CONFUSING CONVERGENT MORPHOLOGIES: DIVERSITY AND DIFFICULTIES IN NEW ZEALAND ERYTHROPELTIDALES AND BANGIALES

Blooms of green macroalgae can devastate important finfish and shellfish habitats. Ulvaria obscura , a relatively unstudied green alga, is a major contributor to these blooms in the San Juan Islands, Washington State, USA. The biomass and productivity of this and other ulvoid algae were measured seasonally for two years. Experiments comparing the growth rates, responses to desiccation, photoacclimation, and grazer preference of U. obscura and Ulva fenestrata were conducted. Ulvaria blooms tended to occur in the subtidal while Ulva blooms were often intertidal. Both genera bloomed between late June and September. Despite their superficial similarity, Ulvaria and Ulva display markedly different physiological and ecological responses. Ulva was capable of faster growth, had higher rates of photosynthesis, and was more desiccation tolerant than Ulvaria. Ulvaria , however, appears to be more resistant to grazing than Ulva.     

Dopamine release by Ulvaria obscura (Chlorophyta): environmental triggers and impacts on photosynthesis,growth, and survival of the releaser

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.     

Dopamine functions as an antiherbivore defense in the temperate green alga Ulvaria obscura

On northeastern Pacific coasts, Ulvaria obscura is a dominant component of subtidal “green tide” blooms, which can be harmful to marine communities, fisheries, and aquaculture facilities. U. obscura is avoided by herbivores relative to many other locally common macrophytes, which may contribute to its ability to form persistent blooms. We used a bioassay-guided fractionation method to experimentally determine the cause of reduced feeding on Ulvaria by echinoderms, molluscs, and arthropods. Our results indicated that dopamine, which constituted an average of 4.4% of the alga’s dry mass, was responsible for decreased feeding by sea urchins (Strongylocentrotus droebachiensis). Subsequent experiments demonstrated that dopamine also reduced the feeding rates of snails (Littorina sitkana) and isopods (Idotea wosnesenskii). Dopamine is a catecholamine that is a common neurotransmitter in animals. The catecholamines dopamine, epinephrine (adrenaline), and norepinephrine also occur in at least 44 families of higher plants. The functions of catecholamines in plants are less well known than in animals but are likely to be diverse and include both physiological and ecological roles. Our results are the first experimental demonstration of a plant or algal catecholamine functioning as a feeding deterrent. This novel use of dopamine by Ulvaria may contribute to the formation and persistence of harmful Ulvaria blooms in northeastern Pacific coastal waters.     

Examination of Ulva bloom species richness and relative abundance reveals two cryptically co-occurring bloom species in Narragansett Bay,Rhode Island

Blooms caused by the green macroalga Ulva pose a serious threat to coastal ecosystems around the world. Despite numerous studies of the causes and consequences of these blooms, we still have a limited understanding of Ulva bloom species richness and abundance due to difficulties in identifying Ulva species using morphological features. Along the northeastern U.S. coastline, all blooms of distromatic Ulva blades were previously identified as Ulva lactuca. Recent molecular sequencing, however, discovered the presence of additional distromatic Ulva species. Therefore, in order to determine the relative abundance of Ulva species within blooms, we conducted monthly surveys at four Narragansett Bay, RI, sites representing a gradient of bloom severity. We found that the biomass of Ulva within blooms was a mix of Ulva compressa and Ulva rigida, not U. lactuca as previously reported. In contrast, sites not impacted by blooms that were located near the mouth of Narragansett Bay were dominated by U. lactuca. We also observed spatial and temporal differences in Ulva and total macroalgal diversity between bloom-impacted sites, indicating that Ulva bloom composition can be radically different between similar sites within close proximity. We discuss our results in the context of Ulva blooms worldwide, highlighting the need to definitively determine bloom species composition in order to fully understand bloom dynamics.     

