Feeding habits of pasiphaeid shrimps close to the bottom on the Western Mediterranean slope

The composition of the diet and daily cicle of predatory activity of pasiphaeid shrimps in the Northwestern Mediterranean were established; special attention was focussed on nocturnal feeding habits close to the bottom. Daily activity in both species was studied in two continuous 24-h sampling periods. Samples were obtained using bottom trawls between 1988 and 1990. Both species fed on benthic prey items at night. The nocturnal diet of Pasiphaea multidentata consisted of gammarid amphipods, isopods (Cirolana borealis) and macruran decapods (Calocaris macandreae). Nocturnal feeding activity was carried out only by large specimens (cephalothorax length >28 mm), which stayed close to the bottom during the nighttime. In contrast, the specimens collected during the daytime exhibited highly digested remains of pelagic prey (hyperiids, fishes, euphausiids, chaetognaths) ingested as a result of predatory higher activity in the water column the night before. The feeding strategy of P. sivado was parallel to that of P. multidentata. At night large specimens were located near the bottom and fed on suprabenthic gammarid amphipods. This nocturnal feeding activity by both these mesopelagic pasiphaeid species furnishes evidence of energy transfer from the benthos to the planktonic system in bathyal communities. Changes were observed in the diet of P. multidentata with depth. Crustaceans made up a larger share of the diet of P. multidentata on the lower slope than on the upper middle slope, probably because of changes undergone by bathyal communities with increasing depth. The feeding rate was higher in the submarine canyons, where the diet is also more specialised. Dietary overlap between the two pasiphaeids was very low, due to the different size range of prey exploited.     

Depth-related enzymic activities in muscle,brain and heart of deep-living pelagic marine teleosts

The activities [units^-1 wet weight tissue] of lactate dehydrogenase (LDH), pyruvate kinase (PK), malate dehydrogenase (MDH) and isocitrate dehydrogenase (IDH) in white skeletal muscle, brain and heart of 24 pelagic teleost fishes were determined. In addition, for several of the foregoing species, citrate synthase (CS) activities were examined in white skeletal muscle. In muscle, the activities of all these enzymes decrease exponentially with increasing minimum depth of occurrence of the species; this decrease closely parallels the decrease in respiratory rate found previously for these same species. The decline in enzymic activity with increasing minimum depth of occurrence is much greater than the decline in body protein content of the whole fishes, suggesting a disproportionately rapid fall in enzyme concentration in comparison to contractile and structural protein concentrations. The similar reductions in activities of both glycolytic (LDH and PK) and citric acid cycle (CS, MDH and IDH) enzymes with depth indicate that both standard and active metabolisms of deeper-dwelling species are reduced relative to shallower-dwelling forms. There is no suggestion of increased anaerobic capacity with depth or in relation to species, occurrence in the oxygen minimum layer. In brain and heart, there is no significant decrease in enzymic activity with increasing minimum depth of occurrence. These two tissues have similar capacities for metabolism in most fishes, when comparisons are based on enzymic activity per gram wet weight of tissue.     

A histological study of reproduction in the serpulids<Emphasis Type="Italic"> Pomatoceros triqueter</Emphasis> and<Emphasis Type="Italic"> Pomatoceros lamarckii</Emphasis> (Annelida: Polychaeta)

The reproductive cycles of the serpulid polychaetes Pomatoceros lamarckii (Quatrefages, 1865, as Vermilia) and P. triqueter (Linnaeus, 1767, as Serpula triquetra) were studied by histological examination during 1999 and 2000 at Bantry Bay, south-west Ireland. Gametogenesis, sex ratios and hermaphroditism were also investigated. The male/female ratio in P. lamarckii was approximately equal, but in P. triqueter it deviated significantly in favour of females. There was no significant variation in the sex ratios throughout the year in either species. Results confirm that the species are protandric hermaphrodites. In P. lamarckii, but not in P. triqueter, sexual dimorphism was exhibited in body size, the females being larger than the males of the same species. In both species, the proportion of females increased with increasing body size. Simultaneous hermaphroditism was recorded in P. lamarckii, but not in P. triqueter. There was no clearly defined annual gametogenic cycle in either species. Both species appear to have an extended reproductive season, with numerous small-scale peaks in reproductive maturity that can vary annually. Spawning was broadly synchronous between sexes. Visual observation alone (i.e. without histology) was insufficient to accurately assess reproductive condition in individuals not in, or close to, a ripe state.     

