Abstract
Many reef invertebrates reproduce through simultaneous broadcast
spawning, with an apparent advantage of overwhelming potential predators
and maximizing propagule survival. Although reef fish have been observed
to consume coral gamete bundles during spawning events, there are no
published records of such predation by benthic invertebrates. Here, we
document several instances of the ruby brittle star, Ophioderma
rubicundum, capturing and consuming egg-sperm bundles of the
mountainous star coral, Orbicella faveolata, and the symmetrical
brain coral, Pseudodiploria strigosa, during spawning events in
the Cayman Islands in 2012 and the Florida Keys in 2022. These
observations are widely separated in space and time (>600
km, 10 years), suggesting that this behavior may be ubiquitous on
western Atlantic reefs. Since O. rubicundum spawns on the same or
subsequent nights as these coral species, we hypothesize that this
opportunistic feeding behavior takes advantage of the coral’s lipid-rich
bundles to recover energy reserves expended by the brittle star during
gametogenesis. The consumption of coral gametes by adult brittle stars
suggests a novel trophic link between reef invertebrates, and also
provides evidence that ophiuroid-coral symbioses may oscillate between
commensalism and parasitism depending on the ontogeny and reproductive
status of both animals. Our observations provide insights into the
nuanced, dynamic associations between coral reef invertebrates and may
have implications for coral fecundity and resilience.