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Protistan pathogens have been found to infect populations of some large brown macroalgae. Infection could reduce the ability of macroalgae to withstand hydrodynamic pressures through weakening tissues and reducing flexibility. Widespread mortality of macroalgae if disease outbreaks were to occur could have important flow-on consequences for biodiversity and ecosystem function. Recent discoveries of the protistan pathogen Maullinia infecting the ecologically keystone southern bull kelp Durvillaea in Chile, Australia, and on Marion Island, raise the possibility that this pathogen is dispersing across ocean basins with buoyant hosts. To determine whether Maullinia also infects southern bull kelp in New Zealand, samples of gall-like tissue from Durvillaea antarctica, D. poha, and D. willana were collected from intertidal sites, and genetic analyses (sequencing of partial 18S rRNA) carried out. Maullinia infections were detected in all three species of Durvillaea. Phylogenetic analyses show a close relationship of New Zealand Maullinia to M. braseltonii previously detected in Chile and on Marion Island. Based on its genetic similarity to distant lineages and its presence on buoyant hosts that have been shown to drift long distances at seas, we infer that Maullinia has dispersed across the Southern Ocean through rafting of infected bull kelp. Understanding the capacity of pathogens to disperse across oceans is critical part of forecasting and managing ecosystem responses to environmental change., Author(s): Abigail L. Mabey [sup.1] [sup.2] , Elahe Parvizi [sup.3] , Ceridwen I. Fraser [sup.3] Author Affiliations: (1) grid.5491.9, 0000 0004 1936 9297, School of Ocean and Earth Science, National [...]

The morphology and shape of algae can affect their survival in wave-swept environments because of the hydrodynamic drag created by water flow. Studies of morphology and drag are typically conducted at relatively low water velocities, and the influence of algal morphology on drag, over the range of water velocities algae must cope with in their natural environment, remains unclear. Here, we tested the link between morphological variation and hydrodynamic drag for a dominant kelp with complex morphology (Ecklonia radiata), over a range of water velocities representative of conditions on wave-swept reefs. Our results indicated that kelps on subtidal reefs must withstand maximal orbital water velocities in excess of 2-3 m [s.sup.-1]. Our measurements of drag, resulting from flows ranging from 1 to 3 m [s.sup.-1], revealed that shape- and width-related thallus and lamina characters were important to drag at low speed, but that total thallus area (or biomass) was the main determinant of drag at high flow. Drag coefficients converged at increasing speed suggesting that, at high flow, significant thallus reconfiguration (more streamlined shape) decoupled drag from morphology. This implies that, at peak velocities, only size (total area), not morphology, is important to drag and the probability of dislodgment., Introduction Important questions in ecology and evolution centre on the relationship between an organism's morphology and its performance. Different morphological characters can lead to different performances, making a specific morphology [...]

Key biological processes such as the timing and synchrony of reproduction, are sensitive to fluctuations in the environment, as well as alterations in the physiology and behaviour of individuals and the ecology of populations. The main aim of this study was to identify patterns in reproductive timing and relationships with prevailing environmental conditions, for the major habitat-forming alga in temperate Australia, Ecklonia radiata (C. Agardh) J. Agardh. We observed strong synchronous patterns of zoospore production across spatial scales from hundreds of metres to tens of kilometres, with populations of E. radiata reproducing from mid-summer to the end of autumn. High zoospore densities were positively related to sea temperature and E. radiata released zoospores in temperatures well above previously documented thermal tolerance limits for other Laminariales. Reproductive timing was also negatively related to seasonal increase in wave exposure. We conclude that E. radiata undergoes synchronous reproduction which can be linked to its annual growth cycle and natural environmental fluctuations, to promote growth and survival of recruits., Introduction Reproductive synchrony is an important evolutionary adaptation that is widely documented in both marine and terrestrial organisms (Ims 1990). Simultaneous reproduction within a population allows for the release of [...]

