Highly diverse mesophotic reef fish communities in Raja Ampat, West Papua

Catherine R. Mitchell,Angela J. E. Beer,Catherine E. I. Head,Steven J. Lindfield,Luigi Colin,Nikola M. Piesinger,Dominic A. Andradi-Brown,Nur Ismu Hidayat,Hastuti Hastuti,Defy N. Pada,Purwanto Purwanto,Gabby N. Ahmadia

doi:10.1007/s00338-020-02020-7

Abstract

Mesophotic coral ecosystems (MCEs; reefs 30–150 m depth) are poorly studied, with existing research heavily geographically biased away from the most species-rich reef regions. Yet, MCEs are of high interest because of their unique species and potential to act as refuges from the impacts of fishing. Using baited remote underwater video systems, we surveyed reef fish communities from 2 to 85 m depths throughout the Raja Ampat archipelago in West Papua, Indonesia—an area considered the heart of the Coral Triangle where coral reef biodiversity is greatest. We sought to provide the first assessment of fish communities across this depth gradient in the region and identify whether human population density and market access differently affected fish abundance based on depth. Here we show that—similar to shallow reefs—Raja Ampat MCEs are exceptionally diverse, with 152 fish species recorded at depths greater than 40 m. We found that fish community structures were highly depth driven, with declines in fish abundance at increased depth. In contrast to previous studies elsewhere in the world, we found that the proportion of planktivores declined across the shallow reef to MCE depth gradient. While greater human population density correlated with lower Epinephelidae and Lutjanidae abundance (two key fisheries families), we did not find evidence that MCEs provide a depth refuge from fishing. Surprisingly, we also found that fish abundance declined at greater distances from the major regional market—likely caused by historical fisheries pressure in more remote areas. These results both expand upon and contrast some previously established MCE-depth patterns and human impact patterns on fish communities, suggesting that regional context and historical pressures matters. Our findings highlight the need for future MCE studies within the Coral Triangle region.

Highlights

Mesophotic coral ecosystems (MCEs)—reefs from approximately 30 to 150 m depth—are of increased conservation and research interest because of their unique species assemblages (Rocha et al 2018; Pinheiro et al.Coral Reefs (2021) 40:111–1302019) and potential to act as refuges from shallow reef impacts (Hinderstein et al 2010; Loya et al 2016)
We found 99 fish species at greater depths than their maximum depth listed on Fishbase, of which 76 were extensions onto MCEs in the 40–85 m depth range, and 23 were extensions on shallow or intermediate depth reefs (\ 40 m maximum depth; Electronic Supplementary Material (ESM) Table 4)
Humphead wrasse were found across all depths at a similar density (ESM Table 5), but bumphead parrotfish were only recorded on intermediate depth reefs and MCEs—where they were observed to 41 m maximum depth (ESM Table 4; ESM Table 5)

Summary

Introduction

Mesophotic coral ecosystems (MCEs)—reefs from approximately 30 to 150 m depth—are of increased conservation and research interest because of their unique species assemblages (Rocha et al 2018; Pinheiro et al.Coral Reefs (2021) 40:111–1302019) and potential to act as refuges from shallow reef impacts (Hinderstein et al 2010; Loya et al 2016). MCEs have been poorly documented compared to shallower coral reefs because of sampling limitations at greater depths. The Coral Triangle (comprising: Indonesia, Malaysia, Papua New Guinea, the Philippines, Timor Leste, and the Solomon Islands) hosts the greatest global shallow reef biodiversity (Veron et al 2009). —despite this diversity—there is comparatively little research effort in the Coral Triangle (Fisher et al 2011) especially for MCEs (Turner et al 2017; Laverick et al 2018). Coral Triangle MCE surveys have been mostly limited to several sites in the Philippines, where highly diverse MCEs have been identified (Cabaitan et al 2019; Pinheiro et al 2019)

Methods

Results

Conclusion