Life-history traits of Plesionika martia (Decapoda: Caridea) from the eastern-central Mediterranean Sea

Life-history traits of Plesionika martia (Milne Edwards, 1883) were studied through data collected during six seasonal trawl surveys carried out in the Ionian Sea (eastern-central Mediterranean) between July 1997 and September 1998. P. martia was found at between 304 and 676 m depth, with the highest density in the 400-600 m range. Intraspecific, size-related depth segregation was shown. Recruitment occurred in summer at the shallowest depths. Juveniles moved to the deepest grounds as they grew. The largest female and male were 26 and 25 mm carapace length, respectively. The sex ratio was slightly in favour of females at depths >400 m. Although a seasonal spawning peak was shown, the reproduction appears to be rather prolonged throughout the year. Females with ripe gonads were found from spring to autumn. Ovigerous females with eggs in late maturity stage were found year round. Large females could spawn more than one time within their annual reproductive cycle. The size at first maturity (50% of the ovigerous females) was 15.5 mm CL. Average brood size of eggs with a well-developed embryo was 2,966ǃ,521. Iteroparity, low fecundity and large egg size patterns were observed. Brood size increased according to the carapace length. Two main annual groups were found in the field population of the Ionian Sea. Estimates of the Von Bertalanffy growth parameters are: L_X=30.5 mm, k=0.44 year^-1 in females; L_X=28.0 mm, k=0.50 year^-1 in males. A negative allometry was detected mostly in the ovigerous females. The life cycle of P. martia is discussed in the light of life-history adaptations shown in other deep-water shrimp species.     

Reproductive cycle of two commercial species of sea cucumber (Echinodermata: Holothuroidea) from Caribbean Panama

The reproductive status of the holothuroid species Isostichopus badionotus (Selenka, 1867) and Holothuria mexicana (Ludwig, 1875) was studied over 16 months in Bocas del Toro (Panama), from November 1999 to February 2001. Sexual reproduction was evaluated by the gonad index method, and by histology of gonad development. In addition, population structure was assessed based on sex ratio, minimum reproductive size, and length and weight distributions of males and females. The sex ratio in both species was 1:1, with a unimodal population distribution composed mainly of mature individuals. The minimum reproductive length and weight were 13-20 cm and 150 g, respectively, for both species, although reproductive individuals 10 cm in length were also found. A consistently higher gonad index was observed in H. mexicana, due to a high proportion of mature females and males and high gonad indices in most monthly samples. Gametogenesis and spawning patterns seemed to occur throughout the year, with periods of enhanced activity. Two periods of maximum reproductive activity were tentatively identified: July-November for I. badionotus and February-July for H. mexicana, but neither species had a single, sharply defined annual spawning event. Further work on these exploited holothuroids should examine the relationships between reproduction and environmental factors and between reproductive status and recruitment.     

A new record of the endosymbiont polychaete Veneriserva (Dorvilleidae), with description of a new sub-species, and relationships with its host Laetmonice producta (Polychaeta: Aphroditidae) in Southern Ocean waters (Antarctica)

