Temporal variability in zooplankton prey capture rate of the passive suspension feeder<Emphasis Type="Italic"> Leptogorgia sarmentosa</Emphasis> (Cnidaria: Octocorallia), a case study

There is increasing evidence that suspension feeders play a significant role in plankton–benthos coupling. However, to date, active suspension feeders have been the main focus of research, while passive suspension feeders have received less attention. To increase our understanding of energy fluxes in temperate marine ecosystems, we have examined the temporal variability in zooplankton prey capture of the ubiquitous Mediterranean gorgonian Leptogorgia sarmentosa. Prey capture was assessed on the basis of gut content from colonies collected every 2 weeks over a year. The digestion time of zooplankton prey was examined over the temperature range of the species at the study site. The main prey items captured were small (80–200 µm), low-motile zooplankton (i.e. eggs and invertebrate larvae). The digestion time of zooplankton prey increased when temperature decreased (about 150% from 21°C to 13°C; 15 h at 13°C, 9 h at 17°C, and 6 h at 21°C), a pattern which has not previously been documented in anthozoans. Zooplankton capture rate (prey polyp^–1 h^–1) varied among seasons, with the greatest rates observed in spring (0.16±0.02 prey polyp^–1 h^–1). Ingestion rate in terms of biomass (g C polyp^–1 h^–1) showed a similar trend, but the differences among the seasons were attenuated by seasonal differences in prey size. Therefore, ingestion rate did not significantly vary over the annual cycle and averaged 0.019±0.002 g C polyp^–1 h^–1. At the estimated ingestion rates, the population of L. sarmentosa removed between 2.3 and 16.8 mg C m^–2 day^–1 from the adjacent water column. This observation indicates that predation by macroinvertebrates on seston should be considered in energy transfer processes in littoral areas, since even species with a low abundance may have a detectable impact.Communicated by S.A. Poulet, Roscoff     

Respiration rates of<Emphasis Type="Italic"> Beroe ovata</Emphasis> in the Black Sea

Metabolic rates of the ctenophore Beroe ovata within the length range from 0.4 mm (newly hatched larvae) to 60 mm were investigated. At 20° the respiration rates (Q, µg O₂ ind.^–1 h^–1) of individuals with wet weights (W, mg) less than or greater than 100 mg changed according to the equations Q=0.093W^0.62 and Q=0.016W^0.99, respectively. The weight-specific respiration rate of the juvenile ctenophores with wet body weights of 0.021–100 mg diminished approximately 20-fold (from 0.35 to 0.017 µg O₂ mg^–1 h^–1, respectively), but did not change within the range from 100 to 30,000 mg. The difference in the slope of the regression lines seems to be attributable to the ontogenetic changes in B. ovata metabolism. For the tested temperature range of 10–28°, the mean Q₁₀ coefficient was equal to 2.17±0.5. The basal metabolism of B. ovata narcotised by chloral hydrate was 4.5±0.9 times lower than total metabolism. Such a metabolic range is considered to be characteristic of aquatic invertebrates with high levels of locomotory activity.Communicated by O. Kinne, Oldendorf/Luhe     

Energy content at metamorphosis and growth rate of the early juvenile barnacle<Emphasis Type="Italic"> Balanus amphitrite</Emphasis>

