Distribution and abundance of ophiuroids on the continental shelf and slope of the East Sea (southwestern Sea of Japan), Korea

The present study was carried out to describe the distribution of ophiuroids on the continental shelf and slope of the East Sea, off the Korean Peninsula. Three cruises were made from 1985 to 1987 in the area between 35 to 38°N and 129 to 130°E. A total of ten species was identified from the samples collected at 136 stations. Among them four species (Amphiodia craterodometa, Amphioplus macraspis, Ophiura leptoctenia and Ophiura sarsi) constituted more than 98% of abundance by number. The continental shelf off Gampo, near 35°40N, could be considered to be the southern limit of cold-water species. The abundance of dominant ophiuroids changed according to depth. Three faunal zones, namely, the inner shelf, the shelf edge and the slope zones, coincided with the topographic divisions of continental shelf and slope. The major inhabitant of the inner shelf was A. craterodometa and that of the continental slope was O. leptoctenia. The shelf edge area revealed a transitional zone where all four species occurred, contributing to the total number of individuals with almost equal proportions. The temperature of bottom waters was considered to be a factor determining zonal distribution. The sediment characteristics were not closely related to ophiuroid distribution.     

Enzyme activities of fish skeletal muscle and brain as influenced by depth of occurrence and habits of feeding and locomotion

Activities of lactate dehydrogenase (LDH), pyruvate kinase (PK), malate dehydrogenase (MDH) and citrate synthase (CS) were measured in the white skeletal muscle of marine fishes having different depths of occurrence and different feeding and locomotory strategies. There were significant depth-related differences in the two glycolytic enzymes, LDH and PK. LDH activity was most variable, and differed by 3 orders of magnitude between the most active shallow-living species and certain deep-sea fishes likely to have only minimal capacities for active locomotion. Superimposed on the depth-related patterns was a high degree of interspecific variation (up to 20-fold) in enzymic activity among species from any given range of depth of occurrence. Variation of both LDH and PK activities, noted for shallow- and deep-living fishes, seems to be largely accounted for by differences in feeding habits and locomotory performance. Active pelagic swimmers have much higher activities of LDH and PK than, for example, deep-living sit-and-wait predators. Benthopelagic fishes like rattails and the sablefish have the highest activities found among deep-living fishes, suggesting that these species engage in relatively active food-searching behavior compared to most other deep-sea fishes. The activity of CS, an enzyme of the citric acid cycle and an indicator of aerobic metabolism, varied little among species. Thus, the large interspecific variation in glycolytic potential (LDH and PK) among species is not associated with a similar variation in aerobic metabolism of white muscle. The much higher and more variable activity of MDH relative to CS suggests that, in addition to its function in the citric acid cycle, MDH may play an important role in redox balance in fish white muscle. In a comparison of white muscle composition between the shallow- and deep-living species, water content did not differ significantly, but protein content was significantly higher in shallow- than in deep-living fishes (211 and 130 mg g^-1 wet wt of muscle, respectively). The differences in muscle protein content are small relative to the differences between shallow- and deep-living species in LDH, PK and MDH activities. Thus, depthrelated differences in muscle enzymic activity are caused by factors other than enzyme dilution. Enzyme activities (LDH, PK and CS) in brain tissue were relatively constant among species regardless of depth of occurrence or feeding and locomotory habits. Habitat and lifestyle do not seem to influence the demands for overall metabolic function in brain. The utility of muscle enzymic activity data for making predictions about the ecological characteristics of difficult-to-observe, deep-living, fishes is discussed.     

