a result of the use and production of inorganic and organic compounds, the algae in these blooms can have detrimental impacts on other organisms. Here, we review some of the effects that green tides have on the chemistry of seawater and the effects of the natural products that they produce. As blooms are developing and expanding, algae in green tides take up inorganic nutrients, such as nitrate and ortho-phosphate, which can limit their availability to other photosynthetic organisms. Their uptake of dissolved inorganic carbon for use in photosynthesis can cause localized spikes in the pH of seawater during the day with concomitant drops in the pH at night when the algae are respiring. Many of the algae that form green-tide blooms produce allelopathic compounds, which are metabolites that affect other species. The best documented allelopathic compounds include dimethylsulfoniopropionate (DMSP), dopamine, and reactive oxygen species (ROS) and their breakdown products. DMSP and dopamine are involved in defenses against herbivores. Dopamine and ROS are released into seawater where they can be allelopathic or toxic to other organisms. Thus, these macroalgal blooms can have harmful effects on nearby organisms by altering concentrations of nutrients and dissolved gas in seawater and by producing and releasing allelopathic or toxic compounds.

Although dimethylsulfoniopropionate (DMSP) has a variety of functions in marine macroalgae including that of a cryoprotectant, an osmolyte, a way to remove excess sulfur and energy, an antioxidant, and an allelopathic precursor, the latter two functions are believed to be the most important in Ulva lactuca L. (=U. fenestrata) in intertidal populations on the coast of Washington state, USA. The present study found significant variation in DMSP concentrations among U. lactuca collected in May 2005 from six sites ranging from 47°54.45′N (Possession Point, Whidbey Island, WA, USA) to 48°30.55′N (Shannon Point Beach, Anacortes, WA, USA), and also among individuals within sites, and among tissues (basal tissues near the holdfast, middle of the blades, and tips). Concentrations ranged from 37 to 224 μmol g−1 fresh mass (FM). In several 10-day experiments between July 2001 and August 2004 with U. lactuca collected from several places on the coast of Washington, the effects of nutrient level (DIN), light intensity and wavelength, and grazing by the herbivorous gastropod Lacuna vincta, were examined. None of these manipulations resulted in DMSP concentrations that differed significantly from controls, and variance in DMSP concentrations within each experiment was very low. Although DMSP concentrations in U. lactuca may be affected by factors not tested in these experiments, it is also possible that the observed spatial differences reflect constitutive genotypic or phenotypic differences among geographically separated U. lactuca populations or among cryptic Ulva species.

This study compared algal palatability and chemical defenses from subtropical green algae that may use different types of defense systems that deter feeding by the rock-boring sea urchin Echinometra lucunter. The potential defense systems present include (1) the terpenoid caulerpenyne and its activated products from Caulerpa spp., and (2) dimethylsulfoniopropionate (DMSP)-related defenses in Ulva spp. Secondary metabolites from these chemical groups have been shown to deter feeding by various marine herbivores, including tropical and temperate sea urchins. Live algal multiple-choice feeding assays and assays incorporating algal extracts or isolated metabolites into an artificial diet were conducted. Several green algae, including Ulva lactuca, Caulerpa prolifera, and Cladophora sp., were unpalatable. Nonpolar extracts from U. lactuca deterred feeding, whereas nonpolar extracts from C. prolifera had no effect on feeding. Polar extracts from both species stimulated feeding. Caulerpenyne deterred feeding at approximately 4% dry mass; however, dimethyl sulfide and acrylic acid had no effect at natural and elevated concentrations. E. lucunter is more tolerant than other sea urchins to DMSP-related defenses and less tolerant to caulerpenyne than many reef fish. Understanding the chemical defenses of the algae tested in this study is important because they, and related species, frequently are invasive or form blooms, and can significantly modify marine ecosystems.

