Intertidal Individuals Research Articles

Specific plasticity of the anemone Anthopleura hermaphroditica to intertidal and subtidal environmental conditions of the Quempillén estuary.

The cellular capacity of marine organisms to address rapid fluctuations in environmental conditions is decisive, especially when their bathymetric distribution encompasses intertidal and subtidal zones of estuarine systems. To understand how the bathymetric distribution determines the oxidative damage and antioxidant response of the estuarine anemone Anthopleura hermaphroditica, individuals were collected from upper intertidal and shallow subtidal zones of Quempillén River estuary (Chile), and their response analysed in a fully orthogonal, multifactorial laboratory experiment. The organisms were exposed to the effects of temperature (10°C and 30°C), salinity (10 ppt and 30 ppt) and radiation (PAR, > 400-700 nm; PAR+UV-A, > 320-700 nm; PAR+UV-A+UV-B, > 280-700 nm), and their levels of lipid peroxidation, protein carbonyl and total antioxidant capacity were determined. The results indicated that the intertidal individuals of A. hermaphroditica presented higher levels of tolerance to the stressful ranges of temperature, salinity, and radiation than individuals from the subtidal zone, which was evident from their lower levels of oxidative damage to lipids and proteins. These results were consistent with increased levels of total antioxidant capacity observed in subtidal organisms. Thus intertidal individuals could have greater plasticity to environmental variations than subtidal individuals. Future studies are needed to understand the mechanisms underlying stress adaptation in individuals from this estuarine anemone subjected to different environmental stressors during their life cycles.

Size specific boldness associated with differences in resource requirements and habitat use: a cross-sectional study in hermit crabs.

Animal personality is often studied within compressed periods of observation that represent narrow windows in comparison to animal lifespans. Although much is known about the relations between repeatable personality traits and cross-situational behavioral plasticity, less is known about how such traits might differ across age classes or life history transitions. We conducted a cross-sectional study of startle response duration in 3 size classes of Pagurus bernhardus, the common European hermit crab. We defined size classes using transitions in the preferred species of gastropod shells that accompany growth, and this change in preference is in turn associated with a transition from intertidal to subtidal habitats. Compared with small- and medium-sized intertidal individuals the larger subtidal hermit crabs behaved cautiously by showing startle responses of greater duration following disturbance. Startle responses were also repeatable within all 3 size classes, confirming the presence of animal personality in intertidal hermit crabs and demonstrating that this pattern is retained within the largest size classes, which have undergone the transition from intertidal to subtidal habitat. Interestingly, there was a trend for the pattern of repeatable startle response durations to increase with size class, with the highest value for repeatability and the greatest range of startle response durations being present within the large subtidal population. The greater range of startle responses indicates that the longer startle response durations in some larger individuals are more likely due to developmental changes with age and habitat use than reflecting selection against the boldest individuals during earlier stages of life.

Impact of short-term elevated temperature stress on winter-acclimated individuals of the marine gastropod Crepidula fornicata

The intertidal zone is an especially stressful thermal habitat, typically exposing residents to air temperatures for up to 6 h at a time, twice daily. Tolerance to elevated temperatures has been particularly well-studied for a variety of intertidal species, especially with regard to upper thermal limits during summers. However, in recent years, as climates have been changing around the world, temperate zone intertidal organisms have sometimes been exposed to periods of unusually high air temperatures during the winter. The present study sought to examine the impact of elevated temperatures on survival and clearance rates of winter-acclimated intertidal individuals of the sedentary marine suspension-feeding gastropod Crepidula fornicata. Individuals were collected intertidally from Nahant, Massachusetts from late January to early April each year for 5 years, maintained in the laboratory at the acclimation temperature of 6 °C, and exposed in the laboratory for 3 h to temperatures as high as 37 °C in seawater either once or twice, 24 h apart. Although mean clearance rates were substantially reduced for at least the next 12–24 h after individuals were returned to the 6 °C control condition following exposures to elevated temperatures as low as 21–26 °C, we saw little mortality even following two 3 h exposures to 35 °C, or single exposures to 37 °C. Mortality was substantial, however, in one experiment following a double exposure to 37 °C. Smaller individuals (~5–12 mm in shell length) were somewhat more sensitive to the thermal stress than adults were. Intertidal members of C. fornicata in Massachusetts seem well-prepared to deal with the increasing range of winter air temperatures associated with the global climate confusion predicted for future years. Additional studies will be required to understand the physiological and biochemical mechanisms used by winter-acclimated individuals of this species to tolerate such periodic substantial temperature increases of 29–31 °C.

