Movements and residency of Caribbean reef sharks at a remote atoll in Belize, Central America

We investigated spatial use patterns of 77 Caribbean reef sharks ( Carcharhinus perezi ) at Lighthouse Reef Atoll, Belize over 7 years using residency patterns, kernel density (KD) estimation and network analysis. We found a high degree individual variation in spatial use of the atoll, but there were significant differences in residency and activity space between sexes, with females being overall more resident. Ontogenetic shifts in movement and residency were largely limited to females, as the residency index increased and activity space estimates decreased as females matured, while for males there was no relationship between space use or residency and size. KD analysis revealed many mature females were highly resident to discrete locations, and average activity space of the intermediate-sized sharks was significantly larger than that of the adults, but not the smallest sharks. Markov chain analyses indicated that the southwestern portion of the atoll was the most important movement corridor for all sharks. Both the Blue Hole and Half Moon Caye Natural Monuments provide some protection for larger Caribbean reef sharks; however, a gear ban on longlines on the southwestern forereef between Long Caye and the channel entrance to the Blue Hole would maximize the benefits for all sharks.

Global change differentially modulates coral physiology and suggests future shifts in Caribbean reef assemblages

Global change driven by anthropogenic carbon emissions is altering ecosystems at unprecedented rates, especially coral reefs, whose symbiosis with algal endosymbionts ise particularly vulnerable to increasing ocean temperatures and altered carbonate chemistry. Here, we assess the physiological responses of the coral holobiont (animal host + algal symbiont) of three Caribbean coral species from two reef environments after exposure to simulated ocean warming (28, 31 °C), acidification (300 - 3290 μatm), and the combination of stressors for 93 days. We used multidimensional analyses to assess how multiple coral holobiont physiological parameters respond to ocean acidification and warming. Our results demonstrate significantly diminishing holobiont physiology in S. siderea and P. astreoides in response to projected ocean acidification, while future warming elicited severe declines in P. strigosa. Offshore S. siderea fragments exhibited higher physiological plasticity than inshore counterparts, suggesting that this offshore population has the capacity to modulate their physiology in response to changing conditions, but at a cost to the holobiont. Plasticity of P. strigosa and P. astreoides was not clearly different between natal reef environments, however, temperature evoked a greater plastic response in both species. Interestingly, while these species exhibit unique physiological responses to ocean acidification and warming, when data from all three species are modeled together, convergent stress responses to these conditions are observed, highlighting the overall sensitivities of tropical corals to these stressors. Our results demonstrate that while ocean warming is a severe acute stressor that will have dire consequences for coral reefs globally, chronic exposure to acidification may also impact coral physiology to a greater extent than previously assumed. The variety of responses to global change we observe across species will likely manifest in altered Caribbean reef assemblages in the future.

Millennial-scale change on a Caribbean reef system that experiences hypoxia

Coastal hypoxia has become an increasingly acknowledged threat to coral reefs that is potentially intensifying because of increased input of anthropogenic nutrients. Almirante Bay (Caribbean Panama) is a semi-enclosed system that experiences hypoxia in deeper waters which occasionally expand into shallow coral reefs, suffocating most aerobic benthic life. To explore the long-term history of reefs in the bay we extracted reef matrix cores from two reefs that today experience contrasting patterns of oxygenation. We constructed a 1800-year-long record of gastropod assemblages and isotope compositions from six U-Th chronologically-constrained reef matrix cores. We extracted two cores from each reef at 3 m water depth and two additional cores from a deeper part (4.8 m) of the hypoxia-exposed reef. Results show that the deeper part of the hypoxic reef slowed in growth and stopped accreting approximately 1500 years BP while the shallow part of the reef continued to accrete to the present day, in agreement with a model of expanding hypoxia at this time. Our proxy-based approach suggests that differences among these palaeoindicators in the two reefs may have been driven by an increase in hypoxia via eutrophication caused by either natural changes or human impacts. Similar patterns of increasing herbivores and decreasing carbon isotope values occurred in the shallow part of the hypoxic reef during the last few decades. This suggests that hypoxia may be expanding to depths as shallow as 3 m and that shallow reefs are experiencing greater risk due to increased human activity.

Variation in herbivore grazing behavior across Caribbean reef sites

Herbivorous fish can increase coral growth and survival by grazing down algal competitors. With coral reefs in global decline, maintaining adequate herbivory has become a primary goal for many managers. However, herbivore biomass targets assume grazing behavior is consistent across different reef systems, even though relatively few have been studied. We document grazing behavior of two scarid species in Antigua, Barbuda, and Bonaire. Our analyses show significant differences in intraspecific feeding rates, time spent grazing, and intensity of grazing across sites, which may alter the ecological impact of a given scarid population. We suggest several hypothesized mechanisms for these behavioral variations that would benefit from explicit testing in future research. As managers set targets to enhance herbivory on reefs, it is critical that we understand potential differences in scarid grazing impact. Our findings demonstrate the variability of grazing behavior across different reef sites and call for further investigation of the drivers and ecological implications of these inconsistencies.