Abstract

Stocks of commercially valuable sea cucumber species have declined in most tropical countries, which supply majority of the global demand. This work aimed to locate priority sites for the management ofHolothuria scabraandStichopus horrensin the western central Philippines. A passive larval dispersal model was run under four monsoonal regimes (Northeast monsoon, dry-transition, Southwest monsoon, and early Northeast monsoon), and the results subjected to theInfomapnetwork detection algorithm. Three clusters of closely related geographical nodes were identified [southeastern Palawan (Group I), western Panay and eastern Mindoro (Group II), and northern and western Palawan with western Mindoro (Group III)]. Remotely sensed habitat data were used to parameterize the degree of connectivity observed among sites (H. scabraspawning and settlement requires the presence of seagrass and mangrove, whileS. horrensrequires corals and seagrass). Local retention, self-recruitment, settlement success and sink diversity were then calculated for each node with suitable habitat. The locations were ranked according to each metric and those with higher larval export rates, a higher diversity of larval sources and a high degree of successful larval contribution to other sites were deemed crucial for the management of wild populations. Sixteen high-priority sites were identified, distributed mainly along northern Palawan and western Panay. Six sites were common for both species at different seasons, and no single location fulfilled all stated criteria across the four seasons and both sea cucumber species considered. The priority sites for management could serve as broodstock selection and juvenile restocking areas for aquaculture production clusters, which when properly implemented, could lead to an increase in sea cucumber production and contribute to natural populations. On a broader scale, the designation of closely related clusters and incorporation of habitat requirements to dispersal data provided critical input for the delineation of ecologically meaningful management units for sea cucumbers within the region.

Highlights

  • Benthic species connectivity in the marine environment relies on the degree of exchange of pelagic larval stages from habitats where adult populations spawn and subsequent recruitment in areas where the juveniles can survive to sexual maturity

  • Hydrodynamic Features of the Domain and Marine Provinces Calculated by Infomap

  • Surface current flow within the domain was highly seasonal, and dominated by the Mindoro Jet, a fast-flowing southward current that moves between Mindoro and northern Palawan islands (Figure 3). It was strongest during the early Northeast monsoon (NEM), followed by the southwest monsoon (SWM), weak during the NEM and weakest during the drytransition period

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Summary

Introduction

Benthic species connectivity in the marine environment relies on the degree of exchange of pelagic larval stages from habitats where adult populations spawn and subsequent recruitment in areas where the juveniles can survive to sexual maturity. The highest demand comes from China and Hong Kong with most of the supply harvested from tropical countries (ToralGranda et al, 2008; Purcell et al, 2018). Aside from their economic importance, sea cucumbers are a crucial part of coastal food chains as they are efficient nutrient recyclers, and are themselves prey of higher trophic level predators (Purcell et al, 2016). Proper management of sea cucumber stock within an ecological framework is a vital concern to maintain the health of coastal ecosystems, increase sea cucumber populations, and safeguard the socioeconomic well-being of fisher folk which rely heavily on the sea cucumber trade (Purcell et al, 2013)

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