Nitrogen is a necessary element for much of seaweed physiology, and is the most common limiting nutrient for marine macroalgae. Therefore, the content of nitrogen in algal tissue is often considered a useful indicator of algal productivity. However, the significance of algal nitrogen content in the field is understudied. We used a factorial manipulation of light and herbivory at three sites in order to evaluate how three factors (light, herbivory, wave exposure) affect the nitrogen content of the brown alga Fucus gardneri. We found that nitrogen content was a function of (1) nitrogen supply via amount of water flow and (2) irradiance, possibly via photoinhibitory effects. This research shows that local effects, by shifting nutrient allocation, can change nitrogen content over spatial scales of centimeters.

Dimethylsulfoniopropionate (DMSP) is an important component of the global sulfur cycle and may be involved, via its cleavage product dimethylsulfide, in climate regulation. Although it is common in many algae, reports of DMSP in animals, particularly tropical invertebrates, are limited. This study examined the distribution of DMSP in a diverse group of coral reef invertebrates. DMSP was present in all 22 species of cnidarians and ranged from 9 to 723 μmol g−1 of dry mass (DM) with a mean (± 1SD) of 110 ± 180 μmol g−1 DM. It was not detected in a flatworm and an ascidian or in two of five sponges. Concentrations in sponges ranged from undetectable to 16 μmol g−1 DM with a mean of 4 ± 7 μmol g−1 DM. Within the cnidarians, DMSP concentrations did not differ among orders. Among cnidarian species, DMSP concentrations were correlated with symbiotic zooxanthellae densities. Within cnidarian species, DMSP concentrations of individuals were positively correlated with zooxanthellae densities in three of the four species examined. We speculate that DMSP is dietarily derived in sponges and derived from zooxanthellae in the cnidarians. The functions of DMSP in coral reef invertebrates are not known.

Diminishing levels of atmospheric ozone are increasing UV stress on intertidal algae. Early developmental stages tend to be more susceptible to environmental stresses; however, little research has examined how these stages are protected from UV radiation (UVR). Many brown algae contain high levels of phlorotannins, which are thought to function in screening UVR. In this study, we tested the effects of ambient levels of UV-B and UV-A on growth and phlorotannin production in 1- to 2-cm juvenile and microscopic postsettlement embryos of the intertidal alga Fucus gardneri Silva. Algae were grown in four light treatments: 1) ambient light; 2) under cellulose acetate, which lowered light quantity but did not affect light quality; 3) under MylarTM, which filtered UV-B; and 4) under PlexiglasTM, which blocked UV-A and UV-B. Over a 3-week period, UV-B inhibited and UV-A enhanced the growth of F. gardneri embryos, whereas the growth of juveniles was not affected. Phlorotannin concentrations of both embryos and juveniles did not differ in any of the light treatments. Our results suggest that embryos of F. gardneri are susceptible to UV light but develop a tolerance to it as they mature. This tolerance may result from increases in phlorotannin concentrations that occur during maturation; however, phlorotannin production in embryonic or juvenile stages is either not induced by UV light or takes more than 3 weeks to occur.

We tested whether experimentally enhancing nutrients around the kelp Hedophyllum sessile would increase growth, tissue nitrogen, or allocation to phenolic compounds. Packets of time-released fertilizer were anchored adjacent to fronds in the field, and algae were monitored for several months. Although fertilizer packets increased the concentration of ammonium, nitrate, and phosphorus adjacent to treatment algae by an order of magnitude, there was little evidence that this increased frond growth or size. Hedophyllum individuals showed no tendency to alter allocation patterns in response to nutrient addition. Tissue carbon and nitrogen was unchanged by the nutrient manipulation; most H. sessile had tissue nitrogen concentrations in excess of 2.0% of dry mass. Additionally, the concentration of phloroglucinol equivalents was also unaffected by the presence of increased water column nutrients. Although nutrient concentrations in the water column surrounding the study site show relatively high mean values for ammonium, nitrate, and phosphorus, they are characterized by high spatial and temporal variation. Nonetheless, these data suggest that this intertidal kelp is not limited by nitrogen or phosphorus in wave-exposed areas in the northeast Pacific Ocean.

