Raymond C. Boland

A comprehensive investigation of mesophotic coral ecosystems in the Hawaiian Archipelago

Although the existence of coral-reef habitats at depths to 165 m in tropical regions has been known for decades, the richness, diversity, and ecological importance of mesophotic coral ecosystems (MCEs) has only recently become widely acknowledged. During an interdisciplinary effort spanning more than two decades, we characterized the most expansive MCEs ever recorded, with vast macroalgal communities and areas of 100% coral cover between depths of 50–90 m extending for tens of km2 in the Hawaiian Archipelago. We used a variety of sensors and techniques to establish geophysical characteristics. Biodiversity patterns were established from visual and video observations and collected specimens obtained from submersible, remotely operated vehicles and mixed-gas SCUBA and rebreather dives. Population dynamics based on age, growth and fecundity estimates of selected fish species were obtained from laser-videogrammetry, specimens, and otolith preparations. Trophic dynamics were determined using carbon and nitrogen stable isotopic analyses on more than 750 reef fishes. MCEs are associated with clear water and suitable substrate. In comparison to shallow reefs in the Hawaiian Archipelago, inhabitants of MCEs have lower total diversity, harbor new and unique species, and have higher rates of endemism in fishes. Fish species present in shallow and mesophotic depths have similar population and trophic (except benthic invertivores) structures and high genetic connectivity with lower fecundity at mesophotic depths. MCEs in Hawai‘i are widespread but associated with specific geophysical characteristics. High genetic, ecological and trophic connectivity establish the potential for MCEs to serve as refugia for some species, but our results question the premise that MCEs are more resilient than shallow reefs. We found that endemism within MCEs increases with depth, and our results do not support suggestions of a global faunal break at 60 m. Our findings enhance the scientific foundations for conservation and management of MCEs, and provide a template for future interdisciplinary research on MCEs worldwide.

A Description of Fish Assemblages in the Black Coral Beds off Lahaina, Maui, Hawai‘i

ABSTRACT A series of scuba dives surveyed patches of black corals and their associated deep-reef fish community in the channel waters (50–73 m depth) of Maui, Hawai‘i. Most of the corals were identified as Antipathes dichotoma and averaged 76 cm (±0.37) in height. Forty fish taxa were surveyed in the patches. Only Oxycirrhites typus was found exclusively within these coral trees. Sixty percent of the fish taxa surveyed were observed to frequent and pass through the coral branches. However, only four fish species were documented to reliably take shelter in the coral branches when evading an approaching diver. An archival video monitored movement patterns of fishes around a cluster of black coral trees for a 60-hr period. During daylight hours Dascyllus albisella, Centropyge potteri, Forcipiger flavissimus, Aulostomus chinensis, and Canthigaster jactator were observed to be the routine users of the coral patch, but only Dascyllus albisella and Centropyge potteri appeared to be resident to specific trees. At night Sargocentron sp. were observed feeding around the base of the coral trees, and Heniochus diphreutes dropped from their daytime position high in the water column to hide in the tree branches throughout the night. These observations indicate that black coral trees are used by many fishes as a general form of habitat, and if the coral trees are the largest relief feature at a site, their removal will likely impact the fish assemblage.

New Records of Commercially Valuable Black Corals (Cnidaria: Antipatharia) from the Northwestern Hawaiian Islands at Mesophotic Depths

Abstract: Mesophotic coral reef ecosystems are notoriously undersurveyed worldwide and particularly in remote locations like the Northwestern Hawaiian Islands (NWHI). A total of 37 mixed-gas technical dives were performed to depths of 80 m across the NWHI to survey for the presence of the invasive octocoral Carijoa sp., the invasive red alga Acanthophora spicifera, and conspicuous megabenthic fauna such as black corals. The two invasive species were not recorded from any of the surveys, but two commercially valuable black coral species, Antipathes griggi and Myriopathes ulex, were found, representing substantial range expansions for these species. Antipathes griggi was recorded from the islands of Necker and Laysan in 58–70 m, and Myriopathes ulex was recorded from Necker Island and Pearl and Hermes Atoll in 58–70 m. Despite over 30 yr of research in the NWHI, these black coral species had remained undetected. The new records of these conspicuous marine species highlight the utility of deepdiving technologies in surveying the largest part of the depth range of coral reef ecosystems (40–150 m), which remains largely unexplored.

Comparison of Reef Fish Survey Data Gathered by Open and Closed Circuit SCUBA Divers Reveals Differences in Areas With Higher Fishing Pressure.

Visual survey by divers using open-circuit (OC) SCUBA is the most widely used approach to survey coral reef fishes. Therefore, it is important to quantify sources of bias in OC surveys, such as the possibility that avoidance of OC divers by fishes can lead to undercounting in areas where targeted species have come to associate divers with a risk of being speared. One potential way to reduce diver avoidance is to utilize closed circuit rebreathers (CCRs), which do not produce the noise and bubbles that are a major source of disturbance associated with OC diving. For this study, we conducted 66 paired OC and CCR fish surveys in the Main Hawaiian Islands at locations with relatively high, moderate, and light fishing pressure. We found no significant differences in biomass estimates between OC and CCR surveys when data were pooled across all sites, however there were differences at the most heavily fished location, Oahu. There, biomass estimates from OC divers were significantly lower for several targeted fish groups, including surgeonfishes, targeted wrasses, and snappers, as well as for all targeted fishes combined, with mean OC biomass between 32 and 68% of mean CCR biomass. There were no clear differences between OC and CCR biomass estimates for these groups at sites with moderate or low fishing pressure, or at any location for other targeted fish groups, including groupers, parrotfishes, and goatfishes. Bias associated with avoidance of OC divers at heavily fished locations could be substantially reduced, or at least calibrated for, by utilization of CCR. In addition to being affected by fishing pressure, the extent to which avoidance of OC divers is problematic for visual surveys varies greatly among taxa, and is likely to be highly influenced by the survey methodology and dimensions used.