ARE “GREEN TIDES” HARMFUL ALGAL BLOOMS? TOXIC PROPERTIES OF WATER‐SOLUBLE EXTRACTS FROM TWO BLOOM‐FORMING MACROALGAE,ULVA FENESTRATA AND ULVARIA OBSCURA (ULVOPHYCEAE)

Toxic properties are more often associated with microalgal blooms than with macroalgal blooms, although herbivore deterrents are well known in macroalgae, and inhibition of invertebrate larval development by extracts from Ulva spp. has been suggested. This study was prompted from our observation that substantial discoloration of seawater occurred in small bays after mass desiccation-induced mortality of Ulvaria obscura (Kützing) Gayral. We examined the effects of extracts from Ulva fenestrata Postels et Ruprecht and Ulvaria obscura on Fucus gardneri Silva zygote development, growth of Ulva and Ulvaria , epiphytic algal accumulation, and oyster larval development. Fucus zygote development was inhibited by extracts from both species, although the effects of Ulvaria extracts were significantly greater. Epiphytic algal accumulation and the growth of Ulva and Ulvaria were inhibited by extracts from both species. Oyster larval development was arrested by the presence of extracts from each species. We conclude that extracts from both Ulva fenestrata and Ulvaria obscura have allelopathic properties. The effects are more widespread and occur at lower concentrations for extracts from Ulvaria than Ulva. These properties could alter competitive interactions by inhibiting germination or development of algae and invertebrates.     

PATTERNS OF RECRUITMENT AND DISTRIBUTION OF ULVA AND ENTEROMORPHA POPULATIONS IN A KOREAN INTERTIDAL SHORE

Patterns of recruitment and abundance of Ulva pertusa and Enteromorpha linza in the three locations on the south coast of Korea where green tide frequently occurred were investigated with respect to the substrate profile, temporal and spatial variations, and their persistence. Artificial substrates (10 to 20 cm) were made of a mixture of a piece of granite rock and cement on ceramic tiles. These setting plates, representing different surface texture, were placed horizontally and vertically along the rocky shoreline, and replaced every 1 to 2 months. Both populations showed highly seasonal blooms, with peaks in October, 1998 to February, 1999 and another slight peak was observed in the fall of 1999 only for Ulva. However, the winter peak of 1998 did not appeared in the following year, indicating that a significant year‐to‐year variation existed. Regarding their settlement onto artificial plates with different roughness, Ulva preferred to settle on the rough surface both in the upper and lower intertidal zone; however, this pattern only appeared in the upper zone for Enteromorpha. Vertical distribution of the two populations was well separated; Enteromorpha was more abundant in the upper zone and Ulva in the lower zone. Their seasonal blooms were concomitant with ammonia levels, but occurrence was not well correlated with nitrate and phosphate. The ability of the populations to persist, once blooms occurred, was also distinct; Ulva persisted ca. twice as long as Enteromorpha, having a greater impact in the presence of green tide in this geographical area.     

BIOMASS AND DYNAMICS OF GROWTH OF ULVA SPECIES IN PALMONES RIVER ESTUARY1

During the last decade, the Palmones River estuary has undergone severe eutrophication followed by a green tide episode; two species of Ulva, rotundata Blid. and Ulva curvata (Kütz.) De Toni, were the main macroalgae responsible for this bloom. From November 1993 to December 1994, we followed the biomass, the growth dynamics, and tissue elemental composition (C:N:P)of Ulva species, as well as some physicochemical variables in the estuary. Maximum biomass (up to 375 g dry wt·m^?2 in some spots, corresponding to a thallus area index of nearly 17 m²Ulva·m^?2 sediment) were observed in June and December. However, the biomass varied among the sampling stations. Water nitrate, ammonia, and phosphate showed high concentrations throughout the year, with extremely high transient pulses, sustaining the high growth rates observed. Growth rates were estimated directly in the field. The rates were generally higher in Ulva discs maintained in net cages than those estimated by changes in biomass standing stock between two consecutive samplings. The difference between both estimates was used to quantify the importance of the processes causing loss of biomass, which were attributable to grazing, exported biomass, and thallus decomposition under anaerobic conditions resulting from extreme self-shading. Maximum chlorophyll content was found in winter, whereas the minimum was in spring. Atomic N:P ratios were generally higher in the algae than in the water. However, the absolute concentrations of tissue N and P were always higher than the critical levels for maximum growth, which suggests that growth was not limited by inorganic N or P availability. The results suggested that the increase in nutrient loading in the river may have triggered the massive development of green algae and that light limitation and temperature stress in summer seem to be the main factors controlling the abundance of Ulva in the estuary. In addition to light availability and thermal stress, the different loss processes may have a decisive role in the dynamics of Ulva biomass.     

