Effects of salinity on the clam <Emphasis Type="Italic">Chamelea gallina</Emphasis>. Part I: alterations in immune responses

In the present study, the effects of differing salinities on some important functional responses of haemocytes from the clam, Chamelea gallina, were investigated. The animals were kept for 7 days at 28‰ (hyposalinity), 34‰ (control) and 40‰ salinity (hypersalinity), and total haemocyte count (THC), haemocyte volume, phagocytosis, lysozyme-like activity (in both haemocyte lysate and cell-free haemolymph) were measured. The survival-in-air test was also performed. Clams kept at 28‰ showed significantly increased THC with respect to animals kept at 34 and 40‰. The analysis of haemocyte size frequency distribution highlighted that in clams kept at 28‰ the haemocyte fraction of about 5 μm in diameter and 50–100 femtolitre in volume increased markedly. Conversely, in animals kept at 40‰ an increase was observed in the haemocyte fraction having about 8–10 μm diameter and 400–500 femtolitre volume. Higher phagocytic activity was recorded in haemocytes from control clams, with respect to that of clams kept at 28 and 34‰. Lysozyme-like activity in haemocyte lysate was shown to increase significantly in animals kept at 28‰ with respect to that of clams kept at 40‰, whereas enzyme activity in cell-free haemolymph from clams kept at 34‰ was significantly higher with respect to that of clams maintained at 40‰. A relationship between phagocytosis and lysozyme secretion is suggested. The resistance to air exposure of clams kept at 28 and 40‰ was shown to decrease significantly; LT₅₀ values fell from 7 days in clams kept at 34‰ to 4 and 5 days in those kept at 28 and 40‰, respectively. Results demonstrated that salinity values far from 34‰ affects the functional responses of haemocytes and reduce the resistance of clams to exposure to air.     

First evidence of gender-related differences in immune parameters of the clam Ruditapes philippinarum (Mollusca, Bivalvia)

For the first time, gender-related differences in some important functional parameters of haemocytes from the clam Ruditapes philippinarum have been studied. Clams were collected during the pre-spawning phase, when sex can be distinguished by microscopic observation of gonadal smears, in order to ascertain whether the two sexes reach the stressful spawning period with different degrees of immunosurveillance. Total haemocyte count (THC), haemocyte size frequency distribution, capability of haemocytes to assume the vital dye neutral red (NR, indicative of endocytotic activity), lysozyme-like and acid phosphatase activities in both haemocyte lysate (HL) and cell-free haemolymph (CFH), and superoxide dismutase (SOD) and catalase (CAT) activities in HL were all evaluated. No differences in THC values were found between the two sexes, but differing haemocyte size frequency distributions were observed: the fraction of larger haemocytes (7–9 μm diameter, 200 fl volume) was markedly increased in females and that of smaller haemocytes (<5 μm diameter, <200 fl volume) markedly increased in males. Interestingly, when haemocytes were observed under the light microscope, a significantly higher percentage of granulocytes was found in haemolymph from females, compared with that of males. Significantly increased NR uptake was recorded in female haemocytes. No significant variation in lysozyme-like activity was observed in HL, whereas in CFH, enzyme activity was significantly higher in females. HL acid phosphatase activity was significantly higher in males with respect to females; no significant variations in enzyme activity were observed in CFH. HL SOD and CAT activities were significantly higher in females than in males. Overall, on the basis of the cell parameters studied here, gender-related differences in immune parameters were found in R. philippinarum, indicating that females have more active haemocytes than males during the pre-spawning period.     

How does salinity tolerance influence the distributions of <Emphasis Type="Italic">Brachionus plicatilis</Emphasis> sibling species?