Interactive effects of large- and local-scale environmental gradients on phenotypic differentiation.

Intraspecific differentiation across a steep environmental gradient depends on the relative influences of evolutionary, organismal, and environmental processes. But steep environmental gradients may be nested within larger-scale, regional conditions that could influence these processes at the local scale. Therefore, we hypothesized that phenotypic differentiation along a steep environmental gradient would vary among regions. To test this hypothesis, we conducted a reciprocal transplant experiment on rocky intertidal shores, a habitat characterized by gradients in abiotic and biotic stress, in three regions of the Gulf of Maine. We used the ubiquitous and ecologically important rockweed species Fucus vesiculosus to quantify differentiation in growth, tissue nitrogen, and nitrogen productivity between upper and lower intertidal individuals. We found that phenotypic differentiation between tide heights varied among traits and regions. Although tissue nitrogen did not vary among any treatment combinations, growth and nitrogen productivity response were region specific. A strong effect of transplant height was found in all regions; however, an effect of home (source) height was only detectable in the central Gulf of Maine. Our study reveals that intraspecific responses to steep environmental gradients vary among populations, but the mechanisms underlying these patterns remain unknown. Given the roles that rockweeds play as food and habitat, these in situ patterns of growth and nitrogen productivity could have important community- and ecosystem-level consequences.

Differences in resource allocation to reproduction across the intertidal-subtidal gradient for two suspension-feeding marine gastropods: Crepidula fornicata and Crepipatella peruviana

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 572:165-178 (2017) - DOI: https://doi.org/10.3354/meps12152 Differences in resource allocation to reproduction across the intertidal-subtidal gradient for two suspension-feeding marine gastropods: Crepidula fornicata and Crepipatella peruviana Jan A. Pechenik1,*, Casey M. Diederich1,4, Oscar R. Chaparro2, Jaime A. Montory3, Francisco J. Paredes2, Amanda M. Franklin1 1Biology Department, Tufts University, Medford, MA 02155, USA 2Instituto de Ciencias Marinas y Limnológicas, Universidad Austral de Chile, Casilla 567, Valdivia, Chile 3Centro i-mar, Universidad de Los Lagos, Camino Chinquihue km 6, Puerto Montt, Chile 4Present address: 50 Fountain Plaza, Suite 600, Buffalo, NY 14202, USA *Corresponding author: jan.pechenik@tufts.edu ABSTRACT: The sedentary, suspension-feeding gastropods Crepidula fornicata and Crepipatella peruviana can be found in large numbers both subtidally and intertidally. Although intertidal animals often show reduced reproductive output compared with that of subtidal animals, we know little about how the reproductive output of marine gastropods is affected by exposure to intertidal stresses. We documented reproductive characteristics for intertidal and subtidal Crepidula fornicata in Rhode Island, USA (2012, 2013), and Crepipatella peruviana from Pelluco Beach, Chile (2010–2012). Females of both species brood encapsulated embryos for at least several weeks before releasing offspring, facilitating determinations of individual fecundity (embryos per egg mass). As expected from the environmental stresses experienced uniquely by intertidal individuals while emersed, including an inability to feed, intertidal females of C. peruviana had lower fecundities, producing significantly fewer egg capsules per brood; the mean number of eggs per capsule did not differ significantly by habitat. In marked contrast, the size-adjusted fecundity of Crepidula fornicata was significantly higher for intertidal females than for subtidal females; however, rather than brooding more egg capsules per individual or making larger egg capsules, intertidal females crowded each capsule with significantly more eggs. This study adds to previous work showing how exceptionally well-adapted C. peruviana is to intertidal life, and may help to explain why this species has been so unusually successful as an invasive among calyptraeid gastropods. Future studies will be required to identify the specific conditions that have provoked these adaptations in C. fornicata, and to understand the mechanisms through which this species achieves them. KEY WORDS: Crepidula fornicata · Crepipatella peruviana · Slipper limpet · Reproduction · Intertidal · Invasive species · Fecundity · Egg capsules Full text in pdf format PreviousNextCite this article as: Pechenik JA, Diederich CM, Chaparro OR, Montory JA, Paredes FJ, Franklin AM (2017) Differences in resource allocation to reproduction across the intertidal-subtidal gradient for two suspension-feeding marine gastropods: Crepidula fornicata and Crepipatella peruviana . Mar Ecol Prog Ser 572:165-178. https://doi.org/10.3354/meps12152 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 572. Online publication date: May 31, 2017 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2017 Inter-Research.

