The “Tsesis” oil spill: Acute and long-term impact on the benthos

The “Tsesis” oil spill in October 1977 resulted in the release of over 1 000 tons of medium grade fuel oil in an archipelago in the brackish Baltic Sea. Considerable oil quantities reached the benthos by sedimentation. Within 16 d benthic amphipods of the genus Pontoporeia, as well as the polychaete Harmothoe sarsi Kinberg, showed reduction to less than 5% of pre-spill biomasses at the most impacted station. The clam Macoma balthica (L.) was more resistant, and showed little or no mortality, but was heavily contaminated by oil (about 2 000 μg g^-1 dry wt total hydrocarbons). The meiofauna was strongly affected, with ostracods, harpacticoids, Turbellaria and kinorhynchs showing clear reductions in abundance, while nematodes, as a group, were more resistant. In the winter following the spill gravid Pontoporeia affinis Lindström females showed a statistically significant increase in the frequency of abnormal or undifferentiated eggs. Food-chain transfer of oil to flounder [Platichthys flesus (L.)] was indicated. Not until the second summer after the spill were the first signs of recovery noted at the most heavily impacted station: Amphipods, H. sarsi and harpacticoids increased and the oil concentrations in M. balthica decreased (to about 1 000 μg g^-1). In the area where amphipods had been virtually eliminated, there was an unusually heavy recruitment of M. balthica, reaching 4 000 juveniles, of 1.5–2 mm length, per square metre, probably from settling in summer 1978. Three years after the spill Pontoporeia spp. biomass was still depressed in the most affected area, while H. sarsi showed normal biomass, and M. balthica abundance was inflated. Oil concentrations in M. balthica (about 250 μg g^-1) and flounder were only slightly elevated and the oil could no longer be confidently ascribed to “Tsesis” origin, even using GC/MS-analysis. Recovery was thus underway, but the long lifespan of M. balthica implies that the disturbed community composition may persist for many years at this station. Full recovery is likely to require more than 5 yr and may take a decade or more. An effort to evaluate the accumulated monetary loss to fishery from the accident indicates that direct costs of shoreline cleanup and vessel damage were considerably greater.     

Cadmium kinetics in oysters — a comparative study of Crassostrea gigas and Ostrea edulis

The accumulation of cadmium was investigated in two species of oysters [Crassostrea gigas (L.) and Ostrea edulis (L.)] from the same environment and in oysters of the same species (O. edulis) from two different environments (contaminated and uncontaminated), under controlled laboratory conditions (33‰ salinity, 10°C, 100 μg Cd l^-1) for up to 111 d in 1982. C. gigas accumulated cadmium twice as fast as O. edulis (1.07 vs 0.52 μg Cd g^-1 wet wt d^-1). Furthermore, O. edulis from an uncontaminated environment accumulated cadmium faster than O. edulis from a metal-contaminated environment (0.52 vs 0.34 μg Cd g^-1 wet wt d^-1). There was no effect of cadmium exposure on total soft-tissue copper and zinc concentrations. Investigation of cytosolic metal-binding using Sephadex G-75 gel-permeation chromatography indicated that binding to very low molecular weight ligands (MW<1000) accounted for>70% of the cytosolic zinc in all oysters and>40% of the cytosolic cadmium in all oysters except O. edulis from Conwy at 83 d. In copper-contaminated oysters, excess copper was also associated with very low molecular weight ligands. Intermediate molecular weight cadmium/copper-binding proteins (similar to metallothionein in molecular weight) were observed in the cytosol and were shown to differ between species in terms of their behavior on Sephadex G-75. Finally, the distribution of accumulated cytosolic cadmium in O. edulis from the contaminated environment was shown to have a unique distribution, i.e., there was no cadmium associated with high molecular weight cytosolic macromolecules. The data indicate that both genetic and environmental factors influence cadmium accumulation in oysters.     

Uptake of L-valine and other amino acids by the polychaete Nereis virens

For valine uptake by the polychaete Nereis virens Sars, the kinetic constants were: V _max=355 nmol g^-1 fresh weight h^-1, K _m=20 M. Leucine and some other amino acids acted as partial inhibitors of valine uptake. Valine uptake rate was 78% higher at 21.5 S than at 14 S. The major portion of valine absorbed by the polychaete could be extracted as free valine, with 6.5 to 15.6% being respired, and 3.6 to 9.5% incorporated into proteins. Calculations indicate that 7 to 12% of the metabolism of N. virens may be sustained by uptake of glycine and aspartic acid from natural concentrations. It is suggested that uptake of amino acids by this worm is important in the nitrogen cycling of marine sediments.     

