Jaap Dorgelo

SALT TOLERANCE IN CRUSTACEA AND THE INFLUENCE OF TEMPERATURE UPON IT

I11 . The influence of temperature on salt tolerance . . . . I . Introduction . . . . . . . . . . 2 . Classification of beneficial effects of temperature on salt tolerance 3 . Discussion . . . . . . . . . . . (a) Classification . . . . . . . . . (I) General remarks . . . . . . . . (2) Evaluation of the temperature effects . . . . (b) Other ecological implications . . . . . . (I) Colonization of dilute media in the tropics . . . . (2) Migration . . . . . . . . . IV . General conclusion . . . . . . . . . .

Effects of diet and heavy metals on growth rate and fertility in the deposit-feeding snail Potamopyrgus jenkinsi (Smith) (Gastropoda: Hydrobiidae)

Evidence for the influence of food type and heavy metals on shell growth and fertility is presented for a freshwater population of the snail P. jenkinsi. When fed an excess of lettuce or lamb heart (protein source), growth rates were higher for lettuce. Highest growth rates occurred at a diet of lettuce plus lamb heart. Fertility was favoured by a diet of lamb heart. When fed an excess of lettuce, the EC50 growth values were 16 µg Cd l−1, 13 µg Cu l−1, and 103 µg Zn l−1 in lake water; snail fertility was inhibited at 25 µg Cd l−1 and 30 µg Cu l−1. A diet of lake detritus spiked with Cd or Cu resulted in a decrease of approximately 50% in growth rates, when compared with growth on non-spiked detritus. Spiked detritus lost metals into lake water. Food type positively interacted with metal stress, both for growth rate and fertility. The assessment of inhibitory effects of detritus contaminated either in the field or, notably, by spiking, and serving as food source for deposit feeders is hampered by sampling problems in the field and by redistribution processes of pollutants between particles and water in laboratory-scale experiments.

Density fluctuations in populations (1982–1986) and biological observations ofPotamopyrgus Jenkinsi in two trophically differing lakes

The hydrobiid snailPotamopyrgus jenkinsi (E.A. Smith), characterized by parthenogenesis and ovovivipary, was quantitatively sampled monthly between June, 1982, and December, 1986, on sandy bottoms in the shallow zones of the meso-oligotrophic Lake Maarsseveen I and the eutrophic Lake Maarsseveen II. The snail demonstrated a very clumped distribution in both lakes. The mean numbers of juveniles and adults taken together fluctuated strongly. Organisms in Lake I showed relatively high densities (up to 25,000 per m2) in 1982, followed by a sudden drop to values approaching zero in December, 1982, with a subsequent rapid increase in densities, fluctuating between 2,000 and 200 per m2. In Lake II, densities of snails fluctuated between 13,000 and 300 per m2 with decreases in the spring of 1985 and 1986. The various types of decreases in the lakes are extensively discussed, but no explanation is presently available. The reduction in Lake I was of catastrophic proportions, but the speed of recovery of the population was remarkable.Floating was observed only in Lake I, and only during the occurrence of the highest densities on the sediment. Burrowing behaviour was very common, but strongly suppressed under an uninterrupted dark regime. A shift of temperature from 15 to 22°C had the same effect. A number of submerged macrophyte species from Lake I proved to attractP. jenkinsi in the absence of sandy substrate, though these plants were only covered by the snail during the period of the highest densities in 1982. Temperatures of 20°C or lower were well tolerated, unlike temperatures of 25 and 30°C. Growth was distinct at 10, 15 and 20°C. Keeled individuals were encountered in much higher numbers in Lake I than in Lake II.

Comparative ecophysiology of gammarids (crustacea: amphipoda) from marine, brackish and fresh-water habitats exposed to the influence of salinity-temperature combinations. III. Oxygen uptake

Abstract Weight-specific respiratory rates in males of 3 gammarids from different salinity regimes, ranging from the marine environment to strictly fresh water, were measured by routine manometric methods in order to assess the main as well as the interaction effects of salinity and temperature. The results were submitted to an analysis of variance. All species demonstrate a reversible more or less decreasing QO2 at increasing salinity. This statistically well established phenomenon does not depend on the salinity boundaries of the various species in nature. Salinity sensitivity increase at higher temperatures. The influence of temperature is great, with exception of the intertidal Chaetogammarus marinus, between 5° and 15° C. The effect of interaction of salinity and temperature on respiration was significant, again with the exception of Chaetogammarus marinus. The absence of the temperature effect as well as the interaction of temperature in salinity-dependent respiration have positive ecological implications in the fluctuating temperature regime of the intertidal area and probably are characteristic for this biotope.

