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

Kurzfassung

Zur biologischen Gütebeurteilung wurden mit Proben von Oberflächenwasser aus der Phosphorescent Bay (Porto Rico) Kulturen vonBacteriastrum hyalinum, Cyclotella nana, Skeletonema costatum undThalassiosira rotula angesetzt.Thalassiosira rotula undBacteriastrum hyalinum dienten außerdem als Testorganismen für Wasserproben aus der Karibischen See. Die Kulturmedien wurden mit verschiedenen Nährsalzen und Wirkstoffen angereichert, wodurch die Vermehrung der Diatomeen in sehr unterschiedlicher Weise stimuliert oder limitiert wurde. Es ergab sich, daß Oberflächenwasser stets toxisch gegenüberBacteriastrum hyalinum war,Cyclotella nana aber in allen Wasserproben gedieh. Die beiden anderen Arten zeigten unterschiedliches Verhalten. Trotz der relativ geringen Entfernungen der einzelnen Stationen in der Phosphorescent Bay (2500 m) traten bezüglich der Wasserqualität Unterschiede auf, die aus den hydrographischen Daten nicht hervorgingen, jedoch im Kulturexperiment anhand der Wachstumsrate der Diatomeen abgelesen werden konnten. Die Befunde werden im Hinblick auf allgemeine Probleme der Sukzession und Verteilung von Phytoplanktonarten diskutiert.

Summary

1. The growth potential of November surface waters collected at 3 stations in Phosphorescent Bay, Puerto Rico, for the diatomsBacteriastrum hyalinum, Cyclotella nana (13–1),Skeletonema costatum, andThalassiosira rotula was determined after enrichment in various ways.

2. Enrichment experiments were also conducted at 14 stations in the Caribbean Sea usingThalassiosira rotula as the bioassay diatom, and at 4 stations usingBacteriastrum 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 toBacteriastrum 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 theThalassiosira rotula response), andCyclotella 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 ofSkeletonema costatum, whereas phosphate omission limited growth ofBacteriastrum 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.