Environmental salinity is important in defining Brachionus plicatilis sibling species distributions. However, while salinity influences distributions, sibling species often co-exist. Three different mechanisms potentially account for the partial co-occurrence of sibling species: (1) siblings have differing salinity tolerances that partially overlap; (2) siblings physiological tolerances may be commonly broad, but relatively small differences in tolerances differentiate distributions via interactions e.g. competition; or (3) siblings distributions may be influenced by physical factors other than salinity. Here, we assess the extent of salinity tolerance in three B. plicatilis sibling species (B. plicatilis 6TUR, B. plicatilis IOM and B. rotundiformis 6TOS) by measuring population growth rate (μ, day⁻¹) and egg development time in response to salinity (5–60‰) and salinity fluctuations (≤ Δ40‰). Sibling species were identified by analysis of the mitochondrial COI gene, and salinity responses were compared by regression analysis. Responses differed significantly between siblings, although the broad trends were similar. Positive growth occurred at all salinities, and highest growth rates ranged between 0.93 and 1.08 day⁻¹ at 16–18‰. Rapid changes in salinity reduced growth rates, but net mortality occurred only in one treatment (100% mortality on transfer from 10 to 40‰). Egg development time was largely invariant with salinity except for B. plicatilis IOM and where rotifers were transferred from 30 to 60‰. We indicate that several siblings are similarly euryhaline and tolerate salinity fluctuations. Undoubtedly, wide tolerances in B. plicatilis are adaptations to ephemeral and seasonally variable habitats. Given common broad salinity tolerances, it is unlikely that the differential distributions of sibling species are a direct result of physiological constraints. Instead, we illustrate using a simple model that subtle differences in physiological tolerances may have important impacts on interactions between sibling species, which may in turn influence distributions.     

Effects of salinity on endogenous rhythm of the Manila clam, Ruditapes philippinarum (Bivalvia: Veneridae)

The Manila clam Ruditapes philippinarum, an intertidal bivalve, was exposed to different salinity regimes (from 31.0–31.7‰ down to 20‰, 15‰, 10‰, 5‰), and the endogenous rhythm in its oxygen consumption was studied using an automatic intermittent-flow respirometer. When exposed to salinities reduced from 31.5‰ to 20‰ and 15‰ under otherwise constant conditions, the clams recovered a clear endogenous circatidal rhythm in their oxygen-consumption rate after having dampened periods of 12 h and 48 h, respectively. At salinities less than 10‰, however, the oxygen-consumption rate was depressed greatly at the beginning of the experiment for about 36 h and then increased to a level higher than normal, but the rhythm of oxygen consumption was not recovered. The results of this study indicate that the Manila clam, a euryhaline organism, cannot maintain a normal metabolic activity at a salinity lower than 15‰. All clams were dead after exposure at a salinity of 5‰ for 7 days. Received: 28 February 2000 / Accepted: 26 August 2000     

Effect of different time of salt stress on growth and some physiological processes of <Emphasis Type="Italic">Avicennia marina</Emphasis> seedlings

Growth and physiological characters of Avicennia marina seedlings cultured under different levels of salinity were compared at 45 and 100 days after sowing. Based on the growth and physiological responses, the levels of salinity were grouped into two kinds, moderate (5–30‰) and extreme (40 and 50‰ as well as 0‰). Root and shoot length, leaf area, biomass of different organs, and net photosynthesis rate all showed a similar trend: the seedlings grew better at moderate levels of salinity but were adversely affected by extreme levels. Longer exposure (100 days) to salinity markedly enhanced the difference between the effects of the two levels on growth. By 45th day, the cotyledons had withered and fallen off. The concentration of ions (K⁺, Na⁺, Ca²⁺, Mg²⁺, Cl⁻) and ash content of the cotyledons were determined before sowing and 45 days later. Ion concentrations and ash content of cotyledons were markedly lower at 45 days—lower than the initial levels—in seedlings irrigated with water at 0‰ salinity level. This suggested that the poor growth of these seedlings at 100 days may be due to lack of ions provided by the cotyledons. The high ion concentrations in the cotyledons grown at moderate salinity levels suggest that these organs may function as ion sinks at this stage, reducing the concentration of ions and consequent toxicity caused by excessive concentrations. Root biomass was higher than shoot biomass 45 days after sowing, whereas after 100 days, shoot biomass was higher. At the early stage of growth (45 days), the rate of photosynthesis at lower levels of salinity (0–30‰) was limited mainly by stomatal closure but at higher levels of salinity (40–50‰), other factors came into play. Later, at 100 days, the causes of reduced photosynthetic rate were other than stomatal closure at both low and high levels of salinity. This indicates that photosynthesis is affected by prolonged exposure to salt stress—including that caused by 0‰ salinity, as shown by poor growth of the seedlings.     