Participation of the Green Algae <Emphasis Type="Italic">Ulvaria obscura</Emphasis> in Bioremediation of Sea Water from Oil Products

Participation of green algae in bioremediation of sea water from oil products (OPs) has been studied. Decrease in the content of OPs in water is accompanied by their accumulation by the alga Ulvaria obscura (Chlorophyta). It has been assumed that neutralization of OPs in Ulvaria occurs, similarly to Fucus vesiculosus (Phaeophyta), all over the thallome: destruction of OPs starts on the alga surface by epiphytic hydrocarbonoxidizing bacteria providing absorption and subsequent degradation of OPs by plant cells. The role of macrophytes in bioremediation of coastal areas from OPs is considerably higher than previously supposed.     

Tracing the origin of green macroalgal blooms based on the large scale spatio-temporal distribution of Ulva microscopic propagules and settled mature Ulva vegetative thalli in coastal regions of the Yellow Sea,China

From 2008 to 2016, massive floating green macroalgal blooms occurred annually during the summer months in the Yellow Sea. The original source of these blooms was traced based on the spatio-temporal distribution and species composition of Ulva microscopic propagules and settled Ulva vegetative thalli monthly from December 2012 to May 2013 in the Yellow Sea. High quantities of Ulva microscopic propagules in both the water column and sediments were found in the Pyropia aquaculture area along the Jiangsu coast before a green macroalgal bloom appeared in the Yellow Sea. The abundance of Ulva microscopic propagules was significantly lower in outer areas compared to in Pyropia aquaculture areas. A molecular phylogenetic analysis suggested that Ulva prolifera microscopic propagules were the dominant microscopic propagules present during the study period. The extremely low biomass of settled Ulva vegetative thalli along the coast indicated that somatic cells of settled Ulva vegetative thalli did not provide a propagule bank for the green macroalgal blooms in the Yellow Sea. The results of this study provide further supporting evidence that the floating green macroalgal blooms originate from green macroalgae attached to Pyropia aquaculture rafts along the Jiangsu coastline of the southern Yellow Sea.     

EFFECTS OF TEMPERATURE,NITROGEN SUPPLY,AND TISSUE NITROGEN ON AMMONIUM UPTAKE RATES OF THE CHLOROPHYTE SEAWEEDS ULVA CURVATA AND CODIUM DECORTICATUM1

Nitrogen uptake rates of Ulva curvata (Kütz.) de Toni (Ulvales) and Codium decorticatum (Woodw.) Howe (Caulerpales) grown under several N addition regimes were determined by perturbation and continuous mode techniques, and as N demand, by the product of growth rate and tissue N. Uptake rates are reported as the slope of rate vs. concentration curves in each case. N uptake rates of U. curvata were inversely correlated with tissue N and affected only slightly by temperature. There was no correlation of N uptake rate with tissue N in C. decorticatum. N uptake rates of C. decorticatum were affected by temperature but to a lesser degree than were growth rates. Neither N addition per se nor light affected N uptake capacity of either species. The proximal mechanism for seaweeds accumulation of N at low light and temperatures may be that N uptake is less limited by light and temperature than is growth. This in turn may partially compensate for the effects of reduced light and temperature on growth by increasing pigment and enzyme levels. Perturbation uptake rates were higher than continuous mode or N demand rates in Ulva but not in Codium. N uptake rates of Ulva were higher than those of Codium, but N storage capacities were lower. These two observations suggest that Ulva experiences a fundamentally more variable N supply than does Codium. This is consistent with the clarification of Ulva as an ephemeral form and of Codium as persistent. A seaweed's functional form therefore appears to influence the spectrum of resource variability available to it as well as its ability to persist in the environment.     

