Occurrence of the semi-catadromous European eel Anguilla anguilla in the Baltic Sea

Strontium (Sr) and calcium (Ca) contents in the otoliths of yellow and silver European eels [Anguilla anguilla (L.)] collected from coastal waters of the Baltic Sea and a freshwater lake in Sweden were examined by wavelength dispersive X-ray spectrometry with an electron microprobe. The mean Sr/Ca ratios from elver check to otolith edge were significantly higher for the eels from coastal waters (5.39 ± 1.09‰) than for those from the lake (0.71 ± 0.89‰). The evidence indicates that European eels in the Baltic Sea do not necessarily migrate into freshwater streams during the growth phase. Received: 30 September 1999 / Accepted: 6 April 2000     

Elevated salinity and isotopic composition of fish otolith carbonate: stock delineation of pink snapper, <Emphasis Type="Italic">Pagrus auratus</Emphasis>, in Shark Bay,Western Australia

Analysis of stable isotopes of oxygen and carbon in the otolith carbonate of pink snapper, Pagrus auratus, from several locations in Shark Bay, Western Australia, indicated that snapper are highly location specific. The hypersaline (36 to >60‰) Shark Bay, on the coast of Western Australia, generated strongly characteristic isotopic signatures in the otolith carbonate of snapper collected from the various locations indicating low levels of individual movement of the species. Oxygen isotopes showed enrichment in ¹⁸O in otolith carbonate with salinity (0.10: Δ δ¹⁸O/Δ salinity ‰) typical for the evaporation of seawater. The enrichment in ¹³C (up to 1.75‰) was attributed to the incorporation of metabolically derived CO₂ from an enrichment of ¹³C in the food web within Shark Bay. This was possibly a result of lower concentrations of dissolved CO₂ with increasing salinity causing a reduction in isotope fractionation during photosynthesis. Results complement recent genetic and tagging studies and provide further evidence of the complex nature of snapper stock structure in the Shark Bay region. Published online: 17 July 2002     

Validation of otolith growth-increment periodicity in tropical gobies

 We assessed the efficacy of tetracycline, calcein and strontium chloride for validating the periodicity of otolith growth-increments in eight species of tropical marine gobies (family Gobiidae). We compared the number of fishes in which the otoliths were successfully marked when each of these chemicals was administered by intraperitoneal injection or immersion bath at a range of doses and immersion times. All three chemicals could produce a detectable mark in the otoliths of five reef-flat gobies, Asterropteryx semipunctatus, Amblygobius bynoensis, Istigobius goldmanni, Valenciennea muralis and Amblygobius phalaena; however, tetracycline injection at 50 mg kg⁻¹ is recommended because it produced a brighter otolith mark than calcein and is cheaper and quicker to detect than strontium chloride. Calcein immersion treatment of 125 mg l⁻¹ for 24 h was the most successful treatment for two estuarine gobiids, Favonigobius reichei and Glossogobius biocellatus. No treatment produced a detectable mark in the otoliths of the coral-dwelling goby Gobiodon histrio. Adequate care in the preparation of otoliths was found to be essential for detection of the validation mark produced by tetracycline and calcein. Otolith growth-increments were deposited daily in the seven species of goby for which validation was possible. Received: 15 October 1999 / Accepted: 15 June 2000     

Comparison of somatic growth and otolith increment growth in laboratory-reared larvae of Pacific saury, Cololabis saira, under different temperature conditions

The relationship between somatic growth and incremental growth of otoliths of Pacific saury, Cololabis saira (Brevoort), larvae under different temperature conditions was studied in the laboratory for three age groups (0 to 9, 10 to 20 and 20 to 30 d posthatch). Larvae were incubated from hatching to 9 d at 24, 20, and 16 °C. Further, larvae initially reared at an ambient temperature of 21.7 °C were transferred to experimental temperatures of 22, 18, and 14 °C on Day 10 and reared to Day 20 and similarly from Day 20 and reared to Day 30 posthatch. Growth trajectories of larvae sampled at the end of the three experiments were back-calculated using the biological intercept method and compared to the measured values 0 and 5 d after the start of each experiment. Back-calculated knob length at the different temperatures indicated no significant difference to the measured knob lengths except for the cases at 20 °C from hatching to 9-d-old larvae and at 14 °C from 20- to 30-d-old larvae. The close correlation between somatic and otolith growth shown in this study indicated the feasibility of estimating the growth history of Pacific saury larvae using otolith readings. Received: 14 April 1999 / Accepted: 27 October 1999     

