Variations between winter and summer in the toxicity of copper to a population of the mysid Praunus flexuosus

 Copper toxicity was tested on a coastal population of the mysid Praunus flexuosus (Müller) from Southampton Water (Southern England) under winter and summer conditions. Ten-day toxicity tests were performed on the different life-cycle stages (female, male and juvenile) present in winter (December/February) and summer (August). The individuals were in winter or summer physiological condition and were exposed to seawater to which 0, 5, 25, 75 and 200 μg l⁻¹ copper was added. There were significantly different copper toxicity effects in winter and summer. In winter mortality was ≤ 1% at all levels of copper exposure, while in summer identical exposure levels caused mortality of up to 93%. The 96 h LC₅₀ was 30.8 μg l⁻¹ copper added in the summer. In winter, the low mortality prevented calculation of LC₅₀. There were differences in responses to copper between the life-cycle stages. Juveniles were more sensitive than adults, and were severely affected within 24 h. Females were more affected than males at lower doses and shorter exposure times. Received: 28 April 1999 / Accepted: 22 June 2000     

Effects of ambient ammonia levels on blood ammonia, ammonia excretion and heart and scaphognathite rates of Nephrops norvegicus

During commercial handling of Nephropsnorvegicus (L.) there are a number of situations when the prawns may be exposed to very high ambient ammonia levels. These experiments evaluated the effects of increased levels of ambient total ammonia (TA = NH₃ + NH₄ ⁺) on␣blood ammonia, ammonia efflux rates and on the cardio-ventilatory performance of N. norvegicus. When prawns were taken from <1 to 2000 μmol TA l⁻¹ medium, blood TA concentrations increased rapidly for the first 2 h but tended to drop thereafter. Original blood TA levels were restored 6 h after the prawns were transferred back from seawater containing 2000 to <1 μmol TA l⁻¹. Sudden exposure to 500, 1000, 2000 or 4000 μmol TA l⁻¹ medium induced blood TA concentrations to increase respectively to 50, 30, 33 and 36% of external concentrations (normally, internal TA values are much higher than external levels). Immediately after transfer back to seawater with low ammonia concentration ( <1 μmol TA l⁻¹), excretion rates were higher than those of control prawns, and the absolute amounts of TA excreted were considerably higher than those calculated to have accumulated in the haemolymph. Heart rate (HR) and scaphognathite rate (SR) were not altered when prawns were subjected to sudden alterations in ambient ammonia ( <1 to 2000 to <1 μmol TA l⁻¹). When water ammonia concentrations were altered more gradually, both rates increased, but only at 4000 μmol TA l⁻¹. These results show that N. norvegicus is able to remove ammonia from the haemolymph and/or transform ammonia into some other substance when subjected to increased levels of ambient ammonia. Possible mechanisms involved (e.g. active transport across the gills; storage in some other tissue; glutamate synthe sis) are discussed. Received: 20 May 1996 / Accepted: 1 July 1996     

Cadmium accumulation in the female shore crab Carcinus maenas during the moult cycle and ovarian maturation

 The influence of moulting and ovarian maturation on cadmium accumulation in the tissues of female shore crabs Carcinus maenas exposed to 1 mg Cd l⁻¹ in the water was investigated. Cadmium accumulation in all tissues examined was markedly increased in crabs in the postmoult stages (A and B) compared to crabs in all other moult stages. During the moult cycle, average cadmium accumulation in the midgut gland ranged from 29 μg Cd g⁻¹ dw at premoult stage (D₂) to 589 μg Cd g⁻¹ dw at postmoult stage (A). Average cadmium concentrations in the haemolymph ranged from 0.56 μg Cd ml⁻¹ at intermoult stage (C₄) to 4.6 μg Cd ml⁻¹ at postmoult stage (A), while the gills accumulated from 103 μg Cd g⁻¹ dw in intermoult stage (C₃) to 352 μg Cd g⁻¹ dw in postmoult stage (A). Cadmium concentration in gills and haemolymph was also significantly higher in crabs in late premoult stage (D₃) compared to C₄-crabs, while midgut gland cadmium concentration remained elevated in C₁- and C₃- intermoult stages relative to C₄. During ovarian maturation the cadmium accumulation in midgut gland, gills, ovaries and haemolymph decreased. Average cadmium concentration in the midgut gland decreased from 63 μg g⁻¹ dw in ovarian Stage I to 19 μg g⁻¹ dw in ovarian Stage VI. The same pattern was observed for gills, haemolymph and ovaries. The present study demonstrates that cadmium accumulation in the female shore crab strongly depends on the physiological status of the animal. A possible association between physiological calcium requirements and cadmium accumulation during moulting is discussed. Received: 20 January 2000 / Accepted: 20 July 2000     