The energetic cost of metamorphosis in cyprids of the barnacle Balanus amphitrite Darwin was estimated by quantification of lipid, carbohydrate and protein contents. About 38–58% (4–5 mJ individual^–1) of cypris energy reserves were used during metamorphosis. Lipids accounted for 55–65%, proteins for 34–44% and carbohydrates for <2% of the energy used. Juveniles obtained from larvae fed 10⁶ cells ml^–1 of Chaetoceros gracilis were bigger (carapace length: 560–616 µm) and contained more energy (5.56±0.10 mJ juvenile^–1) than their counterparts (carapace length: 420–462 µm; energy content: 2.49±0.20 mJ juvenile^–1) obtained from larvae fed 10⁴ cells ml^–1. At water temperatures of 30°C and 24°C and food concentrations of 10⁴ and 10² cells ml^–1 (3:1 mixture of C. gracilis and Isochrysis galbana) as well as under field conditions (26.9±3.1°C and 2.2±0.8 µg chlorophyll a l^–1), juveniles obtained from larvae fed the high food concentration grew faster than juveniles obtained from larvae fed low food concentration until 5 days post-metamorphosis. Laboratory experiments revealed a combined effect of early juvenile energy content, temperature and food concentration on growth until 5 days post-metamorphosis. After 10 days post-metamorphosis, the influence of the early juvenile energy content on growth became negligible. Overall, our results indicate that the energy content at metamorphosis is of critical importance for initial growth of juvenile barnacles and emphasize the dependency of the physiological performance of early juvenile barnacles on the larval exposure to food.Communicated by O. Kinne, Oldendorf/LuheAn erratum to this article can be found at     

Intra-colonial variability in light acclimation of zooxanthellae in coral tissues of Pocillopora damicornis

We investigated heterogeneity of light acclimation of photosynthesis in sun- and shade-adapted coenosarc and polyp tissues of Pocillopora damicornis. The zooxanthellar community within P. damicornis colonies at Heron Island is genetically uniform, yet they showed a large degree of plasticity in their photo-physiological acclimation linked to light microclimates characterised by fibre-optic microprobes. Microscale scalar irradiance measurements showed higher absorption in polyp than coenosarc tissues and higher absorption in the more densely pigmented shade-adapted polyps than in sun-adapted polyps. The combination of an O₂ microelectrode with a fibre-optic microprobe (combined sensor diameter 50–100 μm) enabled parallel measurements of O₂ concentration, gross photosynthesis rate and photosystem II (PSII) quantum yield at the coral surface under steady-state conditions as a function of increasing irradiances. Lower O₂ levels at the tissue surface and higher compensation irradiance indicated a higher respiration activity in sun-adapted polyp tissue as compared to shade-adapted polyps. Shade-adapted coenosarc and polyp tissues exhibited lower maxima of relative electron transport rates (rETR_max) (84±15 and 41±10, respectively) than sun-adapted coenosarc and polyp tissues (136±14 and 77±13, respectively). Shade-adapted tissues showed stronger decrease of rETR at high scalar irradiances as compared to sun-adapted tissues. The relationship between the relative PSII electron transport and the rate of gross photosynthesis, as well as O₂ concentration, was non-linear in sun-adapted tissues over the entire irradiance range, whereas for shade-adapted tissues the relationship became non-linear at medium to high scalar irradiances >200 μmol photons m⁻² s⁻¹. This suggests that rETR measurements should be used with caution in corals as a proxy for photosynthesis rates. The apparently high rates of photosynthesis (oxygen evolution rates) suggest that there must be a considerable electron transport rate through the photosystems that is not observed by the rETR measurements. This may be accounted for by vertical heterogeneity of zooxanthellae in the tissue and the operation of an alternative electron pathway such as cyclic electron flow around PSII.     

Summer copepod production in subtropical waters adjacent to Australia's North West Cape

Growth and secondary production of pelagic copepods near Australia's North West Cape (21° 49 S, 114° 14 E) were measured during the austral summers of 1997/1998 and 1998/1999. Plankton communities were diverse, and dominated by copepods. To estimate copepod growth rates, we incubated artificial cohorts allocated to four morphotypes, comprising naupliar and copepodite stages of small calanoid and oithonid copepods. Growth rates ranging between 0.11 and 0.83 day^–1 were low, considering the high ambient temperatures (23–28°C). Calanoid nauplii had a mean growth rate of 0.43±0.17 day^-1 (SD) and calanoid copepodites of 0.38±0.13 day^-1. Growth rates of oithonid nauplii and copepodites were marginally less (0.38±0.19 day^–1 and 0.28±0.11 day^–1 respectively). The observed growth rates were suggestive of severe food limitation. Although nauplii vastly outnumbered copepodite and adult copepods, copepodites comprised the most biomass. Copepodites also contributed most to secondary production, although adult egg production was sporadically important. The highest copepod production was recorded on the shelf break (60 mg C m^-2 day^-1). Mean secondary production over both shelf and shelf break stations was 12.6 mg C m^-2 day^-1. Annual copepod secondary production, assuming little seasonality, was estimated as ~ 3.4 g C m^-2 year^-1 (182 kJ m^-2 year^-1).Communicated by G.F. Humphrey, Sydney     

