Growth potential bioassay of water masses using diatom cultures: Phosphorescent Bay (Puerto Rico) and Caribbean waters

Abstract

1. The growth potential of November surface waters collected at 3 stations in Phosphorescent Bay, Puerto Rico, for the diatoms Bacteriastrum hyalinum, Cyclotella nana (13-1), Skeletonema costatum, and Thalassiosira rotula was determined after enrichment in various ways. 2. Enrichment experiments were also conducted at 14 stations in the Caribbean Sea using Thalassiosira rotula as the bioassay diatom, and at 4 stations using Bacteriastrum hyalinum. 3. Marked differences in response occurred, based on growth for 5 days at 20° C and 700 ft-c of continuous, artificial illumination. All surface waters were toxic to Bacteriastrum hyalinum; Thalassiosira rotula grew well only in the innermost waters of Phosphorescent Bay, and at 3 of the 14 Caribbean stations. Skeletonema costatum grew only at 2 of the 3 Phosporescent Bay stations (the converse of the Thalassiosira rotula response), and Cyclotella nana (13-1) at all stations. 4. Growth was either stimulated, inhibited or unaffected by certain nutrients; a combination of natural nutrient limitation and inhibition influenced growth. 5. Transect gradients occurred in the relative influence of various nutrients on growth, such as the omission of silicate from the complete enrichment which led to a progressive, offshore improvement in growth of Skeletonema costatum, whereas phosphate omission limited growth of Bacteriastrum hyalinum. 6. The occurrence of marked short scale differences in water quality ("chemical patchiness") is suggested by the station to station variations in effect of a given nutrient or nutrient combination on the growth of a given species and growth differences between species. These effects were not predictable from the hydrographic observations. Individual species responses to a specific nutrient enrichment were likewise unpredictable from a given species' known bioassay response. 7. The relevance of the demonstrated occurrence of "chemical patchiness" to the examination of the general problems of succession and distribution of species is briefly discussed. © 1970 Biologischen Anstalt Helgoland.