Sea-water temperature and spawning behaviour in the seastar Marthasterias glacialis

The seastar Marthasterias glacialis (L.) was seen to spawn in two sea inlets, Lough Hyne (9°18W; 51°30N) and Mulroy Bay (7°42W; 55°12N), Ireland. Spawning occurred during the afternoon and early evening between 13.30 and 21.30 hrs British Summer Time (BST) on sunny days during July and August, 1978. Groups remained assembled for days prior to spawning. Solitary and grouped seastars arched themselves and released their gametes freely. Local moderate onshore winds on sunny days resulted in increases of sea temperature which often induced spawning. Males observed spawning ranged from 2.5 to 26 cm and females from 9 to 22 cm in diameter over the period 1978–1985.     

Studies on the cytolytic effects of seastar (Marthasterias glacialis) saponins and synthetic surfactants in the plaice Pleuronectes platessa

The toxic effects of Marthasterias glacialis (L.) saponins and synthetic surface-active agents were studied using the plaice Pleuronectes platessa L. as test animal. Solutions of M. glacialis saponins caused considerable, although non-uniform, damage to the gill epithelium, death resulting from a disturbance in the levels of oxygen, carbon dioxide, and sodium ions in the tissues and blood. Histological examination showed that solutions of the synthetic surfactants caused less damage to the gill epithelium than did the M. glacialis saponins. There was a linear relationship between the logarithm of the median haemolytic concentration and the logarithm of the median lethal concentration for the synthetic surfactants. Haemolytic inhibition experiments suggest that the M. glacialis saponins damage cell membranes by interacting with membrane cholesterol.     

Phylogeography of the sea star Marthasterias glacialis (Asteroidea, Echinodermata): deep genetic divergence between mitochondrial lineages in the north-western mediterranean

We explore the phylogeography of the broadcast spawner Marthasterias glacialis along south Europe and Azores. Sequences of the cytochrome c oxidase gene from 225 specimens, belonging to 10 localities, were analysed. We found 73 haplotypes grouped within two lineages (divergence 2.9%). One lineage was Atlanto–Mediterranean, whereas another one was exclusively Mediterranean. Estimation of lineages split goes back to 830,000–580,000 (±120,000) years ago. This suggests that sea-level oscillations during the Pleistocene glaciations promoted gene flow interruption, lineage divergence between basins and cryptic speciation. Secondary contact between populations allowed a recolonization of the Mediterranean by the Atlantic lineage. When animals of the Atlanto–Mediterranean lineage were considered separately, F _st index and AMOVA did not show significant differences between populations along either the Iberian Peninsula or basins. Isolation by distance between populations was not detected, and only populations of Plymouth and Azores showed significant differences to all the others. The remoteness of Azores islands might explain the structure of this population. Haphazard arrival of larvae and local extinctions rather than contemporary restricted gene flow might be responsible for the distinctive population structure of Plymouth.     

Intracellular localization of vanadium in the fan worm Pseudopotamilla occelata

A very high level of vanadium was found to be contained in the polychaete worm Pseudopotamilla occelata collected in 1992–1993 from the Sanriku coast on the main island of Japan. The vanadium concentration (mean±SD=5500±1800 g g^-1 dry wt) in the worm's branchial crown which is composed of many bipinnate radioles was approximately 100 times higher than that (mean±SD=60±25 g g^-1 dry wt) in the trunk body. Electron probe X-ray microanalysis revealed that a large amount of vanadium was present in the outer potion of the epidermis of the bipinnate radiole. Analytical electron microscopy for a cryo-section of the bipinnate radioles indicated that vanadium was localized in electron-dense deposits in the apical portion of epidermal cells. From an examination of the fine structures, the locality of the electron-dense deposits were found to correspond to that of the apical vacuoles in the epidermal cells. It was concluded that most of the vanadium in P. occelata was contained in the vacuoles of the epidermal cells of the bipinnate radioles.     

