Role of early post-settlement mortality in recruitment of benthic marine invertebrates

Abstract

Newly settled invertebrates usually are subject to high rates of mortality (Type 111 survivorship). Therefore, knowledge of early post-settlement events is critical in determ~nlng if and when patterns of abundance and distribution of juveniles reflect settlement patterns. Causes of mortality of early juvenile invertebrates include delay of metamorphosis, biological disturbance, physical disturbance and hydrodynamics, physiological stress, predation, and competition. Predation is the best documented cause of early n~ortallty, particularly for mobile species. Other possible causes which have not yet been investigated are developmental abnormalities, insufficient energy reserves, disease and parasitism In most studies of sessile invertebrates, early post-settlement mortality did not obscure the relationship between recruit and settler abundance. This relatlonsh~p appears to be more varlable among mobile species for which migrat~on also can modify the distnbution of settlers. There is still insufficient data to support general conclusions about the conditions under which recruitment rate can be predicted from settlement rate. Studies have found evidence of the effects of both settlement and early post-settlement mortality on the dlstributlon of some sessile species at small spatial scales, but mortality appears to have less influence a t larger scales. Much of the present knowledge of the early postsettlement period has come from studies of barnacles and ascidians and more information is needed for other groups of benthic marine invertebrates, particularly mobile species. The relative importance of mortality during the early post-settlement period compared to other life history stages can only be detel-mined in studies which examlne several stages.