Longevity, life history, and relative body wall size in sea urchins

Annual survival rates in 38 populations of 17 sea urchin species in the Indo-West Pacific were related to relative size of the body wall and exposure to the surf. Populations were studied at Hawaii, Enewetak Atok, Queensland, New South Wales and Western Australia, Sri Lanka, Seychelles, Kenya, Zanzibar, and Isaerl (Eilat). Live animals were dissected to determine the size of body components. Parameters of the Richards growth function were determined from animals tagged with tetracycline. Tagged animals were collected after they had been in the field for 1 yr. Growth parameters were used with parameters from size-frequency distributions to estimate Z, the mortality coefficient. Stepwise multiple regression was used to examine the relationship between annual survival probability (p) and two indepencent variables, ..cap alpha.. and E, where E is a subjective measure of exposure to surf (1 = most exposed). Survivorship increases with increased relative size of the body wall and with increased protection from the surf. The positive relationship between survival probability and relative body wall size supports the hypothesis that survival is related to allocation of resources to maintenance. The significane of longevity in urchins probably is that it is related to the predictability of survival of prereproductivemore » individuals. The greater the unpredictability, the longer life must be. Long life requires a greater investment in maintenance mechanisms and hence, among other adaptations, a more massive body wall.« less