A new record of the genus Veneriserva Rossi, 1984 (Polychaeta: Dorvilleidae) is reported, as an endosymbiont in the coelom of the polychaete Laetmonice producta Grube, 1877 (Aphroditidae) in the eastern Weddell Sea and off King George Island (Southern Ocean, Antarctica). The specimens studied were very similar to Veneriserva pygoclava Rossi, 1984; however, due to the greater morphological variability and larger dimensions of our specimens, as well as different host species and geographic locations, a new sub-species, V. pygoclava meridionalis, was erected. A total of 842 specimens of L. producta were examined, 163 of which hosted 209 symbionts (183 in the Weddell Sea samples and 26 in the King George Island samples). Symbiont prevalence was higher in the Weddell Sea samples, and increased with depth (max. 51% at stn 14, 850 m depth). Symbiont intensity was equal to one for 78% and to two for 19.6% of all hosts examined; a maximum of six symbionts per single host was observed. Mean symbiont density was equal to 0.36 and 0.07 for the Weddell Sea and King George Island host populations, respectively. A weak linear relationship was found between symbiont and host size. Eight symbiont specimens (all found at a single station, 850 m depth) were bearing eggs, ranging between 10 and 200 µm in diameter, while 13 specimens were observed in regeneration of the posterior part, suggesting the occurrence of both sexual and asexual reproduction. The way of feeding is still not clear; reduction of the jaw apparatus suggests a parasitic host-symbiont relationship, however, no evident damage was observed in the tissues of the host. These results point out that occurrence of polychaete endoparasites in large aphroditids may be a more frequent and widespread phenomenon than previously believed, and that more attention should be paid to this aspect also in temperate and tropical aphroditid species.     

The relationship between dissolved oxygen concentration and maximum size in deep-sea turrid gastropods: an application of quantile regression

Bathymetric gradients in body size are the most well-known patterns of geographic variation in deep-sea organisms. The causes of size-depth relationships remain uncertain, but most have been attributed to rates of nutrient input. Chapelle and Peck (1999, Nature 399:114-115) recently hypothesized that body size in marine invertebrates is a function of dissolved oxygen concentration. We tested this hypothesis by using quantile regression techniques to assess the relationship of dissolved oxygen levels to maximum size in deep-sea turrid gastropods collected from the North Atlantic. Relationships were examined for a group of nine turrid species and within the abundant lower bathyal species Benthomangelia antonia (Dall, 1881). We controlled the analysis for depth because size in deep-sea gastropods varies bathymetrically. When the effects of depth are accounted for statistically, maximum size in B. antonia increases with increasing levels of dissolved oxygen. In turrids as a group, both depth and oxygen appear to explain significant proportions of the variance in maximum size. These findings suggest that a suite of factors, including dissolved oxygen concentration, may influence maximum size in deep-sea organisms.     

Maturation and diel reproductive periodicity of round scad (Carangidae: Decapterus punctatus)

The diel reproductive periodicity of Carangidae is poorly known but appears to be highly variable between species. Some species spawn during the day, others are believed to spawn at night, and it is demonstrated here that round scad, Decapterus punctatus, spawn at dusk. We collected D. punctatus in the eastern Gulf of Mexico during three April cruises (1995, 1996, and 1997). Based on histological criteria, size at 50% maturity was 113 mm fork length (FL) for males and 128 mm FL for females. The gonad-somatic index (GSI) of mature males was significantly different between hours and appeared to show diel periodicity. Diel periodicity was also observed in changes in female GSIs, whole oocyte diameters, and ovarian histology. The average GSI of mature females fluctuated two-fold between day and night, and the size distribution of whole oocytes in some fish was bimodal (at 0.3-0.4 and 0.7-0.8 mm diameter) at dusk rather than unimodal during most of the diel cycle. Histological preparations revealed that these rapid changes in ovarian GSIs and oocyte size distributions were the result of final oocyte maturation. Germinal vesicle migration was observed from 0900 to 1400 hours eastern standard time (EST), germinal vesicle breakdown was evident as early as 1100 hours EST, and ovulation occurred as early as 1800 hours EST. Spawning frequency (approximately every 5 days) was similar whether calculated from the proportion of females with hydrated oocytes during the afternoon or from the proportion of females with postovulatory follicles during the morning. Batch fecundity correlated with fish size and ranged from 5,500 to 34,700 hydrated eggs per individual. These findings do not support published hypotheses that young-of-the-year D. punctatus reproduce before their first winter or that D. punctatus reproductive output is bimodal within a year.     

