15. Coral Reproduction in the Eastern Pacific

Sexual reproductive activity has been demonstrated in all reef-building (zooxanthellate) scleractinian corals examined from Mexico to the equatorial eastern Pacific (Galápagos Islands). Eleven of 13 species spawn gametes, six are gonochoric, three hermaphroditic, and four exhibit significant mixed sexuality (both gonochoric and hermaphroditic). Four or 30.1 %, two species each of Pocillopora and Porites, produce autotrophic ova. Porites panamensis is the only known zooxanthellate brooder. Also sexually active are the azooxanthellate scleractinian Tubastraea coccinea and the zooxanthellate hydrocoral Millepora intricata. Reproductive structures, sex ratios, age at sexual maturity, sexuality, and developmental mode have been determined from largely histological evidence. Agariciid corals, comprising more than one-third of investigated species, exhibit predominantly mixed sexual systems with sequential cosexual hermaphroditic cycles in four species. Mixed sexuality is also minimally exhibited in populations of two dominantly gonochoric species. Several eastern Pacific corals spawn mostly on lunar day 17 and 1–2 days following; however, multispecific spawning has not been observed probably because of seasonal, diel, and variable timing in spawning behavior. Factors contributing to the high fecundity of eastern Pacific corals include (1) seasonally prolonged reproductive activity, (2) small size of mature gametes allowing for production of high numbers, (3) split spawning with bimonthly gamete production in some species, (4) alternation of sex maturation in gamete development, and possibly (5) their low latitudinal location under relatively constant and high thermal conditions. Coral community persistence, reef growth and recovery are highly dependent on both sexual and asexual reproductive processes. Asexual fragmentation by physical and biotic causes is particularly important, especially for branching pocilloporid species and the fungiid coral Diaseris distorta. Asexual propagation in massive and encrusting poritid and agariciid species is also common-place, often the result of bioerosion and colony breakage by foraging reef fishes. Some research areas in need of attention are noted, for example (a) timing of spawning and the behavior of gamete release of several species, (b) life cycles of Pocillopora spp. and Millepora intricata, and (c) effects of anthropogenic stressors on eastern Pacific coral reproduction and recruitment.