Attempts to characterize the population dynamics of the softshell clam Mya arenaria are complicated by a lack of nonlethal genotyping techniques and reliable tagging methods. A straightforward and nonlethal technique for clam genotyping is presented here, as well as a new method for the long-term tagging of clams. Hemolymph extracted from M. arenaria was used directly in a polymerase chain reaction to amplify successfully a DNA fragment suitable for sequencing. Tested M. arenaria showed 100% (n = 10) survival after a period of 4 wk. In a separate experiment, passive integrated transponder (PIT) tags were inserted between the mantle and shells of 72 clams that were monitored for tag retention and mortality. Among all PIT-tagged clams, there was 100% survival and 92% tag retention. These methods provide a mechanism by which softshell clams can be genotyped and individually monitored during field experiments.

Hemocytes constitute the cellular part of the mollusc immune system and are involved in phagocytosis; the production of toxic oxygen radicals, antimicrobial peptides, opsonizing molecules, and lysozymes; digestion, excretion, and nutrient transport. In this study, we investigated the phenotypic response, phagocytosis, and respiratory burst activity in hemocytes of Mya arenaria exposed to the bacterium Vibrio splendidus. Exposure to V. splendidus led to a loss of pseudopodia and rounding of hemocytes. The phagocytic ability of hemocytes was significantly reduced in challenged hemocytes, as was the respiratory burst activity of hemocytes. The expression of actin and elongation factor 2 genes was measured to investigate a possible relation between phenotypic response of hemocytes exposed to V. splendidus and genes associated with cytoskeleton. Both actin and elongation factor 2 genes were upregulated in challenged hemocytes. Additional studies are underway to identify other genes of hemocytes whose expression is affected by exposure to V. splendidus.

Results of the histopathological study of mantle tissues of the commercial geoduck Panopea abbreviata hosting the nemertean Malacobdella arrokeana revealed that the normal histology of mantle tissues of the bivalve was not altered by the attachment structure of the nemertean, even when the maximum individuals per clam reached 191 nemerteans. However, the vacuum force generated by the nemertean sucker seems to elicit a slight mechanical stretching of epithelial cells and a negligible infiltration response affecting the connective tissue between inner and outer mantle epithelia beneath the point of attachment. The 99.4% bivalves examined (n = 657) hosted at least 1 specimen of M. arrokeana. Adult nemerteans were able to survive outside the host for up to 3 mo at 13°C. These results suggest that the relationship between M. arrokeana and P. abbreviata should be considered as a commensal rather than a parasitic relationship.

The easternmost commercial population of hard clams, Mercenaria mercenaria, in Maine was discovered recently near the low intertidal in Goose Cove, in the town of Trenton (Hancock County). A fast- and slow-growing morph was identified that reaches commercial size (50.8 mm shell length) in 4 y and 5 y, respectively. Fast-growing individuals were selected as broodstock, and conditioned to spawn at the Downeast Institute. The fate and growth of cultured juveniles was followed for 5 mo beginning in July 2006 at 4 stocking densities (2,500–10,000 animals/1.1 m² floating, nylon window screen-lined tray; n = 20) at a coldwater field nursery approximately 60 km east of Trenton, in the town of Beals, ME (Washington County). Survival was nearly 100%, and growth was density dependent, with animals attaining a final mean shell length ±95% confidence interval of 8.4 = 0.13 mm and 7.6 ± 0.218 mm in the lowest and highest density treatments, respectively. In November 2006, cultured seed was separated into 2 sizes (large, 8.7 ± 0.2 mm; small, 5.1 = 0.2 mm) and overwintered in window-screen bags (0.2 m²) at densities ranging from 0.6–1.6 kg (large) and 0.5–1 kg (small), representing approximate densities ranging from 3,360–15,510 individuals per bag. Bags were placed on horizontal shelves within modified lobster traps (overwintering containers) that were added to a 35,000-L tank receiving ambient seawater for 177 days until May 2007. Seawater temperatures during this interval ranged from -1-10°C. Survival rates exceeded 99%, and no negative effects resulting from stocking density were observed. Hatchery seed was transplanted in May 2007 to the lower intertidal at Goose Cove and a second intertidal location approximately 30 km east of Beals at Duck Brook Flat, in the town of Cutler, and the fate and growth of these juveniles was followed for 6–7 mo. Survival was independent of planting densities (330–1320 individuals/m²), and predator netting did not enhance survival compared with controls without netting. Growth was seasonal, with the greatest incremental shell increases occurring between early July and late September. Growth rates varied between planting locations, with clams adding approximately 10 mm shell length at Goose Cove between May and December (initial shell length, 8.2 mm; final shell length, 17.9 mm) and approximately 5 mm shell length at Duck Brook Flat between June and November (initial shell length, 9.3 mm; final shell length, 14.3 mm). Hard clam farming in eastern Maine may help to diversify a wild shellfish industry that is currently in decline for most species except lobsters; however, additional efforts are needed to explore alternative grow-out sites and methods to enhance growth rates.