Flexibility of Physiological Traits Underlying Inter-Individual Growth Differences in Intertidal and Subtidal Mussels Mytilusgalloprovincialis.

Mussel seed (Mytilusgalloprovincialis) gathered from the intertidal and subtidal environments of a Galician embayment (NW, Spain) were maintained in the laboratory during five months to select fast (F) and slow (S) growing mussels. The physiological basis underlying inter-individual growth variations were compared for F and S mussels from both origins. Fast growing seemed to be a consequence of greater energy intake (20% higher clearance and ingestion rate) and higher food absorption rate coupled with low metabolic costs. The enhanced energy absorption (around 65% higher) resulted in 3 times higher Scope for Growth in F mussels (20.5±4.9 J h−1) than S individuals (7.3±1.1 J h−1). The higher clearance rate of F mussels appears to be linked with larger gill filtration surface compared to S mussels. Intertidal mussels showed higher food acquisition and absorption per mg of organic weight (i.e. mass-specific standardization) than subtidal mussels under the optimal feeding conditions of the laboratory. However, the enhanced feeding and digestive rates were not enough to compensate for the initial differences in tissue weight between mussels of similar shell length collected from the intertidal and subtidal environments. At the end of the experiment, subtidal individuals had higher gill efficiency, which probably lead to higher total feeding and absorption rates relative to intertidal individuals.

Differences in feeding adaptations in intertidal and subtidal suspension-feeding gastropods: studies on Crepidula fornicata and Crepipatella peruviana

Suspension-feeding organisms living in the intertidal zone experience reduced feeding times associated with periodic aerial exposure. The potential morphological and physiological adaptations to this reduced feeding time were investigated for two closely related gastropods, Crepidula fornicata and Crepipatella peruviana. Intertidal C. fornicata had heavier gills than subtidal conspecifics, a difference mediated by larger gill surface areas and greater numbers of gill filaments among intertidal individuals of a given size. In contrast, the gills of intertidal and subtidal C. peruviana were morphologically indistinguishable. Despite relatively larger food-collecting organs, individuals of C. fornicata from the intertidal zone had clearance rates (CR) that were not significantly different from those of subtidal conspecifics. In contrast, the CR of intertidal C. peruviana were significantly lower than those of subtidal conspecifics. The low CR of intertidal C. peruviana may be partially explained by significantly lower measured particle transport velocities across their gills. In the context of feeding, intertidal individuals of C. fornicata performed at least as well as subtidal conspecifics, resulting in a population whose adults were as large as those found subtidally. This suggests that C. fornicata has had a long interaction with the environmental heterogeneity associated with intertidal life. In contrast, intertidal individuals of C. peruviana were on average smaller than subtidal individuals and may be stressed in the intertidal.

Morphological and behavioral differences in the gastropod Trophon geversianus associated to distinct environmental conditions, as revealed by a multidisciplinary approach

The gastropod Trophon geversianus exhibits shell polymorphisms along its distribution in subtidal and intertidal habitats. Our hypothesis is that morphological and behavioral patterns of T. geversianus represent habitat-specific constrains; subsequently we expect an association between shell morphology, attachment behavior, and habitat. In order to test this hypothesis we compared individuals from intertidal and subtidal habitats, at three sites in Golfo Nuevo (Argentina). We analyzed shell morphology using classic morphometric variables, 3D geometric morphometrics and computing tomography scan. The results were complemented with field observations of attachment to substrate and turning time behavior, as well as of the number of shell scars produced by crab predation. Our results showed differences in shell size and shape between intertidal and subtidal-collected individuals. Centroid size, total weight and shell weight, as well as shell density and thickness were significantly lower in intertidal individuals than in subtidal ones. Gastropods from intertidal habitats presented a low-spired shell and an expanded aperture which might allow better attachment to the bottom substrate, while subtidal individuals presented a slender and narrower shell shape. The number of crab scars was significantly higher in shells from subtidal individuals. Observations of the behavior of gastropods placed at the intertidal splash zone showed 100% of attachment to the bottom in the intertidal individuals, while subtidal specimens only attached in average in 32% of the cases. These latter took 12 times longer to re-attach to the bottom when faced up. Phylogenetic analysis of COI gene fragments showed no consistent differences among individuals sampled in both habitats. All these results suggest that T. geversianus has developed two ecomorphs with distinct morphological and behavioral responses to physically stressful conditions registered in north Patagonian intertidals, as opposed to lower physical stress but higher predation pressure in the subtidal habitats. The findings of this work constitute a starting point in the study of ecological adaptation processes in gastropods from Patagonian coastal environments.