The production and secreton of digestive enzymes in the purple seastar Pisaster ochraceus

The purple seastar Pisaster ochraceus contains clearly measurable protease and amylase activity. Centrifuged supernatants of pyloric caeca homogenates undergo a spontaneous threefold increase in protease activity when incubated under toluene for 50 h at 25°C. Amylase activity remains nearly constant over this period. Bovine trypsin at a 1 to 100 ratio (trypsin to supernatant protein) induces a twofold increase in protease activity over that of the control supernatant while having virtually no effect on amylase activity over the control. The data indicate a specific interaction of trypsin with a protease zymogen rather than a conspecific hydrolysis of membrane components or vesicles by trypsin. Two percent Triton X-100 used as a diluent in place of distilled, deionized water causes a sevenfold increase in protease activity and a twofold increase in amylase activity in pyloric caeca supernatants. The use of Triton as a diluent in the preparation of a stomach-tissue supernatant allows quantitative measurement of both protease and amylase activity in that tissue.     

Population genetic structures of the fissiparous seastar Coscinasterias acutispina in the Sea of Japan

The morphological characteristics and the population genetic structures of the fissiparous seastar Coscinasterias acutispina were investigated for eight sites in the Sea of Japan in order to clarify the presence of sexual and asexual reproduction. Morphological observation based on arm length showed that fission was common at all eight sites examined, indicating the likely production of clonal individuals. A random amplified polymorphic DNA (RAPD) marker was used to detect clones arising by fission and to assess gene flow among sites. A simulation approach using RAPD data revealed the presence of clonal individuals at almost all sites, suggesting the existence of asexual reproduction. The result of phylogenetic analysis according to RAPD genotype showed no relationship between genetic and geographic distances. Considering the limited movement ability of seastar species during the adult phase, these observations suggest the existence of marked gene flow among sites, due to dispersal of planktonic larvae produced by sexual reproduction. These observations suggest that multi-locus genotypic compositions depend on the relative amounts of recruitment from sexual and asexual reproduction in each population.     

Isolation,purification and partial characterization of four digestive proteases from the purple seastar Pisaster ochraceus

An investigation of enzymatic activity in the pyloric caeca of Pisaster ochraceus collected at Post Point, Bellingham, Washington, USA, in 1982, revealed the presence of four distinct proteases. These enzymes have been partially purified and characterized and display tryptic, chymotryptic and carboxypeptidase A-like activity. The two distinctive tryptic enzymes have molecular weights of 88 000 and 25 200 daltons, respectively, as determined by reducting SDS-PAGE electrophoresis. The chymotryptic and carboxypeptidase A proteases have molecular weights of 22 800 and 34 400 daltons, respectively. The tryptic and chymotryptic enzymes are inactivated by phenylmethylsulfonyl fluoride, indicating that all are serine proteases. Both trypsins are inhibited by soybean trypsin inhibitor; however, the high molecular weight trypsin was not inhibited by tosyl-L-lysine chloromethyl ketone. The chymotrypsin was inhibited by tosyl-L-phenylalanine chloromethyl ketone. Both reagents indicate the involvement of histidine in the active site. The low molecular weight trypsin and the chymotrypsin were able to activate bovine trypsinogen to trypsin, as determined in a modified PAGE electrophoresis with trypsinogen and casein copolymerized in the gel.     

Ultrastructural localization of metal binding sites in the kidney of the Antarctic scallop Adamussium colbecki

The functional morphology of kidney cells and the intracellular localization of metal storage sites were studied by electron microscopy and X-ray microanalysis in the Antarctic scallop Adamussium colbecki (Smith) collected at Gerlache Inlet, Terra Nova Bay, Antarctic in December 1990. Kidney cells of A. colbecki show the same basic cytoarchitecture of other Pectinidae, but the nephrolithes localized in the main vacuoles show a low degree of mineralization. The sites of heavy metal storage are: (1) the main vacuole of the renal cell, where Fe, Zn and Cu are associated with concretions, (2) the basal membranes and (3) the lysosomes of amoebocytes, in which Ag, Se, Fe and Cu occur in electron-dense particles. Finally a hypothesis for the formation and role of the Ag–Se rich particles is discussed.     