Diet induced differences in carbon isotope fractionation between sirenians and terrestrial ungulates

Carbon isotope differences (Δ¹³C) between bioapatite and diet, collagen and diet, and bioapatite and collagen were calculated for four species of sirenians, Dugong dugon (Müller), Trichechus manatus (Linnaeus), Trichechus inunguis (Natterer), and the extinct Hydrodamalis gigas (Zimmerman). Bone and tooth samples were taken from archived materials collected from populations during the mid eighteenth century (H. gigas), between 1978 and 1984 (T. manatus, T. inunguis), and between 1997 and 1999 (D. dugon). Mean Δ¹³C values were compared with those for terrestrial ungulates, carnivores, and six species of carnivorous marine mammals (cetaceans = 1; pinnipeds = 4; mustelids = 1). Significant differences in mean δ¹³C values among species for all tissue types were detected that separated species or populations foraging on freshwater plants or attached marine macroalgae (δ¹³C values < −6‰; Δ¹³C_{bioapatite–diet} ∼14‰) from those feeding on marine seagrasses (δ¹³C values > −4‰; Δ¹³C_{bioapatite–diet} ∼11‰). Likewise, Δ¹³C_{bioapatite–collagen} values for freshwater and algal-foraging species (∼7‰) were greater than those for seagrass-foraging species (∼5‰). Variation in Δ¹³C values calculated between tissues and between tissues and diet among species may relate to the nutritional composition of a species’ diet and the extent and type of microbial fermentation that occurs during digestion of different types of plants. These results highlight the complications that can arise when making dietary interpretations without having first determined species-specific Δ¹³C_{tissue–diet} values. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Confirmation of longevity in Sebastes diploproa (Pisces: Scorpaenidae) from 210Pb/226Ra measurements in otoliths

Fish ages are often estimated by assuming an annual frequency of the band-like, growth-zones recorded in the largest of their otoliths, the sagittae. The total number of growth-zones are normally determined either by counting external growth-zones (whole otolith technique) or by examining otolith cross-sections (otolith section technique). The two techniques do not always yield the same age, however, particularly in older specimens of certain fishes. To resolve this problem, otoliths of the splitnose rockfish Sebastes diploproa were examined morphologically and were assayed for their natural radionuclide concentrations. Four age groups of otoliths were identified based on growth-zone counting; in the first three, whole otolith and otolith section age estimates agreed, while in the fourth, the otolith section age substantially exceeded the whole otolith age. Radiometric analysis demonstrated that all otoliths were deficient in ²¹⁰Pb activity relative to ²²⁶Ra activity with the deficiency decreasing with increasing number of growth-zones. The magnitude of the ²¹⁰Pb/²²⁶Ra radioactive disequilibrium in each otolith group, when compared to the number of growth-zones and the otolith weight histories derived with the two techniques, identifies the growth-zones revealed by otolith sections as annual features. Thus when otolith section age exceeds whole otolith age (usually occurring after 20 to 25 yr of age for this species), the otolith section technique is the correct method of age determination. Estimates of longevity in the genus Sebastes near 80 yr are therefore confirmed.     

Effects of specimen handling and otolith preparation on concentration of elements in fish otoliths

The use of otolith chemistry as a tool for analysing the biology of fishes assumes that the procedures used to collect and prepare otoliths for analysis do not alter their composition. With otoliths of Nemadactylus macropterus, Hoplostethus atlanticus, and Rhombosolea tapirina, we show that this assumption is not valid for the elements that can be detected using electron-probe microanalysers (those present at concentrations greater than ≃100 parts per million): all six elements routinely measured using these techniques were affected by at least one post-mortem procedure tested. Measured concentrations of calcium and strontium were relatively insensitive to most procedures tested, whereas concentrations of sodium, potassium, sulphur and chlorine were affected substantially by many commonly used procedures. The ease with which otolith composition could be modified post-mortem suggests that apparent geographic, habitat-specific or ontogenetic differences in otolith composition should be interpreted with extreme caution because of easily induced artefacts and the problem of pseudo-replication associated with the ways otoliths are sampled and prepared for analysis. Received: 23 September 1996 / Accepted: 11 April 1998     

Variation in concentrations of trace elements in otoliths and eye lenses of a temperate reef fish, Parma microlepis, as a function of depth, spatial scale, and age