Daily energy requirements and trophic positioning of the sand shrimp<Emphasis Type="Italic"> Crangon septemspinosa</Emphasis>

Sand shrimp, Crangon septemspinosa Say, are important to the trophic dynamics of coastal systems in the northwestern Atlantic. To evaluate predatory impacts of sand shrimp, daily energy requirements (J ind.^–1 day^–1) were calculated for this species from laboratory estimates of energy losses due to routine (R_R), active (R_A), and feeding (R_SDA) oxygen consumption rates (J ind.^–1 h^–1), coupled with measurements of diel motile activity. Shrimp used in this study were collected biweekly from the Niantic River, Connecticut (41°33N; 72°19W) during late spring and summer of 2000 and 2001. The rates of shrimp energy loss due to R_R and R_A increased exponentially with increasing temperature, with the magnitude of increase greater between 6°C and 10°C (Q₁₀=3.01) than between 10°C and 14°C (Q₁₀=2.85). Rates of R_R doubled with a twofold increase in shrimp mass, and R_SDA was 0.130 J h^–1+R_R, irrespective of shrimp body size. Shrimp motile activity was significantly greater during dark periods relative to light periods, indicating nocturnal behavior. Nocturnal activity also increased significantly at higher temperatures, and at 20°C shifted from a unimodal to a bimodal pattern. Laboratory estimates of daily metabolic expenditures (1.7–307.4 J ind.^–1 day^–1 for 0.05 and 1.5 g wet weight shrimp, respectively, between 0°C and 20°C) were combined with results from previous investigations to construct a bioenergetic model and make inferences regarding the trophic positioning of C. septemspinosa. Bioenergetic model estimates indicated that juvenile and adult shrimp could meet daily energy demands via opportunistic omnivory, selectively preying upon items of high energy content (e.g. invertebrate and fish tissue) and compensating for limited prey availability by ingesting readily accessible lower energy food (e.g. detritus and plant material).Electronic Supplementary Material Supplementary material is available in the online version of this article at Communicated by J.P. Grassle, New Brunswick     

Diurnal gut pigment rhythm and metabolic rate of<Emphasis Type="Italic"> Calanus euxinus</Emphasis> in the Black Sea

The vertical distribution, diel gut pigment content and oxygen consumption of Calanus euxinus were studied in April and September 1995 in the Black Sea. Gut pigment content of C. euxinus females was associated with diel vertical migration of the individuals, and it varied with depth and time. Highest gut pigment content was observed during the nighttime, when females were in the chlorophyll a (chl a) rich surface waters, but significant feeding also occurred in the deep layer. Gut pigment content throughout the water column varied from 0.8 to 22.0 ng pigment female^–1 in April and from 0.2 to 21 ng pigment female^–1 in September 1995. From the diel vertical migration pattern, it was estimated that female C. euxinus spend 7.5 h day^–1 in April and 10.5 h day^–1 in September in the chl a rich surface waters. Daily consumption by female C. euxinus in chl a rich surface waters was estimated by taking into account the feeding duration and gut pigment concentrations. Daily carbon rations of female C. euxinus, derived from herbivorous feeding in the euphotic zone, ranged from 6% to 11% of their body carbon weight in April and from 15% to 35% in September. Oxygen consumption rates of female and copepodite stage V (CV) C. euxinus were measured at different temperatures and at different oxygen concentrations. Oxygen consumption rates at oxygen-saturated concentration ranged from an average of 0.67 g O₂ mg^–1 dry weight (DW) h^–1 at 5°C to 2.1 g O₂ mg^–1 DW h^–1 at 23°C for females, and ranged from 0.48 g O₂ mg^–1 DW h^–1 at 5°C to 1.5 g O₂ mg^–1 DW h^–1 at 23°C for CVs. The rate of oxygen consumption at 16°C varied from 0.62 g O₂ mg^–1 DW h^–1 at 0.65 mg O₂ l^–1 to 1.57 g O₂ mg^–1 DW h^–1 at 4.35 mg O₂ l^–1 for CVs, and from 0.74 g O₂ mg^–1 DW h^–1 at 0.57 mg O₂ l^–1 to 2.24 g O₂ mg^–1 DW h^–1 at 4.37 mg O₂ l^–1 for females. From the oxygen consumption rates, daily requirements for the routine metabolism of females were estimated, and our results indicate that the herbivorous daily ration was sufficient to meet the routine metabolic requirements of female C. euxinus in April and September in the Black Sea.Communicated by O. Kinne, Oldendorf/Luhe     