SEASONAL VARIABILITY OF PHYSICOCHEMICAL AND RHEOLOGICAL PROPERTIES OF ULVAN IN TWO ULVA SPECIES (CHLOROPHYTA) FROM THE BRITTANY COAST1

The seasonal variability in the extraction yield, physicochemical characteristics, and rheological properties of ulvan from two Ulva species contributing to Brittany “green tides” has been studied. These seaweeds were collected in the water column for Ulva armoricana Dion, de Reviers et Coat and on hard substrata for Ulva rotundata Bliding. The maximum ulvan extraction efficiency was not related to the maximum ulvan content in the seaweeds, but with the active growth period of the seaweeds. Ulvan chemical structure, macromolecular characteristics, and rheological properties were affected by both species and seasons. The proportion of high‐molecular‐weight ulvan was the major factor positively correlated with the gelling properties. Characteristics of ulvan from U. rotundata subjected to tides were more affected by seasons than ulvan from U. armoricana living in a more constant environment. These results point to several useful recommendations concerning Ulva sp. biomass collected with regard to ulvan characteristics and uses.     

Regulation of spatial and seasonal variation of macroalgal biomass in a brackish, eutrophic lake

Processes leading to biomass variation of Ulva were investigated at two contrasting sites in the eutrophic Veerse Meer (The Netherlands). Ulva species dominated at the Middelplaten site, while at the Kwistenburg site a mixture of Ulva spp. and Chaetomorpha linum dominated. Total summer macroalgal biomass was higher at Middelplaten than at Kwistenburg (282 and 79 g DW m^–2, respectively). Growth rates of Ulva spp. were high at both sites in May 1992 (cage mean 0.28–0.30 day^–1), but quickly dropped to lower values (0.05–0.10 day^–1). In May, growth rates were significantly highest at Kwistenburg, while during the rest of the season growth rates were similar for both sites. Temperature, pH, dissolved oxygen, salinity, light attenuation, phytoplankton and nutrient concentrations did not differ between sites. The relation between variation in Ulva spp. growth rates and environmental parameters was analysed using stepwise multiple regression, showing that light and temperature were the main variables regulating Ulva spp. growth rates. As Ulva growth rates were similar for both sites but biomass was much lower at Kwistenburg it was concluded that a large amount of produced biomass was lost at Kwistenburg. Although the exact reason for this remains unclear, it seems most likely that transport of macroalgae by wind and waves is a very important factor. This study shows the importance of simultaneously measuring growth rates and biomass at a high temporal resolution to reveal the mechanisms responsible for spatial variation in macroalgal biomass in shallow coastal areas. Electronic Publication     

Foliose Ulva Species Show Considerable Inter‐Specific Genetic Diversity,Low Intra‐Specific Genetic Variation,and the Rare Occurrence of Inter‐Specific Hybrids in the Wild

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

Ulva: An emerging green seaweed model for systems biology

Green seaweeds exhibit a wide range of morphologies and occupy various ecological niches, spanning from freshwater to marine and terrestrial habitats. These organisms, which predominantly belong to the class Ulvophyceae, showcase a remarkable instance of parallel evolution toward complex multicellularity and macroscopic thalli in the Viridiplantae lineage. Within the green seaweeds, several Ulva species (“sea lettuce”) are model organisms for studying carbon assimilation, interactions with bacteria, life cycle progression, and morphogenesis. Ulva species are also notorious for their fast growth and capacity to dominate nutrient-rich, anthropogenically disturbed coastal ecosystems during “green tide” blooms. From an economic perspective, Ulva has garnered increasing attention as a promising feedstock for the production of food, feed, and biobased products, also as a means of removing excess nutrients from the environment. We propose that Ulva is poised to further develop as a model in green seaweed research. In this perspective, we focus explicitly on Ulva mutabilis/compressa as a model species and highlight the molecular data and tools that are currently available or in development. We discuss several areas that will benefit from future research or where exciting new developments have been reported in other Ulva species.     