Clam aquaculturists have suspected low water flow over clam grow-out areas as a principal explanation for decreased growth and yield of bivalves; however, empirical data from field studies to support these observations are rare and in some cases contradictory. I conducted two experiments in Back Sound, NC, to examine the effects of water flow and juvenile density on hard clam survivorship and growth. The first experiment assessed differences in early growth and survivorship of juvenile seed clams under three manipulated water flows (enhanced [0–32 cm sec^-1], reduced [0–12 cm sec^-1], and ambient tidal flows [0–22 cm sec^-1]) and three initial stocking density (250, 500, or 1000 m^-2) of juvenile clams (shell length [SL] = 9 mm). The second set experiment examined the effects of two different water flow regimes (ambient [0–22 cm sec^-1] and low [ 0–11 cm sec^-1]), and three stocking densities (250, 500, or 1000 m^-2) on growth of seed clams (SL = 12 mm) to market size. Unlike the first experiment, in which no effort was made to exclude predators to examine survivorship, the second experiment mimicked aquaculture operations and used bottom netting to cover seed clams. Neither planting density nor flow regime affected growth or survivorship of juvenile seed clams in the first experiment. Overall survivorship was high (> 75%) and clams grew to an average SL of 24 mm during the 4 months of grow-out. In the second experiment, clam growth and, consequently, time to marketable size was affected by water flow; however, differences in clam growth were relatively small (< 4 mm SL). After 12 mo, 69% of clams were of harvestable size in the ambient flow (0–22 cm sec^-1) compared with 42% in the low flow (0–12 cm sec^-1). Planting density did not affect this relationship; no interaction between planting density and flow regime was evident in either experiment. This result suggests the positive effect of water flow on clam growth increases with individual clam size, but is not density dependent on the square meter scale of our experiments.

Through histological analyses, this investigation reveals an unusual high incidence of hermaphroditism in Megapitaria squalida, a gonochoric species. A total of 684 specimens were sampled at monthly intervals from February 2007 to January 2008 at Bahía de La Paz and Bahía Magdalena, Baja California Sur, Mexico. Microscopic examination showed that 21.8% of specimens from Bahía de La Paz and 23.5% from Bahía Magdalena were hermaphroditic; in both areas, hermaphroditism was found throughout the year, although in variable proportions. In general, a significantly higher number of females relative to males (chi-square, P < 0.05) were observed in both areas. Our findings indicate that this unusual incidence of hermaphroditism was likely caused by the low population density resulting from overfishing.

Limfjorden has a long tradition of mussel production based on wild stock fisheries. As a result of environmental concern of adverse effects of fishery, farming of mussels on off-bottom longlines has been well established during the past 5 y. Limfjorden is heavily eutrophic, resulting from intensive agricultural production in the catchment area of the estuary. Stimulation of sedimentation and subsequent benthic impacts of mussel farms were investigated with a focus on seasonal and spatial variations. The seasonal study was performed along a transect from inside one of the mussel farms to a reference station 75 m northeast of the farm every season during 1 y (summer to summer). The effects depended significantly on the variation in hanging mussel biomass along the transect as the effects on benthic total oxygen uptake, nutrient release, and sulfate reduction rate was at its maximum at the station with the largest hanging biomass. In addition, stimulation of the mussel farm was strongest during the summer when NH₄ and PO₄^3- release was increased by 400% and 740%, respectively, compared with the reference station. The concentration of reduced sulfur was only significantly stimulated (58%) by the mussel farm during the second summer season, which was characterized by total oxygen depletion in the bottom water and linked to the unavailable oxygen for reoxidation. A significant spatial variation in the benthic impacts was also observed. Eight differently situated mussel farms with variation in water depth and mussel biomass on the longlines were examined. The stimulation on total sedimentation rates, total oxygen uptake (TOU), and NH₄ and PO₄^3- flux of the mussel farms was in the range of 0–92%, 0–67%, 52–290%, and 0–700%, respectively. Furthermore, stimulation of TOU and NH₄ flux was significantly linked by linear regression to the sedimentation rate of particulate organic carbon and particulate organic nitrogen, respectively. Hence, this study shows strong evidence that mussel farms stimulate the benthic degradation rates in an area that is already highly affected by other sources of organic input.