Relationship of oxygen consumption to swimming speed in Euphausia pacifica

Swimming efficiency (the ratio of thrust power required to overcome hydrodynamic drag to net metabolic energy expenditure) was calculated for the vertically migrating euphausiid Euphausia pacifica swimming at speeds of 1–20 cm s^–1 and at temperatures of 8° and 12°C. Efficiencies ranged from 0.014 to 2.8% at 8°C and 0.009 to 1.69% at 12°C. A comparison with efficiency in fishes 2–3 orders of magnitude larger in weight (efficiency range 10–25%) indicates that locomotion in E. pacifica is far less efficient, a probable result of the organism's small size (x=33.5 mg WW) and multiple-paddle mode of propulsion. Net cost of transport of E. pacifica is three to six times the cost of a hypothetical value for sockeye salmon. Low swimming efficiencies in zooplankton such as E. pacifica are responsible for the underestimation of zooplankton swimming costs. Multiple-paddle propulsion is less efficient than the undulatory mode of fishes.     

Influence of food concentration,temperature and salinity on the larval development ofBalanus amphitrite

Influence of food concentration (0.5, 1 and 2 x 10⁵ cell ml^–1 ofSkeletonema costatum), temperature (20 and 30°C) and salinity (15, 25 and 35) on the larval development ofBalanus amphitrite (Cirripedia: Thoracica) was examined. The mortality rate at 20°C was lower than at 30°C in general. Increase in food concentration from 0.5 to 1 x 105 cells ml^–1 improved the survival rate, but this was not evident when food concentration was increased to 2 x 105 cells ml^–1. The results indicate that food availability and temperature jointly determine the energy allocation for metamorphic progress. It was observed that the influence of the tested variables varied with instar. At 20 °C the mean duration of the second instar exceeded 3 d and was much longer than other instar durations. The fourth, fifth and sixth instars and the total naupliar period showed that the effect of different salinities at given food concentrations was negligible at 20°C, while at 30°C there was a marked decrease in duration with increasing salinity.     

Effect of low dissolved oxygen concentrations on behavior and predation rates on red sea bream Pagrus major larvae by the jellyfish Aurelia aurita and by juvenile Spanish mackerel Scomberomorus niphonius

A shift in outcomes of predator-prey interactions in plankton community may occur at sublethal dissolved oxygen concentrations that commonly occur in coastal waters. Laboratory experiments were conducted to investigate how a decline in dissolved oxygen concentration alters the predation rate on fish larvae by two estuarine predators. Behavior and consumption of larval fish by moon jellyfish Aurelia aurita (103.1±12.4 mm in bell diameter) and by a juvenile piscivore, Spanish mackerel Scomberomorus niphonius (30.1±2.1 mm in standard length: SL), were observed under four oxygen concentration treatments (1, 2 and 4 mg l^–1 and air-saturated: 5.8 mg l^–1). Larvae of a coastal marine fish species, red sea bream Pagrus major (7.21±0.52 mm SL), were used as prey for the experiment. Bell contraction rate of the jellyfish did not vary among the oxygen concentrations tested, indicating a tolerance to low oxygen concentration. Gill ventilation rate of the Spanish mackerel increased and swimming speed decreased as the oxygen concentration decreased, indicating that oxygen concentrations 4 mg l^–1 are physiologically stressful for this species. The number of larvae consumed in 15 min. by jellyfish increased whereas those consumed by Spanish mackerel decreased with the decrease in oxygen concentration. Low oxygen concentrations that are commonly observed in coastal waters of Japan during summer have the potential to increase the relative importance of jellyfish as predator of fish larvae and to change the importance of alternative trophic pathways in estuarine ecosystems.Communicated by T. Ikeda, Hakodate     

