Coral death

Yellow band disease (YBD) is a bacterial infection affecting corals of the Montastrea annularis species complex. Recent mortality rates of M. annularis spp. on Bonaire have risen due to YBD and other biotic and abiotic factors. The loss of staghorn coral, Acropora cervicornis, the preferred habitat of the threespot damselfish, Stegastes planifrons, has caused the damselfish to inhabit M. annularis spp. Unfortunately, M. annularis spp. are slower growing corals that take longer to reach reproductive maturity and are thus less able to withstand S. planifrons biting their tissues and creating algal gardens on exposed skeleton. This weakens the coral and makes it more susceptible to diseases like YBD. The objective of this study was to examine the relationship between S. planifrons gardening and YBD. Sample sites of healthy and diseased colonies of M. annularis spp. were established across depths at Yellow Sub dive site in Kralendijk, Bonaire. Sites were monitored for damselfish inhabitants and signs of coral biting. Pictures were taken of each site to chart the progress of the disease over the course of the study, and ImageJ was used to determine percent cover of healthy versus unhealthy coral. No significant relationship was found between S. planifrons activity and YBD, although S. planifrons seemed to select healthy colonies. The increase of damselfish populations and their detrimental effects on Bonaire’s reef calls attention to the need for fishing regulations of predatory species and a heavier focus on the conservation of A. cervicornis thickets.

This student research was retrieved from Physis: Journal of Marine Science XI (Fall 2012)19: 83-87 from CIEE Bonaire.

Abstract

Some excavating sponges of the genus Cliona compete with live reef corals, often kill- ing and bioeroding entire colonies. Important aspects affecting distribution of these species, such as dispersal capability and population structure, remain largely unknown. Thus, the aim of this study was to determine levels of genetic connectivity and dispersal of Cliona delitrix across the Greater Caribbean (Caribbean Sea, Bahamas and Florida), to understand current patterns and possible future trends in their distri- bution and effects on coral reefs. Using ten species-specific microsatellite markers, we found high levels of genetic differentiation between six genetically distinct popula- tions: one in the Atlantic (Florida-Bahamas), one specific to Florida and four in the South Caribbean Sea. In Florida, two independent breeding populations are likely separated by depth. Gene flow and ecological dispersal occur among other popula- tions in the Florida reef tract, and between some Florida locations and the Bahamas. Similarly, gene flow occurs between populations in the South Caribbean Sea, but appears restricted between the Caribbean Sea and the Atlantic (Florida-Bahamas). Dispersal of C. delitrix was farther than expected for a marine sponge and favoured in areas where currents are strong enough to transport sponge eggs or larvae over longer distances. Our results support the influence of ocean current patterns on genetic connectivity, and constitute a baseline to monitor future C. delitrix trends under climate change.