Movements and foraging of predators associated with mesophotic coral reefs and their potential for linking ecological habitats

Abstract

Marine predators will often perform diel and seasonal movements associated with specific habitats. In tropical areas, mesophotic coral reefs may be an important habitat type for many predators, but their use of these areas has rarely been investigated. We used results of acoustic telemetry and stable isotope analyses to investigate the diel and seasonal movements of Galapagos sharks Carcharhinus galapagensis and giant trevally Caranx ignobilis captured from a mesophotic reef (depth: 50 to 70 m) at an uninhabited Pacific atoll. All predators associated with mesophotic reefs performed horizontal and vertical movements over seasonal and diel time frames. Galapagos sharks performed reverse diel vertical movements, diving deeper during the night than during the day, while giant trevally displayed a mix, with some individuals performing regular diel movements (deep during the day, shallow at night) and others performing reverse vertical diel movements. Trevally used very shallow water during the summer spawning periods. The isotopic compositions of predators suggest they primarily forage in shallow reefs, although approximately 35% of resources came from mesophotic reefs. Similar to their variability in vertical movement strategies, giant trevally occupied a wide range of trophic positions, potentially due to individual specialization in diet and high levels of intra-specific competition. Mesophotic reefs may provide some prey to upper level predators but also serve as a refuge habitat. The frequent movements between habitats suggest that marine predators may function as significant transporters of nutrients, particularly from shallow to mesophotic reefs.

Mesophotic Depth Gradients Impact Reef Fish Assemblage Composition and Functional Group Partitioning in the Main Hawaiian Islands

“…In addition, while isotopic evidence suggests predators remain heavily reliant on resources between 0 and 30 m acting as nutrient conduits to mesophotic depths (Meyer et al, 2001;Wetherbee et al, 2004;Papastamatiou et al, 2006Papastamatiou et al, , 2015Hilting et al, 2013), marked increases in schooling mobile invertivores (e.g., goatfishes) and planktivores (e.g., C. jordani, Decapterus macarellus) may serve as deep-water prey-bases for predators in the MHI (Smith and Parrish, 2002). As with schooling behaviors observed on Halimeda meadows (see below), potential prey species were observed seeking shelter in algal canopies or retreating to hard-bottom interstitial spaces during transits by generalist macropiscivores-particularly jacks and A. virescens-within the BRUVS frame of view (J. Asher, pers.…”

“…Despite the apparent linkages maintained by depthgeneralists, particularly those inhabiting shallow water and upper mesophotic strata, (Tenggardjaja et al, 2014;Papastamatiou et al, 2015), community linkages and species movements between strata are still largely uncharacterized in the MHI. This remains an important focus for future MHI research, particularly for those species subject to high fishing pressures around human population centers.…”

Ecological and morphological traits predict depth-generalist fishes on coral reefs

“…Highly mobile species are more capable of moving between shallow and deep habitats on diel or seasonal timeframes [24]. The level in the water column in which species usually forage correlates with swimming ability [12]; therefore, we assigned species to one of three categories based on the position in the water column where they usually forage as adults and/or juveniles: (i) bottom-dwellers are species that remain on or within benthic habitats and are usually sedentary or territorial; (ii) low-level swimmers are demersal fishes that roam just above the reef (usually less than 2 m from the substrate); and (iii) high-level swimmers are semi-pelagic species that normally swim well above (more than 2 m) the substrate, usually roaming from one reef to another within the same day or over a short period of time.…”

Horizontal and vertical movements of Caribbean reef sharks ( Carcharhinus perezi ): conservation implications of limited migration in a marine sanctuary

“…The diet of Caribbean reef sharks is reportedly broad (teleosts and cephalopods [60]); therefore, individuals could be exploiting a diverse prey pool on mesophotic reefs (approx. 50–130 m) extending down the drop-off, as seen in the closely related Galapagos shark ( Carcharhinus galapagensis , [61]). Sharks may then make even deeper excursions (greater than 130 m) to exploit meso- and bathypelagic prey, which move to more accessible depths during the night [62].…”