Oyster farming is one of the oldest aquaculture industries in Australia and, in New South Wales (NSW), its history dates back some 130 y. Like other industries, it has evolved over time, but during the past 5 y, a number of significant changes have occurred. Although Sydney rock oysters (Saccostrea glomerata [SRO]) remain the most important commercial species, the culture of Pacific oysters (Crassostrea gigas), particularly triploids, has increased significantly. Interest in cultivating other commercially important species, such as flat oysters, Ostrea angasi, has also increased. Overall, hatchery-produced oyster seed has become more readily accessible, particularly for S. glomerata, which, prior to 2003, had been largely unavailable to the majority of the rock oyster industry. For both S. glomerata and C. gigas, breeding programs have become an integral part of industry development and have been the primary reason for hatchery seed uptake in NSW. Across the oyster industry, the emphasis placed on the importance of demonstrating environmental sustainability has increased, and both industry and government have been proactive in protecting the estuarine environments in which oyster farming occurs. Collectively, hatchery development, oyster breeding, and environmental research has “spawned” a number of new research initiatives that have increased fundamental oyster research during the past 5 y.

The history of French oyster culture consists of a succession of developmental phases using different species, followed by collapses caused by diseases. The indigenous species Ostrea edulis was replaced first with Crassostrea angulata, then C. gigas. France is now the top producer and consumer of oysters in Europe, producing around 120,000 t of the cupped oyster C. gigas annually, and an additional 15001 of the flat oyster O. edulis. Cupped oysters are produced all along the French coast from natural and hatchery spat. Various structures are used to collect spat from the wild. After a growing-on period, oysters are cultivated by three main methods: (1) on-bottom culture in the intertidal zone or in deep water, (2) off-bottom culture in plastic mesh bags in the intertidal zone, or (3) suspended culture on ropes in the open sea. The main recent development is the increasing use of hatchery oyster spat, especially triploids. Almost all oyster production is sold fresh and eaten raw straight from the shell. There is marked seasonality in sales, with the majority being made during Christmas and New Year. Abundant production and the lack of market organization induce strong competition among the production areas, causing prices to fall. Oyster farmers have developed strategies of sales promotion and regional quality labeling to overcome this difficulty. There are numerous production hazards, including environmental crises (microbiological pollution), unexplained mortality, and overstocking, and recent problems with toxic algae have disrupted oyster sales. However, oyster culture has many assets, including a coastal environment offering favorable sites for mollusc growth and reproduction. Oysters have been consumed in France since ancient times, and their culture is now well established with a concession system that favors small family firms. There is a young, well-educated farmer population, with technical expertise and savoir faire. Careful seawater quality monitoring ensures good consumer protection, and research is making innovative contributions (selection and polyploids). These points and opportunities for market expansion should bolster this industry's future, although the problem of toxic algae, probably linked to global warming and anthropogenic factors, and the threat of new diseases, pose vital questions for future research.

To investigate the in vitro generation of nitric oxide (NO) and superoxide anion (O₂^-) by Crassostrea ariakensis hemocytes stimulated with rickettsialike organisms (RLOs), RLOs were purified from infected C. ariakensis. BALB/c mice were infected with the purified RLOs and the infectious vitality of RLOs for the mice was detected using the smears and histological sections stained with Machiavello and transmission electron microscope (TEM) technology. These experiments proved that the purified RLOs retained considerable vitality. The study of the influence of temperature on phagocytosis activity revealed that the percentage of phagocytic cells was lower at 10°C than at 20°C and 30°C. The in vitro generation of the cytotoxic molecules such as NO and O₂^- by C. ariakensis hemocytes was detected when incubated at 25°C with the purified RLOs and zymosan. The generation of O₂^- and NO indicated a possible formation of the highly bactericidal oxidant peroxynitrite by the hemocyte of C. ariakensis. The generation for O₂^- was reduced significantly by superoxide dismutase, but not by inhibitors of NO synthase. Superoxide dismutase and inhibitors of NO synthase decreased the nitrite/nitrate levels generated by C. ariakensis hemocytes. It is suggested that both nicotinamide adenine dinucleotide phosphate (NADPH) oxidase and NO synthase pathways are involved in the self-defense system of C. ariakensis.