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

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

Salinity stress and hydrogen peroxide regulation of antioxidant defense system in Ulva fasciata

The regulation of antioxidant defense system in macroalgae exposed to salinity stress was examined in Ulva fasciata Delile. As compared to the 30‰ control, a long-term (4 days) exposure to hyposaline (5, 15‰) and hypersaline (60, 90, 120, 150‰) conditions inhibited growth rate and TTC reduction ability. A decrease in maximum quantum efficiency (F _v/F _m ratio) and the maintenance of superoxide dismutase activity under salinity stress indicate the potential generation of reactive oxygen species in chloroplasts. An exposure to 15, 60, and 90‰ decreased seawater H₂O₂ contents but increased thallus H₂O₂ contents that are positively correlated with TBARS and peroxide contents. Alleviation of oxidative damage and H₂O₂ accumulation at 15 and 90‰ by a H₂O₂ scavenger, dimethylthiourea, suggests that oxidative damage occurring under moderate hyposaline and hypersaline conditions is ascribed to accumulated H₂O₂. Increased glutathione reductase activity and glutathione content and decreased ascorbate content are responsible for accumulated H₂O₂ at 15, 60, and 90‰, while ascorbate peroxidase activity increased only at salinity ≥ 90‰. Catalase and peroxidase activities also increased at 60 and 90‰ for H₂O₂ removal, but only catalase showed activity increase at 15‰. For the regeneration of ascorbate, the activities of both dehydroascorbate reductase and monodehydroascorbate reductase were increased at 5 and 15‰ while only monodehydroascorbate reductase activity increased at 60 and 90‰. It is hypothesized that the availability of antioxidants and the activities of antioxidant enzymes are increased in U. fasciata to cope with the oxidative stress occurring in hyposaline and hypersaline conditions.     

Behaviour of echinoid larvae around sharp haloclines: effects of the salinity gradient and dietary conditioning

We examined larval response to a range of sharp haloclines and determined the effect of dietary conditioning on that response in the sea urchins Echinometra lucunter and Arbacia punctulata. We reared larvae in the laboratory under a high or low concentration of either single (Isochrysis galbana) or mixed (Isochrysis galbana, Dunaliella tertiolecta, Thalassiosira weissflogii) microalgal species. For both species of sea urchins, rate of larval development was faster and age-specific larval length and width were greater in high-ration than low-ration diets. We examined the distribution of two- and four-arm larvae of E. lucunter from each diet treatment and of four-arm larvae of A. punctulata from the high-ration diets in cylinders with experimentally constructed haloclines. In three of the halocline treatments, the salinity of the bottom layer was 33‰ and that of the top layer was 21, 24 or 27‰ (21/33, 24/33 and 27/33) and in a fourth one, the salinities of the bottom and top layer were 30 and 21‰, respectively (21/30). The position of larvae in the cylinders varied with the steepness of the halocline and with dietary conditioning for both sea urchin species and all developmental stages tested. Significantly more larvae crossed the haloclines into water of 24 and 27‰ salinity than into water of 21‰ salinity. We observed an effect of diet on the position of larvae in the cylinders, and that effect varied among halocline treatments for both species. The proportion of larvae of E.lucunter that crossed the halocline was greater in low- than high-ration diets in the 24/33 and 27/33 treatments. Position of four-arm larvae in the cylinders also varied with food quality in high-ration diets: for E.lucunter in the 24/33 treatments, and for A. punctulata in the 21/30 treatments, more larvae from the single- than from the mixed-species diets were present above the halocline. Salinity in the adult habitat during most of the active reproductive period ranged from 15 to 40‰. We showed that larvae can respond to gradients in salinity, and therefore can remain within a water mass of higher salinity overlying the adult habitat. However, survival of poorly fed larvae may be increased if they are introduced into a new water mass and carried away from a nutritionally poor environment. Received: 9 July 1997 / Accepted: 12 January 1998     

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

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

Kinetic measurements of metal accumulation in two marine macroalgae

 We measured the uptake kinetics of four metals (Cd, Cr, Se and Zn) in two marine macroalgae (the green alga Ulva lactuca and the red alga Gracilaria blodgettii). Metal uptake generally displayed a linear pattern with increasing exposure time. With the exception of Cr, which exhibited comparable uptake rate constants at different concentrations, uptake rate constants of Cd, Se and Zn decreased with increasing metal concentration, indicating that the seaweeds had a higher relative uptake at lower metal concentration. Uptake of Cd and Zn was higher in U. lactuca than in G. blodgettii, whereas uptake of Cr and Se was comparable between the two species. Only Cd and Zn uptake in U. lactuca was significantly inhibited by dark exposure. A decrease in salinity from 28 to 10‰ enhanced the uptake of Cd, Cr, Se and Zn in U. lactuca 1.9-, 3.0-, 3.6-, and 1.9-fold, respectively. In G. blodgettii, Cd uptake increased twofold when salinity was decreased from 28 to 10‰, whereas uptake of Cr and Zn was not significantly affected by salinity change. The calculated depuration rate constants of metals in U. lactuca were 0.01 d⁻¹ for Cd, 0.05 to 0.08 d⁻¹ for Cr, 0.14 to 0.16 d⁻¹ for Se, and 0.12 to 0.15 d⁻¹ for Zn, and were relatively independent of the metal body burden in the algae. The predicted bioconcentration factor was 3 × 10⁴ for Cd, 2 × 10³ for Cr, 40 to 150 for Se, and 1 to 2 × 10⁴ for Zn in U. lactuca. Our kinetic study suggested that U. lactuca would be a good biomonitor of Cr and Zn contamination in coastal waters. Received: 14 September 1998 / Accepted: 29 May 1999     