Zur physiologie der aminbildung bei der marinen rotalge Polysiphonia urceolata

The ceramiaceaen Polysiphonia urceolata rapidly degrades ¹⁴C(U)-L-leucine, added to sea water at a final concentration of 2.5x10^-5 M/l, to isoamylamine. Under experimental conditions, 22% of the total radioactivity is found in the amine within 160 min. The amino acid decarboxylase responsible for this reaction has been characterized by Hartmann (1972a). No other mechanisms of leucine degradation could be detected, and the rate of ¹⁴C-incorporation into algal proteins is considerably lower than that of decarboxylation. The rate of decarboxylation is optimal at a leucine concentration of about 5x10^-5 M/l. The amine formed is found in almost equal amounts in algal extract and environment. No further degradation of isoamylamine could be detected. The amine is a metabolic end product in P. urceolata. When ¹⁴C-isoamylamine is used as a tracer, relatively high amounts of amine are found in the algal extracts. It is supposed that the amine does not accumulate within the algal cells, but rather is bound to the acid polysaccharides of the cell walls by means of ionic exchange. The results strongly suggest that decarboxylation is the main route by which P. ureolata metabolizes amino acids from the environment which are substrates of the decarboxylase. The endogenous amino acid pool does not seem to be available to the enzyme as a substrate source. A possible ecological significance of amino acid decarboxylations is discussed.     

Exceptionally high concentrations of the insect repellent N,N-diethyl-m-toluamide (DEET) in surface waters from Jakarta,Indonesia

Jakarta is a booming coastal megacity in Indonesia with over 10 million inhabitants. The rivers flowing through the city district receive enormous amounts of untreated wastewaters from households and industries and discharge high pollutant loads into Jakarta Bay. Applying a screening approach for the identification of characteristic site-specific and harmful organic contaminants, we frequently found the insect repellent N,N-diethyl-m-toluamide (DEET) in river water and seawater samples from Jakarta. The compound was previously reported as persistent aquatic contaminant in industrial countries, and we present here the first data set from a tropical megacity. Concentrations in river water and seawater from Jakarta were exceptionally high, up to 24,000 ng L^?1, and exceeded by far all published concentrations in surface waters worldwide. We explained this with massive usage of the compound, lack of wastewater treatment and low average river flow as compared to rivers in other tropical megacities. The usage and properties of DEET indicate its suitability as molecular marker of municipal wastewaters. Such markers are useful to trace emissions from specific pollution sources in aquatic systems as a basis for the investigation of related impacts. We show here that DEET is in particular useful to trace the long-range distribution of municipal wastewaters in tropical freshwater and coastal systems. This application is of great value for tracing such inputs in tropical coastal habitats which are sensitive to changing water quality like coral reefs. This assists to uncover whether specific conditions in these systems could be related to pollutant inputs from land.     

Herbivory and detritivory among gammaridean amphipods from a Florida seagrass community

The gammaridean amphipods Cymadusa compta (Smith), Gammarus mucronatus Say, Melita nitida Smith and Grandidierella bonnieroides Stephensen from a seagrass community in the Indian River estuary of Florida (USA) fed variously upon large drift algae, small algae epiphytic on seagrasses and seagrass leaf debris and detritus. Consumption was measured in the laboratory using an index (CI) equivalent to mg ingested mg^-1 amphipod day^-1. Observations revealed that the amphipods fed by macrophagy, an attack upon large algae and seagrass debris, and by microphagy, small particle detritus feeding and scraping of plant surfaces for diatoms and other epiphytic algae. C. compta was a macrophagous feeder with a generalized diet of algae and seagrass debris, preferring epiphytic algae and drift algae at mean rates of 1.10 and 0.87 CI, respectively. Gammarus mucronatus fed upon epiphytes and seagrass debris equally at mean rates of 0.90 and 0.97 CI, respectively. The diet of M. nitida condisted primarily of epiphytes, consumed at an average rate of 1.05 CI. Grandidierella bonnieroides fed in a specialized microphagous manner, grooming plant surfaces for small particle detritus and diatoms at an approximate CI rate of 1.45. Assimilation of plants ingested, as reflected by carbon-14 uptake, varied similarly among the 4 amphipods. Epiphytic algae appeared to be most useful as food, providing means of 41 to 75% carbon-14 uptake as ingesta. Drift algae and seagrass debris were of less value, with means varying between 11 and 24 % of carbon-14 uptake by the amphipods. The data show a pattern of feeding which resembles resource partitioning of food both by size and kind. Other evidence, however, including population limitation by predators and an apparent overabundance of food, indicate that resource partitioning as seen may be an artifact, and one which has no co-evolutionary basis among the present species.Contribution No. 102 of Harbor Branch Foundation, Inc.     