Effects of inorganic and organic phosphates on feeding, feeding absorption, nutrient allocation, growth and righting responses of the sea urchin Lytechinus variegatus

The sea urchin Lytechinus variegatus is capable of surviving chronic exposure to sodium phosphate (inorganic phosphate) concentrations as high as 3.2 mg l⁻¹, and triethyl phosphate (organic phosphate) concentrations of 1,000 mg l⁻¹. However, chronic exposure to low (0.8 mg l⁻¹ inorganic and 10 mg l⁻¹ organic phosphate), medium (1.6 mg l⁻¹ inorganic and 100 mg l⁻¹ organic phosphate) or high (3.2 mg l⁻¹ inorganic and 1,000 mg l⁻¹ organic phosphate) sublethal concentrations of these phosphates inhibits feeding, fecal production, nutrient absorption and allocation, growth and righting behavior. Food consumption and fecal production declined significantly in individuals exposed to medium and high concentrations of inorganic phosphates and all levels of organic phosphates. Feeding absorption efficiencies for total organics and carbohydrates decreased significantly in individuals held in the highest concentration of organic phosphate. Feeding absorption efficiencies for lipids were significantly reduced in the highest inorganic phosphate concentration only, while they decreased significantly for protein with increasing phosphate exposure. Carbohydrate and lipid levels in gonad and gut tissues decreased significantly with exposure to increasing phosphate concentrations, potentially impairing both gametogenesis and nutrient storage in the gut. Moreover, gonad indices significantly decreased in individuals exposed to the highest concentrations of either phosphate. Growth rates decreased significantly under the influence of all phosphate concentrations, while increasing in seawater alone. Individuals exposed to increasing phosphate concentrations showed reduced righting responses (a measure of stress) and no acclimation in righting times during chronic exposure to phosphates over a 4 week period. These findings indicate that shallow-water populations of L. variegatus subjected to inorganic and organic phosphate pollutants will exhibit stress and be inhibited in their growth and performance due to reductions in feeding, nutrient absorption and allocation of nutrients to key somatic and reproductive tissues. Received: 10 April 2000 / Accepted: 2 October 2000     

A novel symbiosis between a cyanobacterium, Synechococcus sp., an aplastidic protist, Solenicola setigera, and a diatom, Leptocylindrus mediterraneus, in the open ocean

The abundance, biomass and distribution of Solenicola setigera, a colonial heterotrophic protist found only with the centric chain-forming diatom Leptocylindusmediterraneus, are reported for four major ocean basins. The distribution is cosmopolitan, and abundances and biomass are usually low (<500 colonies l⁻¹); however, in the summer of 1993, we observed a major biomass component (range = 5 to 31 μg C l⁻¹) in the surface waters of the North Atlantic attributable to S. setigera. These colonies of S. setigera were exceptionally large, and unusual in possessing high abundances of Synechococcus sp., a normally solitary cyanobacterium, embedded in the matrix covering the cells. We hypothesize that this relationship was mutually beneficial for both Solenicola setigera and Synechococcus sp. Received: 5 January 1998 / Accepted: 22 May 1998     

Standing crops and vertical distribution of four groups of marine planktonic ciliates in relation to phytoplankton chlorophyll a

Standing crops and the vertical distribution of four groups of ciliates, autotrophic naked ciliates (ANC), heterotrophic naked ciliates (HNC ), mixotrophic naked ciliates (MNC) and loricated ciliates (LC ), were analysed in relation to phytoplankton chlorophyll a in the western Pacific. Data were gathered from the upper 60 to 200 m of water in the subarctic North Pacific in spring, in the subtropical North Pacific in spring, in Toyama Bay in summer, off eastern Australia in spring and off Sanriku in spring and fall. Of the four groups, the standing crop of HNC (cells l⁻¹) showed the highest correlation to phytoplankton chloro- phyll a [CHL, μg l⁻¹; r=0.66, n=365 (HNC=490 ×CHL ^0.653)]. Depths of the maximum layers of HNC and MNC were usually shallower than that of chlorophyll a, while those of ANC and LC occurred frequently beneath the chlorophyll maximum layer. This indicates that these four ciliate groups are substantially different from each other, and that each group holds a different ecological position in the marine microbial food web. Received: 27 October 1997 / Accepted: 27 June 1998     