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. lactuca increased 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. lactuca and M. splendens occurring in the lower layers of stacks of algae.

Thermal tolerance of Crepidula fornicata (Gastropoda) life history stages from intertidal and subtidal subpopulations

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 486:173-187 (2013) - DOI: https://doi.org/10.3354/meps10355 Thermal tolerance of Crepidula fornicata (Gastropoda) life history stages from intertidal and subtidal subpopulations Casey M. Diederich*, Jan A. Pechenik Biology Department, Tufts University, Medford, Massachusetts 02155, USA *Email: casey.diederich@tufts.edu ABSTRACT: The ability to withstand high summer temperatures is an extremely important determinant of species distributions in the intertidal zone; most marine organisms cannot live intertidally because of the harsh conditions experienced during aerial emersion. The members of some species, though, live both intertidally and subtidally, and their physiological tolerance to stressors may differ depending on their genetic connectivity, acclimatization, and differential postsettlement mortality. Furthermore, tolerances of organisms at different life-history stages within both habitats may differ and will play an important role in determining adult distributions. To determine the effect of habitat and life-history stage on physiological tolerance and the likely contribution of upper thermal tolerance limits to the native distribution of an important invasive species, the slippershell snail Crepidula fornicata, we compared the thermal tolerance of intertidal and subtidal embryos and adults in relation to conditions that they experience in the field. We found C. fornicata living both intertidally and subtidally in Bissel Cove, Rhode Island, where they experienced drastically different thermal conditions. Intertidal individuals achieved body temperatures as high as 42°C, more than 15°C higher than those recorded in subtidal conspecifics. However, subtidal individuals had remarkably high thermal tolerances that were nearly identical to those of intertidal conspecifics (lethal range = 33-37°C following a 3 h exposure). Furthermore, embryos were even more tolerant to high thermal stress than adults. These results are surprising: the few previous studies that have compared thermal tolerances among individuals at different life-history stages have found differences among them, and early stages are generally more sensitive than adults. Interestingly, the markedly higher temperatures that intertidal animals experienced in this study had little effect on their thermal tolerance. Intertidal (but not subtidal) slippershell snails are now living dangerously close to their upper thermal limits and will almost certainly be relegated to the subtidal as global temperatures rise. KEY WORDS: Intertidal · Subtidal · Crepidula · Thermal stress · Physiological tolerance Full text in pdf format PreviousNextCite this article as: Diederich CM, Pechenik JA (2013) Thermal tolerance of Crepidula fornicata (Gastropoda) life history stages from intertidal and subtidal subpopulations. Mar Ecol Prog Ser 486:173-187. https://doi.org/10.3354/meps10355 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 486. Online publication date: July 12, 2013 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2013 Inter-Research.

