Seasonal variation in the effects of hard substratum biofilming on settlement of marine invertebrate larvae

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Abstract
The effect of season on “biofilming”;, as a cue for the settlement of marine invertebrate larvae, was investigated in a long‐term field study during the years 1992–1994. The series of settlement experiments was conducted in a tidal rapid on the west coast of Scotland, and involved manipulations of artificial panels. Biofilming of substrata, whilst excluding larval settlement, was achieved by the enclosure of panels within tight‐fitting (but removable) mesh screens so that the number of settlers on filmed and unfilmed substrata were counted in the initial absence of other incumbent post‐larvae. Depending on larval species, the effects of biofilming were found to be either facilitatory or inhibitory. Significant within‐ and between‐species seasonal differences in the settlement responses were detected, and a reversal of the effect of biofilming on larval settlement response, from inhibitory to facilitatory and vice versa, was noted with season in the case of some taxonomic groups and species (e.g. Tubulipora sp., Plagioecia sp., Electra pilosa (L.)). The present study emphasizes the need for extended field studies of larval responses to environmental cues, when the focus of interest is in drawing general inferences about naturally occurring behavioural patterns at settlement.