Effects of sudden changes in salinity on endogenous rhythms of the spotted sea bass Lateolabrax sp.

The endogenous rhythm of oxygen consumption in juvenile spotted sea bass (Lateolabrax sp.) was measured to test the effects of sudden changes in salinity on the metabolic activity. Mean oxygen consumption rates of this euryhaline fish decreased by 13.5 to 16.0% and 25.3 to 36.4% when they were transferred from 31.5 to 15‰ seawater and to fresh water (0‰), respectively. The maximum rate of oxygen consumption was observed between 18:00 and 19:00 hrs local time, 1 to 2 h before sunset, even though they were kept in constant darkness. The peaks of oxygen consumption occurred in 23.2- and 23.3-h intervals, which correspond with a circadian rhythm, as revealed by maximum entropy spectral analysis. A markedly weakened rhythm in oxygen consumption occurred from 8 to 10 d after onset of the experiments. This study indicates that spotted sea bass can withstand sudden drops in salinity from 31.5‰ to fresh water, and yet maintain a regular though somewhat dampened endogenous rhythm of oxygen consumption. Received: 16 June 1997 / Accepted: 3 February 1998     

The combined effects of salinity and temperature on larvae of the mussel Mytilus edulis

The combined effects of salinity and temperature on survival and growth of larvae of the mussel Mytilus edulis (L.) were studied. The effects of salinity and temperature are significantly related only as the limits of tolerance of either factor are approached. Survival of larvae at salinities from 15 to 40 is uniformly good (70% or better) at temperatures from 5° to 20°C, but is reduced drastically at 25 °C, particularly at high (40) and low (20) salinities. Larval growth is rapid at a temperature of 15 °C in salinities from 25 to 35, at 20 °C in salinities from 20 to 35. Optimum growth occurs at 20 °C in salinities from 25 to 30. Growth decreases both at 25° and 10 °C; the decline is most drastic at high (40) and low (20) salinities.Part of a study completed at the Bureau of Commercial Fisheries, Biological Laboratory, Milford, Connecticut, USA, while on a UNESCO Fellowship.     

Production of glycine betaine and dimethylsulfoniopropionate in marine phytoplankton. II. N-limited chemostat cultures

The influence of salinity on the time elapsed between two successive molts and the size reached after each molt were studied at 30, 21, 12 and 3‰S in juveniles of two co-occurring grapsid species, Cyrtograpsus angulatus and C. altimanus, cultured under identical conditions of temperature, photoperiod and food. Juvenile growth patterns were compared between these species (which differ in size-at-maturity and maximum size). C. angulatus grew faster than C. altimanus, reflecting a higher increment per molt and a shorter intermolt period. A significant difference existed between the number of instars preceding the size of maturity in both species: >11 in C. angulatus, 6 in C. altimanus. There was evidence of a differential effect of low salinity on growth. By the end of the experiment, individuals of both species were smaller at the lowest salinity (3‰) tested; the largest crabs developed at 21‰ (C. angulatus) and 30‰ (C. altimanus). The size difference between the “optimal” and the less suitable salinities in the sixth crab instar was 12.4% in C. angulatus and 35% in C. altimanus. During early juvenile development (Crab Instars 1 to 4), there were slight differences in intermolt period among salinities in C. angulatus, but large differences in C. altimanus. The longest intermolt period of C. altimanus was at 3‰S and the shortest at 30‰S. In the following instars (5 to 10 in C. angulatus and 5 to 6 in C. altimanus), the longest intermolt period occurred at 21‰S, the shortest at 3‰S, in both species. Interspecific differences in response to low salinities may explain why C. angulatus occurs throughout a whole temperate coastal lagoon, whereas C. altimanus is restricted to its mouth. Received: 12 July 1998 / Accepted: 24 February 1999     

