Effect of Algal Exudates on Substratum Selection by Motile Telotrochs of the Marine Peritrich CiliateVorticella marina

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Abstract
SYNOPSIS.Several species of marine peritrichs are found as epiphytes on small strands of filamentous green and red algae affixed to the substratum of marine intertidal rock pools. In pools located along the coast of Narragansett Bay, the motile vorticellid telotrochs appear to show a substratum selection for specific algae. Exudation products by marine algae have distinct differences; some Phaeophyta have particularly high values for dissolved organic matter (DOM), and for phenolic compounds. Algal exudates appear to influence population growth of vorticellids. The mean survival percentage of vorticellid populations increased with exposure to exudates fromCladophora gracilis, Polysiphonia harveyiandPolysiphonia lanosa; and decreased with exposure to those ofAscophyllum nodosum, Fucus spiralisandScytosiphon lomentaria.Telotroch settlement ofVorticella marinawas enhanced by exudates ofCladophora gracilis, Polysiphonia harveyiandPolysiphonia lanosa, but was reduced by exudates ofAscophyllum nodosum, and was prevented by exudates ofFucus spiralisandScytosiphon lomentaria.Algal exudates were obtained by allowing photosynthetic activity of the experimental algae for 6 hr. The exudates were filtered and the concentration of DOM, total phenols and carbohydrates determined. The filtered seawater containing the exudate was placed in a box‐type plastic dish on which the vorticellids had colonized. Survival percentages and the percentage of population due to telotroch settlement were calculated. This investigation indicates that algal exudates may exert a significant influence on the selection of substrata by vorticellid telotrochs and suggests that the ecologic stability of a given rock pool may be considerably lessened by a high level of Phaeophtya and the consequent reduction of Aufwuchs species.