Fluoride in Antarctic marine crustaceans

The concentration of fluoride in the body parts of a range of Antarctic crustaceans from a variety of habits was examined with the aim of determining whether fluoride concentration is related to lifestyle or phylogenetic grouping. Euphausiids had the highest overall fluoride concentrations of a range of Antarctic marine crustaceans examined; levels of up to 5477 μg g⁻¹ were found in the exoskeleton of Euphausia crystallorophias. Copepods had the lowest fluoride levels (0.87 μg g⁻¹ whole-body); some amphipods and mysids also exhibited relatively high fluoride levels. There was no apparent relationship between the lifestyle of the crustaceans and their fluoride level; benthic and pelagic species exhibited both high and low fluoride levels. Fluoride was concentrated in the exoskeleton, but not evenly distributed through it; the exoskeleton of the head, carapace and abdomen contained the highest concentrations of fluoride, followed by the feeding basket and pleopods, and the eyes. The mouthparts of E.␣superba contained almost 13 000 μg F g⁻¹ dry wt. Antarctic krill tail muscle had low levels of fluoride. After long-term (1 to 5 yr) storage in formalin, fluoride was almost completely lost from whole euphausiids. Received: 1 April 1998 / Accepted: 29 July 1998     

Organic nitrogen uptake and growth by the chrysophyte Aureococcus anophagefferens during a brown tide event

The quantitative importance of light-mediated, dissolved organic nitrogen (DON) utilization in relation to overall nitrogen-assimilation in Aureococcusanophagefferens Hargraves et Sieburth was assessed during a brown tide event in Shinnecock Bay, Long Island, 24 through 26 July 1995. The growth response of A. anophagefferens was maximal in organic-rich Bay water and decreased proportional to the organic:inorganic nutrient ratio of the water. Short-term uptake measurements with six nitrogenous substrates revealed that reduced nitrogen could potentially represent 95% of overall nitrogen uptake of which 70% was due to organic nitrogen alone. Potential uptake of urea by the A. anophagefferens-dominated bloom was substan tially greater than uptake of the other substrates tested during the study, contributing the largest percentage of total nitrogen uptake (58 to 64%; ρ^′ _max(urea) 4.4 μg  atom N l⁻¹ h⁻¹), followed by NH₄ ⁺ (18 to 26%; ρ′_max(NH4+) 2 μg atom N l⁻¹ h⁻¹). The combined rates of uptake of algal extract, lysine and glutamic acid contributed between 11 and 16% of total uptake, whereas NO₃ ⁻contributed 5 to 8%. Based on the kinetic determinations from this study we suggest an ecological framework for the events leading to the dominance and abundance of A. anophagefferens in coastal bays. Received: 29 March 1997 / Accepted: 24 April 1997     

Phytoplankton blooms are strongly impacted by microzooplankton grazing in coastal North Pacific waters

Phytoplankton growth and microzooplankton grazing were measured in two productive coastal regions of the North Pacific: northern Puget Sound and the coastal Gulf of Alaska. Rates of phytoplankton growth (range: 0.09–2.69 day⁻¹) and microzooplankton grazing (range: 0.00–2.10 day⁻¹) varied seasonally, with lowest values in late fall and winter, and highest values in spring and summer. Chlorophyll concentrations also varied widely (0.19–13.65 μg l⁻¹). Large (>8 μm) phytoplankton cells consistently dominated phytoplankton communities under bloom conditions, contributing on average 65% of total chlorophyll biomass when chlorophyll exceeded 2 μg l⁻¹. Microzooplankton grazing was an important loss process affecting phytoplankton, with grazing rates equivalent to nearly two-thirds (64%) of growth rates on average. Both small and large phytoplankton cells were consumed, with the ratio of grazing to growth (g:μ) for the two size classes averaging 0.80 and 0.42, respectively. Perhaps surprisingly, the coupling between microzooplankton grazing and phytoplankton growth was tighter during phytoplankton blooms than during low biomass periods, with g:μ averaging 0.78 during blooms and 0.49 at other times. This tight coupling may be a result of the high potential growth and ingestion rates of protist grazers, some of which feed on bloom-forming diatoms and other large phytoplankton. Large ciliates and Gyrodinium-like dinoflagellates contributed substantially to microzooplankton biomass at diatom bloom stations in the Gulf of Alaska, and microzooplankton biomass overall was strongly correlated with >8 μm chlorophyll concentrations. Because grazing tended to be proportionally greater when phytoplankton biomass was high, the absolute amount of chlorophyll consumed by microzooplankton was often substantial. In nearly two-thirds of the experiments (14/23), more chlorophyll was ingested by microzooplankton than was available for all other biological and physical loss processes combined. Microzooplankton were important intermediaries in the transfer of primary production to higher trophic levels in these coastal marine food webs. Received: 12 November 1999 / Accepted: 4 October 2000     