Morphological and molecular characterization of free-floating and attached green macroalgae Ulva spp. in the Yellow Sea of China

During the summer of 2008 and 2009, massive algal blooms repeatedly broke out in the Yellow Sea of China. These were undoubtedly caused by the accumulations of one or more species in the macroalgal genus Ulva. In previous reports, morphological observation indicated that the species involved in this phenomenon is Ulva prolifera but molecular analyses indicated that the species belongs to an Ulva linza–procera–prolifera (LPP) clade. Correct identification of the bloom species is required to understand and manage the blooms, but the taxonomic status of the bloom species remains unclear. In the current study, the taxonomic status of 22 selected specimens from the Yellow Sea was assessed by using both morphological and molecular (ITS and rbcL sequences) data. In addition, 5S rDNA analyses were performed for those samples clustering in the LPP clade, and phylogenetic tree and ribotype analyses were constructed for determining the possible origin of the bloom. Three free-floating and two attached Ulva species were distinguished and described: Ulva compressa Linnaeus and Ulva pertusa Kjellman were found in free-floating samples; U. linza Linnaeus was found on rocks; and U. prolifera O.F. Müller was found in both habitats. Diversity in free-floating Ulva of the Yellow Sea appears to be greater than previously thought. The dominant free-floating Ulva species, U. prolifera, was not closely related to local populations attached to rocks but was closely related to populations from Japan.     

SEASONAL VARIATION OF PHOTOSYNTHETIC PERFORMANCE AND LIGHT ATTENUATION IN ULVA CANOPIES FROM PALMONES RIVER ESTUARY1

The primary production of Ulva populations relies on their photosynthetic performance, which is dependent on the light availability under natural conditions. This study concerns the light attenuation characteristics in Ulva canopies and the seasonal photosynthetic performance of two different species (Ulva rotundata Blid., Ulva curvata (Kütz.) De Toni) blooming in the Palmones river estuary. Light within canopies differed from that reaching the surface. Light availability was reduced through the water column (at high tide) and Ulva canopies. In addition, light was spectrally filtered. As a result, the photosynthetically usable radiation (PUR) was further attenuated through Ulva canopies, increasing the photosynthetically active radiation/PUR ratio. The muddy sediment deposited on and between the Ulva thalli also drastically restricted the light availability. Thick Ulva mats are frequently found covering the intertidal mudflats, and therefore, thalli within these mats may be subjected to steep light gradients. As a consequence, individual Ulva growth rates cannot be extrapolated to estimate the primary production of Ulva canopies. Interspecific differences were observed for light-saturated photosynthetic rates (P_max) and light compensation points (L_CP), with Ulva curvata generally displaying higher values than did U. rotundata. For both species, maxima were recorded in winter for P_max, quantum yield, chlorophyll content, and absorptance, whereas minima were found in summer. Dark respiration (R_d) was not seasonally affected, and a maximum L_CP was found in summer. To extrapolate these data to field situations, the temperature dependence of photosynthesis should be considered. The Q₁₀ values were 2.44 for R_d and 1.79 for P_max, whereas the photosynthesis rate at subsaturating light levels was unaffected. The Q₁₀ values showed an enhanced respiratory rate in summer and a minimum in winter, whereas the seasonal differences on P_max were damped.     

Discrimination of the common macroalgae (Ulva and Blidingia) in coastal waters of Yellow Sea,northern China,based on restriction fragment-length polymorphism (RFLP) analysis