Feeding by a “nonfeeding” larva: uptake of dissolved amino acids from seawater by lecithotrophic larvae of the gastropod Haliotis rufescens

Larvae of the red abalone (Haliotis rufescens Swainson) are functionally incapable of capturing particulate foods. The aim of this study was to determine whether these larvae could acquire energy from seawater in the form of dissolved organic material. Trochophore and veliger larvae were shown to acquire energy by transporting dissolved organic material from seawater. Both larval stages took up all classes of amino acids tested. The influx of radiolabeled alanine represented the net substrate flux, as determined by direct chemical measurement for both trochophore and veliger larvae. Although veliger larvae have a transport system to take up taurine from seawater, a net efflux was observed for this amino acid. The release of taurine occurred independently of the presence of either taurine or other amino acids in the medium. Transported alanine was used in both anabolic and catabolic pathways. The percent of ¹⁴C-alanine in the trichloroacetic acid-insoluble fraction (macromolecules) of veliger larvae ranged from 21 to 56% of the total radioactivity in the larvae. No lipid biosynthesis was detected from ¹⁴C-labeled alanine. Veliger larvae catabolized 15 to 19% of the total alanine taken up and released it as ¹⁴CO₂. The metabolic rate (oxygen consumption) and the rate of amino acid uptake were both determined for the same group of veliger larvae. The percent contribution that the uptake of amino acids, from a total concentration of 1.6 M, made to the metabolic demand of abalone larvae ranged from 39 to 70%. Thus, these lecithotrophic larvae are not energetically independent of their environment, a result which differs from the current view of energy allocation to nonfeeding larvae.Please address all requests for reprints to Dr. Manahan at the University of Southern California     

Effects of host-tissue homogenate of the scleractinian coral Plesiastrea versipora on glycerol metabolism in isolated symbiotic dinoflagellates

Symbiotic dinoflagellate algae (Symbiodinium sp.) isolated from the scleractinian coral Plesiastrea versipora and incubated in homogenized host tissue released 4 to 7 times as much glycerol (14 to 46 nmol glycerol/10⁶ algae) as those incubated in seawater (3 to 6 nmol glycerol/10⁶ algae) after 4 h incubation in the light. During this period, no release of triglycerides was detected. Intracellular glycerol increased 2- to 3-fold in algae incubated in host homogenate, but remained unchanged in algae incubated in seawater at a concentration of 0.82 ± 0.47 nmol glycerol/10⁶ algae. In each incubation condition, intracellular triglyceride levels increased. However, in algae incubated in host homogenate, the intracellular levels of triglycerides reached only about 75% of the amount reached in algae incubated in seawater (max. 18.55 ± 2.40 nmol glycerol/10⁶ cells). Host homogenate did not stimulate the release of glycerol from algae during dark incubation. These data show that the glycerol released by algae incubated in host-tissue homogenate was derived from increased synthesis of glycerol or from diversion of some glycerol or other photosynthetic intermediates from incorporation into algal triglyceride stores, and did not come from existing stores. Received: 20 December 1996 / Accepted: 9 January 1997     

Photosynthetic acclimation and biochemical responses ofGelidium sesquipedale cultured in chemostats under different qualities of light

