9:30 AM - 9:45 AM
[AOS15-03] Study on 3D oceanic transport of coral larvae in reef areas on the northwest coast of Okinawa Main Island
In recent years, coral bleaching has occurred extensively over the world ocean due primarily to high water temperatures. Mesophotic corals that inhabit in intermediate depth at about 30-150m depth are expected to survive during bleaching events and to reseed shallow water corals afterward. In particular, in Okinawa, Japan, mesophotic coral ecosystems (MCEs) have been reported to serve as a refuge to preserve genotypic diversity of bleaching-sensitive corals (Sinniger et al,. 2017). Connectivity of larval populations between different habitats has been a key element that determines the area to be conserved for desirable coral ecosystems. Coral larvae generally behave passively to the surrounding currents and are transported by the advective and dispersive effects of ambient ocean currents. Numerical ocean circulation models enable us to quantity connectivity with more detailed spaciotemporal network structures than genetic approaches. Previous numerical connectivity studies around the Ryukyu Islands and Okinawa Main Island have investigated rather large-scale coral connectivity with primary attention to horizontal migration of coral larvae (e.g., Uchiyama et al., 2018). However, short-distance, coastal scale transport has been recognized to be much more responsible for maintaining high connectivity.
This study aims at quantifying short-distance and vertical connectivity of coral larvae in reef areas on the northwest coast of Okinawa Main Island. Because both short-distance and vertical larval transports are influenced pronouncedly by complex nearshore topography, a very high-resolution 3-D circulation model is required. Therefore, we develop a quadruple nested high-resolution synoptic ocean modeling at a lateral spatial resolution of 50m based on the JCOPE2-ROMS downscaling system (Kamidaira et al., 2017), coupled with an offline 3-D Lagrangian particle-tracking mode that mimics coral larval transport. After validations of the developed model, short-distance horizontal coral connectivity across reef areas on the northwest coast was successfully evaluated. Furthermore, a series of Lagrangian particle release experiments was conducted for identifying vertical coral migration and thus 3-D connectivity required for preservation of MCEs. In the experiments, particles were released from two depths, 2m (shallow corals) and 30m (mesophotic corals) with sink areas that are vertical divided into three depth zones, 0-10m (shallow corals), 30-40m (upper mesophotic corals), 40-100m (lower mesophotic corals). Horizontal connectivity of shallow corals is characterized by prevailing northward transport and entrainment in topographic kinks in particular on the south side of Motobu Peninsula located near the center of the model domain. The intermediate depth of ~10m receive a substantial number of larvae originated from shallow and mesophotic spawning sites, suggesting that mesophotic coral be sustained by the regional 3-D larval network.
This study aims at quantifying short-distance and vertical connectivity of coral larvae in reef areas on the northwest coast of Okinawa Main Island. Because both short-distance and vertical larval transports are influenced pronouncedly by complex nearshore topography, a very high-resolution 3-D circulation model is required. Therefore, we develop a quadruple nested high-resolution synoptic ocean modeling at a lateral spatial resolution of 50m based on the JCOPE2-ROMS downscaling system (Kamidaira et al., 2017), coupled with an offline 3-D Lagrangian particle-tracking mode that mimics coral larval transport. After validations of the developed model, short-distance horizontal coral connectivity across reef areas on the northwest coast was successfully evaluated. Furthermore, a series of Lagrangian particle release experiments was conducted for identifying vertical coral migration and thus 3-D connectivity required for preservation of MCEs. In the experiments, particles were released from two depths, 2m (shallow corals) and 30m (mesophotic corals) with sink areas that are vertical divided into three depth zones, 0-10m (shallow corals), 30-40m (upper mesophotic corals), 40-100m (lower mesophotic corals). Horizontal connectivity of shallow corals is characterized by prevailing northward transport and entrainment in topographic kinks in particular on the south side of Motobu Peninsula located near the center of the model domain. The intermediate depth of ~10m receive a substantial number of larvae originated from shallow and mesophotic spawning sites, suggesting that mesophotic coral be sustained by the regional 3-D larval network.