Almost half the biogenic sulfur emitted globally originates as dimethylsulfide (DMS) in marine algae. Yet, despite its importance to climate and the global sulfur cycle, the reasons why many diverse algal taxa produce DMS remain unclear. DMS is produced when dimethylsulfoniopro- pionate (DMSP) is cleaved by the enzyme DMSP lyase into DMS and acrylic acid. Because acrylic acid can deter feeding by some herbivores, the production of DMSP has been postulated to be part of an antiherbivore chemical defense system, with DMS being a by-product of the production of the defensive compound acrylic acid. However, we found that DMS plays a more direct role in herbivore deterrence. Using laboratory bioassays, we demonstrated that DMS functions as a potent feeding deterrent against sea urchins Strongylocentrotus droebachiensis at a wide range of concentrations. The defensive function of DMSP cleavage is further supported by the results of a multiple-choice feeding preference assay in which we offered urchins a choice of 8 algal species. In these assays, algae containing DMSP tended to be consumed at lower rates than species that lacked it. By measur- ing headspace DMS concentrations during grazing, we showed that DMS is produced when urchins feed on algae containing DMSP, but not when urchins feed on algae without it. DMS production occurred while the urchins were feeding on the algae and for 18 h after the algae were removed, suggesting that post-ingestive processes might be playing a role in activation. These results demon- strate that DMS is produced when urchins feed on algae containing DMSP and that it functions as an herbivore deterrent, causing species that produce DMSP to be avoided by some herbivores.

Activated defenses against herbivores and predators are defenses whereby a precursor compound is stored in an inactive or mildly active form. Upon damage to the prey, the precursor is enzymatically converted to a more potent toxin or feeding deterrent. In marine systems, activated defenses are only known to exist in a few species of tropical macroalgae. In this study, we examined an activated defense system in temperate marine macroalgae in which the osmolyte dimethylsulfo- niopropionate (DMSP) is converted to acrylic acid or acrylate, depending upon the pH, and dimethyl sulfide (DMS) by the enzyme DMSP lyase upon damage to the alga. We surveyed 39 species of red, green, and brown algae from the Washington and Oregon coasts, and found high concentrations of DMSP in the chlorophytes Acrosiphonia coalita, Codium fragile, Enteromorpha intestinalis, E. linza, Ulva californica, U. fenestrata, and U. taeniata, and in the rhodophyte Polysiphonia hendryi. Con- centrations of DMSP ranged from 0.04% of the alga's fresh mass (FM) to 1.8% FM. We found signif- icant DMSP lyase activity in 1 green alga, U. fenestrata, and 1 red alga, P. hendryi, with DMSP cleav- age rates approaching 300 mmol kg -1 FM min -1 . Loss of DMSP and the production of DMS when the tissues of U. californica and P. hendryi were crushed suggested that physical damage results in DMSP cleavage. In laboratory feeding preference experiments, acrylic acid deterred feeding by the sea urchin Strongylocentrotus droebachiensis at concentrations of 0.1 to 2% FM and by S. purpura- tus at 0.25 to 2% FM, while the precursor DMSP functioned as a feeding attractant to both sea urchins. In contrast, feeding by the isopod Idotea wosnesenskii was not deterred by acrylic acid even at concentrations as high as 8% FM. Our data suggest that DMSP may function as a precursor in an activated defense system in diverse species of temperate macroalgae and may possibly contribute to the widespread success of the Ulvophyceae. This chemical system is also found in unicellular phyto- plankton, and presents an opportunity to compare and contrast the ecological role of chemical defense among micro- and macroorganisms.