The red algaGelidium sesquipedale (Clem.) Born. et Thur. has been cultured in chemostats to assess the effects of light quality and photon-fluence rate (PFR) on growth, photosynthesis and biochemical composition. Plants under blue and red light (BL and RL) showed higher growth rates than under white light (WL) of the same PFR (40 mol m^–2 s^–1). The light-saturated rate of photosynthesis was higher for algae grown under BL and RL than for algae grown under WL. When algae were transferred to WL of moderate PFR (100 mol m^–2 s^–1), the light-saturated rate of photosynthesis decreased, being higher in previously RL-grown algae than in previously BL- and WL-grown algae. The initial slope of photosynthesis-irradiance (PI) curves () was affected by PFR but not by light quality. Pigment content was little affected by light quality. Light-quality treatments also affected the biochemical composition of the alga; previous exposure to various light treatments activate or repress several metabolical pathways that are fully expressed in the subsequent phase of WL of moderate PFR. Thus, phycobiliproteins and soluble proteins increased for previously BL- and RL-grown algae, whereas insoluble carbohydrate concentration was reduced, indicating a change of the C-partitioning between carbon compounds and organic nitrogen compounds. Inorganic nitrogen metabolism was also affected by light: under WL of moderate PFR, NO₃ ^– was totally depleted from sea water, and maximal values of NO₃ ^– uptake were recorded. In addition, neither NO₂ ^– nor NH₄ ⁺ was released. However, when algae were transferred to a low PFR, there was a drastic reduction of NO₃ ^– uptake under WL, which only partially recovered over time. It was accompanied by the release of NO₂ ^–, but not NH₄ ⁺, to the culture medium. Under BL and RL, however, there was a transient enhancement of NO₃ ^– uptake that was followed by a net release of NO₂ ^– and NH₄ ^–. Growth rates were not correlated with PFR. This could be due to the the dynamics of internal carbon mobilization and accumulation in the algae. When algae were exposed to a moderate PFR of WL, carbon requirements for growth were satisfied by photosynthesis. Thus, there was a net accumulation of carbon in the tissue. In contrast, when algae were exposed to low PFRs of either WL, BL or RL, observed growth rates could not be maintained by photosynthesis and carbon was mobilized.     

Nitrate uptake in marine phytoplankton: Energy sources and the interaction with carbon fixation

Field studies of whole natural phytoplankton communities from Knight Inlet, B. C., Canada and laboratory cultures of the diatom Skeletonema costatum indicate inorganic carbon fixation may be temporarily suppressed following 10 to 15% enrichment with NO ₃ ^- or NH ₄ ⁺ . (This effect is suggested to be due to competition between inorganic carbon and nitrogen for adenosine triphosphate (ATP), and is reduced when chlorophyll a is increased intracellularly after 6 to 8 h.) Results imply that the source of ATP for nitrate uptake is primarily from Photosystem I (cyclic photophosphorylation) in the presence of light. It would appear that a transient nutrient-adaptive response occurs upon addition of extracellular nitrogen.     

A mathematical model for the uptake of heavy metals in benthic algae

A mathematical model for the uptake of heavy metals in the benthic algae Ascophyllum nodosum has been developed. The model allows assignment of age-dependent growth parameters which also may be a function of external factors. Mortality curves for A. nodosum corresponding to a highly polluted and a nearly unpolluted area have been used in the study of metal uptake. Uptake has been simulated for different values of growth parameters and different concentrations of heavy metals in seawater. Emphasis has been on the uptake of zinc. The simulations showed that the concentration of zinc in the algae changed much less (6%) than the biomass (30%) with changes in intrinsic growth rate, mortality and carrying capacity.The concentration in the algae was found to be an approximately linear function of the mean concentration in seawater up to about 100 ppb. At very high concentrations, associated with high mortality, the deviation from linearity may be significant (about 13% at 162 ppb at one locality). The calculation indicates further that variations in the zinc concentration in the seawater are considerably damped in the algae.Simulations have also been performed to study the effects of sampling different parts of the algae, and some initial simulations have been performed to study the effects of heavy metal exchange between algae and sea water.     

Distribution of lipopolysaccharide,an indicator of bacterial biomass,in subtropical areas of the sea

Lipopolysaccharide (LPS) concentrations, an indicator of bacterial biomass, were determined in the South China Sea and the Pacific Ocean. The distribution patterns of LPS were compared with those of chlorophyll a (Chl a), zooplankton biomass and the concentrations of several nutrients. LPS and total bacterial numbers in seawater were correlated with each other with a correlation coefficient (r) of 0.84 at Stations 7, 8 and 10. Diurnal fluctuation of LPS was negligible, but Chl a varied slightly in the vertical water column. Zooplankton stayed at a depth of around 400 m during the daytime and ascended quickly to the surface (0–50 m) early in the evening. The profiles of LPS and Chl a were negatively correlated to each other in the water layers above the Chl a maximum peak (r=-0.74; excluding the samples from 75 m at Station 7 and 10 m at Station 11 due to inadequate data for the statistical analysis). LPS and zooplankton biomass during the night-time, in contrast, paralleled each other at 5 stations surveyed (r=0.71). The presence of zooplankton resulted in an increase in bacterial numbers in the seawater in vitro. Based on these results, the factors controlling the occurrence and abundance of bacteria and phyto- and zooplankton in the pelagic sea are discussed.     

