Broadening our horizons: seascape use by coral reef-associated fishes in Kavieng, Papua New Guinea, is common and diverse

Abstract

There is increasing evidence that non-reef habitats in the seascape surrounding coral reefs are widely used by reef-associated fishes. However, our understanding of seascape use in the Indo-Pacific region is incomplete due to its large geographical range and as a consequence, considerable environmental variation (e.g. tidal regimes). We used remote video cameras to survey reef-associated fishes within five habitat types (coral reef slope, coral reef flat, macroalgal beds, mangroves and seagrass meadows) around the Tigak Islands, Kavieng, Papua New Guinea. Of the 282 shallow-water reef-associated species observed across 360 videos, 35% (99 species) were recorded in non-reef habitats, the majority (78 species) on multiple occasions. We found that macroalgal beds dominated by low-complexity algal genera (e.g. Halimeda, Caulerpa) were used extensively by reef-associated fishes, complementing previous research that has documented the use of canopy-forming macroalgae (e.g. Sargassum). Mean species richness and relative abundances (MaxN) of reef-associated fishes were twofold higher in macroalgal beds than mangroves or seagrass. Interestingly, mangroves contained the most distinct fish assemblage of the three non-reef habitats, including several reef-associated species that were not recorded from any other habitat type. This suggests that mangroves possess attributes not shared by other shallow non-reef, or even reef, habitats. Importantly, many of the fish families commonly found in non-reef habitats (i.e. lethrinids, lutjanids) are targeted by local fishers and are thus critical to sustaining local livelihoods. Our study demonstrates that non-reef habitat use is common for many reef-associated fishes and highlights the need to incorporate a range of habitats into study designs to better understand habitat use patterns in the Indo-Pacific. Given the widespread degradation of coral reefs and other shallow-water habitats, we emphasize the need to recognize that reefs are embedded within a mosaic of habitat types that influence patterns and processes and that management strategies should be scaled appropriately.