Aspects of the ecology and physiology of selected rock pool biota

Abstract

The ecology of five rockpools situated at Zonqor Point, Marsascala, on the East coast of Malta, was studied. A survey of the biota, and of the physico-chemical conditions of the pools was carried out for the period October 1970 to September 1971. High level pools were dominated by green algae whereas pools lower down on the shore, were found to be dominated by a red and brown algal flora, and to contain littoral and sublittoral animal species. Variations in temperature and salinity were greatest for the high level pools, whereas variation in oxygen saturation of pool water was most pronounced for those pools with the greatest density of organisms. Low phosphate levels were found in high-level pools in early winter, but high values were attained during long periods of isolation from the sea, during summer. The total niitrogen and pigment content of selected algae inhabiting rockpools and the shore, were determined. Pool algae showed no differences from shore algai in their pigment composition. The chlorophyll and total nitrogen content of Enteromorpha, however, varied considerably during the year. The rates of oxygen consumption of Middendorffia capraerum and of Patella lusitanica were measured for shore and pool animals over various temperature ranges at different times of the year. The rate-temperature curves always indicated that the metabolism of the animals is maintained fairly constant over the temperature range they encounter in their environment. Middendorffia also showed the ability to set limits to the highest and lowest values its metabolic rate can have. The tolerance of high salinities was tested for Middendorffia inhabiting pools during summer. It was found to withstand sea water concentrations ranging from 90% ta 140% normal sea water, indefinitely. An assessment of the limiting effects of the ecological factors studied, on pool biota was made. The rockpools studied were also classified into three major groups, one of the groups being intermediate between the two other groups, both in physico-chemical and biotic factors.