Skeletal growth markers in the deep-sea brittle starsOphiura ljungmani andOphiomusium lymani

Growth bands have been found in the calcitic vertebral arm ossicles of the commonly occurring deep-sea brittle starsOphiura ljungmani Wyville Thomson andOphiomusium lymani (Lyman) (Echinodermata: Ophiuroidea) trawled from the Rockall Trough (N.E. Atlantic) at 2 200 and 2 900 m depth from 1973 to 1982. InOphiura ljungmani, the study of ossicle microstructure by SEM shows that growth bands reflect differences in stereom porosity and surface relief, similar to that previously found amongst shallow-water brittle stars. The pattern inOphiomusium lymani was much less clear from the microstructure, but could be revealed by heating the ossicle to 450 °C and clearing in xylene. The bands showed up as fine, translucent rings separated by more opaque, wider zones, perhaps reflecting differences in organic material incorporated within the calcite. Both growth-banding patterns probably reflect an annual cycle in skeletal growth rate. On this assumption, the number and spacing of the banding in the two species indicates contrasting growth strategies. WithOphiura ljungmani, a rather regular annual growth increment and perhaps shorter lifespan (up to ca. 10 yr) thanOphiomusium lymani is indicated. The latter shows a relatively wide spacing of early bands, followed by tight clustering of the outermost bands corresponding to adult sizes. This growth pattern is characteristic of species escaping from predation by rapid growth to relatively large adult size. AdultO. lymani probably grow slowly, some perhaps reaching 20 yr of age. Growth curves were fitted to size-at-age corresponding to measurements of the size and ordering of growth bands. These corroborate age structure previously estimated from analysis of size frequencies in time series from the stations sampled in the present study. Such skeletal growth markers should be of value in analysis of the demography of deep-sea populations.     

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     

Re-appraisal of age composition,growth and survivorship of the deep-sea brittle star Ophiura ljungmani from size structure in a sample time series from the Rockall Trough

Samples were taken from a 2 900 m deep permanent station (centred on 54°40N; 12°16W) in the southern Rockall Trough, from November 1975 to September 1980, inclusive. Revision of juvenile size frequencies was necessary after removal of postlarvae of an annual non-viable settlement of Ophiocten gracilis (G. O. Sars) that were mistakenly included in a previous analysis. The present study of the revised data shows that settlement of Ophiura ljungmani (Lyman) occurs in summer when disk-size frequencies are dominated by the newly metamorphosed postlarvae. The likely age composition in larger sizes was suggested from the progression of modes along the size axis in juvenile size classes in consecutive were developed from Gaussian mixtures fitted by constrained computer search using, as starting values, component parameter values suggested from the frequency histograms. Choice between competing solutions was made on the basis both of goodness-of-fit and biological plausibility. However, identification of year-class structure amongst sizes >3 to 4 mm disk diameter remained conjectural owing to the low frequencies of adults in the samples. Comparison of the fitted component-means in the time series suggested a marked seasonal growth pattern, with maximal growth in spring. Probable age composition amongst adult sizes was extrapolated from von Bertalanffy growth parameters estimated from the means of juvenile year classes.Communicated by J. Mauchline, Oban     

Ecological aspects of ophiuroids from the phytal of S. W. Atlantic Ocean warm waters

Nine species of ophiuroids — Amphipholis januarii, Axiognathus squamatus, Hemipholis clongata, Ophiocnida scabriuscula, Ophiactis lymani, Ophiactis savignyi, Ophionereis reticulata, Ophioderma appressum and Ophiothrix angulata —were collected in various habitats from the mid-littoral and upper infralittoral on the northern coast of the State of São Paulo, Brazil. The abundance of 6 species occurring in 28 species of algae was investigated. A total of 220 samples was collected at monthly intervals from April, 1969 to May, 1970. The distributional pattern of the populations, as determined by Mobisita's index, shows aggregation of the ophiuroids. No ophiuroid species was limited to one algal species. Each species prefers certain algal species and/or a different level on the shore. The most abundant species on algae was Ophiactis lymani, with a maximum density of 1,510 individuals/100 ml of algae. Four species of ophiuroids occurred inside sponges. The most abundant species in sponges was O. savignyi, with a maximum density of 1,892 individuals/100 g of dry sponge. Two species of ophiuroids occurred inside the bryozoan Schizoporella unicornis. Feeding observations have shown Axiognathus squamatus to capture its food by mucous nets. Decapod crustaceans fed on ophiuroids in aquaria. The copepod Thespesiopsyllus sp. was found in the body cavity of the 2 Ophiactis species. Simultaneous sexual and asexual reproduction were abserved in O. savignyi.     