 Territorial Parma microlepis (Günther) (Pomacentridae) were collected at different depths, at three sites in each of four estuaries near Sydney, Australia. Element concentrations were measured by induc- tively-coupled–plasma mass spectrometry. Significant differences in concentrations of Mn and Ba were found in the otoliths of fish sampled in different depth strata, with concentrations generally greatest in fish found in water <4 m deep. Depth-related differences varied among estuaries (e.g. 0 to 1.2 μg Ba g⁻¹ otolith). In most estuaries there was a negative linear relationship between concentrations of Mn and Ba in otoliths and actual depth. Great variation was found within an estuary among sites separated by 0.5 to 3 km. In the eye lenses, concentrations of Rb differed according to depth of capture of fish. The age of fish (1+ to 34 yr) had no influence on the concentrations of elements in otoliths or lenses. Multivariate comparisons of elemental composition (= fingerprints) detected significant differences among depth strata. Fish collected from shallow water had the clearest multivariate classification according to depth. There was a close match between our shallow strata and the average depths reached by low-salinity/high-temperature estuarine plumes. The element composition of whole otoliths and lenses represents average concentrations experienced by the fish. The temporal resolution of differences in ambient conditions is likely to be coarse in the fish (i.e. months to years). Received: 9 April 1999 / Accepted: 29 February 2000     

Early life history and recruitment of the tropical eel Anguilla bicolor pacifica, as revealed by otolith microstructure and microchemistry

Otolith microstructure and microchemistry of the tropical eel Anguilla bicolor pacifica Schmidt were examined in glass eels collected at the mouth of the Dumoga River, North Sulawesi Island, Indonesia. Ages of the glass eels examined (age at recruitment) ranged from 124 to 202 d (167 ± 19.3 d; mean ± SD), hatching being estimated as having occurred between November 1995 and March 1996. Otolith increment widths markedly increased from age 101 to 172 d (135 ± 18.2 d; mean ± SD), coincident with a drastic decrease in otolith Sr:Ca ratios, suggesting that metamorphosis began during that period. The duration of metamorphosis was estimated as 20 to 40 d, on the basis of otolith microstructural characteristics. The fluctuation patterns in otolith increment widths and Sr:Ca ratios were similar to those of the temperate Japanese eel A. japonica. Received: 20 May 1998 / Accepted: 7 October 1998     

Habitat and age of the giant squid (<Emphasis Type="Italic">Architeuthis sanctipauli</Emphasis>) inferred from isotopic analyses

The age and habitat of the giant squid, Architeuthis sanctipauli Velain, 1877, were determined based on isotopic analyses of the statoliths of three female specimens captured off Tasmania, Australia, between January and March 1996. Assuming that the aragonite of the statoliths formed in equilibrium with seawater, ¹⁸O analyses indicated that the squid lived at temperatures of 10.5–12.9°C, corresponding to average depths of 125–250 m and maximum depths of 500 m. The capture records indicated that these squid may have occasionally ranged still deeper, to as much as 1000 m. All the statoliths were labeled with bomb ¹⁴C (¹⁴C=+22.9 to +44.6), consistent with the depths inferred from ¹⁸O. A thin section through one of the statoliths revealed 351 growth increments grouped into check-ring structures every 10–16 increments. A model for statolith growth and the pattern of temporal change in ¹⁴C in the water column was used to estimate the ages of the three specimens. These estimates were very sensitive to the choice of depth range over which ¹⁴C values were integrated. Assuming that the capture depths represented the maximum habitat depths of these individuals, the calculations suggested an age of 14 years or less. More refined age estimates require a better understanding of the variation of ¹⁴C and temperature with depth in the areas in which the squids live.Communicated by J.P. Grassle, New Brunswick     

Resting spore formation of the marine planktonic diatom Chaetoceros anastomosans induced by high salinity and nitrogen depletion

The marine planktonic diatom Chaetoceros anastomosans, which was isolated from Sagami Bay, was used for a study of resting spore formation mechanisms in batch culture experiments. Vegetative cells could grow at salinities ranging from 20.7 to 45.5‰, and resting spore formation was enhanced significantly in nitrate-depleted, high salinity media (40.0 to 45.5‰). The rate of resting spore formation (1.9 d⁻¹) was comparable to the specific growth rate (1.8 d⁻¹) of vegetative cells in the exponential growth phase in normal salinity medium. The size of resting spores formed under high salinity conditions was smaller than that of spores formed in normal salinity media. Unlike vegetative cells, resting spores seemed to possess some mechanisms to survive over a wider range of salinities by resisting bacterial attacks on their cell walls. Received: 4 August 1996 / Accepted: 27 August 1996     