Annual reproductive cycle, spatial distribution, abundance, and size structure of Oreaster reticulatus (Echinodermata: Asteroidea) in Bocas del Toro, Panama

The structure, distribution, and population abundance of Oreaster reticulatus (Linnaeus, 1758) in 47,157 ha of shallow-water habitat in the archipelago of Bocas del Toro, Panama, were assessed from May to October 2000. The reproductive cycle of the sea star was studied in Isla Solarte, from February 2000 to February 2001. In total, 4,818 sea stars were recorded with a mean density of 149.7 ind. ha^-1, and a population of over 7 million was estimated for the archipelago. O. reticulatus was absent in ca. 50% of the evaluated areas, possibly due to high runoff and sedimentation; highest density was observed in an intermediate-runoff regime (255 ind. ha^-1). About 45% of the population was found in substrata dominated by seagrass (Thalassia testudinum) and coarse, calcareous sand, 51% occurred in habitats where coral reef patches were mixed with seagrass, and 4% exclusively on coral reefs. The average size, based on the major radius, was 9.5 cm (3-21 cm), with a population structure composed of ca. 83% juveniles and 17% adults. The average reproductive size, measured as major radius, was 15 cm, and the minimum was 7 cm. Both males and females with a maximum stage (IV) of gonad development were observed throughout the year. The gonad index showed three peaks of maximum reproductive activity, which is not comparable to studies from other localities. The reproductive cycle did not seem to be related to water temperature, which ranged from 27°C to 30°C, but may respond more closely to changes in local rainfall. This relationship was not statistically significant based on this 1-year study. These data provide a useful baseline for management of local populations in the face of an increasing harvest for the aquarium trade and as souvenirs.     

Isotopic composition, growth rates and biological behaviour of Chamelea gallina and Callista chione from the Bay of Trieste (Italy)

Shells of the bivalve molluscs Chamelea gallina L. and Callista chione L. from the Bay of Trieste (northern Adriatic) were analysed for their oxygen and carbon isotopic composition. The main purpose of this study was to obtain detailed information on the biological behaviour and, particularly, on the growth rates and the settlement time of these two species. Isotopic measurements were carried out on "spot" samples collected from the umbo to the ventral margin of each shell. The results obtained from nine specimens of C. gallina (plus some 20 specimens studied only for the isotopic composition of their initial umbo and for the last section of their ventral edge) and from two specimens of C. chione allow the following conclusions: (1) the calcium carbonate of C. gallina shells is not deposited under isotopic equilibrium conditions with the environmental variables (temperature and oxygen isotopic composition of seawater); (2) this species usually initiates precipitation of carbonate during the springtime, although some late summer-early autumn generation also occurs; (3) the rate of calcium carbonate deposition decreases with increasing age, and the overall accretion rate is a rather slow one; (4) there is a negative correlation between the carbon isotopic composition and the size of each shell; (5) the mean growth rate of the shells can be easily evaluated according to the oxygen isotopic composition of the spot measurements; (6) the specimens of C. chione do not precipitate the calcium carbonate of their shells in isotopic equilibrium with environmental conditions; (7) their accretion rate is rather fast during the first years of their life and progressively and considerably reduced after about 5 years; (8) the carbon isotopic composition of these shells does not show the marked evolution towards more negative values shown by C. gallina, suggesting that neither respiratory CO₂ nor carbon species derived from the oxidation of organic matter are systematically used for the precipitation of shell carbonate; and (9) a marked preference for the warmer half of the year is shown by the oldest specimen of C. chione (12 years).     

Latitudinal variation in the reproductive biology of the commensal crab Pinnaxodes chilensis (Decapoda: Pinnotheridae) along the Chilean coast

The pinnotherid crab Pinnaxodes chilensis is a common commensal of the edible sea urchin Loxechinus albus along the Chilean coast. Several aspects of the reproductive biology of P. chilensis were examined between April and June 1999, along temperature and salinity gradients, at three sampling sites along the Chilean coast (23°45'S-39°24'S). Results demonstrated significant differences in egg number, egg volume, dry egg weight, and reproductive output of ovigerous females, between the studied populations of northern and central-southern Chile. Egg volume, egg dry weight, and reproductive output of females decreased from high to low latitudes, while egg number increased from high to low latitudes, exhibiting a clear trade-off with egg volume. It has been shown that changes in environmental conditions (e.g. temperature, salinity) along a latitudinal gradient, can generate clines in reproductive characteristics in both free-living and parasitic species.     