Tissue-associated bacterial community profiles generated using a nested polymerase chain reaction—denaturing gradient gel electrophoresis (DGGE) approach and culture-dependent and culture-independent isolation techniques were compared. Oyster samples were collected from 2 harvest areas along the coast of Maine, in the United States. Profiles from both isolation strategies were evaluated using Sorensen's index of similarity and cluster analysis of gel banding patterns. Culture-independent profiles were further evaluated using the Shannon diversity index. In general, the culture-dependent strategy resulted in a greater number of bands within a profile. Bacterial DGGE profiles were found to be highly similar within an isolation strategy, with a higher degree of unrelatedness between culture-dependent and -independent techniques. Cluster analysis identified bands present in the culture-dependent strategy and not the total DNA technique, and vice versa. Significant differences in community profiles between oyster-associated and seawater were observed, indicating a diverse group of specialist bacterial species inhabit and are able to proliferate within the oyster.

Crassostrea gigas was introduced in Anegada Bay (North Patagonia, Argentina), in 1981 for aquaculture purposes. The species has, since established in the field, covered all available hard substrata in the bay and gradually expanded south along the coast of the neighboring province of Río Negro, 90 km away from its original introduction site. Our work focused on the reproductive dynamics of the species at the introduction site, with emphasis on the thermal thresholds needed for each stage of gonad development. During early spring, the oysters in Anegada Bay go through active gonad proliferation. Maturity extends mainly from October to January. The first spawning occurs in November, when seawater temperature exceeds 17°C, and peaks from December to February, when seawater temperature lies in the range ot 19–21.5^°C. The timing of gonad development is size dependent. Larger (≥70 mm) and medium-size oysters begin spawning first, whereas small oysters (<40 mm) represent the late spawners of the season. The C. gigas population in Anegada Bay is a clear and well-documented case of an introduction site where optimal environmental conditions are met, both for complete gonad maturation and for successful larval survival and settlement. We compiled a series of C. gigas cases from different parts of the world in which reproduction is related to seawater temperature. We concluded that the thermal threshold for full female gonad ripening in this species is strict (temperature > 17^°C), and spawning only occurs in those sites where this threshold is reached.

Anoxic water events in conjunction with summer high temperatures are thought to be one of the causes of declines in natural oyster reefs on the eastern shore of Mobile Bay. Work is underway to determine whether tolerance to low oxygen can be selected for in hatchery-produced oysters. As a component of this work, the expression of heat shock protein 70 (HSP 70) was examined in control (normoxia) and anoxia-challenged juvenile oysters. Parental Eastern oysters, Crassostrea virginica were collected from 2 sites, Cedar Point Reef (CP), an area considered to have normoxic conditions, and White House Reef (WH), an area suspected to experience periodic anoxia. F1 generation oysters were produced from CP and WH parents that survived an anoxic exposure of 96 h. Control F1 generation oysters from both parental stocks not exposed to anoxia were also produced. The F1 generation oysters were subsequently exposed to anoxia or control normoxic conditions, and differences in expression of HSP 70 were examined. Nitrogen was used to create the anoxic conditions for both the parental and F1 generations. Three HSP 70 isoforms—2 constitutive forms (HSC 77 and HSC 72) and 1 inducible form (HSP 69)—were expressed in both anoxia- and normoxia-exposed oysters from all groups. Although there were differences among groups of oysters from the 2 sites, there were no differences in the expression of HSC 77 and HSC 72 between the control and anoxia-treated oysters within a group. Interestingly, the expression of HSP 69 was higher in oysters exposed to normoxia than the ones from anoxia treatments. These differences are thought to reflect a combination of responses to nutritional stress in the controls and facultative anaerobiosis and metabolic arrest in the anoxia groups.