Respiration and excretion rates of Calanus glacialis in arctic waters of the Barents Sea

The respiration and excretion rates of Calanus glacialis (Jaschnov) Copepodite Stages III, IV, V, and adult females from the drift-ice area east of Svalbard (Barents Sea) were measured in shipboard experiments during the period from 27 May to 13 June, 1983. The phytoplankton biomass and abundance varied considerably between localities, but these variations were not generally reflected in the respiration and excretion rates of the copepod. The respiration and excretion rates of C. glacialis at the ambient temperature of-1.8°C (average respiration rates of 0.95, 0.73, 0.57, and 0.60 l O₂ mg^-1 dry wt h^-1 for Copepodite Stage III, IV, V, and adult females, respectively) were similar to those previously reported for other large-sized copepods from cold or temperate areas. Average respiration and excretion rates tended to decrease with incubation time or time after capture. Measurements on ten occasions within a period of 27 h after capture revealed excretion rates of ammonium ranging between 2.9 and 16.8 for C III, 3.7 and 21.1 for C IV, 1.3 and 28.4 for C V, and 1.6 and 18.7 for adult females, all expressed as nmol mg^-1 dry wt h^-1. In all experiments, excretion rates of inorganic phosphate varied between 0.7 and 1.5 (C III), 0.5 and 1.1 (C IV), 0.2 and 0.8 (C V), and 0.3 and 1.0 (adult females) nmol mg^-1 dry wt h^-1. Ratios of O:N, O:P, and N:P indicated that much of the metabolic energy was derived from catabolism of proteins. Comparison of the turnover rate of carbon and nitrogen showed, however, that nitrogen turnover was between 2.6 and 8.9 times higher than that of carbon. This may indicate that the copepods deaminate ingested protein, with the carbon skeleton of the amino acids subsequently being used in the synthesis of lipid compounds, possibly wax esters.     

Seasonal changes in pyloric caecum and gonad indices during the annual reproductive cycle in the seastar Asterias forbesi

Seasonal changes in pyloric caecum and gonad indices were studied in a population of the seastar Asterias forbesi (Desor) from East Rockaway Inlet (Long Island, New York) during two annual cycles (1980/81, 1982/83). Pyloric caeca indices increased during fall, reached a maximum about April, and declined sharply to a minimum in mid-summer. Gonad indices increased during fall and winter and reached a maximum about May. Judging from gonad size analysis, spawning occurred in late June to early July, at bottom temperatures of 16° to 18°C. There was no long-term inverse relationship between pyloric caecum and gonad indices. Since nutrients and energy ingested during the important fall feeding period are utilized simultaneously for body growth and gonad development, it is unnecessary for the pyloric caeca to store nutrients over long periods as occurs in A. rubens and many other species. The specific caeca-gonad relationship is probably an adaptation to the extreme seasonal thermal fluctuations of the NW Atlantic, which constrain the feeding activity of A. forbesi and limit the possibility of long-term storage. In this population, most individuals grow rapidly in their first year (including first two summers) and spawn in their third summer. Few seastars survive to spawn again in their fourth summer. However, gametogenesis may take place in some individuals in their second summer. Year-to-year variability in mean size at spawning may reflect temporal variation in environmental conditions (weather, food availability) at this site.     

Changes in the biochemical composition of the ovaries of the seastar Asterias rubens during its annual reproductive cycle

The biochemical composition of the ovaries of the asteroid echinoderm Asterias rubens was studied, with emphasis on the changes which are manifest during the annual reproductive cycle. Ovarian dry weight displays only minor changes during ovarian development, constituting about 20% of the organ fresh weight. Levels of all constituents show some variation, but in general increase with ovarian growth. Only the free amino acid level is rather constant. Except for glycogen, the contents of other constituents (total lipids, other reducing sugars, free amino acids and proteins) show a rectilinear increase with ovarian growth. Glycogen content increases rectilinearly with time during early vitellogenesis, but remains constant during further development until ovarian maturity. By plotting constituent levels and contents against a non-linear gonad index axis rather than against sampling date, results can be correlated more easily with ovarian growth stages. The possibility of endocytosis of a vitellogenin-like yolk precursor by the ovary is discussed.     

Egg production of the Arctic copepod Calanus glacialis: laboratory experiments

Egg production of single female Calanus glacialis Jaschnov fed with Thalassiosira antarctica at super-abundant concentrations (>300 g C l^-1) was determined over several weeks. Experiments were performed directly after collection from the East Greeland Current in June 1987 and 1988, and during resumed feeding after long-term starvation over 4 (October 1988), 4.5 (October 1987) and 6.5 (January 1988) mo. In addition, in June 1987, short-term starvation experiments of 5 and 15 d were conducted. Egg production was closely related to feeding in all experiments. While directly after collection eggs were produced within a few days, it took 2 wk (October 1987 and 1988) and 10 d (January 1988), respectively, to resume egg production after long-term starvation. During long-term starvation periods eggs were not laid. The decrease in total egg production with duration of starvation was due to decreasing clutch size and increasing spawning interval. In contrast, short-term starvation experiments only affected spawning interval. Interannual variability in egg production was high, with much higher clutch sizes in 1988. Average production rates in June 1988 correponded to 5% body C female^-1 d^-1, the maximum was 7.4% (1 274 eggs in 23 d). Carbon content of eggs was 0.40 g egg^-1. C. glacialis is well adapted to pulsed food events in the Arctic by its longevity; its ability to preserve its reproductive potential over several months; its rapid mobilization of ovaries; and by its high egg production rates. The implication of prolonged spawning capacity on life cycle studies is discussed.     

