The importance of tolerance and preference experiments for the interpretation of mesopsammon field distributions

Abstract

1. Marine sandy beaches allow interesting basic studies on animal distribution and other marine ecological aspects. 2. The field distributions observed should be accompanied by laboratory experiments in order to establish the specific effects of the different environmental factors. The use of tolerance and preference experiments as simple and highly successful tools is discussed. 3. The distribution of the copepod Parastenocaris vicesimaKlie in a sandy beach on Askö (Baltic Sea) has been investigated and tested in laboratory experiments. Measurements of salinity, temperature, water content, oxygen availability, grain size and organic matter in four successive beach stations are presented. 4. P. vicesima was absent in the two most seaward stations and the vertical distribution in the two inner stations seemed rather irregular. 5. Tolerance experiments with 8 different salinity concentrations showed the greatest survival in 10 to 0.1‰ S. Preference experiments revealed a preference zone at 2.5 to 0.1‰ 6. Tolerance to high temperature was tested at 30° C in 5 different salinities. The survival was best in 5 to 0.5‰ 7. A simple apparatus for testing the responses of small animals to low oxygen availabilities was constructed. A lower tolerance limit in habitat water of 15° C was located around 1×10-7 gO2 cm-2min-1. 8. In preference experiments with different grain sizes, P. vicesima preferred sand with a medium grain size of 250 μ. 9. The results of our laboratory experiments could be used to explain the field distributions of P. vicesima observed. The lack of animals in the outer station was caused by the salinity factor. The vertical distribution in the inner stations was a result of the combined effects of (a) detritus concentration, (b) oxygen availability and (c) great percentages of fine sand, which attracted the animals in several layers. 10. The necessity of knowing the local weather conditions which were effective during the period previous to the field investigations is stressed. © 1967 Biologischen Anstalt Helgoland.