Ecological,genetic, and morphological differences among three <Emphasis Type="Italic">Pavona</Emphasis> (Cnidaria: Anthozoa) species from the Pacific coast of Panama

Ecological, genetic, and morphological differences among three Panamanian Pacific Pavona species with strongly developed collines (Pavona varians, P. frondifera, and P. chiriquiensis) were examined. Ecological factors included geographical distributions of species, habitat preferences, interspecific interactions, reproductive ecology, and tolerance to bleaching. Genetic differences were based on the electrophoretic analysis of ten allozyme loci. Morphological analyses consisted of tissue coloration, colony morphology, and measurements and counts of ten macro- and micro-skeletal characters. P. varians, present on reefs or in coral communities, is the most widely distributed and shows considerable morphological variation. P. chiriquiensis, a recently described species, encrusts basalt rock and has little morphological variation. P. frondifera is a reef dweller with a compact foliose morphology. Tissue coloration varies from light to dark brown in P. varians, from pink to brown in P. frondifera, and from brick red to brown or silvery in Pavona chiriquiensis. Also, the white to silvery polyp mouths of the latter species are a diagnostic feature that allows an easy identification in the field. Aggressive dominance during short-term interspecific interactions were as follows: Pavona chiriquiensis>P. varians>P. frondifera. P. chiriquiensis and P. varians showed contrasting responses to sea warming during the 1997-1998 El Niño Southern Oscillation. Whereas entire P. chiriquiensis bleached and died within 4 weeks of exposure to 30-31°C, colonies of P. varians did so only on their upper surfaces. The response of P. frondifera to elevated temperatures was not observed because it is mainly present in the Gulf of Panama where coral bleaching was absent in 1997-1998. The genetic data indicated that P. chiriquiensis differed strongly from both P. varians and P. frondifera, with Nei's unbiased genetic distances of 0.434 and 0.379, respectively. A fixed difference between P. varians and P. frondifera, and P. chiriquiensis exists at the triose phosphate isomerase (TPI-2) locus. A nearly fixed difference between P. chiriquiensis and P. frondifera and between P. chiriquiensis and P. varians was found at the hexokinase (HK) locus. P. varians differed slightly from P. frondifera with Nei's unbiased genetic distance of 0.068. No fixed difference was found between P. varians and P. frondifera. There were strong differences between P. chiriquiensis and P. varians in spawning times and gamete characteristics. Spawning in P. varians and P. chiriquiensis is 12 h out of phase. Also, eggs of the former species are white to beige and positively buoyant whereas those of the latter species are dark green and neutrally to negatively buoyant. No reproductive data are yet available for P. frondifera. Calicular diameters are significantly greater in P. chiriquiensis than in the other two species. In contrast, corallum thickness is greater in P. varians and P. frondifera than in P. chiriquiensis. Canonical discriminant function analysis readily separated the three species.     

Population structure of two Antarctic ice-associated copepods, Drescheriella glacialis and Paralabidocera antarctica, in winter sea ice

The spatial distribution and population structure of two dominant ice-associated copepods, Drescheriella glacialis and Paralabidocera antarctica, were studied during winter at nine locations in east Antarctic fast ice. These species accounted for at least 90% of the total metazoan abundance at each location. Abundances were high, reaching 175 individuals l^-1 (190,000 m^-2) for D. glacialis and 660 l^-1 (901,000 m^-2) for P. antarctica. These abundances were probably partly supported by the high biomass of ice-algae (Pearson correlation coefficient, r=0.75), as indicated by chlorophyll-a concentrations (1.7-10.1 µg l^-1). The population structures of each species suggested very different life-history strategies. All developmental stages of D. glacialis were isolated from the ice cores, including females with egg sacs, supporting the hypothesis that this species reproduces in the sea ice during winter. This strategy might assist D. glacialis in leading a continually colonising existence, whereby it responds opportunistically to the availability of favourable habitat patches. The populations of P. antarctica were composed primarily of nauplii (>99%), consistent with past observations of a synchronised life cycle for this species. The strong coupling of the developmental cycle of P. antarctica to the growth and decay of sea ice suggests that local extinctions might occur in areas where ice break-out is unpredictable.     

