Abstract

IN a recent study1 on the occurrence of the planktonic genus Sagitta in weekly collections at Port Erin 1928–37 (excepting 1935) and the Mersey Channel, More cambe Bay,Anglesey coast 1937, interesting facts have emerged. It seems desirable to give some of the results here pending publication of the whole. Two species are found: S. elegans Verrill, the oceanic form2, is predominant at Port Erin; S. setosa J. Muller, the coastal form, is predominant in Liverpool Bay and is recorded here for the first time. S. elegans is absent from the Liverpool district until February-March, when an influx occurs correlated with the appearance of high salinities (see graph). S. setosa is absent from Port Erin until September-December with a maximum in October (see graph). These interchanges of species occur at about the periods of the equinoctial tides and indicate (a) extensive mixing of inshoreand offshore waters in the greater volume and movements of the equinoctial tides, and (6) the occurrence of relatively stable bodies of water in Liverpool Bay in periods between the equinoxes. The occurrence of relatively stable bodies of water oscillating in estuaries has long been known, but stability in an open bay such as Liverpool Bay is of great interest and worthyof further investigation.

References

1. Pierce, E. Lowe, Thesis, Cohen Library, University of Liverpool (1938).
2. Russell, F. S., J. Mar. Biol. Assoc., 20 (2), 309 (1935).