Resource-allocation models predict trade-offs between growth and chemical defense. The carbon/nutrient balance hypothesis (CNBH) predicts that plants will allocate carbon to growth when nutrients are abundant and allocate it to carbon-based antiherbivore defenses when nutrients are limiting. In marine systems, field and laboratory tests of the CNBH with phlorotannin-producing algae have generally supported the predictions of the model. However, these tests have all measured phlorotannin concentrations in adult algae rather than juveniles, which are susceptible to higher grazing pressures. We experimentally tested some of the predictions of the CNBH in early post-set- tlement stages of a common intertidal macroalga, Fucus gardneri, by growing F. gardneri embryos in media enriched with 3 nutrients: nitrogen, phosphorus, and iron. Phlorotannin concentrations across all treatments were correlated with embryo size but not with growth rates. As predicted by the model, nitrogen enrichment significantly enhanced embryo growth rates and decreased phlorotannin con- centrations. Iron enrichment alone had no effect on phlorotannin concentrations, but did affect growth. The effects on growth were primarily in altering morphology rather than changing the over- all size of the embryos. Phosphorus enrichment had no effect on growth, but did significantly lower phlorotannin concentrations. Surprisingly, there was a significant iron-phosphorus interaction effect on both growth and phlorotannin concentrations. Enrichment with a combination of iron and phos- phorus had a stronger negative effect on growth and phlorotannin concentrations than would have been predicted based on the individual effects of these 2 nutrients. The combination of iron and phos- phorus enrichment may have physiologically stressed the embryos, resulting in decreased phlorotan- nin production. Our results suggest that ontogeny plays a strong role in determining secondary metabolite levels and that nutrient addition can affect secondary metabolite production in embryos by (1) altering resource allocation patterns, or (2) providing a physiological stress that results in reduced secondary metabolite production.

Optimal defense theory (ODT) predicts antiherbivore defensive compounds will be allocated so that the most valuable or most susceptible tissues will be best defended. The growth–differentiation balance hypothesis (GDBH) predicts that defense allocation will be a result of trade-offs between growth and defense. Thus, these two theories predict opposite allocation patterns with respect to “valuable,” actively growing meristematic and reproductive tissues. ODT predicts that meristems and reproductive tissues should have higher defense levels than nonmeristematic vegetative tissues; the GDBH predicts the defense levels of meristems and reproductive tissues will be lower than vegetative tissues. We examined allocation patterns of phlorotannins in 21 species of kelps (Order Laminariales) and rockweeds (Order Fucales) from nine sites on the west coast of the United States to determine if allocation patterns better matched the predictions of ODT or the GDBH and to look for differences in allocation patterns among sites. Within-species differences in phlorotannin levels occurred in 10 of the 21 species examined. Meristems of both kelps and rockweeds had higher phlorotannin levels than nonmeristematic vegetative tissues, consistent with ODT. Phlorotannin levels in reproductive tissues of kelps were higher than vegetative tissues, but levels in reproductive tissues of rockweeds were lower than vegetative tissues, indicating that allocation strategies may follow taxonomic lines. Allocation patterns differed among sites in four of the 16 species collected from more than one site. Differences in allocation patterns among sites were usually changes in the ratios of phlorotannins in well-defended compared to poorly defended tissues, rather than changes in which tissues were well defended or poorly defended. We concluded that environmental variability can have large effects on the concentration of phlorotannins in algae but has limited effects on allocation patterns among tissues.

Oceanic dimethylsulfoniopropionate (DMSP) is the precursor to dimethylsulfide (DMS), which plays a role in climate regulation through transformation to methanesulfonic acid (MSA) and non-seasalt sulfate (NSS-SO 4 2− ) aerosols. Here, we report measurements of the abundance and sulfur isotope compositions of DMSP from one phytoplankton species ( Prorocentrum minimum ) and five intertidal macroalgal species ( Ulva lactuca , Ulva linza, Ulvaria obscura, Ulva prolifera , and Polysiphonia hendryi ) in marine waters. We show that the sulfur isotope compositions (δ 34 S) of DMSP are depleted in 34 S relative to the source seawater sulfate by ∼1–3‰ and are correlated with the observed intracellular content of methionine, suggesting a link to metabolic pathways of methionine production. We suggest that this variability of δ 34 S is transferred to atmospheric geochemical products of DMSP degradation (DMS, MSA, and NSS-SO 4 2− ), carrying implications for the interpretation of variability in δ 34 S of MSA and NSS-SO 4 2− that links them to changes in growth conditions and populations of DMSP producers rather than to the contributions of DMS and non-DMS sources.