Effect of nutrient enrichment in the field on the biomass, growth and calcification of the giant clam Tridacna maxima

Nutrients were added separately and combined to an initial concentration of 10 μM (ammonium) and/or 2 μM (phosphate) in a series of experiments carried out with the giant clam Tridacna maxima at 12 microatolls in One Tree Island lagoon, Great Barrier Reef, Australia (ENCORE Project). These nutrient concentrations remained for 2 to 3 h before returning to natural levels. The additions were made every low tide (twice per day) over 13 and 12 mo periods for the first and second phase of the experiment, respectively. The nutrients did not change the wet tissue weight of the clams, host C:N ratio, protein content of the mantle, calcification rates or growth rates. However, ammonium (N) enrichment alone significantly increased the total population density of the algal symbiont (Symbiodinium sp.: C = 3.6 · 10⁸ cell clam⁻¹, N = 6.6 · 10⁸ cell clam⁻¹, P = 5.7 · 10⁸ cell clam⁻¹, N + P = 5.7 · 10⁸ cell clam⁻¹; and C = 4.1 · 10⁸ cell clam⁻¹, N = 5.1 · 10⁸ cell clam⁻¹, P = 4.7 · 10⁸ cell clam⁻¹, N + P = 4.5 · 10⁸ cell clam⁻¹, at the end of the first and second phases of the experiment, respectively), although no differences in the mitotic index of these populations were detected. The total chlorophyll a (chl a) content per clam but not chlorophyll a per cell also increased with ammonium addition (C = 7.0 mg chl a clam⁻¹, N = 13.1 mg chl a clam⁻¹, P = 12.9 mg chl a clam⁻¹, N + P = 11.8 mg chl a clam⁻¹; and C = 8.8 mg chl a clam⁻¹, N = 12.8 mg chl a clam⁻¹; P = 11.2 mg chl a clam⁻¹, N + P = 11.3 mg chl a clam⁻¹, at the end of the first and second phases of the experiment, respectively). The response of clams to nutrient enrichment was quantitatively small, but indicated that small changes in inorganic nutrient levels affect the clam–zooxanthellae association. Received: 2 June 1997 / Accepted: 9 June 1997     

Microsensor studies of photosynthesis and respiration in the symbiotic foraminifer Orbulina universa

Oxygen and pH microelectrodes were used to investigate the microenvironment of the planktonic foraminifer Orbulina universa and its dinoflagellate endosymbionts. A diffusive boundary layer surrounds the foraminiferal shell and limits the O₂ and proton transport from the shell to the ambient seawater and vice versa. Due to symbiont photosynthesis, high O₂ concentrations of up to 206% air saturation and a pH of up to 8.8, i.e. 0.5 pH units above ambient seawater, were measured at the shell surface of the foraminifer at saturating irradiances. The respiration of the host–symbiont system in darkness decreased the O₂ concentration at the shell surface to <70% of the oxygen content in the surrounding air-saturated water. The pH at the shell surface dropped to 7.9 in darkness. We measured a mean gross photosynthetic rate of 8.5 ± 4.0 nmol O₂ h⁻¹ foraminifer⁻¹. The net photosynthesis averaged 5.3 ± 2.7 nmol O₂ h⁻¹. In the light, the calculated respiration rates reached 3.9 ± 1.9 nmol O₂h⁻¹, whereas the dark respiration rates were significantly lower (1.7 ± 0.7 nmol O₂ h⁻¹). Experimental light–dark cycles demonstrated a very dynamic response of the symbionts to changing light conditions. Gross photosynthesis versus scalar irradiance curves (P vs E _o curves) showed light saturation irradiances (E _k) of 75 and 137 μmol photons m⁻² s⁻¹ in two O. universa specimens, respectively. No inhibition of photosynthesis was observed at irradiance levels up to 700 μmol photons m⁻² s⁻¹. The light compensation point of the symbiotic association was 50 μmol photons m⁻² s⁻¹. Radial profile measurements of scalar irradiance (E _o) inside the foraminifera showed a slight increase at the shell surface up to 105% of the incident irradiance (E _d). Received: 26 January 1998 / Accepted: 11 April 1998     