Biodiversity in the ecosystem of the Portuguese continental shelf: distributional ecology and the role of benthic amphipods

The biodiversity and distributional ecology of amphipod crustaceans were analysed from benthic surveys in 1985 and 1986 along the coast of Portugal, from the Tagus canyon to the coast of Minho, in order to determine their role in the ecosystem of the Portuguese continental self. In samples obtained from different types of substrate between 18 and 545 m, we identified 113 species belonging to 51 genera of 24 families. Seventeen of these species were new records for the Portuguese coast. The relative frequencies and number of individuals of all species were analysed. The genus Ampelisca clearly dominated the group of the most frequent and abundant species, which also exhibited a large range of vertical distribution. Most of the 113 species were found only down to 150 m depth, corresponding roughly to the lower limit of the continental shelf. Fifteen species exhibited clear bathyal traits, being consistently found deeper than 100 m, especially in the Tagus canyon and the upper zone of the continental slope. The most frequent and abundant species were found predominatly or in large numbers in medium to fine sand bottoms. This type of substrate also contained the highest number of species. The granulometric structure of the habitat could constitute the most important factor controlling both biodiversity and development of large amphipod populations, since oxygen level, water exchange, number of available shelters, and probably the quantity and quality of nutritional resources all vary as a function of substrate texture. Because of their dominance in both frequency and abundance, several Ampelisca species may constitute an important food source for many secondary consumers of the shelf sediments, especially for demersal fishes.     

Deep-water decapod crustacean communities in the Northwestern Mediterranean: influence of submarine canyons and season

The specific composition and abundance of bathyal decapods in the Catalan Sea were investigated. A total of 109 bottom trawls were effected at depths ranging from 141 to 730 m on the continental slope in the Catalan Sea (northwestern Mediterranean) during two sampling cruises in spring and autumn 1991. Multivariate analysis of the samples revealed four groups of the decapod crustacean communities: (1) A shelf-slope transition-zone group at depths between 146 and 296 m, primarily characterized by the presence of Plesionika heterocarpus; (2) an upper-slope community between 245 and 485 m, characterized by the presence of the mesopelagic species Pasiphaea sivado and Sergestes arcticus, with Processa nouveli, Solenocera membranacea and Nephrops norvegicus as secondary species; (3) a middle-slope community below 514 m, with Aristeus antennatus and Calocaris macandreae as the most abundant species; (4) a group at 430 to 515 m, comprising all samples collected exclusively within or in the vicinity of submarine canyons. Mesopelagic decapods were predominant on the slope, while benthopelagic fishes (Merluccius merluccius, Micromesistius poutassou, Gadiculus argenteus) replaced mesopelagic decapods on the shelf. There were seasonal variations, with higher densities of mesopelagic species in spring, which were probably related, among other factors, to variations in the photoperiod. Our surveys also revealed higher species richness in the canyons together with seasonal changes in the megafaunal biomass. Generally, the upper and middle-slope communities both displayed seasonal changes in the composition and abundance of megabenthos.     

Spatial variation of growth and gonadal developments of Maurolicus muelleri in the Norwegian Sea and in a Norwegian fjord

The epibenthic megafauna of the high-Arctic Northeast Greenland shelf was investigated by means of seafloor photography and Agassiz trawl catches. At 54 stations in water depths between 40 and 770 m, sequences of color slides, each depicting about 1 m² of the seafloor, were obtained along photographic transects of about 100 to 600 m length. The photographs were quantitatively analyzed for abundance of epibenthic organisms identified by comparison with specimens collected from trawl catches. Megabenthic biomass was estimated by multiplying density values with averge body mass figures. For five dominant brittle star species, the population oxygen uptake and, thus, organic carbon mineralization potential were approximated by applying individual respiration rates of average-sized specimens to density figures. Multivariate analyses of the megabenthic species distribution revealed a distinct depth zonation. Shallow shelf banks (<150 m), characterized by coarse sediments, many stones and boulders as well as negative bottom water temperatures, housed a rich epifauna (30 to 340 ind m^–2, 1.8 to 10.5 g AFDW m^–2), strongly dominated (80 to 98% by numbers) by the brittle stars Ophiocten sericeum and Ophiura robusta. The oxygen uptake by brittle stars ranged from 0.4 to 95 mol O₂ m^–2 h^–1 (i.e., assuming a respiratory quotient of 0.8, an organic carbon mineralization of 0.1 to 21.9 mg C m^–2 d^–1). At the bank flanks sloping to the shelf troughs (100 to 580 m), finer sediments prevailed, stones were rare, and bottom water temperatures were positive due to the inflow of Atlantic water. Compared to bank sites, total epibenthic abundances as well as carbon mineralization by brittle stars were roughly ten times and total biomass about four times smaller. In deep shelf depressions as well as at the continental slope (200 to 770 m), stones were completely lacking, and sediments very fine. Epibenthic standing stock and carbon mineralization were one to two orders of magnitude lower than on the banks. The estimation of brittle star oxygen uptake indicates that a considerable portion of the organic carbon produced in the polynya and partitioned to the benthos may be remineralized by epibenthic bank assemblages.     