Ammonium, but not nitrate, stimulates an increase in glutamine concentration in the haemolymph of Tridacna gigas

The concentration of glutamine in Tridacna gigas haemolymph increased >35-fold following exposure to sea water supplemented with ammonium (20 μM), but no increase was observed with nitrate (20 μM). Lack of a diel cycle, no decrease in haemolymph glucose levels, the expression patterns of glutamine synthetase in zooxanthellae and host, and the lack of glutamine release in response to nitrate supplementation all support the proposition that the increase in haemolymph glutamine is a product of the host and not the zooxanthellae. Unlike ammonium, nitrate accumulates rapidly in the haemolymph. It has no effect on the concentration of glutamine in the haemolymph, but there is an increase in arginine, histidine and lysine in the haemolymph, suggesting the release of these essential amino acids from zooxanthellae. Glutamine synthetase (GS) activity decreased markedly in the gill and less so in the mantle over a period of 6 d exposure to elevated ammonium (20 μM). In contrast, GS activity in zooxan- thellae doubled. The response of zooxanthellae in situ was confirmed by incubating freshly isolated zooxanthellae for 4 d in ammonium, which resulted in a ten-fold increase in GS activity. Comparison of the in situ response of zooxanthellae with that obtained in vitro indicates that the symbionts are likely to be exposed to ammonium concentrations lower than that found in the haemolymph. Received: 14 November 1997 / Accepted: 28 April 1998     

The respiratory metabolism of Tilapia mossambica (Teleostei)

In a series of experiments 174, 120 and 139 individuals of the teleost Tilapia mossambica (Peters), were acclimated to 30°C and to salinities of 0.4, 12.5 and 30.5, respectively. The effect of temperature and salinity upon oxygen consumption was studied by abruptly transferring fish of different wet weights to temperatures from 15° to 40°C at an average initial pO₂ of 250mm Hg. At each salinity, the proportionate response to temperature is size-independent. The metabolic rate increases as a function of temperature at 15° and 30°C but not at 40°C. Oxygen consumption is, however, salinity dependent; maximum rates are obtained at 12.5S. This salinity is isotonic in the 80 g fish and, to a lesser extent, in the 5 g fish. Reduction in osmotic load is suggested as the probable cause for a greater scope for activity and greater rate of oxygen consumption in 12.5 salinity.     

Aspects of nitrogen metabolism of the common mussel Mytilus edulis: Adaptation to abrupt and fluctuating changes in salinity

Mytilus edulis L. were exposed to abrupt (3015 and 1530) and fluctuating (sinusoidal 12 h cycles of 301530) changes in salinity, and the changes in the total osmoconcentration of the haemolymph were recorded. The response of nitrogen metabolism to the altered extracellular osmotic concentrations was investigated in terms of the concentrations of the total NPS (ninhydrin-positive substances) pool and the individual amino acids of the tissues, the concentration of the amino acids of the haemolymph, and the rates of excretion of ammonia and amino acids by whole individuals. The haemolymph became isosmotic with the seawater with abrupt changes in salinity, but with fluctuating salinity was slightly hyperosmotic as the salinity decreased and then slightly hypo-osmotic as the salinity increased. This resulted in a reduction in the extent of the extracellular osmotic change compared to the change in fluctuating salinity to which it was exposed. Total NPS of the tissues decreased with an abrupt decrease in salinity and increased with an abrupt increase in salinity, but a seasonal dependence of the response was indicated. The short-term response of tissue NPS to fluctuating salinity was equivocal, but with long-term exposure the concentration declined. Ammonia and amino acid excretion increased with both an abrupt decrease in salinity and fluctuating salinity and decreased with an abrupt increase in salinity. Haemolymph amino acids increased with an abrupt decrease in salinity. The increased rates of nitrogen excretion accounted for the reductions in the NPS concentrations of the tissues except in the early stages of fluctuating salinity. Taurine, aspartate, threonine, serine, glycine and arginine declined with an abrupt decrease in salinity while alanine and glutamate increased slightly. With an abrupt increase in salinity, alanine and ammonia accumulated in the tissues and then declined while the other amino acids increased slowly over a longer time-course. Similar individual amino acid responses were seen with long-term exposure to fluctuating salinity, except for taurine which did not decrease in concentration. On the basis of the changes in tissue amino acids and ammonia, it is suggested that the alanine dehydrogenase reaction is the primary nitrogen-fixing reaction in marine bivalves such as M. edulis.     

