Temperature limits to fertilization and early development in the tropical sea urchin Echinometra lucunter

Temperature limits for fertilization and early development were examined in the tropical sea urchin Echinometra lucunter to test the hypothesis that t he temperature range for normal development limits the geographical distrib ution of marine species (Andronikov, V.B., 1975. Heat resistance of gametes of marine invertebrates in relation to temperature conditions under which the species exist. Mar. Biol. 30, 1-12). Eggs could be fertilized from 12 t o 37 degrees C, with high fertilization at temperatures above 15 degrees C. Development to echinoplutei occurred at 16, 18 and 23 degrees C, but appea red to be optimal at temperatures from 27-34 degrees C. Hatched embryos (bl astulae, gastrulae) and echinoplutei larvae could survive temperatures betw een 38 and 40 degrees C for 2 ii, which might be important for larvae that are carried into the shallow, heated waters of the Caribbean reef flat. Exa mination of the seawater temperatures at the northern and southern geograph ical Limits (Beaufort, North Carolina; Florianopolis, Brazil) showed winter monthly minimum temperature of 18 degrees C and summer monthly maximum of 27.5 and 25.5 degrees C, respectively. Fertilization and normal development can occur at temperatures outside those seen in natural conditions in any part of the geographical range. Thus, the geographical distribution of Echi nometra lucunter does not appear to be limited by the temperatures at which normal development occurs, in refutation of Andronikov's hypothesis. The d istribution of E. lucunter may instead be limited by factors such as adult temperature tolerances, temperatures needed for growth or spawning, or hydr ographic features that limit larval settlement and juvenile survival. (C) 1 999 Elsevier Science BN. All rights reserved.