A model-based assessment of reef larvae dispersal in the Western Indian Ocean reveals regional connectivity patterns — Potential implications for conservation policies

Abstract

International audienceMarine resources are under increasing pressure from a wide variety of threats such as overfishing, offshore energy development, and climate change. As marine ecosystems degrade, so do the well-being and livelihoods of humans that depend directly on the ecosystem goods and services they provide. Marine protected areas have been proposed to protect biodiversity, restore damaged ecosystems, sustain fisheries, and rebuild overexploited stocks. The effectiveness of marine protected areas depends in part on their effectiveness as connected networks, linked over large areas by ecological processes such as larval dispersal. Here, we applied a biophysical model driven by ocean currents derived from satellite altimetry to evaluate connectivity between Western Indian Ocean reefs. We applied graph-theoretic analysis, including clustering and a betweenness centrality metric. Our results show high interconnectivity within several regions (Mozambique Channel, Mascarene archipelago) and lower connectivity across the WIO region. We compared the results with the current MPA network, and proposed sites/reefs that should be considered priority sites for MPA implementation: Pebane, Cosmoledo, Majunga, Masoarivo, Platte Island, Farquhar, Agalega and Geyser bank. Our results are timely, considering the oil and gas exploration that is ongoing in the region. We discuss implications for transboundary marine policies and regional cooperation in the Western Indian Ocean, and advocate the creation of a regional-scale organization to structure interactions among the different actors

Population genetic structure and connectivity of the seagrass Thalassia hemprichii in the Western Indian Ocean is influenced by predominant ocean currents

“…The cluster in Mozambique is under the influence of the eddies in the Mozambique. The findings byCrochelet et al (2016) strongly confirm our hypothesis that the major hydrodynamic features shape population genetic structure of T. hemprichii in the WIO region. The most geographically isolated populations were those at Inhaca Island, which were also genetically the most differentiated populations.…”

“…The only genetic cluster that was not predicted by this hydrodynamic model was the one based on individuals from the Zanzibar channel, which is most likely because the spatial resolution of this large-scale model does not fit the small-scale detection level needed to show this separation. The findings byCrochelet et al (2016) strongly confirm our hypothesis that the major hydrodynamic features shape population genetic structure of T. hemprichii in the WIO region. In the future, it would be valuable to examine historical, geographic, and environmental factors in depth as they may partly contribute to shaping the distribution of genetic variation of T. hemprichii.…”

“…These populations receive no gene flow from the other assessed sites and supply only few migrants to other sites.Interestingly, a model-based assessment of coral reef larvae dispersal in the WIO(Crochelet et al, 2016) found oceanographic clusters that are very similar to our genetic clusters. Pemba (ZP) in the Mozambique channel has the highest number of polymorphic loci observed in our study, supporting the hypothesis of Obura (2012) that the Mozambique channel exhibits high species and genetic diversity for a number of taxa, because of high immigration with the NEMC and retention by the Mozambique channel eddies.…”

Estimating Connectivity Through Larval Dispersal in the Western Indian Ocean

“…The number of larvae released from each release location reaching the recruitment zone was recorded for each PLD. Initial work by Crochelet et al () represented the main East African reef (from Angoche, Northern Mozambique, to Kiunga, Northern Kenya) as a single unit or node. In this study, habitat cells that define the release (centroids) and settlement (polygons) locations were used to give more detailed results about dispersal and potential connections along the East African coast.…”

“…While modeling using Lagrangian models has been extensively used on global to regional scales (e.g., Cowen et al, ; Cowen & Sponaugle, ; Kool et al, ; Paris et al, ; Treml et al, ; Wood et al, , ), their use in the WIO has been limited. Crochelet et al () used altimetry data and a two‐dimensional Eulerian advection‐diffusion algorithm to simulate larval transport across the WIO as a whole. However, all the East African coastal reefs from northern Mozambique to Somalia were aggregated as a single contiguous reef.…”