Many species of macroalgae have flat, strap-like blades in habitats exposed to rapidly flowing water, but have wide, ruffled 'undulate' blades at protected sites. We used the giant bull kelp, Nereocystis luetkeana, to investigate how these ecomorphological differences are produced. The undulate blades of N. luetkeana from sites with low flow remain spread out and flutter erratically in moving water, thereby not only enhancing interception of light, but also increasing drag. In contrast, strap-like blades of kelp from habitats with rapid flow collapse into streamlined bundles and flutter at low amplitude in flowing water, thus reducing both drag and interception of light. Transplant experiments in the field revealed that shape of the blade in N. luetkeana is a plastic trait. Laboratory experiments in which growing blades from different sites were subjected to tensile forces that mimicked the hydrodynamic drag experienced by blades in different flow regimes showed that change in shape is induced by mechanical stress. During growth experiments in the field and laboratory, we mapped the spatial distribution of growth in both undulate and strap-like blades to determine how these different morphologies were produced. The highest growth rates occur near the proximal ends of N. luetkeana blades of both morphologies, but the rates of transverse growth of narrow, strap-like blades are lower than those of wide, undulate blades. If rates of longitudinal growth at the edges of a blade exceed the rate of longitudinal growth along the midline of the blade, ruffles along the edges of the blade are produced by elastic buckling. In contrast, flat blades are produced when rates of longitudinal growth are similar across the width of a blade. Because ruffles are the result of elastic buckling, a compliant undulate N. luetkeana blade can easily be pushed into different configurations (e.g., the wavelengths of the ruffles along the edges of the blade can change, and the whole blade can twist into left- and right-handed helicoidal shapes), which may enhance movements of the blade in flowing water that reduce self-shading and increase mass exchange along blade surfaces.

Net primary production (NPP) is influenced by disturbance-driven fluctuations in foliar standing crop (FSC) and resource-driven fluctuations in rates of recruitment and growth, yet most studies of NPP have focused primarily on factors influencing growth. We quantified NPP, FSC, recruitment, and growth rate for the giant kelp, Macrocystis pyrifera, at three kelp forests in southern California, USA, over a 54-month period and determined the relative roles of FSC, recruitment, and growth rate in contributing to variation in annual NPP. Net primary production averaged between 0.42 and 2.38 kg dry mass*[m.sup.-2]* [yr.sup.-1] at the three sites. The initial FSC present at the beginning of the growth year and the recruitment of new plants during the year explained 63% and 21% of the interannual variation observed in NPP, respectively. The previous year's NPP and disturbance from waves collectively accounted for 80% of the interannual variation in initial FSC. No correlation was found between annual growth rate (i.e., the amount of new kelp mass produced per unit of existing kelp mass) and annual NPP (i.e., the amount of new kelp mass produced per unit area of ocean bottom), largely because annual growth rate was consistent compared to initial FSC and recruitment, which fluctuated greatly among years and sites. Although growth rate was a poor predictor of variation in annual NPP, it was principally responsible for the high mean values observed for NPP by Macrocvstis. These high mean values reflected rapid growth (average of ~2% per day) of a relatively small standing crop (maximum annual mean = 444 g dry mass/[m.sup.2]) that replaced itself approximately seven times per year. Disturbance-driven variability in FSC may be generally important in explaining variation in NPP, yet it is rarely examined because cycles of disturbance and recovery occur over timescales of decades or more in many systems. Considerable insight into how variation in FSC drives variation in NPP may be gained by studying systems such as giant kelp forests that are characterized by frequent disturbance and rapid rates of growth and recruitment. Key words: biomass; disturbance; giant kelp; growth; Macrocystis pyrifera; net primary production; nutrients; recruitment; resource supply; standing crop.

Abstract: The symbiosis of a brown alga, Ascophyllum nodosum (L.) Le Jolis and its obligate fungal symbiont, Mycophycias ascophylli (Cotton) Kohlmeyer and Volkmann-Kohlmeyer, was studied using transmission electron microscopy. A [...]

Growth as an integrative parameter of all physiological processes was measured in young sporophytes of temperate Laminaria digitata, Laminaria saccharina and Laminaria hyperborea exposed in the laboratory to irradiance consisting of either only photosynthetically active radiation (PAR) or to a spectrum including ultraviolet radiation (UVR) (PAR + UVA + UVB) by use of cut-off glass filters. Size increment was measured every 10 min over a period of 18-21 days using growth chambers with on-line video measuring technique. In the chamber, plants were grown at 10 [+ or -] 2[degrees]C and 16:8 h light-dark cycles with 6 h additional UVR exposure in the middle of the light period. Tissue morphology and absorption spectra were measured in untreated young sporophytes while chlorophyll a content and DNA damage were measured in treated thalli at the end of the experiment. Sensitivity of growth under UVR was found to be related to the observed upper depth distribution limit of the upper sublittoral L. digitata, upper to mid sublittoral L. saccharina and lower sublittoral L. hyperborea. Tissue DNA damage is, however, dependent on thallus thickness which minimizes UVR effect where outer cell layers shade inner cells and provide longer pathlength for UVR. Exposure to UVR causes cellular, enzymatic and molecular damage. Presence of UV-absorbing compounds further reduces effective UVR from reaching physiological targets. The cost of producing higher amount of UV-absorbing compounds and effective DNA repair mechanism can, however, divert photosynthate at the expense of growth. Tissue chlorophyll a content was not significantly different between treatments suggesting a capacity for acclimation to moderate UVR fluence. Growth acclimation to repeated UVR exposure was observed within a period of 12 days while growth inhibition was observed after a longer UVR exposure period of 21 days. The results give further insight into the effects of UVR on the cellular level and show how ecological parameters such as the upper depth distribution limit are dependent on cellular processes., Introduction The three kelp species from Helgoland grow in characteristic belts with Laminaria digitata (Hudson) Lamouroux in the upper sublittoral, Laminaria saccharina (Linnaeus) Lamouroux in the mid-sublittoral and Laminaria hyperborea [...]