Distribution et synécologie des fonds à Gryphus vitreus (Brachiopoda) en Corse

In the Mediterranean Sea, the brachiopod Gryphus vitreus (Born) was collected off Corsica by dredging and trawling during three cruises (June 1983; April and July 1984) and from along the French continental coast by dredging during many cruises (1975–1985). The upper limit of its bathymetric distribution lies between 115 and 125 m (rarely, from 90 m), the lower limit between 140 and 200 m depth, forming a belt along the edge of the continental shelf. The horizontal distribution of G. vitreus varies from 250 m to >4 km, and is directly related to geomorphological and hydrodynamic variations resulting from local topography and/or geographical location. The G. vitreus bottoms are bounded on the continental slope by the bathyal mud biocoenosis and on the shelf by the coastal detritic or shelf-edge detritic biocoenosis, both circalittoral. The bottoms correspond to a bathylittoral ecosystem characterized by (1) prevailing environmental conditions which result in a biotope characterized by coarse detritic sediment clogged by fine sand and mud with a high content of small hard substrates, by constant moderate bottom-currents which become weaker with increasing depth, and by small annual variations in temperature and salinity; the occurrence of an ostreobium sp. alga in the shell of G. vitreus indicates the involvement of the phytal system, as defined by Pérès (1982); (2) the G. vitreus biocoenosis, comprised of characteristic macrobenthic stocks (particularly polychaetes, mollusks, and epifaunal species on small hard substrates). Whatever the geomorphology, neighbouring circalittoral and bathyal biocoenoses have little influence on the G. vitreus biocoenosis, which displays a comparatively greater species richness and density. However, immigration of circalittoral species is encouraged by detrital sediments and water currents. The occurrence of this ecosystem as a distinct belt intercalated between circalittoral and bathyal zones is discussed. The ecosystem is considered to be bathylittoral.     

Ecological investigations of the late-stage phyllosoma and puerulus larvae of the western rock lobster Panulirus longipes cygnus

The distribution and abundance of the late-stage phyllosoma larvae of Panulirus longipes cygnus George and the distribution and densities of the final larval stage, the puerulus, both in the plankton and at settlement along the coast, were investigated. A total of 3,617 late-stage phyllosoma (Stages VI to IX) and 301 puerulus larvae were caught at 187 plankton stations during the July to November periods 1974, 1975 and 1976 off the west coast of Australia between 29°00 to 32°30S and 113°30 to 115°00E. The depth range sampled was 0 to 35 m on the continental shelf and 0 to 90 m off the shelf. During onshore/offshore cruises with similar sampling effort on and off the shelf, 1,169 late-stage phyllosoma larvae were taken, of which only 9 were caught on the shelf, and these near the outer edge. A series of cruises sampling two areas beyond the shelf near 29°30 and 32°00S yielded 2448 late-stage phyllosoma, with greater densities of larvae in the northern location. The settlement of puerulus-stage larvae along the coast in the same geographical range was also greater in the north than in the south. The data from the onshore/offshore cruises showed a definite effect of moon phase on numbers of puerulus larvae caught on the shelf, with higher catches near new moon. The low numbers of puerulus larvae (usually 0, 1 or 2 individuals) caught at all stations showed that the puerulus stage is sparsely distributed in the plankton. Fewer puerulus larvae were present at the surface than at lower depths, but it was not possible to determine a depth preference for the puerulus between 10 m and the lowest depths sampled because of the low catch numbers. No relationships were found between puerulus larvae density and surface-water temperature, salinity, or plankton biomass at each station. Data on the larval distributions indicate that, near the end of their planktonic existence, the majority of the late-stage phyllosoma larvae of P. longipes cygnus are not carried onto the shelf, where mixing of oceanic and continental shelf waters occurs only on the outer third, but are transported southward by oceanic circulation beyond the shelf. The puerulus moults from the last phyllosoma stage beyond the shelf and completes the larval cycle by swimming across the shelf and settling in the shallow reef areas.     