Effects of temperature on photosynthesis and respiration in hermatypic corals

Photosynthesis and respiration rates of the reef corals Pocillopora damicornis (Linn.), Montipora verrucosa (Lamarck), Porites compressa Dana and Fungia scutaria Lamarck were measured under controlled temperatures. Results indicate that coral metabolism is closely adapted to ambient temperature conditions. Tropical corals measured at Enewetak, Marshall Islands, showed greater primary production compared to maintenance requirements at elevated temperatures than did subtropical varieties of the same species in Hawaii. Photosynthesis: respiration (P:R) ratios were significantly and negatively related with temperature between 18° and 31°C for all Hawaiian corals, whereas at Enewetak this ratio generally showed a curvilinear relationship for this temperature range. Extrapolations of P:R regressions on temperatures to a value of 2.0 (estimated as a minimum required for long-term functional autotrophy) coincide for Hawaiian specimens with published upper lethal temperatures. Extrapolation of P:R regressions for Enewetak specimens at temperatures above 25°C suggests lethal temperatures for these corals to be 2 to 5 C° higher than for Hawaiian corals, in good agreement with recent experimental findings. Interspecific differences in P:R temperature regressions for Hawaiian corals correlating with upper lethal temperature tolerances are described.Contribution No. 505 of the Hawaii Institute of Marine Biology.     

Embryogenesis and larval biology of the ahermatypic scleractinian<Emphasis Type="Italic"> Oculina varicosa</Emphasis>

The ivory tree coral Oculina varicosa (Leseur, 1820) is an ahermatypic branching scleractinian that colonizes limestone ledges at depths of 6–100 m along the Atlantic coast of Florida. This paper describes the development of embryos and larvae from shallow-water O. varicosa, collected at 6–8 m depth in July 1999 off Fort Pierce, Florida (27°32.542 N; 79°58.732 W). The effect of temperature on embryogenesis, larval survival, and larval swimming speed were examined in the laboratory. Ontogenetic changes in geotaxis and phototaxis were also investigated. Embryos developed via spiral cleavage from small (100 µm), negatively buoyant eggs. Ciliated larvae developed after 6–9 h at 25°C. Embryogenesis ceased at 10°C, was inhibited at 17°C, and progressed normally at 25°C and 30°C. Larval survival, however, was high across the full range of experimental temperatures (11–31°C), although mortality increased in the warmest treatments (26°C and 31°C). Larval swimming speed was highest at 25°C, and lower at the temperature extremes (5°C and 35°C). An ontogenetic change in geotaxis was observed; newly ciliated larvae swam to the water surface and remained there for approximately 18 h, after which they swam briefly throughout the water column, then became demersal. Early larvae showed no response to light stimulation, but at 14 and 23 days larvae appeared to exhibit negatively phototactic behavior. Although low temperatures inhibited the development of O. varicosa embryos, the larvae survived temperature extremes for extended periods of time. Ontogenetic changes in larval behavior may ensure that competent larvae are close to the benthos to facilitate settlement. Previous experiments on survival, swimming speeds, and observations on behavior of O. varicosa larvae from deep-water adults indicate that there is no difference between larvae of the deep and shallow populations.Communicated by J.P. Grassle, New Brunswick     

Effects of changes in water salinity upon exercise and cardiac performance in the European seabass (<Emphasis Type="Italic">Dicentrarchus labrax</Emphasis>)

