Chemical defense of embryos and larvae of a West Indian gorgonian coral, Briareum asbestinum

The complex life cycles of colonial marine invertebrates provide an unusual opportunity to examine potential constraints in chemical defense because colonies are often chemically well defended, and the multiple developmental stages are accessible. Briareum asbestinum is unique among Caribbean gorgonians in surface brooding newly fertilized, conspicuously colored eggs and larvae; therefore, all developmental stages can be collected from the surface of a colony. In St. Croix, US Virgin Islands, maternal colonies and their embryos, larvae and newly metamorphosed juveniles have high levels of asbestinane diterpenoids. Although the embryos are brooded for approximately 8 months, and the four major compounds are present in adult colonies and their early embryonic progeny in similar concentrations, there is not a significant correlation between the levels of secondary compounds in embryos and their natal colonies. Levels of compounds did not vary significantly with stage nor change linearly through development. Instead, levels of compounds measured every two days fluctuated significantly during ontogeny, declining abruptly at transitions in development, such as between the embryo and larval stage and during the metamorphosis from larva to juvenile. This pattern suggests that compounds are not simply sequestered in oocytes by the maternal colony, since we would expect a monotonic decline in levels as development proceeds if no new compounds were produced. Instead, significant increases in concentration of three diterpenes during the larval stage suggests that larvae are capable of synthesizing their own diterpenes. One potential function of the compounds in developmental stages of Briareum asbestinum is as a deterrent to predators or microorganisms. A generalist fish (Thalassoma bifasciatum) does not appear to consume embryos or larvae, but a specialist fish (Chaetodon capistratus) and a specialist invertebrate predator (Hermodice carunculata) do consume some stages.