Title: DEPTH IS A MORE POTENT STRUCTURING FORCE FOR BRACHYURAN CRAB ASSEMBLAGES THAN LATITUDE, GEOGRAPHY, OR HUMAN IMPACT ACROSS THE HAWAIIAN ARCHIPELAGO

Abstract: Shallow coral reefs are extensively studied, and although scleractinian corals have been recorded to 165 m, little is known about other mesophotic coral reef ecosystem (MCE) inhabitants. Brachyuran crabs fill many ecological and trophic niches on reefs, making them ideal candidates for evaluating species composition among depths. Here we ask if MCEs host the same communities as the shallower reefs spread across the entire 2400 km Hawaiian Archipelago. We deployed Autonomous Reef Monitoring Structures (ARMS) for two years among shallow sites (12 m) across the latitudinal gradient of the Hawaiian Archipelago to compare directly with a depth gradient (12, 30, 60, and 90 m) south of Oʻahu island. Over 650 brachyuran crabs representing 130 morphospecies (21 families) were found. Community composition was not significantly different among shallow sites spread across the archipelago, but was significantly different and highly stratified across the depth gradient. We show that 90 m of depth is a more potent determinant of brachyuran community composition than the latitudinal, geographic (high vs low islands), or anthropogenic impact (human population size) gradient across the archipelago. Deeper reefs host significantly different brachyuran communities than shallow ones in Hawai'i, and only 3 of 130 morphospecies (~4%) occurring across the entire depth range (mesophotic to shallow) sampled. Further research on the cryptic reef-dwelling fauna is needed for identifying areas of unique biodiversity, as well as boundaries between depth- stratified reef ecosystems.

Authors: Hurley KK, Timmers MA, Godwin LS, Reardon KG, Skillings DJ, Toonen RJ

Presentation: Oral

Session: 28A

Date: 06/20/16

Time: 14:30

Location: 308 A/B

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