Relationship between C/N ratio of food types and growth rate in the snail Potamopyrgus jenkinsi (E.A. Smith)

Measurements of shell growth rate showed that a difference in the population structure of Potamopyrgus jenkinsi between the northern and the southern shore of a small Dutch lake could be a result of food quality of the sediment. In further studies, a series of diets differing in organic C and N content was offered to the snails. There was no functional relationship between growth rate and C or N content of the diets. Growth rate plotted against the C/N ratios of the diets followed an optimum curve with a maximum at a C/N value of 15.9. Highest growth rate was followed by successful reproduction. In the lower C/N range, growth rate rapidly increased with small increases in C/N values. This kind of relationship supports previously disregarded findings for Artemia.

Comparative ecophysiology of gammarids (crustacea: amphipoda) from marine, brackish- and fresh-water habitats exposed to the influence of salinity-temperature combinations. IV. Blood sodium regulation

Abstract Blood sodium regulation as a function of salinity and temperature has been determined for matures of gammarid species from marine littoral (Chaetogammarus marinus), oligohaline (Gammarus tigrinus) and fresh water (G. fossarum) environments in order to get quantitative data on their regulatory characteristics in relation to the salt regime in which they occur in nature. Literature records of Crustacea show that the curves describing the regulation of sodium and total osmoconcentration in relation to those in the environment have the same shape. The three species are hyperosmotic over the whole salinity range, tested at 5°, 15° and 25° C, except for G. fossarum in supranormal, potentially lethal salinities. They show hyperregulation at homoiosmotic levels that decrease from coastal to brackish water to fresh water origin. The influence of temperature on the level of regulation has no ecological implications for the populations of the 3 species studied. In its osmotic regulation G. tigrinus resembles C. marinus more than G. fossarum, which may be linked with its great salt tolerance. Small males of C. marinus have a higher blood sodium content as compared with big ones.

Comparative ecophysiology of gammarids (Crustacea: Amphipoda) from marine, brackish and fresh-water habitats, exposed to the influence of salinity-temperature combinations: I. Effect on survival

Summary1.Survival of mature males of 3 gammarids from different salinity regimes, ranging from marine to limnetic conditions, was established in order to analyze the main as well as the interaction effect of salinity and temperature. The results were submitted to an analysis of variance.2.A new modification for treatment of the survival data has been applied.3.Chaetogammarus marinus, from the marine littoral, tolerates sub- and supranormal salinities according to an optimum curve pattern.Gammarus tigrinus, from oligohaline water, tolerates supranormal salinities up to seawater concentration equally well. Survival drops distinctly in concentrated seawater.Gammarus fossarum, the fresh-water species, shows a rapidly decreasing tolerance at supranormal salinities.4.Salt tolerance is neither favoured nor inhibited by temperature interaction in the natural salinity ranges of the species.5.Increasing temperature influences survival negatively in all species.6.G. tigrinus is most susceptible in spring to both salinity and temperature.7.The results are discussed with regard to the evolutionary migration from the marine environment to freshwater.

Blood osmoregulation and temperature in crustaceans

‘All animals (and plants) need to osmoregulate their salt and water content’ (Sutcliffe 1978), since blood electrolytes are very important for processes involved in (de)hydration, metabolism, permeability and active transport, and cell excitability. From the beginning of this century, temperature has been known to affect osmoregulation (see Dorgelo 1976), and since Kinne (1956) introduced the temperature-salinity relationship many publications have appeared dealing particularly with coastal and estuarine animals.

Preliminary data on size composition and settlement ofDreissena polymorpha (Pallas) (Mollusca: Bivalvia) in lakes differing in trophic state

Size composition of colonies and settlement of larvae on nylon substrates as function of depth inDreissena polymorpha demonstrated differences in three lakes of different trophic state. In one lake, the data on size distribution in the colony and of the settled larvae also differed. The explanation requires further research.

Growth in a freshwater snail under laboratory conditions in relation to eutrophication

Shell growth in the snail Potamoryrgus jenkinsi (Prosobranchia, Hydrobiidae) was measured under laboratory conditions. Individuals of populations from two lakes differing in trophic status were kept in water with sandy substrates from each environment. Growth was faster in the environment of the more eutrophic lake, regardless of the origin of the snails; this held in particular for the smallest size class.