Geostatistical analysis of spatial distribution of Liocarcinus depurator,Macropipus tuberculatus and Polybius henslowii (Crustacea: Brachyura) over the Galician continental shelf (NW Spain)

Geostatistics was used to analyze the spatial structure and distribution of three species of brachyurans, Liocarcinus depurator, Macropipus tuberculatus and Polybius henslowii, from sets of data collected during three survey cruises (1983 and 1984) over the Galician continental shelf. The present study investigates the feasibility of using geostatistics with data collected according to traditional methods and of thereby improving the sampling methodology. In order to investigate the spatial structure of the species studied, experimental variograms were calculated and fitted to a spherical model. The spatial structure model was used to estimate and map abundance and distribution of the populations studied using the so-called Kriging technique. Geostatistical analysis enabled the determination of spatial density gradients as well as patch size (14 to 22 km, L. depurator; 10 to 28 km, M. tuberculatus; 7.5 to 28 km, P. henslowii) along the continental shelf. Depth was revealed as a limiting factor, restricting the distribution of L. depurator and M. tuberculatus on a large scale, whereas upwelling processes and nutrient-rich waters from the rías affected the spatial structure on a smaller scale, especially in the case of P. henslowii. A spatial segregation in the distribution of the three species also emerged; this probably arose from differences in physical and biological factors that result in different habitat-exploitation patterns. The study demonstrates the existence of spatial covariance and that the variograms vary as a function of population density and geographical area. This information will be useful in improving the design of future sampling cruises.     

Molecular association of Cu,Zn, Cd and 210Po in the digestive gland of the squid Nototodarus gouldi

In July 1985, very fine burrows extending at least to a sediment depth of 50 cm were found in sediments of the Vöring-Plateau, Norwegian continental slope, at depths of 1 261 to 1 969 m. Such burrows have been described from other areas of the oceans, but until now the producers have been unknown. In the box-cores from Vöring-Plateau sipunculans of the genus Golfingia, subgenus Nephasoma, were identified as inhabitants and producers of these Lebensspuren, which correspond with the fossil ichnogenus Trichichnus.     

Non-viable seasonal settlement of larvae of the upper bathyal brittle star Ophiocten gracilis in the Rockall Trough abyssal

Re-examination of ine structure of postlarvae previously identified as the abyssal species Ophiura ljungmani (Lyman) in a time series of samples taken from 1975 to 1980 from a 2900 m deep permanent station in the southern Rockall Trough (Northeast Atlantic Ocean) has shown the majority of the large summertime peak of brittle-star postlarvae to belong to a second species. Most were incomplete and probably corpses when collected. The few intact specimens present were identical to postlarvae collected in benthic samples from the neighbouring continental slope, where a dense population of the bathyal species Ophiocten gracilis (G. O. Sars) is present from 600 to 1 200 m depth. Examination of population size-structures indicates synchronous reproduction in January/February and annual recruitment to the population. The presence both of Ophiopluteus ramosus and intact postlarvae of Ophiocten gracilis in midwater plankton samples from the vicinity of the permanent station in March/April are thought to derive either from the adjacent slope population or, less probably, from larvae transported in the North Atlantic Current from the Flemish Cap area off Newfoundland. In deep water, viability of these benthic postlarvae is low, none surviving longer than the following winter in the Rockall Trough. These observations suggest a large seasonal transfer from the slope of non-viable larvae and postlarvae as food to the abyssal benthic community.Communicated by J. Mauchline, Oban     

