Variation in the planktonic larval duration of the temperate wrasse Semi-cossyphus pulcher

Abstract

Recently settled juveniles of the temperate wrasse Semicossyphus pulcher were studied for evidence of patterns in otolith microstructure corresponding to developmental stages. Fish collected at settlement were found to range in age from 37 to 78 d, yet size only ranged from 12.7 to 16.0 mm. Examination of otolith increment width, used as a measure of daily growth, revealed 2 patterns: (1) fish with long larval lives (e.g. 50 to 78 d) had an abrupt slowing of growth after ca 35 to 37 d in the plankton, with continued slow growth until settlement; and (2) fish that settled early (e.g. 35 to 40 d) had no evidence of slow growth. It would appear that 35 to 37 d is the minimum development period (i.e. precompetent period) required for this species. In addition, little variation occurred in the duration of the precompetent phase relative to the duration of the slow-growth, competent period. Post-settlement growth was unaffected by the duration of the larval life, regardless of the presence of the slow-growth phase, suggesting that extended competent phases are not detrimental to the fish. Constraints on the larvae to delay metamorphosis may be related to the need to find a suitable settlement site within the appropriate stage of their development. A longer precompetent phase may require a longer competent period to ensure that the larvae encounter a settlement site.