Eleven isolates representing populations from the Caribbean, eastern Atlantic, and Indo-West Pacific were compared. Use of random amplified polymorphic DNA (RAPD) markers clearly revealed an Indo-West Pacific group, a Caribbean/Cape Verde Islands group, and a Canary Islands group. Crossing studies showed different levels of interfertility. Temperature tolerance studies indicate that Pacific isolates have a broader temperature survival range than Atlantic isolates, which may be correlated to local temperature extremes.