Carbon and nitrogen exchange between sandy beach clams (Donax serra) and kelp beds in the Benguela coastal upwelling region

Carbon consumption and nitrogen requirements were estimated for populations of the sandy beach bivalve Donax serra on nine beaches of the west coast of South Africa. Subtidal populations composed mainly of adult clams were responsible for the bulk of standing stock (3538 g C m⁻¹), annual carbon consumption (13 444 g C m⁻¹ yr⁻¹), faeces production (6478 g C m⁻¹ yr⁻¹ ) and nitrogen regeneration (2525 g N m⁻¹ yr⁻¹). Kelp detritus, bacteria and kelp consumers' faeces available in the water column surpass several times the carbon and nitrogen requirements of intertidal and subtidal clam populations. Individual Donax serra pop ulations, in turn, may regenerate up to 3.2% of the total nitrogen requirements of all primary producers from kelp beds and 14% of the requirements of phytoplankton. These high standing stocks of clams are presumably supported mainly by organic matter originating from kelp which, in contrast to phytoplankton, is in constant supply and comprises the largest proportion of the annual production of particulate organic matter on this coast. Wide and shallow continental shelves with gentle slopes probably limit the penetration of upwelled waters to the nearshore waters, decreasing the influence of external inputs and increasing the importance of internal flows of nutrients and carbon within the nearshore zone. In this context, sandy beaches, rocky shores and kelp beds may be more closely interlinked compartments of a larger ecosystem encompassing the whole nearshore than traditionally thought. Received: 28 August 1996 / Accepted: 7 October 1996     

Fitting fertilisation kinetics models for free-spawning marine invertebrates

 To determine how fertilisation varied with sperm concentration for two species of scallop, Chlamys (Equichlamys) bifrons (Lamarck) and C. asperrima (Lamarck), we performed a simple series of sperm dilution experiments, and measured egg size and sperm swimming speeds. C. bifrons eggs were much larger (average diam=116.5 μm), and sperm swimming speeds faster (209.8 μm s⁻¹), than C. asperrima (71.2 μm, 166.0 μm s⁻¹). In both species, maximum fertilisation occurred at an ambient sperm concentration of around 100 sperm μl⁻¹; the maximum proportion of eggs fertilised was less than 0.70 in the C. bifrons experiments, but nearer 1.0 with C. asperrima. At high sperm concentrations (>100 sperm μl⁻¹), fertilisation decreased (presumably due to polyspermy) with increasing sperm concentration, but decreased more rapidly in C. bifrons than C. asperrima. A polyspermy-adjusted fertilisation kinetics model could be fitted to the experimental data, but unique parameter estimates could not be determined. Received: 7 October 1999 / Accepted: 8 July 2000     

Selective feeding in shellfish: size-dependent rejection of large particles within pseudofaeces from Mytilus edulis, Ruditapes philippinarum and Tapes decussatus

Mytilus edulis L., Ruditapes philippinarum (Adams & Reeve) and Tapes decussatus L. were fed particles of the same shape (spherical), the same density (2.1 g cm⁻³) and the same chemical composition (SiO₂), but which varied in diameter from 5 to 37 μm. Findings obtained at different particle concentrations (mean ± SD) of 51 ± 2, 105 ± 18 and 171 ± 17 mg l⁻¹ invariably indicate that significant proportions of all particles with diameters larger than from between 7.5 and 22.5 μm were preferentially rejected as pseudofaeces. We define the preferential ingestion index (PII) as the ratio between average particle volume in pseudofaeces and average particle volume in food. Whatever the particle concentration or the species, this PII was always statistically higher than 1. Irrespective of particle concentration, PII values in M. edulis were lower than in T. decussatus (averages of 1.2 and 2, respectively). PII values in M. edulis were also lower than in R. philippinarum maintained at particle concentrations above 171 ± 17 mg l⁻¹. We suggest that preferential size-dependent rejection of larger particles could be of significant adaptive value in the natural environment, either if there are large inorganic particles, or if the average organic content of smaller particles is higher. Received: 11 January 1997 / Accepted: 8 March 1997     

Feeding and assimilation kinetics of Artemia franciscana fed Isochrysis galbana (clone T. Iso)