Influence of food quantity on the kinetics of cadmium uptake and loss via food and seawater in Mytilus edulis

The difference between the cadmium uptake via food and seawater in Mytilus edulis has been studied. This was done by labelling algae with Cd-109 and seawater with Cd-115m. Mussels were fed on six different quantities of Isochrysis galbana. Cadmium uptake via algae was more efficient at low food levels, while accumulation from seawater was linearly correlated with food quantities. Cadmium from food contributed only little to the body burden (0.2–0.5%). Half-lives for the elimination of cadmium ranged from 96–190 d and increased with decreasing availability of algae, presumably due to slowed down metabolism. Differences in elimination patterns suggest a release of both isotopes from different storage depots. A computer model shows that the food pathway can only play a significant role if algae are highly contaminated. It also demonstrates the paradox that in long-term studies the highest contribution of food-derived cadmium to the body burden must be expected near maintenance food concentrations.     

Uptake and loss of radioactive cadmium by the sea-skater Halobates robustus (Heteroptera: Gerridae)

Sea-skaters, Halobates robustus Barber, caught around the Galápagos Islands, were exposed over a period of 3 days to radioactive cadmium dissolved in seawater. Although ^115mCd (metastable ¹¹⁵Cd) was accumulated by the insects, they did not concentrate it above the seawater level. The experiments clearly showed that cadmium is taken up into the body, not merely adsorbed onto surfaces. The uptake of Cd followed a biphasic time course. When sea-skaters labelled in this way were transferred back into unlabelled seawater, the rate of loss of Cd was likewise biphasic. During uptake and loss, the biological half-life times for the first compartments were almost identical (0.64 and 0.79 h), indicating that the same compartment might be involved. On the other hand, the biological half-life times for the second compartments were different (1.7 days during uptake, 19.5 days during loss), indicating that the site or chemical form of bound Cd in the sea-skater had changed. For an adult female, weighing about 8.5 mg wet weight, the drinking rate of seawater was estimated at 2.5 l day^-1, equivalent to 29% body weight.     

Biological production of nitrite in seawater

The relative importance of 3 different sources for biological production of nitrite in seawater was studied. Decomposition of fecal pellets of the copepod Calanus helgolandicus (at a concentration of approximately 12 g-at N/l), in seawater medium, released small amounts of ammonia over a 6 week period. It nitrifying bacteria were added to the fecal pellets nitrite was barely detectable over the same period. Decomposition of phytoplankton (present at a concentration of about 8 g-at particulate plant N/l) with added heterotrophic bacteria, released moderate amounts of ammonia over a 12 week period. If the ammonia-oxidizing bacterium Nitrosocystis oceanus was added to the decomposing algae, nitrite was produced at a rate of 0.2 g-at N/l/week. Heterotrophic nitrification was not observed when 7 open-ocean bacteria were tested for their ability to oxidize ammonia. The diatom Skeletonema costatum, either non-starved or starved of nitrogen, produced nitrite when growing with 150 or 50 g-at NO ₂ ^- -N/l at a light intensity of about 0.01 ly/min. When nitrate in the medium was exhausted, S. costatum assimilated nitrite. If starved of vitamin B₁₂, both non-N-starved and N-starved cells of S. costatum produced nitrite in the medium with 150 g-at NO ₃ ^- -N/l. Nitrate was not exhausted and cell densities reached 2x10⁵/ml due to vitamin B₁₂ deficiency. If light intensity was reduced to 0.003 ly/min under otherwise similar conditions, cells did not grow due to insufficient light, and nitrite was not produced. In the sea, it appears that, in certain micro-environments, decomposition of particulate matter releases ammonia with its subsequent oxidation to nitrite. The amounts of these nutrients and the rate at which they are produced are dependent upon the nature of the materials undergoing decomposition and the associated bacteria. In certain other areas of the sea, where phytoplankton standing stock is high and nitrate is non-limiting, excretion by these organisms is a major source of nitrite.     