Control of populations of the coral-feeding nudibranch Phestilla sibogae by fish and crustacean predators

Juvenile lesser blue crabs, Callinectes similis Williams, were exposed to a range of salinities for measurement of survival and bioenergetics. Effects of salinity on survival were determined by exposing juvenile crabs to salinity treatments ranging from 0 to 74‰. All crabs survived 21 d of exposure to 5 and 45‰S. The 21 d LC₅₀ values for salinity tolerance (calculated from survival data) were 2.6 and 60.8‰S at low and high salinities, respectively. Energy-budget components and scope for growth were determined for crabs exposed to 2.5, 10, 25, 35 and 50‰S. Energetic absorption rates were highest at 2.5 and 35‰S. Energetic expenditure rates (energy lost to respiration and excretion) were greatest at 2.5‰S, and decreased as salinity increased. Respiration constituted the majority of energetic expenditure at all salinities (92.3% average). Scope for growth was significantly affected by salinity and was highest in crabs exposed to 35‰S. Increased respiration at low salinity may indicate that C. similis incurs greater costs due to osmoregulation. The results of this study indicate that C. similis is capable of surviving and growing in waters with salinities as low as 10‰. Received: 10 January 1997 / Accepted: 11 February 1997     

Reproduction in the seagrass Zostera novazelandica on intertidal platforms in southern New Zealand

This study investigates the reproductive periodicity and reproductive output of the seagrass Zostera novazelandica on two intertidal reefs. Peak numbers of flowering shoots occurred during March (late summer) of two years at both sites and no flowering shoots occurred during the winter months of July to September. There were greater numbers of flowering shoots in seagrass patches in the low intertidal zone (up to an average of 55 per 0.1 m²) compared to the middle (up to 20 per 0.1 m²) and upper (up to 9 per 0.1 m²) zones, and about three times greater reproductive output in patches associated with tidepools compared to those not bordering tidepools. The average number of inflorescences per shoot was 3.1 (±0.25) at one site vs 1.2 (±0.08) at the other, and showed a progressive decrease from the lower shore to the upper shore. Patches associated with tidepools had twice the number of inflorescences per shoot (2.8 ± 0.24) than patches not bordering tidepools (1.5 ± 0.16). The number of flowering shoots was highly correlated with leaf width, leaf length, and ramet density, while the leaf-area index decreased from the lower shore to the upper shore. The reproductive effort of plants, as measured by the percent biomass invested in flowering shoots during peak reproduction, was significantly different between sites, tidepool associations, and shore level. For all the variables measured, there was considerable spatial variation, with significant interaction terms between most factors investigated. In laboratory experiments, more inflorescences were produced at light intensities of 30 and 300 μE m⁻² s⁻¹ than at 100 μE m⁻² s⁻¹. At a salinity of 17‰, 1.5 × the number of flowers was produced than at 33‰, while none was formed at 70‰. Plants cultured at 5 °C had about three times the number of inflorescences than those at 15 °C, while none was formed at 25 °C. Received: 25 June 1997 / Accepted: 24 September 1997     

Otolith record of age, growth, and ontogeny in larval and pelagic juvenile Stephanolepishispidus (Pisces: Monacanthidae)

Juveniles of the planehead filefish Stephano-lepishispidus (Pisces: Monacanthidae) (Linnaeus, 1766) are a major component of the Sargassum spp. community, yet little is known of their ecology. In this study, the otolith record of age, growth, and ontogeny in S. hispidus was examined. Juveniles caught off Beaufort Inlet, North Carolina (USA) on 30 June 1996 were marked with alizarin complexone and reared in a flow-through, outdoor tank for up to 19 days. Examination of marked otoliths at several time intervals showed that increment formation was not significantly different than one increment per day, and thus, increment number was used to estimate age. Depth-distribution, morphology, and meristics of larvae and juveniles collected (1990–1992) between Cape Romain, South Carolina, and Cape Hatteras, North Carolina, were examined to identify the timing of the larval to juvenile transition. All indicators suggested the transition occurred between 17 and 20 days. Mean otolith increment widths exhibited a marked change at about 20 days, coinciding with the timing of the larval to juvenile transition and a change in the depth distribution from bottom to surface waters. Increment width of individual juveniles, however, did not exhibit the same pattern; only 40% conformed to the pattern identified for all fish. Thus, the record of the larval to juvenile transition is clear at the population level, but unresolved at the individual level. Received: 1 November 1999 / Accepted: 18 December 2000     