Genetic variation in eastern oysters (Crassostrea virginica) collected from 13 sites in the Gulf of Mexico was examined using a combination of mitochondrial DNA (mtDNA) sequencing, mtDNA restriction fragment length polymorphism analysis, and nuclear single nucleotide polymorphism analysis. Both mitochondrial and nuclear markers showed significant differentiation among samples. Combined with previous allozyme and microsatellite data, these results indicate considerable population subdivision throughout the Gulf of Mexico, despite the potentially homogenizing effect of larval dispersal.

We evaluated the development of metabolic capacities, immunocompetence, and growth patterns according to sex, age, and gametogenesis stages among scallops Placopecten magellanicus from the Magdalen Islands (Québec, Canada). Our 2-y study allowed us to evaluate in detail both seasonality and interannual variability of their physiological state. Enzymes— namely, phosphoglucose isomerase, phosphomannose isomerase, pyruvate kinase, aspartate aminotransferase, citrate synthase, chymotrypsin, and lipase were assessed in muscles and digestive glands of scallops. Immunocompetence was evaluated by measuring hemocyte activity in hemolymph and the efficiency of phagocytic cells. The various reproductive stages were identified with histological examination, and growth was estimated using digestive gland and gonadosomatic indices. Lipase and phagocytosis appeared to be good biomarkers of the physiological state of scallops in relation to their age and reproductive stage: Lipase activity is higher in young scallops (2 y old) as well as during the development and the ripe stages, and is associated with low phagocytic activity. Results suggest that the lipid digestion capacity may increase to improve lipid conversion during the development and ripe stages. After this period, metabolic reserves were presumably used to synthesize hemocytes at a higher rate and to rebuild gonadal tissue. The regulation of the reproductive cycle and immunocompetence was observed to depend directly on the environmental parameters without concomitant changes in the activity of the measured enzymes of the energy metabolism.

We examined the inhibitory effects of 2,4-dibromophenol (DBP) and 2,4,6-tribromophenol (TBP), which are released by the large perennial brown algae Eisenia bicyclis and Ecklonia kurome, on settlement and survival of veliger larvae of the Japanese abalone Haliotis discus hannai. The proportion of larvae attached to a polycarbonate chip coated with pregrazed diatom films and abalone trail mucus reached 70% by 2 h, and the proportion of larvae that underwent metamorphosis rose gradually to 65% at 8 h and 85% at 24 h. DBP and TBP at 1 ppm had no effect on larval health or settlement. However, in the presence of 10 ppm DBP, the proportions of larvae attached and metamorphosed were reduced to less than 15% and less than 2%, respectively, and those of overturned and dead larvae were increased to 50% and 41% at 24 h, respectively. In the presence of 10 ppm TBP, the proportion of metamorphosed larvae was reduced to 53% and that of overturned larvae increased to 30% at 24 h. All larvae exposed to 50 ppm DBP or TBP died after 2 h or 8 h, respectively. These findings suggest that DBP and TBP strongly inhibit attachment, metamorphosis, or both at 10 ppm, and that DBP is more toxic than TBP. DBP and TBP may explain low recruitment levels of abalone in kelp forests.

Predation by drilling gastropods is preservable in the fossil record and thus provides valuable examples for the study of evolutionary concepts that emphasize the importance of biotic interactions. For cost-benefit analyses, accurate measurement of drilling rate and consumption rate is essential. We experimentally determined the drilling, excavation, and consumption rates of the muricid gastropod Nucella lamellosa preying upon the mussel Mytilus trossulus. Our results indicate that although drilling rate is independent of predator size, excavation rate is proportional to the size of the driller, as one might expect on biomechanical grounds. In addition, consumption rate is also a function of predator size, which might have important implications in cost-benefit analyses applied to varied-sized predators, as we illustrate with an example.

The banded murex Hexaplex trunculus was sampled at Menzel Jemil and Bizerta Channel (Bizerta Lagoon, northern Tunisia) to study imposex, growth, and reproduction. Butyltin concentrations were analyzed in females from the 2 sampling sites using the gas chromatographic flame photometric detection technique. Results showed that the Bizerta Channel population was severely affected by imposex, which was confirmed by the high level of butyltins recorded in females from this site. Growth in shell width and shell weight was higher in Bizerta Channel, whereas growth in shell aperture and flesh weight was favored in Menzel Jemil. The assessment of reproductive activity, made by calculating fecundity and using 2 condition indices, showed that the Menzel Jemil population was reproductively more active.