Artemia franciscana was grown on Isochrysis galbana Green (clone T. Iso) at saturated food concentrations (13 to 20 mg C l⁻¹) for 11 d at 26 to 28 °C, and 34 ppt salinity. Three groups of brine shrimp were used in the feeding experiments: metanauplius III and IV (Group 1), post-metanauplius II and III (Group 2) and post-metanauplius VIII (Group 3), corresponding to 4-, 7- and 11-d-old animals, respectively. The ingestion rate, clearance rate and carbon balance were estimated for these stages at different concentrations of ¹⁴C-labeled I. galbana ranging from 0.05 to 30 mg C l⁻¹. The handling time of algae was determined for all three groups. The ingestion rate (I, ng C ind⁻¹ h⁻¹) increased as a function of animal size and food concentration. In all three groups, the ingestion rate increased to a maximum level (I _max) and remained constant at food concentrations ≥10 mg C l⁻¹ (saturated food concentrations). The clearance rate (CR, μl ind⁻¹ h⁻¹) increased with increasing food concentration up to a maximum rate (CR _max), after which it decreased for even higher food concentrations. The functional response of A. franciscana was most consistent with Holling's Type 3 functional response curve (sigmoidal model), which for the two oldest groups (Group 2 and 3) differed significantly from a Type 2 response (p < 0.05). The gut passage time for the three groups of A. franciscana, feeding on saturated food concentration (20 mg C l⁻¹), varied between 24 and 29 min. As the nauplii developed to pre-adult stage the handling time of the algae increased as a function of animal size. The assimilation rate (ng C ind⁻¹ h⁻¹) in the youngest stages (Group 1 and 2) increased with increasing food concentrations, reaching a maximum level close to 10 mg C l⁻¹. At higher food concentrations the assimilation rate decreased, and the proportions of defecated carbon increased, reaching 60 to 68% in the post-metanauplius stages (Group 3). The assimilation efficiency (%) was high at the lowest food concentrations in all three groups (89 to 64%). At higher concentrations, the assimilation efficiency decreased, reaching 56 to 38% at the highest concentrations. Received: 2 February 2000 / Accepted: 25 March 2000     

Temporal and spatial occurrence of UV-absorbing mycosporine-like amino acids in tissues of the antarctic sea urchin Sterechinusneumayeri during springtime ozone-depletion

From September to November 1991, UV-absorbing mycosporine-like amino acids (MAAs) were monitored in a natural population of the sea urchin Sterechinusneumayeri from a coastal area of Anvers Island (Antarctic Peninsula). MAA concentrations were determined for specific tissues (gonad, digestive tract and body wall) from adults collected at four depths (intertidal, 8, 15 and 24 m). Four MAAs were identified: mycosporine-glycine, shinorine, porphyra-334 and paly-thine. Concentrations of MAAs among replicate individuals varied considerably. Ovaries had high concentrations of MAAs (84 to 1389 μg g⁻¹ dry wt), while testes had non-detectable levels. The relative abundance of specific MAAs in ovaries appeared to be related to the spawning cycle. Digestive-tract samples had MAA concentrations as high as 3000 μg g⁻¹ dry wt, but the mean MAA content in intertidal individuals decreased by 70% over 3 mo during spring. The body walls of sea urchins had very low amounts of MAAs (≤ 0.08 μg g⁻¹ dry wt). There were significant depth differences in the␣total MAA content of the ovary ( p <0.001), ( p <0.015), digestive tract ( p <0.001), and body wall with organisms from the intertidal and 8 m depth having the highest concentrations of MAAs. Biological dosimetry indicated that UV-B (280 to 320 nm) wavelengths penetrated 3 to 7 m below the sea ice during the study period. The total MAA content in ovaries decreased with depth on all sample dates; however, the MAA content of the digestive tract and body wall did not exhibit a consistent pattern of change with depth. The MAA content of tissues did not change significantly with the temporal gradient of light exposure that was established by both ozone depletion and increasing photoperiod, except in the digestive tract sampled from intertidal specimens. Adult urchins are probably well-protected from UV exposure by the water column and a calcareous test; however, the results of this study suggest that, even under ice cover, depth of habitation is a determinant of MAA content in S. neumayeri. Large daily and seasonal fluctuations in the light regime, which are characteristic of Antarctic coastal environments, apparently do not provide reliable cues to elicit a detectable, temporal, biochemical response. Received: 19 February 1997 / Accepted: 26 March 1997     

