On the Effect of the severe Winter of 1928–1929 on the Oyster Drills (with a record of five years' observations on sea-temperature on the oyster-beds) of the Blackwater Estuary.

Abstract

During the year 1928 the writer was engaged in a study of the bionomics of the oyster drills on the oyster beds in the region of the River Blackwater, Essex. At this time the presence of a foreign species was detected (1) and definite records were made of the relative abundance of the three following drills or tingles:—Murex erinaceus (=Ocinebra), Purpura lapillus (=Nucella), and Urosalpinx cinerea. It so happened that the winter of 1928–29 was unusually cold; the temperature of the water over the oyster beds was unusually low in January and February, 1929, ranging about the freezing-point of fresh water (see Table II and Fig. 1). The oyster-cultivators in this locality had many years previously stated that during severe winters many marine animals, such as the oyster drills or tingles and the burr Echinus miliaris, are killed in such great numbers as sometimes to exterminate the species. The observations made by the writer in 1928 offered an opportunity to test these statements, and of estimating the effect of the extreme cold in early 1929 on the animals mentioned above.