The objective of this study was to determine at what level the shell mineralization of Anodonta cygnea, a shallow freshwater bivalve, is influenced by external physical—chemical factors, mainly concerning the habit and microstructure of the calcium carbonate crystals. A detailed examination of the inner shell layers of A. cygnea was carried out by scanning electron microscopy in animals living under natural environment conditions and after being exposed to artificially high hydrostatic pressure. Groups of 6 animals were exposed to different hydrostatic pressure (10, 20, 40, or 80 bar) in a hyperbaric chamber for 10 days. In general, we noted that the high pressure induced strong changes in the microstructure of all regions of the shell inner layer in A. cygnea, probably by altering organic matrix deposition, under every hyperbaric value. In fact, observations of the prismatic layer showed some significant alterations, presenting fibrous spherulitic crystalline arrangements instead of the nondenticular composite crystals. At the beginning of the nacreous layer, experimental animals showed several (5–7) superimposed lamellae consisting of unconnected round tablets. In the following regions, the nacreous layer with hexagonal-rhombohedral crystals displayed an intense growth resembling columnar formations resulting from a greater number of mineral layers, many more than would be expected. A similar phenomenon was also revealed in the inner palliai line regions of the exposed A. cygnea bivalves, with simultaneous visualization of more than 10–15 layers of nacre in contrast with 3–4 seen in natural situations. Curiously, similarly altered microstructures were observed in shell calcareous layers of a hydrothermal vent deepsea bivalve Bathymodiolus azoricus, particularly in the nacreous layer. This natural occurrence, together with the experimental work on A. cygnea, might imply that hydrostatic pressure is a physical parameter of great importance in microstructure definition. The basic mechanism is probably related to deficient chitin (or similar) polymerization, which promotes the vertical growth of the nacre crystals.

Hemolymph from the American lobster (Homarus americanus) was analyzed by optical spectroscopy for the concentration of total hemolymph proteins and results were compared with a more traditional technique: refractometry. Absorbance peaks at 280 nm for total hemolymph protein concentration and 334 nm for hemocyanin concentration were studied, compared with equivalent refractometry readings, and correlated to the vitality of the lobster. These spectroscopic measurements constitute engineering data in the design a future noninvasive, field-deployable microinstrument to sort lobster according to their health and long-term viability.

Epizootic shell disease (ESD) is a recently described form of shell disease affecting the American lobster (Homarus americanus, H. Milne Edwards). The disease has caused serious losses to the American lobster fishery. Affected lobsters are unmarketable as a result of the severe biofouling present on the carapace surface. Eukaryotic micro- and macro-organisms have been observed in ESD lesions, but their identity and the extent of their presence has not been determined. We amplified 18S rRNA gene sequences from eukaryotic communities in ESD lesions and separated them for sequencing using denaturing gradient gel electrophoresis. The diversity of the eukaryotic communities was surprisingly high, with as many as 7 different organisms detected in a number of lesions. The eukaryotes identified belonged to broad taxa, including Metazoa, Protozoa, and Fungi. Some organisms were detected in a number of samples and may have a specific role in ESD lesion development and biofouling, including the nematode Geomonhystera disjuncta, various barnacles, stramenopiles, and bryozoans. Aside from G. disjuncta, the other eukaryotes were only sporadically detected and were, therefore, likely opportunistic. However, G. disjuncta is a known bacterivorous nematode; thus, it, too, is likely opportunistic because high numbers of bacteria are known to exist in ESD lesions. Although the eukaryotic organisms in ESD lesions are likely secondary invaders, they may contribute significantly to the biofouling of the carapace seen in severe ESD.