Frequency of sublethal injury in a deepwater ophiuroid, <Emphasis Type="Italic">Ophiacantha bidentata</Emphasis>, an important component of western Atlantic <Emphasis Type="Italic">Lophelia</Emphasis> reef communities

The occurrence and relative abundance of tissue (arm) regeneration in the ophiuroid, Ophiacantha bidentata (Retzius), was examined in individuals collected primarily among colonies of the deep-water coral Lophelia pertusa off the southeastern United States. Seven deep-water coral sites (384–756 m), located between Cape Lookout, NC, and Cape Canaveral, FL, were sampled in June 2004 using a manned submersible. The presence of regenerative tissue was evaluated by visual inspection of each individual ophiuroid, and the proportion of regenerating arms per individual was examined relative to size of individual, geographic location, and depth of collection. Ophiacantha bidentata, the dominant brittle star collected, commonly displayed signs of sublethal injury with over 60% of individuals displaying some evidence of regeneration. These levels of regeneration rival those reported for shallow-water ophiuroids. Larger individuals (>6.5 mm disc size) had a higher incidence of regeneration than smaller individuals. Size of individual and percent of regeneration were negatively correlated with depth. Although O. bidentata was significantly less abundant in southern versus northern sites, ophiuroid abundance did not appear to be influenced by amount or density of coral substratum. Presence of dense aggregations of O. bidentata indicates that they are an important component of the invertebrate assemblage associated with deep-water coral habitat especially in the northern part of the study area. Assuming that observed frequencies of injury and subsequent regeneration represent predation events then dense ophiuroid aggregations in deep-water coral habitats represent an important renewable trophic resource within these communities.     

Genetic variability in the cosmopolitan deep-water ophiuran Ophiomusium lymani

A population of the cosmopolitan deep-sea ophiuran Ophiomusium lymani was studied by gel electrophoresis, and proved to be highly variable genetically; about 53% of the 15 loci studied are polymorphic, and the average individual is heterozygous at about 17% of the loci. This is approximately the same genetic variability displayed by other species, belonging to other phyla or classes, from the same deep-sea trawl. A similarly high level of genetic variation occurs in deep-sea organisms in general, and in a shallow-water tropical species. Both the deep-sea and the tropics are trophically stable environments. On the other hand, low genetic variabilities have been found in marine species from trophically unstable environments. These data suggest that any phylogenetic effects on genetic variability are secondary, and that the trophic regime may be of major importance in determining genetic strategies of adaptation.This study is no. 5 of a series of reports on the results of Expedition Quagmire.     

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.     

Reproduction of<Emphasis Type="Italic"> Ophiactis resiliens</Emphasis> (Echinodermata: Ophiuroidea) in New South Wales with observations on recruitment

Reproduction of the ophiuroid Ophiactis resiliens Lyman 1879, a common species in the shallow waters around Australia, was examined over 1 year in two populations near Sydney, New South Wales. Gametogenesis was documented by histological examination of the gonads. Vitellogenesis in females and spermatocyte proliferation in males started in February and March. O. resiliens had an annual spawning period from May to September/October with peak gamete release from May to July. Thereafter, spawning occurred in some specimens through November. Gravid gonads were present for approximately 2 months longer in O. resiliens from Clovelly Bay than in those from Little Bay. At both sites spawning was episodic and gametogenesis continued through most of the spawning season. Most specimens (50–100%) collected from November to March had indeterminate/recovery stage gonads, the sex of which, could not be determined. The timing of gametogenic renewal during these months varied among individuals. O. resiliens has a 3-month planktonic stage and the presence of juveniles, 0.5 –1.5 mm disk diameter, in the coralline algal turf at Little Bay from February to May, suggests that settlement occurs in summer and autumn at this site. In contrast, juveniles were rarely encountered in coralline turf at Clovelly.     

Genetic variance in Ophiomusium lymani (Ophiuroidea: Echinodermata) from lower bathyal depths in the Rocklall Trough (northeast Atlantic)

Specimens of the deep-sea brittle-star Ophiomusium lymani were collected from six sites in the Rockall Trough (northeast Atlantic_. Four monomorphic and four polymorphic loci were detected, with up to 75 individuals screened at any one locus. The results showed little difference in allele frequencies between sites and, consequently, estimates of genetic identity indicated no significant genetic differentiation between the populations sampled. Deficits of heterozygotes were observed at all polymorphic loci, but the deficiencies were only significant at the phosphoglucose isomerase locus from two locations. The deficit of heterozygotes was not the same across loci, suggesting that inbreeding is not the cause of the excess homozygosity. No relationship between heterozygosity and depth was observed.     