Reproduction and larval development in three scalpellid barnacles, Scalpellum scalpellum (Linnaeus 1767), Ornatoscalpellum stroemii (M. Sars 1859) and Arcoscalpellum michelottianum (Seguenza 1876), Crustacea: Cirripedia: Thoracica): implications for reproduction and dispersal in the deep sea

We studied reproduction and larval development in three species of pedunculated barnacles with different depth distribution, that is, Scalpellum scalpellum (30–200 m), Ornatoscalpellum stroemii (100–1,600 m) and Arcoscalpellum michelottianum (64–5,190 m). Morphology, position and number of males in the female/hermaphrodite, type of larval development and the number and size of eggs were recorded. All three species have a pair of pocket-like receptacles, each of which can host only a single male in O. stroemii, up to five males in S. scalpellum and up to 12 males in A. michelottianum. Eggs and larvae were smallest in S. scalpellum, intermediately sized in O. stroemii and largest in A. michelottianum. Brood size was comparable for S. scalpellum and O. stroemii, but five times higher in A. michelottianum. The ratio for body/egg size is almost similar in S. scalpellum and A. michelottianum, but much smaller in O. stroemii. Both S. scalpellum and A. michelottianum have nauplii that spend upwards of 10 days in the plankton while the larvae of O. stroemii hatch as cyprids that settle soon after release. All these reproductive data indicate that O. stroemii invests considerably more in each propagule than the other two species. We hypothesize that the observed differences in reproductive system and mode of development in the three species represent adaptations to their different habitats. S. scalpellum are mainly transported by currents in the coastal sublittoral zone. O. stroemii is presumably spread by intermediate deep currents along the shelf and shelf-slope, while A. michelottianum occurs on seamounts and is probably transported by demersal currents over wide areas of inhospitable soft-bottoms. Our observations are in accordance with the general pattern that, egg-size and propagule-size are positively correlated to bathymetric and geographic distribution, and that the continental slope environment represents a high disturbance environment, where a short larval stage is an advantage.     

Distribution pattern, reproductive biology, and fishery of the wedge sole Dicologlossa cuneata in the Gulf of Cadiz, south-west Spain

The wedge sole Dicologlossa cuneata (Moreau, 1881) is a coastal species that lives along the inner shelf waters of the Gulf of Cadiz down to a depth of 115 m. Its fishery, the size composition of the exploited population, and its reproduction have been studied on the basis of data acquired from commercial statistics from 1984 to 1994 and from sampling carried out during 1993 and 1994. The relative abundance of the species and its geographic and bathymetric distribution have been examined by analysis of four trawl surveys carried out from 1992 to 1994. D. cuneata is captured mainly by the trawl fleet, and to a lesser extent by gillnet gears. Wedge sole fishery has a marked seasonality. Size-frequency distributions from commercial samples and from bottom-trawl surveys are very similar, ranging from 12 to 26 cm total body length (TL). D. cuneata is a “repeat-spawner”. Peak spawning is from January to May. Females attain sexual maturity at 18 cm TL, while sexually mature males have been observed at 15 cm TL. The flexibility of the spawning strategy of D. cuneata throughout its distribution range is discussed. The scarcity of small specimens in the monthly samples and sequential spawning throughout the year prevented the estimation of growth parameters by means of length-frequency analysis. D. cuneata is present in greatest abundances in the sandy–muddy bottoms of the Guadalquivir River mouth at 15 to 30 m depth. Its optimum habitat coincides with the principal commercial fishing grounds. The possibility of reproductive vertical migration is discussed, but more precise data are needed before a viable hypothesis can be made. Received: 1 July 1997 / Accepted: 27 November 1997     