Effects of DDT sediment-contamination on macrofaunal community structure and composition in San Francisco Bay

The objectives of this study were to determine the effects of sediment contamination on the benthic macrofauna and to predict macrofaunal changes following remediation at a Superfund (uncontrolled hazardous waste) site in San Francisco Bay, California, USA. DDT and its metabolites (ΣDDT) were the contaminants of concern. With few small-scale exceptions, all (>100) other sediment contaminants ever measured at the site were present at background or non-toxic levels. In hierarchical regressions [Y=f(X ₁, X ₂, X ₃), where X ₁=sediment %silt + clay, X ₂=sediment total organic carbon (OC), and X ₃=log ₁₀ (ΣDDT μg g⁻¹ OC)] with data from samples collected at the study site, log₁₀(ΣDDT μg g⁻¹ OC) explained a highly significant amount of the variance in the infaunal index (II ) and log₁₀(number of Amphipoda excluding Grandidierella japonica + 1) after statistically controlling for the potential effects of sediment %silt + clay and OC. The ratios of change of II and log₁₀(number of Amphipoda excluding G. japonica + 1) with respect to log₁₀(ΣDDT μg g⁻¹ OC) were about −9:1 and −0.4:1, respectively. Most of the 92 species collected were present at low to moderate densities over the entire range of ΣDDT sediment concentrations. The bivalve Theora lubrica, tubificids, most polychaetes, a tanaid (Zeuxo normani), and an amphipod (G. japonica), were common, while four other amphipods (Ampelisca abdita, Corophium heteroceratum, Photis brevipes, Dulichia rhabdoplastis), a phoronid (Phoronis cf. pallida), a bivalve (Cryptomya californica), and a cumacean (Eudorella pacifica), were rare or absent from sites with high ΣDDT sediment-concentrations. Received: 1 August 1997 / Accepted: 13 August 1997     

Zooplankton responses to hypoxia: behavioral patterns and survival of three species of calanoid copepods

Seasonally recurrent and persistent hypoxic events in semi-enclosed coastal waters are characterized by bottom-water dissolved oxygen (d.o.) concentrations of < 2.0 ml l⁻¹. Shifts in the distribution patterns of zooplankters in association with these events have been documented, but the mechanisms responsible for these shifts have not been investigated. This study assessed interspecific differences in responses to hypoxia by several species of calanoid copepods common off Turkey Point, Florida, USA: Labidocera aestiva (Wheeler) (a summer/fall species), Acartia tonsa (Dana) (a ubiquitous year-round species), and Centropages hamatus (Lilljeborg) (a winter/spring species). Under conditions of moderate to severe hypoxia 24-h survival experiments were conducted for adults and nauplii of these species from August 1994 to October 1995. Experiments on adults used a flow-through system to maintain constant d.o. concentrations. Adults of A. tonsa showed no decline in survival with d.o. as low as 1.0 ml l⁻¹, sharp declines in survival at d.o. = 0.9 to 0.6 ml l⁻¹, and 100% mortality with d.o. = 0.5 ml l⁻¹. Adults of L. aestiva and C. hamatus were more sensitive to oxygen depletion: both species experienced significant decreases in survival for d.o. = 1.0 ml l⁻¹. Nauplii of L. aestiva and A. tonsa showed no significant mortality with d.o. = 1.1 to 1.5 ml␣l⁻¹ and d.o. = 0.24 to 0.5 ml l⁻¹, respectively. In addition, experiments investigating behavioral avoidance of moderate to severe hypoxia were carried out for adults of all three species. None of the three species effectively avoided either severely hypoxic (d.o. < 0.5 ml l⁻¹) or moderately hypoxic (d.o. ≈ 1.0 ml l⁻¹) bottom layers in stratified columns. These results suggest that in␣nearshore areas where development of zones of d.o. < 1.0 ml l⁻¹ may be sudden, widespread, or unpredictable, patterns of reduced copepod abundance in bottom waters may be due primarily to mortality rather than avoidance. Received: 31 August 1996 / Accepted: 24 September 1996     

Irradiance and temperature regulation of oxygenic photosynthesis and O2 consumption in a hypersaline cyanobacterial mat (Solar Lake, Egypt)