Since 2007, reoccurring large-scale green algae blooms have caused deleterious effects to the estuarine ecosystem of Yellow Sea, northern China and subsequent economical losses. Previous surveys indicated the green tides were initiated in the coastal water of southern Jiangsu province where Porphyra farming was intensively conducted; however, the main ‘seed source’ of floating green algae is still under debate. Ulva prolifera was confirmed to be the major causative species of green tides. The multiple sympatric ulvoid species in the natural environment has complicated species identification in both field surveys and laboratory studies due to their morphological plasticity. Thus, we developed a genetic identification key based on restriction fragment length polymorphism (RFLP) analysis of the ITS nuclear marker to discriminate the common Ulva and Blidingia species in the Yellow Sea. Ten genetic lineages (1 in Blidingia, 9 in Ulva) were detected along the coast of China through phylogenetic analysis of ITS sequences. They can be separated by virtual restriction digestion using the four selected restriction enzymes (BspT107 I, EcoO109 I, Hin1 I and VpaK11B I). With additional PCR amplification of the 5S spacer region, we were able to discriminate U. prolifera from Ulva linza. Using this genetic key, we screened macroalgal samples collected from the coast of the Yellow Sea, and the results indicated 6 common lineages (U. prolifera, U. linza, Ulva compressa, Ulva pertusa, Clade 6 and Blidingia sp.) in this region, which could be explicitly distinguished by a single enzyme (BspT107 I) coupled with 5S spacer polymorphism. U. prolifera was confirmed to be present on the Porphyra aquaculture rafts with seasonal variation in the species composition. This genetic key will facilitate our long-term field surveys to investigate the origin of the floating U. prolifera and furthermore to explore its bloom dynamics along the coast of the Yellow Sea. It also provided a framework for the future inclusion of more Ulva species, which will expand the usage of this key.     

The fine structure of motile cells in the generaUlvaria andMonostroma,with special reference to the taxonomic position ofMonostroma oxyspermum (Ulvophyceae,Chlorophyta)

The zoospores and isogametes ofUlvaria obscura var.blyttii, the isogametes ofMonostroma bullosum, and the anisogametes ofM. grevillei have a flagellar apparatus with counterclockwise absolute orientation and terminal caps, and therefore belong to theUlvophyceae. On the basis of the absence or presence of body scales and the morphologies of certain flagellar apparatus components,Ulvaria obscura var.blyttii is retained in theUlvales, whileM. bullosum, M. grevillei andM. oxyspermum are referred to theUlotrichales. Differences in scale morphology, certain flagellar apparatus components, and early thallus ontogeny support the transfer ofM. oxyspermum to the genusGayralia. Mating structures and their positional relationships within the cell are described from the gametes examined. A plasmalemma-associated plaque that may be a degenerate mating structure occurs in someG. oxysperma motile cells.     

Does the abundance of girellids and kyphosids correlate with cover of the palatable green algae,Ulva spp.? A test on temperate rocky intertidal reefs

This study assessed whether the abundance of girellids and kyphosids was related to cover of the palatable green algae, Ulva australis and Ulva compressa, on rocky intertidal reefs in Jervis Bay, New South Wales, Australia. No relationship was found between Ulva spp. cover and abundance of Girella tricuspidata, Girella elevata and Kyphosus sydneyanus during a period of relatively low Ulva spp. cover (i.e. February 2011 to March 2011), but during a period of significantly higher Ulva spp. cover (i.e. October 2011 to November 2011) there was a strong correlation between Ulva spp. cover and G. tricuspidata abundance. Spatial analysis indicated that the abundance of G. tricuspidata was consistent across time, suggesting G. tricuspidata were not moving between reefs in response to variation in Ulva spp. cover between periods but rather that large schools of G. tricuspidata resided on reefs that had relatively higher Ulva spp. cover at certain times of the year.     

164 Chemical Antiherbivore Defenses of Temperate Green Macroalgae

Many temperate green macroalgae contain secondary meatbolites that provide protection from grazing by some herbivores. These include the production of dopamine hydrochloride by the ulvoid green alga Ulvaria obscura and the production of dimethylsulfoniopropionate (DMSP) by many species of Ulvales and Caulerpales. The dopamine hydrochloride defense was isolated using bioassay‐guided fractionation and is effective against sea urchins (Strongylocentrotus droebachiensis) and littorinid snails (Littorina sitkana). The DMSP activated defense system involves enzymatic cleavage of DMSP into dimethyl sulfide (DMS) and acrylic acid. It is found in many of the Ulvales and several species of Codium in the northeastern Pacific and Australasian regions. Many green algae such as Ulva fenestrata and Enteromorpha linza are avoided by urchins, which are deterred by DMS and acrylic acid in laboratory assays. However, these algae are often preferred foods of snails, which are deterred by DMS and acrylic acid. Snails may preferentially consume ulvoid green algae, despite being deterred by DMS and acrylic acid, because these algae contain relatively high nitrogen concentrations.