Concentrations and types of antipredator defenses vary among tissues within colonies of many colonial marine invertebrates. However, experimental tests have rarely been conducted to assess the consequences of differences in defenses among tissues. We used field bioassays at Guam with generalist carnivorous fishes to compare feeding rates on artificial diets that contained physical and chemical defenses from three species of tropical soft corals, Sinularia maxima, S. polydactyla , and an undescribed species of Sinularia . Crude extracts and sclerite concentrations were added to the diets in concentrations similar to those found in two areas of the colonies, the polypcontaining tips and the sterile bases. By manipulating extract and sclerite concentrations in the diets, we determined that extracts were the major form of protection in the tips of the colonies of all three species. Sclerites from the tips had little impact on predator deterrence. In the bases of two species, S. polydactyla and Sinularia sp., both extracts and sclerites contributed to the deterrence of predators. However, in S. maxima , only base sclerites affected the foraging rates of fishes, the addition of base extracts had no effect. We also manipulated crude extract concentrations without sclerites present to determine whether differences in crude extracts concentrations between the bases and the tips of the colonies were responsible for the differences in the effectiveness of the extracts as predator deterrents. When tested at the same concentrations, tip and base extracts were equally effective deterrents. Field bioassays with flash coloumn fractions demonstrated that in all three species of soft corals, predator deterrence is due to the combined effect of several different compounds. Our results show that differences in the types and concentrations of antipredator defenses present in different locations within the colonies of benthic invertebrates affect the susceptibility of those tissues to predation.

Gastropods from wave-exposed shores are typically smaller and thinner-shelled with a larger foot than gastropods from protected shores. We investigated the value of these adaptations by comparing the survival and growth of one exposed shore species and one protected shore species of Littorina transplanted to wave-exposed and protected shores. Adult snails on exposed shores with heavy surf had reduced winter growth rates and low over-winter survival rates. Demographic studies of the exposed shore species showed that few adults survived the winter at the most exposed sites; recruitment to the following year's population was primarily from small juveniles that overwintered between barnacles and within algae. The protected shore species had slightly lower survival than the exposed shore species on exposed shores. The protected shore species was also more susceptible to dislodgement in a flow tank. The low winter growth rates and survival may explain why the large, late-maturing, protected shore species does not occur on exposed shores. Adult snails on protected shores had moderate winter growth rates and moderate over-winter survival. The exposed shore species survived very poorly on protected shores, in part because of predation by shore crabs. In laboratory experiments the thin-shelled exposed shore species was significantly preferred by shore crabs and withstood significantly less force. The small size, thin shell, and large shell aperture of the exposed shore species makes it vulnerable to the shore crabs and may explain why it does not occur on protected shores.

Halimeda spp. are among the most common seaweeds on tropical reefs where herbivory is intense. These calcified seaweeds produce diterpenoid feeding deterrents; the major metabolites are halimedatetraacetate and halimedatrial. We found that most species of Halimeda on Guam immediately convert the less-deterrent secondary metabolite halimedatetraacetate to the more potent feeding deterrent halimedatrial when plants are injured by grinding or crushing. This conversion would therefore occur when fishes bite or chew Halimeda plants. We term this process of rapid conversion “activation”. Extracts from injured plants contained higher amounts of halimedatrial and were more deterrent toward herbivorous fishes than extracts from control plants. Herbivore-activated defenses are common in many families of terrestrial plants: however, this is the first example of an activated defense in a marine plant.