The European seabass is an active euryhaline teleost that migrates and forages in waters of widely differing salinities. Oxygen uptake (M_O2) was measured in seabass (average mass and forklength 510 g and 34 cm, respectively) during exercise at incremental swimming speeds in a tunnel respirometer in seawater (SW) at a salinity of 30 and temperature of 14°C, and their maximal sustainable (critical) swimming speed (U_crit) determined. Cardiac output (Q) was measured via an ultrasound flow probe on their ventral aorta. The fish were then exposed to acute reductions in water salinity, to either SW (control), 10, 5, or freshwater (FW, 0), and their exercise and cardiac performance measured again, 18 h later. Seabass were also acclimated to FW for 3 weeks, and then their exercise performance measured before and at 18 h after acute exposure to SW at 30. In SW, seabass exhibited an exponential increase in M_O2 and Q with increasing swimming speed, to a maximum M_O2 of 339±17 mg kg^–1 h^–1 and maximum Q of 52.0±1.9 ml min^–1 kg^–1 (mean±1 SEM; n=19). Both M_O2 and Q exhibited signs of a plateau as the fish approached a U_crit of 2.25±0.08 bodylengths s^–1. Increases in Q during exercise were almost exclusively due to increased heart rate rather than ventricular stroke volume. There were no significant effects of the changes in salinity upon M_O2 during exercise, U_crit or cardiac performance. This was linked to an exceptional capacity to maintain plasma osmolality and tissue water content unchanged following all salinity challenges. This extraordinary adaptation would allow the seabass to maintain skeletal and cardiac muscle function while migrating through waters of widely differing salinities.Communicated by S.A. Poulet, Roscoff     

Metabolism and body composition of a copepod (<Emphasis Type="Italic">Neocalanus cristatus</Emphasis>: Crustacea) from the bathypelagic zone of the Oyashio region,western subarctic Pacific

Metabolism [respiratory oxygen consumption, electron-transfer-system (ETS) activity] and body composition [water, ash, carbon (C), nitrogen (N), carbon/nitrogen (C/N) ratio] of stage C5/C6 Neocalanus cristatus from 1000 to 2000 m depth of the Oyashio region, western subarctic Pacific, were determined during the period of July 2000 through June 2003. Compared with the C5 specimens from shallow depths (<250 m), those from 1000 to 2000 m were characterized by quiescent behavior, reduced respiration rates (30% of the rates at active feeding), very low water content (61–70% of wet weight), but high C content (56–64% of dry weight) and C/N ratios (7.2–10.6, by weight). Artifacts due to the recovery of live specimens from the bathypelagic zone appeared to be unlikely in this study, as judged by the consistent results between re-compression (100 atm) and non-compression (1 atm) respiration experiments, and between ETS activities and respiration rates directly measured. In addition, the respiration rates of C6 males and females of N. cristatus from the same 1000–2000 m depth were two to three times higher than the rates of C5 individuals, but were similar to the rates of a bathypelagic copepod, Paraeuchaeta rubra. Combining these results with literature data, C budgets of: (1) diapausing C5 specimens, weighing 6–10 mg dry weight; (2) molt to C6 females; and (3) the complete the life span were established, taking into account assorted losses in respiration during diapause at stages C5 and C6, molt production and egg production. Respiratory C losses by C5 and C6 specimens were estimated on the basis of body N as adjusted metabolic rates [AMR; µl O₂ (mg body N)^–0.843 h^–1], then N budgets were also computed subtracting N lost in the form of cast molts and eggs from the initial stock. Calculations revealed that allocation of the C stock was greatest to egg production (34–57%), followed by respiration (27%) and cast molts (3%), leaving residual C of 13–36% in spent C6 females. The present results for N. cristatus from the North Pacific are compared with those of Calanus spp. in the North Atlantic.Communicated by O. Kinne, Oldendorf/Luhe     

Population biology of hyperbenthic crustaceans in a cold water environment (Conception Bay,Newfoundland). I.<Emphasis Type="Italic"> Mysis mixta</Emphasis> (Mysidacea)