Seasonal migrations of plaice (Pleuronectes platessa) through the Dover Strait

Analysis of paired-haul mid-water trawling experiments conducted in the five months November to March during the years 1985 and 1988 revealed the seasonal pattern of migration of plaice (Pleuronectes platessa L.) moving through the Dover Strait between the Southern Bight of the North Sea and the English Channel. Mid-water catches of maturing fish were highest on south-going tidesprior to peak spawning (late January), while catches of spent fish, were highest on north-going tidesafter peak spawning. Detailed analysis of the catch data provided evidence that males complete their pre-spawning migration earlier, and their post-spawning migration later, than female fish and consequently spend more time on the spawning ground. Catches of immature female fish indicated a migration south following that of the mature fish. This dummy run may be a method by which immature plaice use the presence of high densities of mature and spawning fish to learn the location of the spawning ground. The analysis also indicated that differences in catch rates between day and night are unlikely to be the result of gear avoidance by day. The results confirm that selective tidal-stream transport is a key migratory mechanism for plaice in areas of fast tidal streams on the European continental shelf.     

Metabolism,enzymic activities and cold adaptation in Antarctic mesopelagic fishes

Several species of Antarctic mesopelagic fishes that have different minimal depths of occurrence but the same environmental temperature were collected in November–December 1983 and in March 1986 between 0 and 1 000 m in the open water near the marginal ice zone in the vicinity of 60°S 40°W (1983) and 65°S 46°W (1986), and oxygen consumption rate (V _{O 2}) and the activity of two metabolic enzymes, lactate dehydrogenase (LDH, an indicator of the anaerobic potential of locomotory muscle) and citrate synthase (CS, an indicator of citric acid cycle activity or aerobic potential), were determined. In four dominant species, whole-individual oxygen-consumption rate (y, ml O₂ individual^–1 h^–1) varied with weight (X, g) according to the equation y=aX ^b, with b values falling between 0.889 and 1.029. The relation of weight-specific LDH activity (y, U g^–1 wet wt) with weight (x, g) was also described by the equation y=aX ^b, with b values varying between 0.229 and 1.025. Weight-specific CS activity declined with weight, with b values from-0.031 to-0.369. V _{2 O}, LDH activity and CS activity all declined markedly with increased species' minimum depth of occurrence (the depth below which 90% of a species' population lives). Comparisons with previous studies on ecologically equivalent species of the California Borderland indicate that depth-related decreases in metabolism are the result of adapted traits of deeper-living species, not declining temperature within the water column. The metabolic rate of Antarctic mesopelagic fishes is approximately twice that of California species at equivalent temperatures; similar rates were found at the normal habitat temperatures of the two groups. Thus, a well-developed compensation for temperature is present in the Antarctic fishes: cold adaptation. Differences in enzymic activity among species, and among different sized individuals of a species are related to differences in metabolic rate and locomotory capacity. Enzymic indices can be used to estimate metabolic rates and evaluate ecological parameters such as predatory strategies and niche separation.     

Growth and production of Euphausiacea (Crustacea) in the Rockall Trough

The euphausiid fauna of the Rockall Trough has been sampled in time series at approximately two-monthly intervals between 1973 and 1976 between surface and depths greater than 2000 m. Length/frequency histograms have modes that are coherent for periods of at least 4 to 6 mo, indicating that populations are being sampled. Rates of growth were determined for six species. Epipelagic species have winter checks to the growth rates, but such checks are absent in the growth of Thysanopoda acutifrons, Nematobranchion boöpis and Stylocheiron maximum. Ratios of annual production: biomass were determined and are all within the previously determined range of values for epipelagic and coastal populations. Lack of a winter check to the growth rate in deep-living species enables these potentially to have overall rates of growth comparable to those of temperate, epipelagic, shelf and coastal species.     