Brown seaweeds can serve as habitat and food for a number of mesoherbivore species, but the effect of mesoherbivore grazing on the fitness of individual seaweed plants is not well documented. Here we investigate how mechanical wounding, which mimics the grazing damage made by the herbivorous gastropod Littorina obtusata, affects the biomass change, apical growth, and individual shoot strength of the fucoid seaweed species Ascophyllum nodosum both in natural field populations and in the laboratory. We did not detect a significant effect of wounding on apical shoot growth in the laboratory, but wounding decreased the plant biomass in half of the studied A. nodosum populations in the field. Furthermore, we found that the strength of individual A. nodosum shoots was significantly lower when compared with unwounded control shoots initially after wounding. However, after 11 days incubation in the laboratory, the strength of the wounded shoots had increased almost to the level of the control shoots, although there was still a significant difference in the force required to break the shoots. These results indicate that wounding can increase the tissue loss (and thereby decrease the fitness) of A. nodosum plants in natural populations, probably through weakening of individual shoots. However, A. nodosum appears to have a mechanism to strengthen the shoots after mechanical wounding, and therefore, the timing of damage (e.g. prior to a storm) probably determines the amount of plant tissue lost through wave-induced forces., Introduction Fucoids (Fucales) and kelps (Laminariales) are the most conspicuous and abundant marine plants in temperate areas around the world, where they can form extensive underwater forests. The plants often [...]

The kelp Laminaria hyperborea provides a habitat for a diverse invertebrate community. Invertebrate abundance is particularly high in the kelp holdfasts and associated with epiphytes on the stipes. We investigated colonisation patterns of this fauna on artificial substrata (holdfast and epiphyte mimics) exposed for short time periods in the kelp forest in two seasons, summer and late autumn. Within 7 days, 99 taxa common on natural kelp substratum colonised the artificial substrata in large numbers, demonstrating high mobility and indicating that there may be a rapid exchange of individuals and species among algae. Gastropods and amphipods were the most abundant colonisers. In summer, a specific 'epiphyte fauna' could be distinguished from a 'holdfast fauna', and species associated with epiphytes were significantly more abundant on the artificial substrata. Colonisation was more rapid in summer than in late autumn, which may be related to animal population density. The high dispersal rate can facilitate the interaction with other communities and with higher trophic levels in the kelp-forest food web.

Marine algae rely on currents and waves to replenish the nutrients required for photosynthesis. The interaction of algal blades with flow often involves dynamic reorientations of the blade surface (pitching and flapping) that may in turn affect nutrient flux. As a first step toward understanding the consequences of blade motion, we explore the effect of oscillatory pitching on the flux to a flat plate and to two morphologies of the kelp Eisenia arborea. In slow flow (equivalent to a water velocity of 2.7 cm [s.sup.-1]), pitching increases the time-averaged flux to both kelp morphologies, but not to the plate. In fast flow (equivalent to 20 cm [s.sup.-1] in water), pitching has negligible effect on flux regardless of shape. For many aspects of flux, the flat plate is a reliable model for the flow-protected algal blade, but predictions made from the plate would substantially underestimate the flux to the flow-exposed blade. These measurements highlight the complexities of flow-related nutrient transport and the need to understand better the dynamic interactions among nutrient flux, blade motion, blade morphology, and water flow., Introduction Lacking the means to transport water actively, marine algae rely on currents and waves to move water over their surfaces, thereby replenishing the supply of nutrients required for photosynthesis. [...]

Research has been conducted on the regulation of the invasive green alga Codium fragile ssp. by sea urchins and the effect of this seaweed on the growth and reproduction of these urchins. The urchins have been fed Codium and kelp and the results indicate that that urchins graze kelp rather than the seaweeds.

