Modeling Larval Connectivity of Coral Reef Organisms in the Kenya-Tanzania Region

C Gabriela Mayorga-Adame,Yvette H Spitz,Harold P Batchelder

doi:10.3389/fmars.2017.00092

C Gabriela Mayorga-Adame, Yvette H Spitz + Show 1 more

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https://doi.org/10.3389/fmars.2017.00092

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Abstract

Most coral reef organisms have a bipartite life-cycle; they are site attached to reefs as adults but have pelagic larval stages that allow them to disperse to other reefs. Connectivity among coral reef patches is critical to the survival of local populations of reef organisms, and requires movement across gaps that are not suitable habitat for recruitment. Knowledge of population connectivity among individual reef habitats within a broader geographic region of coral reefs has been identified as key to developing efficient spatial management strategies to protect marine ecosystems. The study of larval connectivity of marine organisms is a complex multidisciplinary challenge that is difficult to address by direct observation alone. An approach that couples ocean circulation models with individual based models (IBMs) of larvae with different degrees of life-history complexity has been previously used to assess connectivity patterns in several coral reef regions (e.g., the Great Barrier Reef (GBR) and the Caribbean). We applied the IBM particle tracking approach to the Kenya-Tanzania region, which exhibits strong seasonality in the alongshore currents due to the influence of the monsoon. A 3-dimensional (3D) ocean circulation model with 2 km horizontal resolution was coupled to IBMs that track virtual larvae released from each of 661 reef habitats, associated with 15 distinct regions. Given that reefs provide homes to numerous species, each with distinctive, and in aggregate very diverse life-histories, several life-history scenarios were modeled to examine the variety of dispersal and connectivity patterns possible. We characterize virtual larvae of Acropora corals and Acanthurus surgeonfish, two coral reef inhabitants with greatly differing pelagic life-histories, to examine the effects of short (50 days) pelagic larval durations (PLD), differences in swimming abilities (implemented as reef perception distances), and active depth keeping in reef connectivity. Acropora virtual larvae were modeled as 3D passive particles with a precompetency period of 4 days, a total PLD of 12 days and a perception distance of 10 m. Acanthurus virtual larvae were characterized by 50 days precompetency period, a total PLD of 72 days and a perception distance of 4 km. Acanthurus virtual larvae were modeled in

Highlights

Tropical coral reef ecosystems are very important from both the ecological and economical points of view (Spalding et al, 2001)
Regional connectivity matrices with reefs grouped into 15 regions (Figure 1) show a dominant South to North connectivity pattern along the Kenya-Tanzania coast (Figure 3), as represented by the predominance of circles below the 1:1 diagonal line, which indicates sites where local retention occurred
For the 2000 Acanthurus simulation (Figure 3A) small proportions of north to south connections occur in most regions, but mainly at the northern-most (Somalia [south Somalia (sS)], Kenya regions [north Kenya (nK), south Kenya (sK)]) and southern-most regions and in some central regions (Dar es Salaam Peninsula [DP] and central Tanzania [cT])

Summary

Introduction

Tropical coral reef ecosystems are very important from both the ecological and economical points of view (Spalding et al, 2001). They are fragile, and have been declining in recent years in most regions of the world (Hughes et al, 2003; Pandolfi et al, 2003; Melbourne-Thomas et al, 2011), since they are highly susceptible to anthropogenic stressors operating at global scales (e.g., global warming and ocean acidification) and local scales (e.g., pollution/eutrophication, fishing, over-commercialization for recreation). Coral reef organisms exhibit various degrees of site attachment ranging from completely sessile, like corals and sponges, to highly mobile, like fish and crustaceans. Most adult reef organisms are distributed in metapopulations connected by pelagic larvae that disperse subject to the ocean currents (Bode et al, 2006; Cowen and Sponaugle, 2009)

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