Seasonal population dynamics of Mysis mixta Lilljeborg were studied from December 1998 to November 2000 at a 240 m deep site in Conception Bay, Newfoundland. At this depth, temperature was <0°C and salinity between 32.0 and 34.0 psu year-round. The spring phytoplankton bloom began in early or late March and reached a maximum in late April to mid-May. M. mixta exhibited a highly synchronised life cycle, with spawning and mating occurring in October to November, embryos brooded for ~5 months, and juveniles released during spring bloom sedimentation in April and May. Females were semelparous and died at age 2.5 years, following release of juveniles in spring, whereas the majority of mature males died at age 2 years, following mating in November. The biennial life cycle of this population resulted in the presence of two cohorts in the hyperbenthos at any given time. Variation in density and biomass was low among cohorts but high within cohorts, the latter probably due to the high motility of mysids. Densities in 1999 and 2000 were 242±379 and 544±987 ind. per 100 m³ (mean±SD), respectively. Although growth rates were similar between years, rates measured from changes in dry mass differed both seasonally and among life-history stages (range from –4 to 7 mg month^–1). Annual secondary production was estimated at 29–73 mg C m^–2 in 1999 and 53–205 mg C m^–2 in 2000. The annual P/B ratios were 1.62 and 1.19 in 1999 and 2000, respectively.Communicated by J.P. Grassle, New Brunswick     

Influence of sex and age on the feeding habits of the common soleSolea solea

The lethal concentration of cadmium was determined for the mysidLeptomysis lingvura G.O. Sars, a Mediterranean species from surface coastal waters, and the effect of sublethal doses on respiration, ammonia excretion, and feeding efficiency at different temperatures, and on activities of 19 hydrolases was tested. Experiments were carried out on individuals collected in spring 1987 near Marseille. At 18°C, respiration rate was significantly affected only by concentrations >0.05 mg Cd l^–1. At 0.1 mg Cd l^–1, respiration rate was more significantly depressed at 20°C than at 10°C. There was a concomitant decrease in the Q₁₀ rate (by 23 to 59%, according to the particular experiment), indicating a strong synergistic effect of temperature. Ammonia excretion was likewise affected by cadmium, also with a concomitant decrease in the Q₁₀ rate (by 34%). Daily faecal pellet production was maximum at 18°C; it was inhibited by cadmium at temperatures between 14 and 20°C, and enhanced at extreme temperatures (10 and 22°C). The assimilation efficiency of contaminated individuals was reduced by 9%. These decreases in faecal pellet production and assimilation efficiency reflect a significant decrease in energy (by about 43%) which could rapidly lead to an unbalanced energy budget with a consecutive lowering of the reproductive potential. Generally, hydrolase activities usually increased initially in the presence of 0.2 mg Cd l^–1, but after 48 h they declined, reaching very low values at 72 h. Most physiological processes are therefore affected by exposure to cadmium and the unbalanced energy budget arises from the inability to utilize environmental food. These results are consistent with the literature data on cadmium contamination in marine organisms. Physiological and biochemical changes appear to be very informative in studies of in vitro sublethal effects of micropollutants and in situ environmental modifications.     

Life in a warm deep sea: routine activity and burst swimming performance of the shrimp<Emphasis Type="Italic"> Acanthephyra eximia</Emphasis> in the abyssal Mediterranean

Measurements of routine swimming speed, tail-flip escape responses, and oxygen consumptions were made of the deep-sea shrimp Acanthephyra eximia using autonomous landers in the Rhodos Basin at depths of up to 4,400 m and temperatures of 13–14.5°C. Routine swimming speeds at 4,200 m averaged 0.18 m s^–1 or 3.09 body lengths s^–1, approximately double those of functionally similar oceanic scavengers. During escape responses peak accelerations of 23 m s^–2 or 630.6 body lengths s^–2 were recorded, with animals reaching speeds of 1.61 m s^–1 or 34.8 body lengths s^–2. When compared to shallow-water decapods at similar temperatures these values are low for a lightly calcified shrimp such as A. eximia despite a maximum muscle mass specific power output of 90.0 W kg^–1. A preliminary oxygen consumption measurement indicated similar rates to those of oceanic crustacean scavengers and shallower-living Mediterranean crustaceans once size and temperature had been taken into account. These animals appear to have high routine swimming speeds but low burst muscle performances. This suite of traits can be accounted for by high competition for limited resources in the eastern Mediterranean, but low selective pressure for burst swimming due to reductions in predator pressure.Communicated by J.P. Thorpe, Port Erin     