Metabolism in blue mussel: intertidal and subtidal beds compared

Mytilids occur worldwide, and mussel beds are a prominent intertidal and subtidal system feature. Brittany (France) has a complex population structure in which pure genotypes alternate with hybrids of Mytilus edulis and M. galloprovincialis, referred to here as 'mussels'. Mussels live attached to the substrate in subtidal and intertidal areas and are regularly exposed to strong environmental variations (e. g. desiccation, light, and temperature). The resistance of mussels to emersion is based on a combination of different strategies, such as metabolic rate depression, anaerobic metabolism and air breathing. In the present study, we have evaluated the differences in aerial and underwater mussel metabolism between an intertidal mussel bed and a subtidal one. Metabolism was measured seasonally for small (shell length 24 to 26 mm) and large (43 to 66 mm) individuals. Mussel aerial respiration fluxes were directly correlated with air temperature. In contrast, underwater carbon (DIC) fluxes seemed to be influenced by additional factors such as food availability and/or reproduction period. Underwater metabolism was higher in small mussels (intertidal: 35.9 mu mol DIC g AFDW(-1) h(-1); subtidal: 51.4 mu mol DIC g AFDW(-1) h(-1)) than in large mussels (intertidal: 26.4 mu mol DIC g AFDW(-1) h(-1); subtidal: 21.3 mu mol DIC g AFDW(-1) h(-1)). In contrast, aerial respiration showed different adaptations: small intertidal and subtidal mussels had similar respiration under emerged conditions, while large intertidal individuals showed higher carbon fluxes during emersion compared to subtidal individuals. These data suggest that while underwater fluxes were similar for the 2 mussel beds, all small and large intertidal mussels are far better able to tolerate emersion than large subtidal animals. Subtidal mussels seem thus to lose their ability to respire in air after becoming adult.

Morphological diagnosis of the two genetic lineages ofAcrocnida brachiata(Echinodermata: Ophiuroidea), with description of a new species

The burrowing brittle-starAcrocnida brachiatahas so far been regarded as a single, easily identifiable species. Recent studies showed habitat-related differences in maximum size, life span, breeding time and recruitment between intertidal and subtidal populations, which at first were attributed to environmental effects on individuals within the same species. Molecular data, however, strongly suggested the existence of two distinct lineages and ultimately two cryptic species with clear bathymetric segregation. Morphological evidence had so far not been presented, because any differences were interpreted as intraspecific variation. We collectedA. brachiatafrom intertidal and subtidal habitats at the coast of Brittany, France, and examined 15 specimens of each group externally by SEM. A key character ofA. brachiatais that the scales at the edge of the disc and on the ventral side are conically enlarged. Intertidal individuals showed a sparser disc scalation, more spine-like than conical ventral disc scales and spatulate, distally widened arm spines. In addition, we dissected several specimens of different size and examined the internal skeleton by SEM. The oral plates showed a rib-like structure on their abradial face that differs between individuals from either habitat. Subtidal specimens have fewer ribs than intertidal ones. These consistent differences support the existence of two species withinA. brachiata. To describe the second species, we needed to establish the identity ofA. brachiata. We describe a neotype, because no type material has been preserved since it was first described; it corresponds mainly to subtidal samples. The new species is described asAcrocnida spatulispinasp. nov. The taxonomic status ofAcrocnidahas been debated over the years with reference to its close affinities withAmphiura chiajei. We compared the species ofAcrocnidawithA. chiajeiandAmphiura filiformisand found thatAcrocnidais indeed morphologically similar toA. chiajei, among other characters by a similar oral plate structure, whereasA. filiformisdiffers greatly fromAcrocnidaas well asA. chiajei. Most strikingly, it has a different type of oral plate. These findings indicate that fundamental taxonomic changes may need to be made in the family Amphiuridae in the future.

Energy metabolism and performance of Mytilus galloprovincialis under anaerobiosis

Intertidal individuals of Mytilus galloprovincialis were exposed to anaerobiosis in laboratory at 22°C and a set of biochemical metabolites and survival potential determined. Differences in survival potential between individuals emersed or kept in oxygen-free seawater were residual according to ST50 values (survival time, P[asymp ]0.05) but emersed individuals survived significantly longer when considering ST90–100 values (P<0.05). Anaerobiosis was similarly activated under both emersion and incubation in anoxic seawater after 6 h according to a seven-fold increase in succinate. Longer exposure of individuals (up to 48 h) caused succinate (and propionate) to increase but in a higher magnitude under incubation with anoxic seawater. Propionate appeared in soft tissues after 24 h of incubation in anoxic seawater and after 48 h when individuals were emersed. Glycogen was not utilized after 6 h in any case, but was progressively used with longer exposure times and in a higher magnitude under incubation in anoxic seawater (48 h). Adenylate energy charge (AEC) was highly affected by both exposure time (P<0.001) and anaerobic treatment (P<0.01). Rapid breakdown of ATP and phospho-L-arginine (PLA) did occur during the first 24 h of anaerobiosis, the latter ATP drop was accompanied by slight increase of ADP but strong increase of AMP that accumulated in a higher magnitude under incubation in anoxic seawater. Biochemical results of the present study suggested a certain degree of aerobiosis for emersed M. galloprovincialis that in turn is linked to a slight but significant longer survival performance. Most significant biochemical changes occurred during the first 24 h of oxygen deprivation, but significant differences between treatments were observed after 24–48 h. These lag differences in biochemical metabolites together with more accurate survival analyses have to be considered when investigating the energy metabolism linked to the anaerobic performance of M. galloprovincialis.