The green crab (Carduus maenas L.) is an exotic species in many parts of the world. It successfully invaded, at the end of the 1990s, the coast of Prince Edward Island, Canada, where rock crabs (Cancer irroratus Say) are commonly found. The relationship between these 2 species is still not well documented. The short-term time budget of both species was studied in autumn 2006 and spring 2007 under different experimental conditions to assess the effect of the green crab on the behavior of the rock crab. Crabs were observed in 3 competition treatments (1 crab, 2 conspecifics, or 2 heterospecifics) using 3 temperatures (5, 12, or 20°C) and 2 prey densities (4 or 30 mussels). The time spent foraging and in agonistic interactions by both species generally increased in high-temperature challenges, whereas the time spent inactive decreased, regardless of the season. Both crab species responded differently when facing a conspecific. Time spent foraging increased in certain cases whereas it decreased in others. Overall, the time budget of the green crab was only affected by temperature during autumn observations whereas the time budget of the rock crab varied according to (1) the competition treatment, (2) temperature, and (3) number of prey available. Temperature influenced the time budget of both crab species during springtime. The behavior of both species was unaffected by the presence of a heterospecific. These results suggest that rock crabs, in contrast to what was expected, are not much affected by the presence of green crabs and that they may coexist in nature.

This study evaluated the effects of astaxanthin (AX) injected at 1.34 nmol/g body weight on survival, antioxidant capacity, total hemocyte count, and hepatopancreas AX content of the giant freshwater prawn Macrobrachium rosenbergii (De Man 1879) challenged with Lactococcus garvieae. Injected AX significantly increased the survival of M. rosenbergii challenged with L. garvieae (P ≤ 0.05) and enhanced to some extent its antioxidant capacity (superoxide dismutase, glutathione peroxidase, and glutathione reductase) and total hemocyte count. AX-injected M. rosenbergii yielded significantly higher hepatopancreas AX content compared with non-AX-injected control. Overall results of this study indicate that AX plays an important role in enhancing M. rosenbergii resistance against L. garvieae.

We gauged the effect of the sea urchins Hemicentrotus pulcherrimus and Anthocidaris crassispina on an Eisenia bicyclis kelp bed on the Kii Peninsula in southwestern Japan. We monitored sea urchin density, size, and vertical algal distribution every 2 months from September 2000 to March 2002 and in September 2002 in a 40-m² plot that stretched from the intertidal (reef) zone to the subtidal zone at depth of up to 2 m. The sea urchin densities were more than 40 individuals/m² (H. pulcherrimus) and more than 5 individuals/m² (A. crassispina) during September 2000 to May 2001. These densities decreased abruptly to less than 20 and less than 1 individual/m² in October 2001, respectively, coincident with low salinities of less than 23 practical salinity unit (PSU) in late June because of river water inflow. Until May 2001, adult E. bicyclis grew only on the intertidal reef, and articulated coralline turf was predominant in the subtidal zone. From January 2002, the kelp bed expanded slightly to the upper subtidal zone, but most young kelp growing at a depth of more than 1.5 m disappeared, despite the low sea urchin density. It is likely that abiotic factors resulting from the river water inflow inhibited the growth of E. bicyclis.

A range of factors may affect the composition and abundance of macroalgae on subtidal rocky reefs. We experimentally determined the interactive effect of the occurrence of the long-spine sea urchin, Diadema antillarum, depth and sedimentation levels on macroalgal assemblage structure on eastern Atlantic rocky reefs. Specifically, we manipulated sea urchin densities (removal of all individuals vs. untouched controls at natural densities) on rocky reefs devoid of erect vegetation, and predicted (1) that removal of sea urchins would differently affect macroalgal assemblage structure between deep (16–18 m) and shallow (8–9 m) reef strata, and that (2) the effect of sea urchin removal on macroalgae would be altered under different scenarios of sedimentation (ambient vs. enhanced). Experimental circular plots (2 m in diameter) were set up at 3 locations at Gran Canaria (Canarian Archipelago), and were maintained and monitored every 4 wk for 1 y. At the end of the experimental period, the structure of the algal assemblages differed between urchin treatments and depth strata, with a larger cover of turf and bushlike algae where urchins were removed and at the shallow reef stratum. More important, differences in algal assemblage structure between urchin treatments were irrespective of sedimentation levels, but shifted from the shallow to the deep stratum. This interactive effect was, in turn, observed for bushlike algae, as a result of a larger magnitude of response (i.e., larger cover) in the shallow stratum relative to the deep stratum, but was not detected for either turf or crustose coralline algae. These results highlight the importance of some physical conditions (here, differences in depth) to interact with biotic processes (here, urchin abundance) to create patterns in the organization of subtidal and benthic assemblages.