Abstract:
Temperature limits for fertilization and early development were examined in the tropical sea urchin Echinometra lucunter to test the hypothesis that the temperature range for normal development limits the geographical distribution 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 to 37°C, with high fertilization at temperatures above 15°C. Development to echinoplutei occurred at 16, 18 and 23°C, but appeared to be optimal at temperatures from 27–34°C. Hatched embryos (blastulae, gastrulae) and echinoplutei larvae could survive temperatures between 38 and 40°C for 2 h, which might be important for larvae that are carried into the shallow, heated waters of the Caribbean reef flat. Examination of the seawater temperatures at the northern and southern geographical limits (Beaufort, North Carolina; Florianópolis, Brazil) showed winter monthly minimum temperature of 18°C and summer monthly maximum of 27.5 and 25.5°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 Echinometra lucunter does not appear to be limited by the temperatures at which normal development occurs, in refutation of Andronikov's hypothesis. The distribution of E. lucunter may instead be limited by factors such as adult temperature tolerances, temperatures needed for growth or spawning, or hydrographic features that limit larval settlement and juvenile survival.