Respiratory responses of the estuarine mysid Neomysis integer (Peracarida: Mysidacea) in relation to a variable environment

The euryhaline mysid Neomysis integer (Peracarida: Mysidacea) is a common member of the hyperbenthos of the upper reaches of European estuaries. In the East Looe River Estuary (Cornwall, England), this species experiences extensive tidal and seasonal changes in temperature (3 to 15 °C) and salinity (1 to 34‰). In this investigation, the effects of temperature (5, 10 and 15 °C) and salinity (1, 10, 20 and 30‰) on the oxygen consumption of male and female N. integer are reported, and are related to field measurements to identify the adaptive responses of the respiratory physiology to such a variable environment. The general responses were similar for each sex; however, at any given temperature/salinity combination, male N. integer consumed more oxygen than females. The general trends were increased oxygen consumption with increasing temperature (Q₁₀ values ranged from ∼1.7 to 2.5) and decreased oxygen consumption with increasing salinity. Temperature and salinity interacted at high water antagonistically to minimise changes in mysid oxygen-consumption. When related to tidal fluctuations in temperature and salinity experienced by N. integer inhabiting the East Looe River Estuary, the results reveal how the respiratory physiology of this species is adapted to its variable environment. Received: 16 June 1998 / Accepted: 15 December 1998     

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

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

Heavy metal contamination and physiological variability in the Brazilian mangrove crabs Ucides cordatus and Callinectes danae (Crustacea: Decapoda)

 Physiological studies were made on the crabs Ucides cordatus (L.) and Callinectes danae sampled from populations living in “polluted” mangroves on the southeast littoral of Brazil. Analysis of Cu, Cd, Zn, and Fe of sediments and crab tissues showed interspecific differences in tissue concentrations, and significantly higher levels of Cu, Cd, and Zn in “polluted” populations compared to “unpolluted” crabs living in uncontaminated mangrove in the same geographical area. Individuals of both species from the polluted site showed significantly greater capacities for regulating blood osmotic concentrations at low salinity (9‰). However, U. cordatus showed a reduced hypo-regulatory ability in 34‰S. Differences in ionoregulation were also seen. “Polluted”C. danae showed significantly higher Na/ K-ATPase levels in posterior gills compared to “unpolluted” crabs. Oxygen consumption rates (M˙ _O2) were elevated in U. cordatus, but depressed in C. danae from the “polluted” population. Individuals of both species from this site showed significantly lower O:N ratios, mainly because of an increased net efflux of ammonia. Adenylate energy charge (AEC) values of muscle and hepatopancreas in “unpolluted” and “polluted” populations of both species were not significantly different. These physiological differences are discussed in relation to the known acute physiological and metabolic effects of heavy metals in crustaceans, and interpretated in the light of possible adaptive changes following long-term exposure to contamination. Received: 6 August 1999 / Accepted: 22 June 2000     

Effects of temperature and salinity on larval development ofNecora puber (Brachyura: Portunidae)

Temperature and salinity affected both length of larval development and mortality inNecora puber collected in the Ría de A Coruña during December 1984 and January 1985. Development time decreased considerably with increased temperature. This decrease was sharper when temperature increased from 15° to 20°C than when it increased from 20° to 25°C. At 35S, average development took 48, 32 and 28 d at 15°, 20° and 25°C, respectively. At the three salinities tested (25, 30 and 35), larval development was completed only at 15°C, at 20°C/30 and 35S, and at 25°C/35S. Development times at 15° and 20°C were highly significantly different at both 35 and 30S (P 0.01). However, there were no significant differences between development times at 20° and 25°C (P > 0.05). Within any one specific temperature series, no significant difference was observed between the salinity values tested (P > 0.05). The duration of each of the five zoeal stages was similar within each and the same temperature/salinity combination, whereas the duration of the megalop was twice as long as any of the zoeal stages. The combination of the lowest temperature (15°C) and the highest salinity (35) tested resulted in the greatest larval survival of 28%. Highest mortality occurred at 25°C, at which temperature development was completed only at 35S. A sharp drop in larval survival was observed in the transition period Zoea V — megalop in all combinations of temperature and salinity tested. Within the limits of tolerance to temperature and salinity, the former effected more pronounced differences in the duration of larval development, while salinity appeared to constitute a limiting factor for survival.