A laboratory experiment is conducted to prove that the swimming of macroalgal spores is made possible by fuel obtained from endogenous lipid reserves. The experiment, which allowed the neutral lipid content of actively swimming zoopores of the palm kelp Pterygophora californica to be monitored, proved that spore-swimming is fueled by the lipid reserves. The experiment also showed that the amount of lipid reserves used as a fuel depends on a variety of factors such as the spores' light environment, photosynthetic efficiency and swimming patterns.

Reproductive investment of the intertidal kelp Alaria nana was manipulated experimentally to investigate costs of reproduction. Allocation patterns were examined using treatments that employed vegetative and reproductive tissue removal. Growth, survivorship, size, reproductive investment, carbon, nitrogen, and phenolic secondary metabolites were monitored in tagged experimental plants. Further experiments investigated the contribution of reproductive tissue to drag forces on the plant in intertidal environments. Carbon, nitrogen, and phenolics were all higher in reproductive tissue (sporophylls) compared to vegetative tissue (the frond) in control plants. When some vegetative tissue was removed, carbon and nitrogen in the sporophylls decreased while percent phenolics remained unchanged. Reproductive tissue removal had no effect on plant survivorship, growth, or size compared with control plants. When the entire frond was kept clipped, sporophyll number decreased, often to the point of complete attrition. Although allocation patterns in Alaria nana are consistent with reproductive costs (i.e., the sporophylls are not self-supporting), there is no evidence that reproduction imposes costs on the plant that are demographically important such as growth, size, and survivorship. Instead, both reproductive investment and percent phenolics were positively correlated with growth and size in control plants., Reproductive costs in the intertidal kelp Alaria nana was investigated using an experimental design that involved the removal of vegetative and reproductive tissues. In a separate study, drag force on kelps with and without sporophylls was measured with a commercial fish spring scale. The results showed that reproductive structures are dependent on vegetative structures, but do not impose demographically important costs on the plant such as growth, size and survivorship.

The distance over which propagules can successfully colonize new sites depends on processes that increase the time they remain competent while being dispersed. As do feeding larvae, algal spores can contribute to their own nutrition (via photosynthesis) during dispersal. We explored the dispersal potential of the kelps Macrocystis pyrifera and Pterygophora californica in laboratory experiments by examining (1) how long their spores can swim, (2) the contribution of energy derived from photosynthesis to spore swimming duration, and (3) the ability of spores to germinate and attach after they stop swimming. Results indicate that under photosynthetically saturating irradiance no spores of either species can swim longer than 120 h; < 10% of the spores were still swimming after 7 2 h. When placed in the dark, spores did not swim longer than 72 h; < 10% remained swimming after 48 h. More importantly, spores did not die after they stopped swimming; most germinated in the water column and retained their capacity to produce viable sporophyte recruits. The ability of spores to attach after they stopped swimming differed between the two species; settlement density declined in Macrocystis and increased in Pterygophora. Thus, the viable planktonic stage of these alpe is not necessarily restricted to the spore but may include later life history stages. These results provide biological evidence that the spores and germlings of these kelps can remain competent in the plankton for extended periods of time, which is consistent with our previous findings that their dispersal can occur over greater distances than previously thought possible., Duration of spore swimming, effect of photosynthesis on swimming duration, and ability to germinate and attach after spore swimming stops were examined in the kelps Macrocystis pyrifera and Pterygophora californica. The results showed that photosynthesis contributes energy to spore swimming, but spore swimming did not last more than 120 hours. After swimming stopped, spores retained the ability to germinate in the water column and to produce viable sporophytes. These results show that the viable planktonic stage of the kelps include later life history stages, thus allowing greater dispersal distances.

At one site in the Narragansett Bay, the tenacity (attachment strength) of the kelp Laminaria saccharina was determined in and out of mussel bed areas. With a recording spring scale, the force required to remove just the blade (pruning) and remove the holdfast (clearing) was examined in areas where mussels were not present and algal holdfasts directly attached to bare substrate and in areas where mussels were present under the algal holdfasts. T-tests were used to compare the force required to prune and clear algae within and area and between mussel beds and bare substrate. Results indicate the L. saccharina in mussel beds are significantly weaker than kelps attached to bare substrate, and show on bare substrate a significant difference between the force required to prune and clear algae. The blue mussel Mytilus edulis may recruit to the holdfasts of the kelps for refuge from predation or dislodgement, and ultimately weaken the attachment strength of Laminaria saccharina increasing the probability of dislodgement.