Validation of age determination from otoliths of the King George whiting Sillaginodes punctata (Perciformes)

The otoliths of the King George whiting Sillaginodes punctata were assessed for their usefulness in adult-ageing. Whole, transverse-sectioned and broken/burnt sagittae displayed alternating opaque and translucent zones. Some small whole otoliths contained accessory areas of pigment, whilst large otoliths were too thick to transmit light, resulting in ambiguous counts in each case. Both marginal-increment analysis and treatment of fish with tetracycline demonstrated that the first three opaque zones formed annually, the first during the spring/summer of the second year of life, and the second and third in each subsequent spring. Otolith thickness increased linearly with the completion of each new opaque/translucent zone. An ageing protocol based on whole otoliths, supplemented with the breaking/burning of ambiguous otoliths is recommended. An algorithm for calculating age in months from otolith counts based on a fixed birth-date of the mid-point of the spawning season is presented. Received: 18 August 1997 / Accepted: 15 October 1997     

Use of otoliths and eye lenses for measuring trace-metal incorporation in fishes: a biogeographic study

The otoliths and lenses of the temperate damselfish Parma microlepis (Günther) (Pomacentridae) showed similar differences in trace-metal profile for selected locations along the coast of New South Wales, Australia. Otoliths and lenses displayed a differential ability to accumulate metals. Metal concentrations were ranked differently in the two structures (e.g. Sr > Ba > Pb > Rb > Hg in otoliths, and Hg > Sr ≃ Rb > Pb > Ba in lenses), and where similar metals were accumulated, they were accumulated at vastly different concentrations (e.g. Ba concentrations in otoliths are a thousand-fold greater than in lenses). Analyses of the otoliths and lenses of P. microlepis from locations close to Sydney and up to 100 km from the city were able to distinguish amongst these locations with respect to a number of metals, namely Ba, Mn and Hg. Multivariate analyses of otolith and lens data gave similar results among locations (agreement was obtained for 11 out of 15 pair-wise comparisons), and differences were attributable to the differential ability of the two structures to accumulate metals such as Mn and Hg. Trace-metal differences between locations were found to coincide with the proximity of sewage (including industrial waste) and petroleum storage facilities to the different locations. Received: 23 June 1997 / Accepted: 4 August 1997     

Validation of daily increment deposition in otoliths. Age and growth determination of Aphia minuta (Pisces: Gobiidae) from the northwest Mediterranean

The transparent goby Aphia minuta (Risso, 1810) is one of the main target species of the small-scale fishery off the Island of Majorca. Otolith microstructure and length-frequency analysis were used to study the age and growth of this species during the 1982/1983 and 1992/1993 fishing seasons. Daily periodicity of increment formation was determined by experiments with marked otoliths in individuals maintained in captivity. The length range of the catches during the 11 yr period was between 12 and 49 mm, with a main distribution (89%) between 24 and 40 mm. Otolith age-readings indicate that the population exploited in the commercial fishery consists of seven age-groups (2 to 8 mo old), with a very high proportion of individuals (95%) between 3 and 6 mo old. Population growth-curves revealed no differences between males and females. The growth parameters for the whole population are: asymptotic length, L _∞ = 53.69 mm; growth coefficient, K = 2.23 yr⁻¹; theoretical age at length zero, t ₀ = −0.005 yr. Those individuals of A. minuta caught in Majorca during the winter period reached a maximum age of 7 or 8 mo. Received: 30 December 1996 / Accepted: 16 April 1997     

Resource acquisition in two intertidal fucoid seaweeds, Fucus serratus and Himanthalia elongata : seasonal variation and effects of reproductive development