INTRASPECIFIC VARIATION IN STRESS‐INDUCED HYDROGEN PEROXIDE SCAVENGING BY THE ULVOID MACROALGA ULVA LACTUCA1

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

Non‐toxic protection against epibiosis

Epibiosis on four marine benthic invertebrate species was found to be reduced relative to other nearby surfaces, suggesting the existence of an underlying protection against fouling. In all four cases, toxic chemical antifouling defenses were wanting or inconsistent. However, the lack of epibionts could be attributed to the existence of non‐toxic protective properties in all instances, viz. periodic emergence and mutual grazing in the gastropod, Littorina littorea, cumulative filtration and an as yet unidentified fouling‐reducing property of the periostracum of the bivalve Mytilus edulis, repellency and, possibly, mucus secretion in the colonial ascidian, Cystodytes lobatus, burrowing, periodic emergence (intertidal individuals) and moulting in the crustacean, Carcinus maenas. It seems that such protective systems are often multiple, consisting of several, more or less overlapping, adaptations to reduce fouling. Characteristics of these non‐toxic, multiple protection systems and their significance for potential epibionts are discussed.

Temporal and spatial occurrence of UV-absorbing mycosporine-like amino acids in tissues of the antarctic sea urchin Sterechinusneumayeri during springtime ozone-depletion

From September to November 1991, UV-absorbing mycosporine-like amino acids (MAAs) were monitored in a natural population of the sea urchin Sterechinusneumayeri from a coastal area of Anvers Island (Antarctic Peninsula). MAA concentrations were determined for specific tissues (gonad, digestive tract and body wall) from adults collected at four depths (intertidal, 8, 15 and 24 m). Four MAAs were identified: mycosporine-glycine, shinorine, porphyra-334 and paly-thine. Concentrations of MAAs among replicate individuals varied considerably. Ovaries had high concentrations of MAAs (84 to 1389 μg g−1 dry wt), while testes had non-detectable levels. The relative abundance of specific MAAs in ovaries appeared to be related to the spawning cycle. Digestive-tract samples had MAA concentrations as high as 3000 μg g−1 dry wt, but the mean MAA content in intertidal individuals decreased by 70% over 3 mo during spring. The body walls of sea urchins had very low amounts of MAAs (≤ 0.08 μg g−1 dry wt). There were significant depth differences in the␣total MAA content of the ovary ( p <0.001), ( p <0.015), digestive tract ( p <0.001), and body wall with organisms from the intertidal and 8 m depth having the highest concentrations of MAAs. Biological dosimetry indicated that UV-B (280 to 320 nm) wavelengths penetrated 3 to 7 m below the sea ice during the study period. The total MAA content in ovaries decreased with depth on all sample dates; however, the MAA content of the digestive tract and body wall did not exhibit a consistent pattern of change with depth. The MAA content of tissues did not change significantly with the temporal gradient of light exposure that was established by both ozone depletion and increasing photoperiod, except in the digestive tract sampled from intertidal specimens. Adult urchins are probably well-protected from UV exposure by the water column and a calcareous test; however, the results of this study suggest that, even under ice cover, depth of habitation is a determinant of MAA content in S. neumayeri. Large daily and seasonal fluctuations in the light regime, which are characteristic of Antarctic coastal environments, apparently do not provide reliable cues to elicit a detectable, temporal, biochemical response.

