Relationship between planktonic dinoflagellate abundance, cysts recovered in sediment traps and environmental factors in the Gullmar Fjord, Sweden

In order to study the relationship between planktonic dinoflagellates, cyst production and environmental factors,a sediment trap study was conducted i n the Gullmar Fjord, Swedish West coast, during 21 days in May-June 1998. F ive locations for sediment traps were randomly selected every third day. Th e traps were moored at the five locations and moved to new locations after 3 days. At every location, a CTD depth profile was obtained and Water sampl es were collected for plankton, chlorophyll a and nutrient analysis. Meteor ological and hydrographic data for the period were obtained from continuous monitoring. Three dinoflagellate species, which have not previously been r ecorded from the Kattegat or the Skagerrak (Scrippsiella crystallina, Scrip psiella lachrymosa and Scrippsiella trifida), were encountered during the a nalysis of cysts from. the sediment traps. The abundance of the different s pecies in the motile form encountered in the water column and cyst form enc ountered in the sediment traps varied greatly. The discrepancy between the number and species encountered in traps and water samples is discussed. No density-dependent relationship between the abundance of planktonic gst-form ing dinoflagellates and the number of cysts recovered could be observed. A multiple regression showed that the variation in cyst yield from the traps for the most abundant species was correlated with water sur a,face temperat ure, ambient light radiation and the depth of the halocline. The nutrient c oncentrations (NH4+, NO2-, NO3- and PO43-), which are known to play a cruci al role in induction of sexuality and cyst formation. under laboratory cond itions, correlated poorly with the number of dinoflagellate cysts encounter ed in the traps.