Predation on euphausiids by cod,Gadus morhua,in winter in Icelandic subarctic waters

The euphausiids consumed by cod (Gadus morhua Linnaeus, 1758) taken in November 1983 and February–March 1984 on feeding grounds in the subarctic shelf area north-west, north-east, and south-east of Iceland have been examined. A total of 2 714 euphausiids occurred in the 1 029 stomachs with food which were analysed; of these 1 640 (60%) could be identified to species. Thysanoëssa inermis (Krøyer, 1846) and Meganyctiphanes norvegica (M. Sars, 1857) were most numerous, constituting 58 and 40%, respectively, of the euphausiids which could be identified. The other euphausiids were, in declining numbers of abundance, T. raschii (M. Sars, 1864), T. longicaudata (Krøyer, 1846), and Nematoscelis megalops G. O. Sars, 1883. The mean number of euphausiids occurring per stomach showed considerable variation between both sampling areas and time of sampling. In each area, the mean number of M. norvegica occurring per stomach was similar at both sampling times, while for T. inermis it was greater in February–March than in November. The mean number of euphausiids occurring per stomach increased with increasing size of cod, being 1 to 2 and 4 to 6 in 10 to 30 cm and 50 to 70 cm cod, respectively. An examination of the diel variation in the occurrence of the euphausiids in the stomachs indicated two peaks, one in the morning before sunrise and another in the evening around and after sunset.     

Epizoic diatoms on the euphausiidNyctiphanes australis: Consequences for gut-pigment analyses of whole krill

We report the first record of infestation by the epizoic pennate diatoms (Licmophora sp.) of the euphausiidNyctiphanes australis (G. O. Sars, 1883) collected from Otago Harbour and coastal waters, New Zealand (45°50S; 170°37E) between October and April 1986–1989: at times up to 50 to 70% of the krill examined were infested. Infestation by epizoic diatoms introduces a significant source of error into determinations of egestion rates using gut fluorescence of whole individuals, and prevents measurement of background fluorescence in krill. Diatom infestation can lead to overestimation of ingestion rates by a factor of 2 to 5. We suggest that investigators using the gut fluorescence method to measure grazing rates should determine the occurrence of epizoic diatoms in samples prior to analysis. If diatoms are present, it is necessary to hold krill in the laboratory until diatoms are shed at moult before makingin vitro gut-pigment measurements. Alternatively, the stomachs must be dissected for analyses, negating the benefits of rapid sample preparation and quantitative recovery of pigments that are the advantage of the technique. Epizoic diatoms can significantly contribute to variability of apparentin situ ingestion rates inN. australis.     

Ultrastructure of the gonad and gametogenesis in the eastern oyster,Crassostrea virginica. II. Testis and spermatogenesis

The pelagic harpacticoid copepod, Macrosetella gracilis (A. Scott), is found in association with colonies of the nitrogen-fixing (diazotrophic), bloomforming cyanobacterium Trichodesmium spp. in tropical and subtropical waters. M. gracilis is one of the few direct grazers of these often toxic cyanobacteria. Experiments investigating NH ₊ ⁴ regeneration by M. gracilis were conducted in the Caribbean in September 1992 and the Coral Sea, Australia in November 1994. Rates of M. gracilis ingestion of Trichodesmium thiebautii labelled with ¹⁵N₂ measured in the eastern Caribbean indicated that M. gracilis could consume 33 to 45% of total T. thiebautii colony N d^-1 and >100% of new N fixed d^-1. We also measured the release of NH ₊ ⁴ by M. gracilis feeding on T. thiebautii, as well as by non-feeding copepods, using ¹⁵N isotope dilution methods. In non-feeding copepods, rates of NH ₊ ⁴ release increased as numbers of copepods were increased as both copepod numbers and food availability increased. In the presence of T. thiebautii colonies, M. gracilis had an average rate of NH ₊ ⁴ regeneration of 7.7±1.5 nmol N copepod^-1 h^-1 (±SE), which was significantly higher than when food was absent (1.9±0.7 nmol N copepod^-1 h^-1). Rates of M. gracilis excretion were relatively high based on excretion: ingestion ratios, which could be due to having a high-N food source readily available, to sloppy-feeding effects, or as a response to toxins in the cyanobacterium. Incubations of M. gracilis with and without T. erythraeum resulted in significant increases in [NH ₊ ⁴ ] as a function of copepod density only. Ammonium leakage from the cyanobacterium and/or microheterotroph associates was relatively low. M. gracilis, through excretion and possible mechanical breakage of cells while grazing, appears to provide a direct link between atmospherically derived new nitrogen and regenerated NH ₊ ⁴ in the oligotrophic systems where Trichodesmium spp. are abundant.     