Cyphoma gibbosum is an ovulid predatory gastropod that specializes on gorgonians, many of which contain secondary metabolites and calcified sclerites that serve as antipredator defenses. In field and shipboard feeding assays, we examined the role of gorgonian crude extracts and sclerites as feeding deterrents to generalist predators and to C. gibbosum. Crude extracts and sclerites were isolated from Gorgonia ventalina, a Caribbean sea fan on which C. gibbosum feeds, and incorporated into a carrageenan-based artificial diet. In shipboard feeding experiments, artificial diet containing G. ventalina crude extracts was consumed 49% less by C. gibbosum, than artificial diet lacking extracts. The addition of G. ventalina sclerites to the diet also reduced feeding by Cyphoma by about one half. The addition of extracts to the artificial diet reduced feeding by natural assemblages of tropical fishes at Cross Harbor, Great Abaco Island, Bahamas by 87%; sclerites reduced feeding by fishes by 95%. Gorgonia ventalina extracts were composed of at least a dozen nonpolar terpenoids. Fractions containing these compounds were feeding deterrents towards fishes in the field. Unlike many terrestrial oligophagous specialists, C. gibbosum is not immune to the defenses produced by its prey.

Environmental context Dimethyl sulfide (DMS) is released by marine algae and is important to sulfur transfer between the oceans and the atmosphere. We measured DMS emissions from algae that form large blooms, and found that the hydration of the plants, seawater temperatures and salinity affect DMS release, but their effects were species-specific. Thus, the effect of algal blooms on sulfur transfer will depend on the bloom’s species composition and the environmental conditions experienced by the algae. Abstract Bloom-forming ulvoid macroalgae produce dimethylsulfoniopropionate (DMSP), which when cleaved in response to biotic and abiotic stresses results in the emission of dimethyl sulfide (DMS) into the atmosphere. We quantified DMS emission rates from three intertidal seaweeds (Ulva intestinalis, Ulva lactuca and Ulvaria obscura) that form green tide blooms in the Salish Sea. The algae were subjected to different salinities (freshwater to seawater), temperatures (15 to 35°C) and desiccation levels, and DMS emission rates were measured. We also quantified tissue DMSP concentrations and DMS emissions by different life history stages of U. intestinalis. All three species had significantly higher emission rates if the plants were dry, relative to damp or submerged plants, with highest emissions in the high intertidal species and lowest emissions in the low intertidal species. Seawater temperature did not affect emission rates by U. intestinalis or U. lactuca, but emission rates by U. obscura were significantly higher at 35°C. Hyposaline conditions also increased emission rates by U. obscura and U. lactuca but had no effect on emission by U. intestinalis. DMSP concentrations did not differ in sporophytes and gametophytes, but were twice as high in the tips as the bases of sporophytes. Most spores were released from the tips of the blades. Spores had average DMSP concentrations of 258±114 fmol spore–1. Our results demonstrate that the amounts of DMS emitted by green tides will depend on the bloom’s species composition and the environmental conditions experienced by the algae.

Small (3–7 cm long) Fucus distichus ssp. edentatus (de la Pyl.) Pow. Plants were tagged at three sites in which densities of the herbivorous snails Littorina sitkana and L. scutulata ranged from 367–4690 animals · M-2. From April–August 1986, the growth rate, degree of wounding, and reproductive status of individual thalli were monitored at 2–4 week intervals. Grazer-inflicted damage to the thalli varied within and among sites. Mean growth rates at the site with low densities of littorines were about twice those at the site with intermediate densities and about four times those at the high density site. At the site with high densities of littorines, F. distichus growth rates were negatively correlated with the degree to which the plants were wounded. There appeared to be no correlation of grazer density with F. distichus survivorship. Thalli at the site with few herbivores tended to reproduce earlier and at a larger size than did those at the other two sites. In all three areas, only thalli that had received little damage from herbivores became reproductive. By lowering growth rates and delaying reproduction in F. distichus, grazing by littorine snails can potentially cause variation in reproductive output among individual thalli.

