Peter Houk

Climate‐change refugia in the sheltered bays of Palau: analogs of future reefs

Coral bleaching and mortality are predicted to increase as climate change-induced thermal-stress events become more frequent. Although many studies document coral bleaching and mortality patterns, few studies have examined deviations from the expected positive relationships among thermal stress, coral bleaching, and coral mortality. This study examined the response of >30,000 coral colonies at 80 sites in Palau, during a regional thermal-stress event in 2010. We sought to determine the spatial and taxonomic nature of bleaching and examine whether any habitats were comparatively resistant to thermal stress. Bleaching was most severe in the northwestern lagoon, in accordance with satellite-derived maximum temperatures and anomalous temperatures above the long-term averages. Pocillopora populations suffered the most extensive bleaching and the highest mortality. However, in the bays where temperatures were higher than elsewhere, bleaching and mortality were low. The coral-community composition, constant exposure to high temperatures, and high vertical attenuation of light caused by naturally high suspended particulate matter buffered the corals in bays from the 2010 regional thermal-stress event. Yet, nearshore reefs are also most vulnerable to land-use change. Therefore, nearshore reefs should be given high conservation status because they provide refugia for coral populations as the oceans continue to warm.

Coral Reef Benthic Video Surveys Facilitate Long-Term Monitoring in the Commonwealth of the Northern Mariana Islands: Toward an Optimal Sampling Strategy.

ABSTRACT This study describes a step-by-step process used to design an effective benthic video survey component of the Commonwealth of the Northern Mariana Islands long-term monitoring program. Documenting abundance of major benthic groups at relatively large spatial scales, at the appropriate localities, can empower monitoring programs with the capacity to detect changes over time and assess whether management practices are working. Most pertinent to any long-term monitoring program is the overriding question: do we have enough information, or statistical power, to detect changes if changes occur? To assess the power of our benthic video surveys to detect change in coral cover and diversity we varied (1) transect lengths, (2) number of transects, (3) number of frames per transect, and (4) number of data points per frame. Five replicated 50-m transects yielded the most consistent estimates with the highest statistical power, compared with more numerous replicates of shorter (35-m and 15-m) transects. Increasing the number of frames analyzed per 50-m transect yielded greater power than increasing the number of data points per frame, but increasing the number of data points was more effective at estimating species richness. The greatest power of detecting a change in the benthos at each site, within a feasible sampling period, was evident using 5 by 50 m random transects, extracting 60 frames per transect, and analyzing five data points on each frame. This optimal sampling strategy was tested at 23 other long-term monitoring sites and yielded 90% power to detect a 20–30% relative change in dominant benthos abundance estimates (benthos >20% coverage). Our study addresses the sampling unit, accuracy, and ways to improve estimates, but this does not remove the onus of concisely stated questions for monitoring programs pertaining to management.

Progress and Perspectives on Question-Driven Coral-Reef Monitoring

Despite a steady growth in coral-reef monitoring efforts, the application of the monitoring results to decisionmaking often remains limited, because questions that can be answered are frequently posed after monitoring commences, rather than having the questions define the data to be gathered. We review how hierarchical, question-driven frameworks can improve monitoring designs and how added attention to high-population-variance structures play a central role in this process. Stratification is necessary to avoid the high variance and low power caused by sampling across coral-reef habitats. Yet, knowing when and where to introduce stratification into sampling designs requires information on the environmental and biological processes that drive species abundance patterns. Using case studies, we review some limitations of approaches that back-calculate the effort required to attain desirable statistical power and highlight some approaches to better account for the heterogeneous nature of coral-reef assemblages in monitoring designs.

Aspects of biology and ecological functioning of coral reefs in Guam and the Commonwealth of the Northern Mariana Islands

This publication does not have an abstract. The first paragraph of the Introduction is displayed as the abstract. n nThe Mariana Islands are a chain of 16 volcanic peaks stretching over a distance of approximately 2,500km from 13 to 21 N latitude and centered at 145 E longitude (Fig. 19.1). Politically, the area is divided into two jurisdictions, Guam and the Commonwealth of the Northern Mariana Islands. Guam is a US territory located at 1328 N, 14445E and is the southernmost island in the Mariana nArchipelago. It is the largest island in Micronesia, nwith an area of 560km2 and a maximum elevation of napproximately 405m above sea level. The northern portion of the island is relatively flat and consists primarily of uplifted limestone. The southern half of the island is primarily volcanic, with more topographic relief, and large areas of highly erodible lateritic soils (Siegrist and Randall 1992; Chapter 18, Riegl et al. ). The island possesses fringing reefs, patch reefs, submerged reefs, offshore banks, and a barrier reef surrounding the southern nshores. The reef margin varies in width, from tens of meters along some of the windward areas, to well over 100m. The combined area of coral reefs and lagoons is approximately 69km2 in nearshore waters between 0-3nmi, and an additional 110km2 in federal waters greater than 3nmi offshore (Hunter 1995).