Prolonged reproductive consequences of short-term biomass loss in seaweeds

This study describes the reproductive collapse of a large giant-kelp forest (Macrocystis pyrifera; Point Loma, southern California, USA) and the dynamics of its subsequent recovery. High-frequency sampling within a 100-m² area, combined with a 3-year reproduction time-series from four other sites over a broad depth gradient, were used to (1) quantify temporal and spatial patterns of change in size and fertility of adult sporophytes, and (2) examine physical and biological factors that regulate such changes. Giant-kelp sporophytes have the potential for continuous reproduction, yet from March to November 1999, sporophytes at the high-frequency sampling site went from completely sloughing (actively releasing zoospores) to completely sterile, despite a relatively constant biomass of sporogenous tissues. This shift to sterility was rapid, with 65% of sporophytes ceasing to slough during late-June/early-July 1999, and did not co-occur with stressful physical conditions (i.e. high temperatures, low nutrients, or high wave intensity). Instead, the cessation of reproductive output corresponded to an episodic, sublethal amphipod-grazing event that stripped blade biomass from all sporophytes. Although the grazer infestation affected the entire kelp forest, peaks in grazer abundance were localized, moving through the population during late spring and summer, and causing patchiness in sporophyte size and fertility on a scale of meters. The reproductive collapse was size-dependent, since smaller sporophytes were the first to cease sloughing. The grazing event waned in the fall and sporophyte vegetative growth rapidly recovered lost biomass (within ~2 months). Such growth, however, occurred at the expense of the production of sporogenous tissue and caused a prolonged period (>4 months) of decreased reproductive output. These results suggest a trade-off between sporophyte growth and reproduction, allowing short-term disturbances to have lasting impacts on the reproductive output of giant-kelp populations.     

Biomass, photosynthesis and growth of Laminaria saccharina in a high-arctic fjord, NE Greenland

Biomass, photosynthesis and growth of the large, perennial brown alga Laminaria saccharina (L.) Lamour. were examined along a depth gradient in a high-arctic fjord, Young Sound, NE Greenland (74°18'N; 20°14'W), in order to evaluate how well the species is adapted to the extreme climatic conditions. The area is covered by up to 1.6-m-thick ice during 10 months of the year, and bottom water temperature is <0°C all year round. L. saccharina occurred from 2.5 m depth to a lower depth limit of about 20 m receiving 0.7% of surface irradiance. Specimen density and biomass were low, likely, because of heavy ice scouring in shallow water and intensive feeding activity from walruses in deeper areas. The largest specimens were >4 m long and older than 4 years. In contrast to temperate stands of L. saccharina, old leaf blades (2-3 years old) remained attached to the new blades. The old tissues maintained their photosynthetic capacity thereby contributing importantly to algal carbon balance. The photosynthetic characteristics of new tissues reflected a high capacity for adaptation to different light regimes. At low light under ice, or in deep water, the chlorophyll a content and photosynthetic efficiency (!) were high, while light compensation (E_c) and saturation (E_k) points were low. An E_c of 2.0 µmol photons m^-2 s^-1 under ice allowed photosynthesis to almost balance, and sometimes exceed, respiratory costs during the period with thick ice cover but high surface irradiance, from April through July. Rates of respiration were lower than usually found for macroalgae. Annual elongation rates of leaf blades (70-90 cm) were only slightly lower than for temperate L. saccharina, but specific growth rates (0.48-0.58 year^-1) were substantially lower, because the old blades remained attached. L. saccharina comprised between 5% and 10% of total macroalgal biomass in the area, and the annual contribution to primary production was only between 0.1 and 1.6 g C m^-2 year^-1.     