Estimation of coral growth-rates from laboratory 45Ca-incorporation rates

Laboratory ⁴⁵Ca-incorporation rates in hermatypic coral skeletons have previously been used successfully as an index of physiological function. This laboratory method would become more meanigful if it also provided an absolute measure of coral growth rates. In two coral species, Porites compressa and Pocillopora damicornis, ⁴⁵Ca incorporation rates were obtained from short (0.5 h) laboratory incubations using apical (determined as fast growing) portions of freshly collected coral branches. ⁴⁵Ca exchange across the coenosarc was not significant and not corrected for, whereas diurnal fluctuation in ⁴⁵Ca in Pocillopora damicornis was significant and a necessary correction. A calculated surface area is used to express calcification rate. Typical growth rates calculated from the ⁴⁵Ca-incorporation rates were 20 and 6 mm/year for Porites compressa and Pocillopora damicornis, respectively. These rates are considerably higher than those previously obtained in the laboratory, and compare favorably with field growth rates — 24 and 14 mm/year, respectively.     

Nitrogen fixation by blue-green algae associated with the siphonous green seaweed Codium decorticatum: effects on ammonium uptake

Nitrogen fixation (acetylene reduction) at rates of up to 1.2 g N₂ g dry wt^-1 h^-1 was measured for the siphonous green seaweed Codium decorticatum. No nitrogenase activity was detected in C. isthmocladum. The nitrogenase activity was light sensitive and was inhibited by the addition of DCMU and triphenyl tetrazolium chloride. Additions of glucose did not stimulate nitrogen fixation. Blue-green algae (Calothrix sp., Anabaena sp., and Phormidium sp.) were implicated as the organisms responsible for the nitrogenase activity. They occurred in a reduced microzone within the C. decorticatum thallus where nitrogen fixation was optimized. Nitrogen fixation did not affect the kinetic constants for ammonium uptake in C. decorticatum (K_s=12.0 M, V_max=13.4 mol NH₃ g dry wt^-1 h^-1) determined using the perturbation method. Nevertheless, C. decorticatum thalli which fixed nitrogen had internal dissolved nitrogen concentrations which were over 1.4 times higher than in non-fixing thalli. This suggests that if C. decorticatum does derive part of its nitrogen requirement from the blue-green algae which it harbors, the transfer does not involve competition between this process and the uptake of ambient ammonium.     

Growth and form in the reef-building coral Montastrea annularis

The in-situ growth rate of the reef coral Montastrea annularis on a reef at Jamaica, W. Indies was determined for a 1-year period using Alizarin Red-S staining techniques. Growth rate is correlated with water depth and growth form. The flattened growth form of M. annularis allows for continued rapid increase in colony surface area at low light intensities. The geomorphology of Jamaican reefs may in part be controlled by the population ecology of M. annularis.     

Meiofauna and the thiobios in the east flower garden brine seep

Special hydrodynamic-chemical conditions at the East Flower Garden brine seep have provided the opportunity to examine the community structure of the thiobios and the oxybiotic-thiobiotic boundary. The boundary between the thiobios, whose population maxima occur in sulfidedependent chemoclines and which presumably have an ecologic requirement for sulfide, and the oxybios, which occur in oxidized zones above the chemocline, is controlled by sulfide, not oxygen. The boundary, which may not be at zero sulfide, is determined by a time-concentration phenomenon based on a dynamic interplay of sulfide and oxygen supply rates and the biota's sulfide detoxification capabilities. In Gollum's Canyon, where oxygen is plentiful, the boundary is at 10–40 μg-atoms·l^-1 sulfide. Total abundances of organisms at thiobiotic stations were comparable to total abundances at oxybiotic stations. Highest thiobiotic abundance was 202 051 organisms per m²; highest oxybiotic abundance was 240 572 organisms per m². The thiobios is dominated by representatives of the lower Bilateria (viz. Gnathostomulida, Platyhelminthes and Aschelminthes). These groups accounted for 50–80% of all the organisms present in the thiobiotic stations but less than 20% of all organisms in the oxybiotic stations. At two thiobiotic stations, over 50% of all organisms were gnathostomulids. Thiobios included macrofaunal as well as meiofaunal components. Peak abundances of amphipods were associated with the thiobiotic environment.