Cross-shelf distribution of copepods and fish larvae across the central Great Barrier Reef

The distribution of total dry weight of zooplankton, copepod numbers and ichthyoplankton across the outer continental shelf in the central Great Barrier Reef was examined at bi-weekly intervals for three months over summer of 1983. Copepods were sampled (236 m net) within 10 m of the surface and within 10 m of the bottom. Mean densities in surface waters decreased markedly from the mid-shelf to outer shelf and the Coral Sea, but no cross-shelf gradient occurred in the bottom-water. Densities of copepods on the mid-shelf (surface and bottom waters) and in bottom-waters of the outer shelf were typically ca. 400 m^–3. Significantly lower densities (ca. 100 m^–3) occurred in surface waters of the outer shelf, except during outbursts of Acartia australis, when densities in these waters differed little from those elsewhere on the shelf. In oceanic waters, 10 km from the outer shelf station, copepod densities in surface waters were ca. 40 m^–3. Four of the five most abundant copepod taxa in surface waters, Paracalanus spp., Eucalanus crassus, Acrocalanus gracilis and Canthocalanus pauper, tended to be most abundant at the mid-shelf end of the transect. Acartia australis was sporadically very abundant in surface waters of the outer shelf, as was Paracalanus spp. in bottom-water of the outer shelf. An assemblage of Coral Sea species of copepod occurred in bottom-water of the outer shelf during two major intrusions, but not at other times. Densities of all common species varied considerably between cruises. Maximum densities of all common species except A. australis tended to be associated with diatom blooms linked to intrusions but a bloom did not necessarily mean all common species were abundant. Fish larvae included both reef and non-reef taxa, with reef taxa predominating on the outer shelf (approx 2:1 in density of individuals) and non-reef taxa dominating in nearshore samples (approx 2:1). Nine of the ten most abundant taxa analysed showed highly significant variation in numbers among stations and all but one of these also exhibited significant station x cruise interactions. Interactions generally reflected changes in the rank importance of adjacent stations from one cruise to the next or lack of any significant cross-shelf variation on some cruises where overall abundance of the taxa was low.     

Metabolic responses of the squat lobster (Pleuroncodes monodon) larvae to low oxygen concentration

Squat lobster populations found in the Humboldt Current System over the continental shelf from ~28 to 37°S release pelagic larvae in sub-surface cold (~11 °C) hypoxic waters. Larvae subsequently spread throughout the water column encountering both normoxic and hypoxic conditions. We analyzed some short- and long-term responses of Pleuroncodes monodon larval metabolism to hypoxia at 11 °C. Routine and postprandial aerobic respiration rates were lower in hypoxia than in normoxia for all zoeal stages. Zoea V oxyconformed, while megalopae oxyregulated down to very low oxygen concentrations. Throughout zoea I development, the rate of nitrogen (protein) accumulation in zoea I was lower, and C:N ratios were higher under hypoxic conditions than in normoxia. Citrate synthase (CS) and malate dehydrogenase (MDH) apparent specific activities (as indicators of aerobic and metabolic potentials, respectively) decreased and remained at the same level, respectively, throughout zoea I reared under hypoxic conditions. Anaerobic to aerobic potential (lactate dehydrogenase (LDH)/CS) was higher in organisms reared under hypoxia, and MDH/LDH potential ratios were characteristic of organisms tolerant to hypoxia. In spite of P. monodon zoea endurance and metabolic adaptations to decreasing oxygen tensions, intense hypoxia as such of their release site would affect their overall condition especially toward the end of the molt cycle. Our results indicate the importance of considering the interaction between environmental oxygen variability and recruitment success.     

Diets of calanoid copepods on the West Florida continental shelf: Relationships between food concentration,food composition and feeding activity

Bottle incubations were conducted in March, July/August and October 1992. to measure the daily rations (R) and objectively characterize the diets of the calanoid copepodsEucalanus elongatus, Undinula vulgaris, Centropages velificatus andTemora stylifera from the west Florida continental shelf. Daily rations,R, were clustered around two, order-of-magnitude different means, 1.3 and 11.2% of body C d^–1, representative of quiescent and active feeding modes, respectively. The food concentration at which the transition from quiescent to active mode occurred was influenced by food particle size. In the quiescent mode, diets were dominated by nanoplankton, whereas no food type dominated the diet in the active mode. Selective feeding, defined as a statistically significant difference between the frequency distributions of foods in the diet and environment, occurred in both quiescent and active copepods. However, what appeared to be selective feeding in quiescent copepods could be explained by processes that passively modified the distribution of the diet relative to that of the food supply. Conversely, selective feeding in active copepods apparently resulted from foraging for particles >5 m in diameter in food environments dominated by nanoplankton (<5 m).     

