Physiological constraints upon marine organisms

Abstract

ABSTRACTWhen compared with sea water, most marine invertebrates are isosmotic but show varying degrees of ionic regulation, from accumulation of potassium and calcium to reductions of magnesium and sulphate. A reduction of sulphate in pelagic animals such as jellyfish and salps, and an accumulation of ammonium ions in arrow-worms (Sagitta) contribute to their near-neutral buoyancy. Marked reductions in salinity exclude mahy marine invertebrates. In the Baltic, polychaetes, bivalve molluscs and decapod crustaceans are reduced from 193, ninety-two and sixty-four species in the Belt Sea (salinity S 10-30‰) to three, four and two in the Gulf of Finland (salinity S 5-9‰). The chelicerateLimuluscan stand a wide range in salinity, a few insect larvae can tolerate concentrations of 200% sea water, while the branchiopod shrimpArtemiacan stand crystallising brine (36-37% NaCl). Very few species can tolerate temperatures of 40°C. One such species is the polychaeteAlvinella pompejana,a hydrothermal vent animal at East Pacific Ridge (to the W of S America). The harpacticid copepodTigriopusliving in evaporating rockpools has a lethal temperature of 42°C at a salinity of S 90‰, but at S 8‰ that temperature is 34°C. Lack of oxygen and presence of hydrogen sulphide limit the distribution of animals in certain areas. Most active animals have respiratory pigments in their principal body fluid. Burrowing invertebrates such asArenicolaandLingulahave respectively haemoglobin in the blood and haemerythrin in the coelomic fluid, with mean oxygen capacities of 6 ml O2per 100 ml in each case, compared to 0·6 and 0·5 ml in sea water at 10° and 20°C.