Patterns of larval and early juvenile growth in a semiterrestrial crab, Armases angustipes (Decapoda: Sesarmidae): comparison with a congener with abbreviated development

In a semiterrestrial and estuarine tropical crab, Armases angustipes Dana (Grapsoidea: Sesarmidae), changes in biomass (measured as dry mass, W; carbon, C; nitrogen, N; and hydrogen, H; per individual) and relative elemental composition (C, N, H, in percent of W; C:N mass ratio) were studied during development from an early egg stage through hatching, the complete larval phase, metamorphosis and the first juvenile crab stage (CI). In the megalopa and CI, growth was measured also within the moulting cycle, and biomass and elemental composition were determined in cast exuviae. From an early egg stage to the freshly hatched larva, A. angustipes lost about 20% of W, 29% of C, 5% of N and 32% of H. Proportionally higher losses in C than in N were reflected also in a significantly decreasing C:N mass ratio (from 5.02 to 3.74). These results indicate that lipids mobilised from yolk reserves represented the principal metabolic substrate for embryonic energy production, while proteins were catabolised at a much lower rate. The present data of growth and exuviation are compared with previously published data from a congener, A. miersii Rathbun, which has an abbreviated and facultatively lecithotrophic mode of larval development (with three instead of four zoeal stages; stages I and II in principle independent of food). When growth is measured as an increase in the final (premoult) biomass of successive developmental stages, both species show an exponential pattern. Within the moulting cycles of the megalopa and the first juvenile, both species show parabola-shaped growth curves, with a rapid biomass increase in postmoult and intermoult stages, and losses in the premoult phase. Thus, the two Armases species show, in general, similar patterns of larval and early juvenile growth. However, the initial size of eggs and larvae is about four times larger in A. miersii, and its biomass remains higher throughout the period of larval and early juvenile development. A. angustipes is able to partially make up for this difference, as it has an additional zoeal stage, and its megalopa and CI stages show higher relative biomass increments (in percent of initial values). Due to this compensatory growth pattern, A. angustipes reaches in its CI stage about half the biomass of a juvenile A. miersii. When exuvial losses of megalopae and juveniles are compared between these two species, A. miersii shows higher biomass losses per individual (corresponding with its larger size), but lower relative losses (C, N, H, in percent of late premoult body mass or in percent of previously achieved growth increments). Differences in larval and early juvenile growth and in the exuvial losses of megalopae and juveniles of these two congeners are discussed in relation to their differential ecology, life history and reproductive strategy.     

Feeding ecology of Spinocalanus antarcticus, a mesopelagic copepod with a looped gut

Spinocalanus antarcticus, an abundant mesopelagic copepod in polar seas, has a greatly elongated and looped midgut, contrary to most other copepod species. The total gut length is 1.77, 1.86 and 1.90 times the total body length in adult females, CV and CIV, respectively. Gross morphology of the midgut is similar in all copepodite stages and adults. It is described here from specimens collected in the Arctic Ocean. In stratified samples from the deep Amundsen and Makarov Basins S. antarcticus showed a clear preference for the depth layer between 100 and 500 m. Generally, the guts were packed with material, but most of it was impossible to identify. In most specimens the digestive tract was filled with undefined detritus particles ("detritus balls"). They were almost spherical, heterogeneous organic aggregates of 40-100 µm diameter, with small clay-sized mineral flakes imbedded. Mineral particles in the size range of 1-10 µm were found in large quantities in the guts of many specimens. Cysts of Chrysophycea and dinoflagellates and fragments of dinoflagellates, diatoms, tintinnids and radiolarians, as well as skeletons of silicoflagellates, were rather rare; some animal remnants were also found. A high carbon/nitrogen ratio (8.9) and very high lipid content (54% of dry weight) indicated a very good nutritional state. The adaptive significance and possible feeding strategy of this deep-water copepod is discussed.     

Seasonal variation in ecophysiological patterns in macroalgae from an Arctic fjord. I. Sensitivity of photosynthesis to ultraviolet radiation