Movement patterns of the seastar Heliaster helianthus in central Chile: relationship with environmental conditions and prey availability

The rates and patterns of feeding and displacement of predators constitute two of the most important plastic behavioral responses that allow individuals to respond quickly to changes in abundance of their prey, predation risks and to rapid alterations in environmental conditions. In this study, we quantified seasonal and spatial variation in displacement (net changes in location in 12 or 24 h periods) and prey consumed of marked individuals of the keystone seastar Heliaster helianthus at six sites spanning 600 km along the coast of north-central Chile. We evaluated the hypotheses that: (1) at sites with low availability (cover) of the main prey, the mussel Perumytilus purpuratus, Heliaster displays larger displacements and consumes a greater proportion of other prey (e.g. mobile species) than at sites with high mussel cover, (2) daily displacements will be correlated with sea surface temperature (SST) and (3) increased wave action will reduce seastar daily displacement. Our results show that Heliaster displacement is higher at sites with lower availability of P. purpuratus; and at these sites, a larger proportion of Heliaster individuals are observed feeding, mostly on other prey (e.g. limpets), which could offset the higher costs associated with increased movement. In addition, wave forces affected the activity of Heliaster negatively. Contrary to our expectations, the daily displacements did not show any relationship with SST measured on the day or the previous days of the surveys, despite the fact that average displacement was generally higher in summer than in winter months. Future studies should examine Heliaster movement during single foraging excursions and determine whether these responses affect the growth and reproductive output of individuals. Such information is vital to understand how changes in prey abundance and environmental conditions alter the behavior and energy budget of this predator and its ability to control prey populations.     

Effects of feeding and starvation on proteolytic and tryptic activities in pyloric caecal tissues and duct fluids of the seastar Pisaster ochraceus

Pisaster ochraceus were collected at Post Point, Bellingham, Washington, USA, in 1980. Total protease and tryptic specific activities were measured in pyloric caecal tissues and pyloric duct fluids of fed and starved individuals. Feeding resulted in increased levels of total protease and tryptic activities, and led to an increase in the ratio of total protease to tryptic specific activity in pyloric caecal tissue and a decrease in that ratio in pyloric duct fluid, indicating a release of trypsin into the duct with feeding. Trypsin activity showed little variability in fed seastars, but was quite variable in starving individuals. Total proteolytic acitivity, unlike that of tryptic activity, was always present in both fed and starved seastars. This way indicate a much broader role of generalized proteases in the cells of the pyloric caecum (e.g. as lysosomal enzymes of absorptive cells) in comparison to tryptic enzymes.Please address all correspondence and requests for reprints to Dr. D. C. Williams at the Department of Biology     

Grazing rates of the copepods Calanus glacialis and C. finmarchicus in arctic waters of the Barents Sea

Natural feeding rates of Copepodite Stages IV and V, and adult female Calanus glacialis (Jaschnov) and Copepodite Stage V and adult female C. finmarchicus (Gunnerus) were estimated using fluorescence analysis of gut contents. Measurements were made on copepods sampled from arctic waters east of Svalbard (Barents Sea) during the spring phytoplankton increase, in the period from 27 May to 13 June, 1983. Observations on Copepodite Stages IV and V and adult female C. glacialis suggest that the gastric evacuation rate is independent of developmental stage, whereas C. finmarchicus Copepodite Stage V showed a lower gastric evacuation rate than adult females. Gut fullness displayed a low correlation with the ambient chlorophyll concentrations. Ingestion rates calculated for C. glacialis were 0.3, 2.3, and 11.0 g C h^-1 for Copepodite Stages IV and V and adult females, respectively. Copepodite Stage V and adult female C. finmarchicus ingested 0.9 and 1.1 g C h^-1 at a temperature of ca.-1.0°C. The maximum ingestion rate in terms of percent body carbon d^-1 was higher for adult female C. glacialis and C. finmarchicus than for the respective Copepodite Stage V's. The results are discussed both in relation to the physiological state of the species and to the environmental conditions.     