Respiration,photosynthesis and carbon metabolism in planktonic ciliates

Release of¹⁴C-labelled carbon dioxide from uniformly labelled cells was used to measure respiration by individual ciliates in 2-h incubations in 1989 and 1990. In a strictly heterotrophic ciliate,Strobilidium spiralis (Leegaard, 1915), release of labelled carbon dioxide was equivalent to ca. 2.8% of cell C h^–1 at 20°C, and there was no difference between rates in the dark and light. In the chloroplast-retaining ciliatesLaboea strobila Lohmann, 1908,Strombidium conicum (Lohmann, 1908) Wulff, 1919 andStrombidium capitatum (Leegaard, 1915) Kahl, 1932, release of labelled carbon dioxide was less in the light than in the dark in experiments done at 15°C. InL. strobila release of radiolabel as carbon dioxide was equivalent to ca. 2.4% of cell C h^–1 in the dark but ca. 1% at 50µE m^–2 s^–1, an irradiance limiting to photosynthesis. InS. conicum release of radiolabel as carbon dioxide was equivalent to ca. 4.4% of cell C h^–1 in the dark, but at an irradiance saturating to photosynthesis (250 to 300µE m^–2 s^–1) there was no detectable release of labelled carbon dioxide. InS. capitatum release of radiolabel as carbon dioxide was equivalent to ca. 4.3% of cell C h^–1 in the dark but at an irradiance saturating to photosynthesis was ca. 2.4% of cell C h^–1. These data, combined with data from photosynthetic uptake experiments, indicate that¹⁴C uptake underestimates the total benefit of photosynthesis by 50% or more in chloroplastretaining ciliates.Contribution no. 7510 from the Woods Hole Oceanographic Institution     

Age,growth, and mortality of the prosobranch<Emphasis Type="Italic"> Zidona dufresnei</Emphasis> (Donovan, 1823) in the Mar del Plata area,south-western Atlantic Ocean

The volutid snail Zidona dufresnei is a benthic top predator in the Mar del Plata (Argentina) shelf area where it was subjected to unregulated commercial exploitation for more than 20 years. So far there is no stock management, and hitherto even the most basic information on population dynamics of this species is missing. Annual formation of internal shell growth bands visible by x-ray was confirmed by the stable oxygen isotope record in the shell carbonate that reflects seasonal oscillations in water temperature. A Gompertz growth function ( , K=0.211 year^–1, t₀=5.496) fitted 142 pairs of size-at-age data (30 shells) best. Maximum individual production amounted to 26.8 g shell-free wet mass (SFWM) at 115 mm shell length. Based on a size-frequency distribution derived from commercial catches, annual mortality rate of Z. dufresnei was estimated to be 0.61 (±0.21) year^–1.Communicated by O. Kinne, Oldendorf/Luhe     

Effects of particulate peat on the behavior and physiology of the Jamaican reef-building coral Montastrea annularis

Corals in an in situ respirometer exposed to suspended peat during the day greatly decreased net oxygen production, probably due to a reduction of intensity and spectral quality of light reaching the symbiotic zooxanthellae. Net production returned to pre-exposure levels after the chambers were cleared; the corals showed no behavioral effects. In contrast, after exposure during the night, corals displayed clearing behavior (such as extreme distension of the coenosarc and trapping of peat particles in thick clumps of mucus) and an increase in respiration rate comparable to the decrease in net production observed during the daytime exposure. The following morning, net production values were significantly lower than pre-exposure production values although ambient light intensity was slightly higher. This decrease in production as well as a 22% reduction of chlorophyll content in the coral tissue indicated loss of zooxanthellae from the stressed corals. Long-term exposure to such a stress could reduce coral growth rates and substantially alter coral reef communities.