Modeled differences of coral life-history traits influence the refugium potential of a remote Caribbean reef

Sarah W Davies,Carly D Kenkel,Johnathan T Kool,Marie E Strader,Mikhail V Matz

doi:10.1007/s00338-017-1583-8

Abstract

Remote populations can influence connectivity and may serve as refugia from climate change. We investigated two reef-building corals (Pseudodiploria strigosa and Orbicella franksi) from the Flower Garden Banks (FGB), the most isolated, high-latitude Caribbean reef system, which, until recently, retained high coral cover. We characterized coral size-frequency distributions, quantified larval mortality rates and onset of competence ex situ, estimated larval production, and created detailed biophysical models incorporating these parameters to evaluate the source–sink dynamics at the FGB from 2009 to 2012. Estimated mortality rates were similar between species, but pre-competency differed dramatically; P. strigosa was capable of metamorphosis within 2.5 d post-fertilization (dpf) and was competent at least until 8 dpf, while O. franksi was not competent until >20 dpf and remained competent up to 120 dpf. To explore the effect of such contrasting life histories on connectivity, we modeled larval dispersal from the FGB assuming pelagic larval durations (PLD) of either 3–20 d, approximating laboratory-measured pre-competency of P. strigosa, or 20–120 d, approximating pre-competency observed in O. franksi. Surprisingly, both models predicted similar probabilities of local retention at the FGB, either by direct rapid reseeding or via long-term persistence in the Loop Current with larvae returning to the FGB within a month. However, our models predicted that short PLDs would result in complete isolation from the rest of the Caribbean, while long PLDs allowed for larval export to more distant northern Caribbean reefs, highlighting the importance of quantifying larval pre-competency dynamics when parameterizing biophysical models to predict larval connectivity. These simulations suggest that FGB coral populations are likely to be largely self-sustaining and highlight the potential of long-PLD corals, such as endangered Orbicella, to act as larval sources for other degraded Caribbean reefs.

Highlights

Caribbean reefs have experienced some of the most dramatic coral declines over the last few decades[1 ], the Flower Garden Banks (FGB) – a system of two very unusual reefs located 185 km south of the Texas-Louisiana border in the Gulf of Mexico– appear to be the exception
Size-frequencies and larval traits of Psuedodiploria strigosa and Orbicella franksi at Surveys of O. franksi and P. strigosa revealed similar size frequency ranges across the sampled reefs, P. strigosa colonies were consistently in smaller size classes than O. franksi (Fig 1B; Wilcoxon sum rank test, P=2E-04)
14-20 dpf for O. franksi, indicating that competency patterns reported here are consistent across years for populations of these species at the FGB

Summary

Introduction

Caribbean reefs have experienced some of the most dramatic coral declines over the last few decades[1 ], the Flower Garden Banks (FGB) – a system of two very unusual reefs located 185 km south of the Texas-Louisiana border in the Gulf of Mexico– appear to be the exception. The FGB’s isolation, buffering from increased sea surface temperatures due to its high- latitude location, low degradation and high coral cover make it the ideal potential refugium from climate change for Caribbean corals. In order to be a good refugium the FGB must meet three requirements: first, FGB coral populations must be self-seeding (i.e., not requiring larval input from elsewhere to sustain populations), and second, coral larvae originating from the FGB must be capable of emigrating and surviving at other Caribbean reefs. These reefs must be relatively resilient to recurrent disturbances such as bleaching

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