Larval distribution and reproductive ecology of Thysanoessa macrura (Crustacea: Euphausiacea) in the Scotia Sea

In the Scotia Sea, the larvae of Thysanoessa macrura G.O. Sars, 1885 were scarce in spring (September 27 to October 6, 1971) and mainly present at the Calyptopis I stage, while in summer (December 17, 1974 to January 3, 1975) they were much more abundant and much further developed (up to Furcilia VI). The spawning season commences as early as September and, as indicated by the presence of numerous nauplii and metanauplii in summer, is rather long. T. macrura begins to spawn much earlier in West-Wind-Drift waters than in waters of the Weddell Sea. It starts to spawn simultaneously with Euphausia frigida and E. triacantha, but significantly earlier than E. superba. These timings of the breeding process are related to differential biogeographical characteristics of these species. Plankton collections made at depths of 500 or 1000 m have, for T. macrura, revealed a developmental ascent analogous to that of E. superba. Ontogenetical deep-water migrations are, consequently, characteristic not only for E. superba, but also for other Antarctic euphausiids (in particular E. frigida, but possibly not for inshore E. crystallorophias) and, as correctly postulated by several other investigators, for all oceanic euphausiid species.     

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.     

Dietary constraints on reproductive periodicity in two sympatric deep-sea astropectinid seastars

Examination of the diet of two sympatric species of seastar, Bathybiaster vexillifer and Plutonaster bifrons from 2200 m depth in the Rockall Trough, NE Atlantic Ocean (57°18'N; 10°28'W), suggested that diet may determine the different reproductive patterns found between these two species. In the non-seasonally breeding B. vexillifier, the diet showed a high Shannon-Wiener prey diversity index, the dominant prey being the irregular echinoid Hemiaster expergitus together with a variety of prosobranch gastropods and protobranch bivalves. By contrast, the prey diversity in the seasonally breeding P. bifrons was significantly lower than that of B. vexillifer. In addition, organic carbon content in the sediment residue in the stomachs of P. bifrons displayed a seasonal cycle, while no such seasonality was detected in B. vexillifer. The stomachs of P. bifrons also contained a higher proportion of scavenged material, including the seasonally available remains of mesopelagic blue whiting. These data, together with Bathysnap (time-lapse camera) observations of feeding behaviour in both species, suggest that B. vexillifer is a predator feeding deep in the sediment, whereas P. bifrons feeds close to the sediment surface where it is affected by the seasonal availability of phytodetritus and fish carcasses.     

Functional feeding morphology of the euphausiid Nyctiphanes australis

The structure of the feeding basket, mandible and stomach armature of the krill Nyctiphanes australis (G. O. Sars, 1883) was examined by scanning electron microscope with the aim of predicting its diet. N. australis were collected during February 1986 and October 1986 to February 1987 in Otago Harbour, New Zealand (45° 50 S; 170° 37 E). Predictions based on the functional morphology were tested by examining stomach contents with SEM. Intersetule distances of the feeding basket (1 to 7.5 m) are finer than in other krill species, suggesting that N. australis can efficiently collect nanoplankton-sized particles (2 to 20 m). The mandibular edge index (0.74) matched the edge index of Meganyctiphanes norvegica. This indicates, in contrast to the fine feeding-basket setulation, that N. australis has a mandible resembling that of predominantly carnivorous krill species. The ratio of mandibular palp length to mandible width is 3.2±0.2, or relatively longer than the elongate palp thought to be indicative of herbivorous habit in Euphausia superba. The fine structure of the molar shows specialized surfaces which differ from those of other krill species. The internal armature of the stomach is heavily spinose, as is common in krill of herbivorous habit. Layers of various-shaped spines at differing densities were observed. The functional morphology suggests that N. australis is an opportunistic omnivore. The stomach contents tentatively support this prediction, containing fragments of phytoplankton and detrital material. However, stomach contents were generally amorphous, making identification of dietary components in the field difficult.     