Seasonal variations and the effect of reproductive development on resource acquisition by two intertidal fucoid species, the iteroparous Fucus serratus L. and the semelparous Himanthalia elongata (L.) S. F. Gray were examined. The oxygen-exchange characteristics of vegetative apical tissue of both non-fertile and fertile plants and receptacle tissue were compared at monthly intervals throughout reproductive development. Respiratory rates in non-fertile F. serratus varied seasonally between 1.5 and 8.0 μmol g⁻¹ fresh wt h⁻¹; in fertile plants the receptacle had a significantly lower respiratory rate than the vegetative tissue. The respiratory rate of the vegetative button of fertile H. elongata displayed less seasonal variation and was lower than that of the receptacle, which varied from a maximum of 9.5 μmol g⁻¹ fresh wt h⁻¹ at receptacle initiation in October to a minimum of 2.0 μmol g⁻¹ fresh wt h⁻¹ in February. The maximum photosynthetic rate (P _max) of non-fertile plants of both species did not vary in a distinct seasonal manner (∼60 μmol g⁻¹ fresh wt h⁻¹ for F. serratus and ∼12 μmol g⁻¹ fresh wt h⁻¹ for H. elongata). In fertile plants, the P _max of the receptacle tissue was (∼50% lower in F. serratus, and at its peak three times higher in H. elongata, than that of vegetative tissue. The stable carbon-isotope ratio (δ¹³C) did not differ between different tissue types in F. serratus, but values did vary seasonally, being less negative in the summer than in the winter (−13.5‰ compared to −18‰). The receptacle tissue of H. elongata also displayed a distinct seasonal variation in δ¹³C values (−12‰ in summer, −16‰ in winter), whilst the δ¹³C of the vegetative button did not vary seasonally. The rate of uptake of inorganic nitrogen by the vegetative thallus was lower in H. elongata than in F. serratus. The receptacle tissue of F. serratus had lower uptake rates than the vegetative tissue, whilst the uptake rate by H. elongata receptacle tissue was higher than that of the vegetative button. Received: 14 March 1997 / Accepted: 22 April 1997     

Asymptotic growth trajectories of larval sardine (Sardinops melanostictus ) in the coastal waters off western Japan

Growth trajectories of individual larvae of Japanese sardine, Sardinops melanostictus, caught in the coastal waters off western Japan were back-calculated from the first feeding stage up to date of capture (approximate size of 20 to 35 mm total length; TL) based on individually determined allometric relationships between otolith daily ring radii and fish total lengths. The larvae in January-, February-, and March-hatched cohorts in the coastal waters grew faster and more uniformly than those in the oceanic waters offshore of the Kuroshio current. Growth trajectories of the three hatch-month cohorts were similar and could be expressed by the Gompertz model. The inflection points of the growth curves were reached at 9 to 11 d after hatching, when larvae were 10.8 to 11.8 mm TL. Maximum growth rates at these points were 0.80 to 0.85 mm d⁻¹. Growth rates gradually declined after the inflection points, and larval TLs converged into the infinite length of 29 to 32 mm, the sizes at which metamorphosis from larvae to juveniles is initiated. This asymptotic growth pattern in the larval stage resulted in the narrow ranges in TLs in spite of the wide range of ages of the larvae caught by boat seiners in the coastal waters. Slow growth and therefore long duration of the metamorphosing stage could be influential in determining the cumulative total mortality in the early life stages of the Japanese sardine. Received: 14 July 1996 / Accepted: 20 August 1996     

Trophic ecology of Rimicaris exoculata : a combined lipid abundance/stable isotope approach

The alvinocaridid shrimp Rimicaris exoculata is an abundant component of the biota of Mid-Atlantic Ridge hydrothermal vents. To determine the nutritional strategy of this organism, we analysed the molecular abundance and carbon isotopic composition of its phospholipid fatty acids. High abundances of n-7 fatty acids (>40% total fatty acids) were observed in R. exoculata muscle tissues, in bacterial epibionts scraped from its gill bailers, and from the bacterially infested metal sulphides that the shrimp ingest. The phospholipid fatty acid abundance data indicates that the bacteria in the sulphides are closely related to the bacterial epibiota inhabiting the shrimp gill bailers, carapace and other body parts. Compound specific δ¹³C analyses of the phospholipid fatty acids gave average values of −12‰ for the epibiont bacteria and −21‰ for the sulphide bacteria. This difference may be largely due to the expression of different forms of RuBisCO (Forms I and II) which fractionate against ¹³C to different extents. Carbon limitation within the shrimp epibiont population may be an additional factor. The δ¹³C values (mean = −13‰) of the saturated and monounsaturated fatty acids isolated from the muscle tissues of R. exoculata were very close to those of the epibionts, indicating that the predominant source of dietary carbon for the shrimp is their epibionts, with a lesser contribution from free-living bacteria. The δ¹³C values (−26‰) of shrimp cholesterol were much more negative than those of the fatty acids, and this cholesterol is likely to have derived from the oceanic photic zone. Received: 26 June 1997 / Accepted: 6 November 1998