No abstract

Remote reefs off southwest Puerto Rico have experienced recent losses in live coral cover of 30 to 80%, primarily due to the decline of Montastraea annularis and M. faveolata from disease and bleaching. These species were formerly the largest, oldest, and most abundant corals on these reefs, constituting over 65% of the living coral cover and 40 to 80% of the total number of colonies. From 1998 to 2001, outbreaks of yellow band disease (YBD) and white plague (WP) affected 30 to 60% of the M. annularis (complex) colonies. Disease prevalence declined beginning in 2002, and then increased immediately following the 2005 mass bleaching event. Colonies of M. annularis (complex) have been reduced in abundance by 24 to 32%, and remaining colonies are missing more than half their tissue. Both M. annularis and M. faveolata have failed to recruit, resheeting has been minimal, and exposed skeletal surfaces are being colonized by macroalgae, bioeroding sponges, and hydrozoans. Other scleractinian corals were smaller in size (mean = 28 cm diameter) and exhibited lower levels of partial mortality; these taxa were affected to a lesser extent by coral diseases and bleaching-associated tissue loss over the last decade. The numbers of small colonies (1 to 9 cm) of these species identified since 2005 also exceeded numbers of larger colonies that died. These reefs appear to be exhibiting shifts in species assemblages, with replacement of M. annularis (complex) by shorter-lived brooding species and other massive and plating corals (Agaricia, Porites, Meandrina, Eusmilia, Diploria, and Siderastrea spp.). To avoid a catastrophic and permanent loss of the dominant, slow-growing reef-building corals, the causes and effects of diseases need to be better understood, and possible control mechanisms must be developed. In particular, steps must be taken to mitigate environmental and anthropogenic stressors that increase the spread and severity of disease.

No abstract

The mangrove-seagrass-patch reef (MSP) ecosystem serves as the principal back-reef nursery for many reef fishes in the Caribbean, but the functional roles of habitats that form this seascape remain unclear. We assessed ecosystem and trophic connectivity of two common reef fishes (schoolmaster, Lutjanus apodus; white grunt, Haemulon plumierii) and one predator (great barracuda, Sphyraena barracuda) in a Caribbean MSP ecosystem using acoustic telemetry and natural dietary tracers. Triangulated positions from an acoustic positioning system indicated that L. apodus and H. plumierii relied on multiple habitats within this MSP ecosystem, occupying areas with more cover (lower risk) during the day and areas with less cover (higher risk) at night. During the day, both species exhibited limited movement away from structured habitats (e.g., mangroves, patch reef) and avoided the primary activity space of S. barracuda in the central channel over sand bottom or seagrass. At night, L. apodus moved into the channel and adjacent seagrass beds on the margin of this high-risk area when S. barracuda occurrence was reduced, suggesting that this species adjusts its foraging activities to minimize encounter rates with predators. Haemulon plumierii also displayed distinct day-night shifts with directed movements at twilight across higher risk habitat to nighttime locations in seagrass. Conspicuous changes in the rate of movement were also detected at different times of the day, and observed mismatches between movement rates of S. barracuda and our two potential prey species appeared to be a behavioral response to reduce their vulnerability. Dietary tracer analysis supported the premise that observed shifts to nocturnal habitats were associated with foraging, with significant contributions of organic matter derived from nighttime locations. Findings from this study clearly demonstrate that the configuration of habitats and spatiotemporal variability in predation risk are key determinants of movement and foraging activities for these species, indicating that an improved understanding of seascape connectivity is critical to the management of reef-dependent species.