Notes on the Biology of Tellina tenuis da Costa

Abstract

SUMMARYThe present paper deals with the results of investigations into certain phases in the life-history of the bivalve mollusc Tellina tenuis carried out during the autumn of 1926 and 1927.Collections in the intertidal zone and below L.W.M., were made in a number of bays in the Cumbrae and neighbourhood, Kames Bay, Millport, being selected for intensive study.In Kames Bay Tellina tenuis ranges from a little below H.W.M. to depths of about 4 fm. The maximum concentration of about 1000 per sq. m. is found at L.W.M. springs and the numbers decrease to zero at H.W.M. and 4 fm.In Kames Bay the density of Tellina tenuis falls in a progressive manner from L.W.M. to H.W.M.The size-frequency distribution shows a regular gradation from the lower to the higher levels. At L.W.M. and below individuals of small size predominate, while at H.W.M. they are proportionately few.At higher levels growth is more rapid than at the lower levels.The size-frequency curves and density of Tellina tenuis in the other bays at L.W.M. correspond with those of half-tide in Kames Bay.The rate of growth may therefore be influenced by the density of population as well as by the habitat.In all areas the 1926 brood predominates.The Tellina tenuis population in Kames Bay seems to be composed of four year-groups, one of which is almost unrepresented. Collections from neighbouring bays indicate that older groups may be present.The amount of young brood on the bottom seems to vary considerably from year to year, being large and small in alternate years.The two closely related species, T. tenuis and T. fabula, are both plentiful in Kames Bay, but their range is not coincident.Eipe sperms were found from May onwards and ova were rounding off in June.Young Tellina tenuis, passing the 2-mm. sieve but retained by the 1-mm. sieve, were found in Kames Bay in August, chiefly below L.W.M., but in October plentifully distributed up to half-tide and in lesser numbers higher up the shore.The food usually consists of vegetable detritus, but during the spring increase diatoms appear almost exclusively in the gut.