Effects of Phytoplankton Taste and Smell on Feeding Behavior of the Copepod Centropages hamatus

Adult copepods Centropages hamatus were induced to feed on 10 to 40 µm Sephadex beads by adding Thalassiosira weissflogii or Scrippsiella trochoidea whole­-cell extract, or filtrate from a T. weiss flogii culture , to a bead suspension. Beads were neither ingested in the absence of a chemical stimulus, nor in the presence of filtrates from cultures of S. trochoidea and Olisthodiscus luteus , or 0. luteus extracts. Extracts from both S. trochoidea and 0. luteus, and filtrate from an 0. luteus culture, appear to exert an inhibitory effect when applied in combination with T. weissflogii extract. Copepods acclimated to T. weissflogii for 24 h did not significantly increase their feeding rate on T. weissflogii­ flavored beads and did not ingest S. trochoidea-flavored beads

Effects of Nutrient Enrichment on Growth and Phlorotannin Production in Fucus gardneri Embryos

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 highe

Dimethylsulfide Release during Macroinvertebrate Grazing and Its Role as an Activated Chemical Defense

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 dimethylsulfoniopropionate (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 measuring 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 demonstrate 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

The Distribution of DMSP in Green Macroalgae from Northern New Zealand, Eastern Australia and Southern Tasmania

The sulphonium compound diinethylsulphoniopropionate (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 in Ulva and Codium spp. 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 genera Codium and Ulva; however, the invasive subspecies of Codium fragile, C. fragile ssp. tomentosoides, had significantly higher concentrations of DMSP than the non-invasive subspecies. The herbivorous sea slug Elysia maoria had whole body concentrations that were not significantly different from those of its host alga C. fragile ssp. tomentosoides. The distribution patterns of DMSP in Codium spp. 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

Herbivore Grazing Increases Polyphenolic Defenses in the Intertidal Brown Alga Fucus Distichus

Although predator-induced defenses have been reported for several species of terrestrial vascular plants, they have not been previously described in aquatic or nonvascular plants. In this study, field manipulations were used to demonstrate the presence of inducible chemical defense production in the intertidal brown alga Fucus distich us. When experimentally damaged, Fucus increased its concentrations of polyphenolic compounds by ≈20% over uninjured control plants within 2 wk. These increases occurred in the area where the plant was injured and within adjacent undamaged branches. The increase in concentrations of polyphenolic compounds in clipped plants in these experiments corresponded well with differences in phenolic levels in naturally grazed and ungrazed algae. Herbivorous snails (Littorina sitkana) showed a preference for clipped plants immediately after they were wounded. However, over a 2-wk period the snails shifted their preference towards the uninjured control plants, corresponding with the increase in polyphenolic levels within the experimentally damaged plants. L. sitkana spent less time feeding on clipped plants, and these plants lost ≈50% less tissue (by surface area) to grazers than did uninjured algae. The presence of induced defenses in algae causes plant quality to vary spatially and temporally. This may result in variation in intra- and interspecific food preferences of herbivores, and ultimately may affect benthic algal community structure

Herbivore Impacts on Two Morphologically Similar Bloom-Forming Ulva Species in a Eutrophic Bay

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

The Effects of Salinity on Dimethylsulfoniopropionate Production in the Green Alga Ulva fenestrata Postels et Ruprecht (Chlorophyta)

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 cm2 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

Estimating Variation in Surface Emissivities of Intertidal Macroalgae using an Infrared Thermometer and the Effects on Temperature Measurements

Accurate measurements of surface temperatures with an infrared (IR) thermometer require input of the emissivities of the surfaces being measured; however, few determinations of the emissivities of intertidal organisms’ surfaces have been made. Emissivities of intertidal macroalgae were measured to determine whether algal species, measurement angle, hydration, and layering affected them. Emissivities were similar and averaged 0.94 among 11 of 13 species. The species with lower and more variable emissivities (Chondracanthus exasperatus and Desmarestia viridis) differed in morphology from the other species, which were relatively flat thin blades with little surface texture. Measurement angle caused emissivities to decrease significantly in Mazzaella splendens but not in three other species. Hydration and layering of Ulva lactuca also had no effect. At 22 °C, measured temperatures were within 1 °C of actual temperatures when thermometer emissivity settings ranged from 0.75 to 1.00. When emissivities were set lower than actual values, measured temperatures were lower than actual temperatures at 15 °C and higher than actual temperatures at 60 °C. When the IR thermometer was used to measure surface temperatures of nine species of intertidal algae immediately before they were inundated by the incoming tide, temperatures were higher in mid intertidal than low intertidal individuals and higher on a sunnier day than an overcast day. Temperatures of U. lactucaincreased with increasing height on the shore, but temperatures of Ulvaria obscura did not. Temperatures were also higher in Fucus distichus blades than receptacles, and lower in U. lactucaand M. splendens occurring in the lower layers of stacks of algae

Sulfur Isotope Variability of Oceanic DMSP Generation and Its Contributions to Marine Biogenic Sulfur Emissions

Oceanic dimethylsulfoniopropionate (DMSP) is the precursor to dimethylsulfide (DMS), which plays a role in climate regulation through transformation to methanesulfonic acid (MSA) and nonseasalt sulfate (NSS-SO4 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 (δ34S) of DMSP are depleted in 34S 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 δ34S is transferred to atmospheric geochemical products of DMSP degradation (DMS, MSA, and NSS-SO4 2−), carrying implications for the interpretation of variability in δ34S of MSA and NSS-SO4 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

Activated Defense Systems in Marine Macroalgae: Evidence for an Ecological Role for DMSP Cleavage

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 intestinaUs, E. linza, Ulva californica, U. fenestrata, and U. taeniata, and in the rhodophyte Polysiphonia hendryi. Concentrations of DMSP ranged from 0.04 % of the alga\u27s fresh mass (FM) to 1.8% FM. We found significant DMSP lyase activity in 1 green alga, U. fenestrata, and 1 red alga, P. hendryi, with DMSP cleavage rates approaching 300 mmol kg-1 FM mi-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, acryhc 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 phytoplankton, and presents an opportunity to compare and contrast the ecological role of chemical defense among micro- and macroorganisms