Arm regeneration in two populations of Acrocnida brachiata (Montagu) (Echinodermata: Ophiuroidea) in Douarnenez Bay, (Brittany: France): An ecological significance

The incidence of arm regeneration in the brittlestar Acrocnida brachiata is assessed for an intertidal and a subtidal population in the Bay of Douarnenez, France. The growth rate of regenerating arm parts in the field and under laboratory conditions and the annual regenerating biomass production complete the study. The frequency of arm regeneration is extensive and comprises nearly 70% of the total arm population in both sampling sites. The position of the breakage points mostly occur in mid-arm level in the tidal flat area and mainly in the distal third part of the arms in the subtidal site. The biomass composed of regenerating tissue is significantly different in both zones accounting for 11.1% (±9.5%) of the total individual biomass in the intertidal area and 6.4% (±8.4%) subtidally. Actively feeding arms appear to be the least damaged. To maximize fitness, the intertidal individuals of Acrocnida brachiata seem to allocate energy to arm regeneration at the expense of somatic growth. Highest arm growth per individual was recorded in the field and comprises 1.2 mm·day −1 for individuals with two amputated arms. Subtidally, the annual production invested in regenerating tissue is 33 g dry wt·m −2 (19 g AFDW·m −2).

Feeding and Digestion in Suspension-Feeding Bivalve Molluscs: The Relevance of Physiological Compensations

SYNOPSIS. Intertidal suspension-feeding bivalves face reductions in the time available for feeding proportional to the duration of aerial exposure. Such individuals do not compensate by increasing their rates of feeding during immersion. Simulations of feeding behaviour, in terms of the energetic balance between the costs and the gains of changes in feeding rate, suggest that variation from the rates characteristic of the sublittoral condition would not enhance net energy gain for intertidal individuals. These findings are consistent with evidence of potential food limitation in the natural sublittoral habitat. Nevertheless, hydrodynamic factors may enhance the supply of food on the shore, so ameliorating the disadvantages of reduced feeding time. In addition, potential physiological compensations for reduced dietary quality include changes in gut residence time, the volume of gut occupied for digestion and (possibly) also in the provision of appropriate digestive enzymes. However, these compensations require days or weeks and are inappropriate on tidal time scales.

Adaptive advantages of patterns of growth and asexual reproduction of the sea anemone Metridium senile (L.) in intertidal and submerged populations

Individual size, rate of growth, and mode and frequency of asexual reproduction are life-history traits of primary importance for sea anemones. These traits determine sexual reproductive output, affect an individual's probability of survival, and are crucial in adapting an individual to its environmental surroundings. The sea anemone Metridium senile (L.) is highly variable in ecological distribution and life history, including rate of growth, individual size, and rate of asexual reproduction. Gonad size (measured as cross-sectional area of gonadal tissue) increases with body weight, so individuals should grow as large and as rapidly as possible to maximize individual sexual reproductive output. Cessation of growth and small body size in intertidal populations suggest that growth is constrained by genetic or environmental conditions. The growth of intertidal individuals transplanted to harbor-float panels demonstrated that growth limits are imposed by environmental factors, most probably limited food and feeding time and damage from wave exposure (which stimulates fragmentation). Individuals in harbor-float populations, which are continuously immersed, grow much larger, and large individuals comprise a greater proportion of the population than in the intertidal zone. The highest rate of fragmentation observed was on harbor-float panels. Patterns of growth and asexual reproduction provide adaptive advantages for M. senile. For harborfloat individuals, large individual size increases gamete production and may increase feeding efficiency. For intertidal individuals, asexual reproduction allows growth despite individual size constraints and rapid population growth, with specific advantages resulting from clone formation.

β-Glucuronidase activity and detritus utilization in the sea anemones Metridium senile and Anthopleura Elegantissima

1. 1. Activity of β-glucuronidase, an enzyme associated with digestion of detritus, was measured in the intertidal sea anemone Anthopleura elegantissima and the subtidal anemone Metridium senile. The enzyme was present in freshly-collected individuals of both species. 2. 2. β-glucuronidase and chymotrypsin-like potease activities were both similar in high- and low- intertidal individuals of Anthopleura elegantissima. High-shore anemones do not appear to respond to shorter feeding times by increasing digestive capacity for detritus. 3. 3. β-glucuronidase activity increased in individuals of Metridium senile that had been fed detritus compared to starved and Artemia-fed individuals. 4. 4. Metabolic heat dissipation, measured by direct calorimetry, increased in Artemia-fed and detritus-fed individuals of Metridium senile compared to starved individuals. Increased heat dissipation is direct evidence of the potential nutritional importance of organic detritus in this species.