Molting rates and cohort development of Calanus finmarchicus and C. glacialis in the sea off southwest Nova Scotia

Species of Calanus were sampled at stations off southwest Nova Scotia during an 8-d cruise in June, 1982. A simple model using shipboard measurement of molting rates of predominant copepodite stages accurately predicted the changes in cohort structure that occurred at stations along a transect at the beginning and end of the cruise. The combined durations of C. finmarchicus (Gunnerus) stages CIII and CIV, calculated from the inverses of molting rates corrected for presence of diapausing C. glacialis Jaschnov, corresponded well with development times based on laboratory rearing experiments. We conclude that our molting rate measurements accurately reflected processes in nature. This methodology is useful for analyzing the dynamics and production of copepod populations.     

Diel variations in the nutritional physiology of Calanus glacialis from Lat. 78°N in the summer

Calanus glacialis (Jaschnov) from Isfjord, western Spitzbergen, showed no tendency to pronounced diurnal vertical migration or cyclic variations in feeding activity. The samples, taken regularly over a 24-h period and at three different depths in the beginning of August, did however show considerable individual variations in feeding activity. These variations, reflected in the results of gut analyses, were not related to variations in the concentrations of particulate protein, carbohydrate or algal pigments in the water. Analyses of the activities of two digestive enzymes and the electron-transport system (ETS) indicated that those few individuals always present below the photic zone were there temporarily, and showed no signs of slowing down their metabolism. The results suggest that the population of C. glacialis, during the Arctic summer, feeds continuously in the upper water layer, but that intermittent, non-synchronous individual feeding rhythms are the rule.     

Depression of feeding and growth rates of the seastar Evasterias troschelii during long-term exposure to the water-soluble fraction of crude oil

To test the effect of petroleum hydrocarbons on predation by the seastar Evasterias troschelii (Stimpson, 1862) on the mussel Mytilus edulis (L.), we exposed the predator with the prey to six concentrations of the water-soluble fraction (WSF) of Cook Inlet crude oil. Seastars and mussels were collected at Auke Bay, Alaska, in November 1980. During a 28 d exposure in a flow-through system, seastars were more sensitive to the WSF than mussels: the LC₅₀ for the seastars was 0.82 ppm at Day 19 and, although no mussels were exposed to WSF for more than 12 d, none died. Daily feeding rates (whether in terms of number of mussels seastar^-1 d^-1 or dry weight of mussels seastar^-1 d^-1) were significantly reduced at all concentrations above 0.12 ppm. At 0.20, 0.28 and 0.72 ppm WSF, daily feeding rates (in terms of dry weight of mussels) were, respectively, 53, 37, and 5% of the control rate; at the two highest concentrations (0.97 and 1.31 ppm WSF), the seastars did not feed. Seastars at concentrations greater than 0.12 ppm WSF grew slower than individuals from the control group and the 0.12 ppm-treatment group combined. These laboratory results show that E. troschelii is more sensitive to chronic low levels of the WSF of crude oil. The possibility that such oil pollution could reduce predation and permit M. edulis to monopolize the low intertidal zone of southern Alaska remains to be studied.     

Metabolic responses of the sympagic amphipodsGammarus wilkitzkii andOnisimus glacialis to acute temperature variations

Acutely elevated seawater temperatures had pronounced metabolic effect on the Arctic under-ice amphipodsGammarus wilkitzkii andOnisimus glacialis, collected in May 1986 and 1988 in the Barents Sea. An increased rate of oxygen consumption vs temperature was observed for both species. In the range from 0° to 10 °CG. wilkitzkii andO. glacialis exhibit Q₁₀ values of 3.4 and 3.6, respectively. The results also indicate increased ammonia excretion rates forG. wilkitzkii andO. glacialis by an elevation of temperature from 0° to 10°C, with an overall Q₁₀ of 1.9 and 2.3, respectively. The present study demonstrates an increased O:N ratio with ambient temperature elevation from 0° to 10°C forG. wilkitzkii andO. glacialis, with overall Q₁₀ values of 2.0 and 1.6, respectively. This indicates a temperature-induced change in the metabolic substrate towards lipids.