Marine macroalgae inhabiting Arctic coastal ecosystems are exposed to pronounced seasonal variations in the radiation regime, including harmful UVB radiation. This study presents the first data on the seasonal changes in the sensitivity of macroalgal photosynthesis towards UV exposure by comparing under-ice, clear-water and turbid-water conditions characteristic for late winter, spring and summer. Various brown (Laminaria saccharina, L. digitata, L. solidungula, Saccorhiza dermatodea, Desmarestia aculeata), red (Palmaria palmata, Devaleraea ramentacea) and one green macroalgal species (Monostroma aff. arcticum) were collected at the same water depth throughout the seasons in the Kongsfjord (Spitsbergen, Svalbard, Norway). Maximum quantum yield (F_v/F_m) and maximum photosynthetic electron transport rates (ETR_max) were determined immediately after collection, after 2 h exposure to artificial UV radiation and after 18 h recovery in dim white light. Photosynthesis of the studied species showed different responses depending on their morpho-functional and physiological characteristics, their life strategies, phenology and depth distribution. Within the genus Laminaria, maximum quantum yield of adult specimens of the deep-water species L. solidungula was most strongly UV sensitive. Adult L. saccharina exhibited a lower UV sensitivity than a 6-month-old specimen. Inhibition of photosynthesis after UV exposure remained at the same level throughout the study period, both in adult L. saccharina and S. dermatodea. However, adult specimens of L. saccharina collected in May showed partial recovery only, whereas photosynthesis of specimens from both species collected later recovered fully. D. aculeata exhibited a remarkable decrease of UV sensitivity during the study period. Photosynthesis of specimens collected under the ice was strongly inhibited by UV, but the degree of inhibition decreased during spring and summer. Concomitantly ETR_max values were low after UV exposure in specimens collected in June, but increased later in the season. P. palmata exhibited a relatively flexible response. Photosynthesis in specimens collected under the ice in June or in turbid water in July/August was relatively strongly inhibited; specimens collected during sunny periods and in clear water in spring showed a much lower degree of photoinhibition after UV exposure. The seasonal pattern of low/high ETR_max values in spring/summer is probably a characteristic of the life strategy of this species. The UV sensitivity of D. ramentacea exhibited a similar seasonal pattern. In M. aff. arcticum, UV sensitivity increased and ETR_max values decreased during the study period, reflecting the life strategy of this annual late winter/spring species. The physiological basis for the seasonal changes in UV sensitivity of photosynthesis is presented in a companion paper (this issue).     

Reproductive cycle of Zidona dufresnei (Caenogastropoda: Volutidae) from the southwestern Atlantic Ocean

Gonadal development of Zidona dufresnei (Donovan, 1823) (Caenogastropoda: Volutidae) was studied over a period of two consecutive years, through analysis of gonadal tissue. Individuals were sampled monthly at the Mar del Plata area, Argentina. Gonadosomatic index was estimated for males and oocyte size was used to estimate the stage of gonadal development in females. The reproductive season in this species in the sampled locality extended from October to March (austral spring-summer). During summer, a stage of advanced gonadal development and spawning predominated in the adult population. In autumn, gonads were generally under atresia; during wintertime (June-August), they underwent a period of recovery that lasted until the spring months, when gametes were released again. Synchronism between both sexes was evident. Marked periods of spawning were followed by resorption periods and then a growing phase; it was very clear that reproductive seasonality was linked to changes in bottom water temperature. These results suggest that Z. dufresnei gonads have a yearly cycle of gamete production, with two major activity peaks in September-October and January-February.     

Morphological, reproductive, and genetic variability among three populations of Crucibulum quiriquinae (Gastropoda: Calyptraeidae) in northern Chile

Crucibulum quiriquinae (Lesson, 1830) is the only species of Crucibulum currently recognized in northern Chile. Recent analysis of three Crucibulum populations obtained in northern Chile demonstrates the existence of morphological, genetic, and reproductive differences among populations. Two populations present in Bahía Tongoy (30°15'S), one inhabiting the shells of the snail Turritella cingulata and the other shells of the pectinid Argopecten purpuratus, showed morphological differences. However, both had planktonic larval development and show low genetic divergence (D=0.002). A third population from Bahía La Herradura (29°58'S), which also inhabits the shells of T. cingulata, did not show morphological differences compared with its counterpart from Bahía Tongoy. However the Bahía La Herradura population had intracapsular development and metamorphosis, and a larger genetic distance (D=0.06) from both Tongoy populations. The results of the reproductive and genetic analyses strongly suggested that the two Tongoy populations, although showing morphological differences, are biologically the same species, Crucibulum quiriquinae, whereas the La Herradura population is a new species.