Towed-Diver Surveys, a Method for Mesoscale Spatial Assessment of Benthic Reef Habitat: A Case Study at Midway Atoll in the Hawaiian Archipelago

Abstract

We thank more than two dozen fellow NOAA-certified divers for building the safety record of towed-diver surveys, the officers and crew of the NOAA ship Townsend Cromwell for logistic support and field assistance, and Greta Aeby for sharing belt-transect data. An integrated method for benthic habitat assessment is described, in which divers maneuver boards equipped with digital video, temperature, and depth recorders while being towed behind a small boat. The tow path is concurrently recorded by a GPS receiver, and a layback model is applied to more accurately map the data. Percent cover of salient benthic categories is quantified by whole-image analysis of still frames sampled at 30-s intervals. The results of 15 towed-diver surveys at Midway Atoll in theHawaiian Archipelago during a mass coral bleaching event are presented to exemplify the method and are compared to results derived from conventional methods. Towed-diver surveys bridge a gap between large-scale mapping efforts using satellite data and small-scale, roving diver assessments, providing a mesoscale spatial assessment of reef habitats. The spatial coverage of towed-diver surveys provides comprehensive data to managers concerning the extent, intensity, differential taxonomic response, and bathymetric correlates of bleaching.

Community structure of hermatypic corals at Maro Reef in the northwestern Hawaiian Islands: A unique open atoll

“…Habitat digital videotapes were sampled at 0-sec intervals (interframe distance ~ 26 m) and quantitatively analyzed for coral percent cover using the methods of Kenyon et al (2006a). The coral categories that could be distinguished were Pocillopora, massive and encrusting Porites (e.g., P. lobata, P. evermanni), Porites compressa, Montipora, Acropora, and other live coral (e.g., Pavona, Fungia, faviids).…”

“…Non-overlapping towed-diver surveys were conducted in 2000(17-20 September), 2001, and 2002 (1-2 October) according to the methods of Kenyon et al (2006a). Habitat digital videotapes were sampled at 0-sec intervals (interframe distance ~ 26 m) and quantitatively analyzed for coral percent cover using the methods of Kenyon et al (2006a).…”

Characterization of Coral Communities at Rose Atoll, American Samoa

“…Habitat digital videotapes recorded during towed-diver surveys in 2002 were sampled at 30-sec intervals (interframe distance ~ 24 m) and quantitatively analyzed for benthic percent cover by a single analyst (J. Kenyon) using the methods of Kenyon et al (2006). Digital photographs recorded in 2004 were sampled at 30-sec intervals and quantitatively analyzed for benthic percent cover by a single analyst (C. Wilkinson) using point-count software (Coral Point Count with Excel Extension; Kohler and Gill, 2006) and using 50 stratified random points per frame.…”

“…Towed-diver surveys were conducted in 2002 (23-26 February) and2004 (8-11 February) according to the methods of Kenyon et al (2006) (Fig. 2).…”

Characterization of Coral Communities at Kingman Reef in the Remote Central Pacific Ocean

“…Towed-diver surveys were conducted in 2004 (2-4 April) according to the methods of Kenyon et al (2006a) in the fore-reef slope, lagoon slope, reef flat, and eastern lagoon pool habitats (Figs. 2;3a,b,c,e).…”