Dimethylsulfoniopropionate (DMSP) in marine algae has been hypothesized to serve as a compatible solute which functions in osmotic acclimation or cryoprotection. However, many macroalgae that produce large quantities of DMSP live in habitats where they are unlikely to experience large fluctuations in salinities or freezing temperatures. We hypothesized that DMSP has other functions in these algae and that they should not show large changes in DMSP concentrations in response to salinity changes. We tested this hypothesis by placing 1.5 cm 2 diameter disks of the chlorophyte Ulva fenestrata in artificial seawater (ASW) at salinities from 10 % ASW to 300 % ASW. Over the next 24 h, DMSP concentrations tended to be lower in the algae in the higher salinity media. After 4 weeks, the final DMSP concentrations tended to be highest in the algae grown at the highest salinities, but the mean DMSP concentrations were only 23 % higher or 12% lower in algae grown in the high and low salinity media, respectively, relative to algae in 100 % ASW. This suggests that osmotic acclimation is not a primary function of DMSP in U. fenestrata. Disks acclimated in 25 % ASW, 100 % ASW, or 200 % ASW then transferred to a higher or lower salinity did not generate measurable amounts of dimethylsulfide (DMS), demonstrating that U. fenestrata is not using DMSP cleavage as a short-term mechanism for reducing internal DMSP stores, as occurs in some phytoplankton. Survival, as measured by the absence of bleaching, was highest in intermediate to high salinities. Growth was highest in low to intermediate salinities and reproduction only occurred in intermediate salinities. These results suggest that U. fenestrata can tolerate salinity changes, but uses metabolites other than DMSP for osmotic acclimation. Based on the results of this and previous studies, we propose that DMSP has other functions in U. fenestrata such as acting as an herbivore deterrent or antioxidant.

The Wood River watershed, a small well-defined drainage basin in Rhode Island was monitored seasonally for all macrophytic vegetation and various physical variables. Twenty-four segments, 20 m in length were sampled. Mean stream depth, width and current velocity increased by 3 to 8 fold from 1st- to 4th-order segments. Light penetration was positively correlated with the above variables (p < 0.05) and increased by 11 fold from the headwaters to the mouth during September when the riparian canopy was maximum. 74 subgeneric taxa of macrophytes were collected in the Wood River basin, 36% algae, 13% bryophytes, 4% vascular cryptograms and 45% angiosperms. The highest diversity occurred in the 4th-order segments throughout the year. Species numbers were positively correlated with depth, width and light penetration (p < 0.05). Vascular plants dominated all orders, but their proportion doubled from 1st- to 4th-order streams. Macrophyte cover was twice as high in the 4th-order segments in June and September as in the other orders. Macrophyte abundance was positively correlated to light penetration and negatively correlated to the ratio of nonvascular: vascular plants (p < 0.05). Two distinct clusters were found for the predominant species. The first cluster contained mostly large angiosperms, which were rooted in sediments, while the second cluster was composed of small epilithic algae and bryophytes. The moss, Fontinalis antipyretica, was the most frequent species, occurring in 51% of the samples and in all 4 orders throughout the year.

Over a dozen species of the genus Halimeda have been chemically investigated and found to produce the diterpenoid metabolites halimedatrial (1) and halimedatetraacetate (2) in varying concentrations. These meabolites have been proposed to play a role in chemical defense against herbivores based on their chemical structures and their demonstrated biological activities in laboratory and aquarium assays. We examined and compared the feeding deterrent effects of these two compounds tovard herbivorous fishes in field experiments on Guam reefs. Halimedatrial is a more effective feeding deterrent than halimedatetraacetate. It is the major secondary metabolite in young Halimeda macroloba and in the newly produced segments of growing plants. The organic extracts from young plants and new segments were significantly more deterrent than extracts from mature plant tissue. Some populations of Halimeda growing in reef-slope habitats, where herbivory is intense, also have high concentrations of halimedatrial. We compared extracts between reef slope and reef flat collections of Halimeda opuntia on Guam and Pohnpei (= Ponape), and H. discoidea and H. macroloba on Guam. We found that halimedtrial was the major metabolite in reef-slope collections of H. opuntia from Pohnpei and Pago Bay, Guam, and that halimedatetraacetate was the major metabolite a non-reef slope populations. In the cases examined, chemical defenses were greatest in (1) plant parts and (2) populations that were at greatest risk to herbivores.