Seasonal and daily dynamics in pelagic larvae of marine shelf bottom invertebrates in nearshore waters of Kandalaksha Bay (White Sea)

Abstract

Seasonal and daily population dynamics have been studied in pelagic larvae of littoral and upper-sublittoral bottom invertebrates in the plankton of the shallow, narrow Velikaya Salma Sound, which connects the inner and outer areas of the Kandalaksha Bay in the western part of the White Sea. Hydrologically, this Sound is characterised by a clearly defined cycle of great seasonal variations in water temperature coupled with more or less stable salinities and regular, pronounced semi-diurnal tides corresponding to daily and lunar monthly tidal cycles. The seasonal dynamics of larvae in the Sound reflect differences in occurrence of spawning periods in local waters of various species and systematic groups of bottom invertebrates. These differences are caused by the correlation of spawning periods of local species of different zoogeographical origin with the different water temperatures. They reflect, also, lunar periodicities of spawning and larval hatchings. The daily dynamics of larval abundancies are related to the daily spawning rhythms of many species with pelagic development affected by the daily tidal cycles of the Velikaya Salma Sound. A daily invasion of the Sound by pelagic larvae of bottom invertebrates from the inner and the outer parts of the Kandalaksha Bay occurs at ebb tide, and also at flood tide; the rhythms of the invasions coincide with the daily spawning rhythms of the Sound's invertebrates. From literature data summarized by Mileikovsky (1958a, b, 1960a, b, c, 1961, 1965, 1968, 1970), it is concluded that seasonal, lunar and daily (tidal) reproductive periodicities for the marine shallowshelf bottom invertebrates concerned, follow world-wide ecological patterns. It is evident that the effects of these rhythms upon the population dynamics of pelagic invertebrate larvae, as demonstrated by the present data on the Velikaya Salma Sound (White Sea), must also follow world-wide regularities.