The influence of irradiance on the biochemical composition of three phytoplankton species and their nutritional value for larvae of the Pacific Oyster (Crassostrea gigas)

Three species of phytoplankton grown at high (HL) or low light (LL) were fed as saturating rations to laboratory-reared larval Crassostrea gigas. Larval C. gigas fed diets of HL grown Chaetoceros gracilis and HL grown Isochrysis aff. galbana grew faster than those fed LL grown cells of the same phytoplankton species. Faster growth of C. gigas larvae was consistently associated with increases in the percent composition of short chain saturated fatty acids (FA) 14:0+16:0 in the HL grown cells. There were no consistent and significant differences between HL and LL grown phytoplankton cells in their content of carbon, nitrogen, protein, lipid or carbohydrate. Intraspecific increases in percent composition of essential fatty acids (EFAs), 20:53 and 22:63, in the phytoplankton were not associated with improvements in the growth or survival of the oyster larvae. Oyster larvae fed diets of Phaeodactylum tricornutum with a relatively high proportion of EFAs grew more slowly than those fed C. gracilis. In this experiment the proportion of dietary EFA 20:53 was negatively correlated with oyster growth rates. The faster growing oyster larvae contained relatively more of the FAs 14:0+16:0 which may be useful as measures of larval oyster condition. After a diet of one phytoplankton species for ca. 10 d, oyster larvae acquired distinctive FA profiles resembling that of their phytoplankton prey.     

Hydrolytic enzymes in the two North Sea ctenophores Pleurobrachia pileus and Beroe gracilis

Hydrolytic enzyme activities were determined in tissue extracts of the two North Sea ctenophores Pleurobrachia pileus and Beroe gracilis. The following activities were measured in field samples and characterized according to their mean specific activities and their pH optima: protease, aminopeptidase, amylase, N-acetylglucosaminidase, -glucosidase, chitinase, carboxylesterase, phosphatase. Many of the enzyme activities are correlated, indicating their control by the same factors (i.e. nutritional conditions). Differences found between the phosphatase activities and the apparent lack of the chitinolytic system in B. gracilis reflect the differences in body composition and food specialization in both ctenophores, respectively. The low amylase and -glucosidase activities in both ctenophores agree with the low carbohydrate content of their prey. In spite of high carboxylesterase activities, no lipolytic activity was detected in either of the ctenophores. In a laboratory feeding experiment with P. pileus, the enzyme activities increased but did not reach the activities found in the field samples. In B. gracilis, seasonal variations of some enzyme activities are discussed in relation to the seasonal abundance of its prey, P. pileus.     

Growth,production and ecological significance of Ophiura albida and O. ophiura (Echinodermata: Ophiuroidea) in the German Bight

Growth and production of the shallow-water ophiuroids Ophiura albida and O. ophiura were investigated at two stations in the German Bight from 1988 to 1991. Growth rings visible on the vertebral ossicles of the ophiuroid arms were interpreted as annual age markers. A correction for overgrown first rings allows for more exact estimations of growth and age. In both species growth could be described by Von Bertalanffy growth functions with the asymptotic disc diameter D =10.1 mm, K=0.229 and t _o=-0.192 in O. albida and D =27.7 mm, K=0.084 and t _o=0.042 in O. ophiura. Somatic production was calculated from mass specific growth rates. Annual production:biomass (P:B) ratios were estimated at 0.32 for O. albida and 0.43 for O. ophiura.AWI Publication Number: 618     

Juvenile growth of the polychaete Nereis virens feeding on a range of marine vascular and macroalgal plant sources

A laboratory experiment was conducted to examine variation of juvenile growth (% d^-1) of the polychaete Nereis virens (Sars) in relation to tidal flat plant species as food sources. We used vegetable materials (algae and vascular plants) which are carried along by tidal currents and are found abundantly at the upper tidal level. Juveniles (2-yr-old) markedly increased in wet weight with the algae Laminaria longicruris (weight-specific growth rate : 1.7% d^-1) and Enteromorpha intestinalis (: 1.6% d^-1) as food sources. A higher value of assimilation efficiency was observed for algal species (L. longicruris 55.1±7.9%; E. intestinalis 54.8±0.5%; Fucus vesiculosus 40.6%) than for marine vascular plants (Spartina alterniflora 26.8±10.9%; Zostera marina 1.4%). The digestion of marine vascular species lasts longer (19 to 38 h) than that of algal species. All these characteristics (growth, assimilation efficiency and duration of the digestive process) seem to correlate positively with lignin and cellulose concentrations in the plant structure.