 Short-term effects of temperature and irradiance on oxygenic photosynthesis and O₂ consumption in a hypersaline cyanobacterial mat were investigated with O₂ microsensors in a laboratory. The effect of temperature on O₂ fluxes across the mat–water interface was studied in the dark and at a saturating high surface irradiance (2162 μmol photons m⁻² s⁻¹) in the temperature range from 15 to 45 °C. Areal rates of dark O₂ consumption increased almost linearly with temperature. The apparent activation energy of 18 kJ mol⁻¹ and the corresponding Q ₁₀ value (25 to 35 °C) of 1.3 indicated a relative low temperature dependence of dark O₂ consumption due to mass transfer limitations imposed by the diffusive boundary layer at all temperatures. Areal rates of net photosynthesis increased with temperature up to 40 °C and exhibited a Q ₁₀ value (20 to 30 °C) of 2.8. Both O₂ dynamics and rates of gross photosynthesis at the mat surface increased with temperature up to 40 °C, with the most pronounced increase of gross photosynthesis at the mat surface between 25 and 35 °C (Q ₁₀ of 3.1). In another mat sample, measurements at increasing surface irradiances (0 to 2319 μmol photons m⁻² s⁻¹) were performed at 25, 33 (the in situ temperature) and 40 °C. At all temperatures, areal rates of gross photosynthesis saturated with no significant reduction due to photoinhibition at high irradiances. The initial slope and the onset of saturation (E _k = 148 to 185 μmol photons m⁻² s⁻¹) estimated from P versus E _d curves showed no clear trend with temperature, while maximal photosynthesis increased with temperature. Gross photosynthesis was stimulated by temperature at each irradiance except at the lowest irradiance of 54 μmol photons m⁻² s⁻¹, where oxygenic gross photosynthesis and also the thickness of the photic zone was significantly reduced at 40 °C. The compensation irradiance increased with temperature, from 32 μmol photons m⁻² s⁻¹ at 25 °C to 77 μmol photons m⁻² s⁻¹ at 40 °C, due to increased rates of O₂ consumption relative to gross photosynthesis. Areal rates of O₂ consumption in the illuminated mat were higher than dark O₂ consumption at corresponding temperatures, due to an increasing O₂ consumption in the photic zone with increasing irradiance. Both light and temperature enhanced the internal O₂ cycling within hypersaline cyanobacterial mats. Received: 30 November 1999 / Accepted: 11 April 2000     

Feeding, metabolism and growth in the Antarctic limpet, Nacella concinna (Strebel 1908)

Post-prandial increases in metabolism, the specific dynamic action of feeding (SDA), were evaluated in the Antarctic limpet Nacella concinna. O₂ consumption rose to a peak value 2.3 times higher than pre-feeding standard metabolic rates. This peak rise is low for marine ectotherms, but is typical of polar species. There were three peaks in the SDA, the first lasted only for the 1st day, was caused by handling, and was minor. The second was the major peak. It lasted from post-prandial days 4–9 inclusive, and accounted for around 70% of the SDA response. The third peak lasted from day 11 to day 15 and accounted for 30% of the total SDA. A 15-day SDA is much longer than values for temperate species, but is again typical for polar marine ectotherms. NH₃ excretion declined post-prandially from around 0.4 μmol animal⁻¹ h⁻¹ to values between 0.025 and 0.223 μmol animal⁻¹ h⁻¹ throughout the SDA. The total O₂ consumed in the SDA was 90.2 μmol O₂, which converts to 44.7 J of energy. This was 45–50% of the energy consumed in the meal (93.5 J). Pre-feeding O:N ratios, after 26 days without food, were around 1, indicating protein as the sole metabolic substrate prior to initiating the SDA. After feeding, O:N ratios rose to between 2.5 and 19, indicating significant use of lipid or carbohydrate from the food. Experiments were conducted in ambient seawater with enhanced levels of Sr (SrCl added at 800 mg kg⁻¹), and limpets were fed microalgal films also grown in enhanced Sr media. Sr incorporated in the shells during the experiment allowed the measurement of shell increments deposited during the SDA. Between five and eight microgrowth bands were present in the Sr-enhanced increments, which was similar to the number of days in the second SDA peak. The mean shell increment laid down was 17.6 μm. Estimating tissue deposition from measured growth increments and published ash-free dry mass (AFDM) to length relationships produced a value of 0.81 mg AFDM, which converted to 26.4 J of energy, or 25–30% of the energy ingested in the meal. Estimates of growth increments associated with a single SDA have not previously been possible. Overall energy used in the SDA and tissue deposition accounted for 75–80% of the energy ingested; the remainder was probably accounted for by unmeasured costs such as mucus production. Received: 6 June 2000 / Accepted: 20 September 2000