Physioecology of zooplankton. I. Effects of phytoplankton concentration,temperature, and body size on the growth rate of Calanus pacificus and Pseudocalanus sp.

Changes in dry weight and in weight-specific growth rates were measured for copepodite stages of Calanus pacificus Brodsky and Pseudocalanus sp. cultured under various combinations of phytoplankton concentration and temperature. Mean dry weight of early copepodites was relatively unaffected by either food concentration or temperature, but mean dry weight of late stages increased hyperbolically with food concentration and was inversely related to temperature. The food concentration at which maximum body weight was attained increased with increasing temperature and body size, and it was considerably higher for C. pacificus than for Pseudocalanus sp. This suggests that final body size of small species of copepods may be determined primarily by temperature, whereas final body size of large species may be more dependent on food concentration than on temperature. Individual body weight increased sigmoidally with age. The weight-specific growth rate increased hyperbolically with food concentration. The maximum growth rate decreased logarithmically with a linear increase in body weight, and the slope of the lines was proportional to temperature. The critical food concentration for growth increased with body size proportionally more at high than at low temperature, and it was considerably higher for C. pacificus than for Pseudocalanus sp. Because of these interactions, early copepodites optimized growth at high temperature, even at low food concentrations, but under similar food conditions late stages attained higher growth at low temperature. The same growth patterns were found for both species, but the rates were significantly higher for the larger species, C. pacificus, than for the smaller one, Pseudocalanus sp. On the basis of findings in this study and of analyses of relationships between the maximum growth rate, body size, and temperature from other studies it is postulated (1) that the extrapolation of growth rates from one species to another on the basis of similarity in body size is not justified, even for taxonomically related species; (2) that the allometric model is inadequate for describing the relationship between the maximum weight-specific growth rate and body size at the intraspecific level; (3) that the body-size dependence of this rate is strongly influenced by temperature; and (4) that species of zooplankton seem to be geographically and vertically distributed, in relation to body size and food availability, to optimize growth rates at various stages of their life cycles.Contribution No. 1127 from the Department of Oceanography, University of Washington, Seattle, Washington 98195, USA     

Metabolic responses to changing environmental conditions in the brackish water polychaetes Marenzelleria viridis and Hediste diversicolor

The metabolic strategies of the polychaete Marenzelleria viridis (Verrill 1873), a successful immigrant into Baltic shallow eutrophic coastal waters with meso-to oligohaline salinities since the 1980's, were determined by simultaneous calorimetry and respirometry. Resistance to oxygen deficiency under varying ecological conditions was also examined. The results of the studies with this immigrant were compared to those with the common indigeneous polychaete Nereis (Hediste) diversicolor (O.F. Müller). At 10 and 20 °C and the average habitat salinity of 5 M. viridis gradually reduced its metabolic activity with declining oxygen partial preessures (pO₂), whereas H. diversicolor maintained its metabolic activity. The metabolism of both species remained fully aerobic down to a pO₂ of 2 kPa. An additional hyposmotic stress of 0.5 salinity at a temperature of 20 °C led to a decrease in the rate of oxygen consumption in H. diversicolor below a pO₂ of 10 kPa, whereas metabolic heat dissipation remained constant. M. viridis, however, further reduced both, metabolic heat dissipation and oxygen consumption. The metabolic rates of both species under anoxia were similar, amounting to ca. 20% of the normoxic rate. The resistance of the two species to oxygen deficiency was also similar, ranging between 21 and 290 h (median survival time LT₅₀), depending on temperature and salinity. Specimens used in the present study were collected from the Southern Baltic coastal inlet of Darß-Zingster-Boddenkette during 1992 and 1993.