Satellite monitoring of thermal stress on coral reefs has become an essential component of reef management practice around the world. A recent development by the U.S. National Oceanic and Atmospheric Administration's Coral Reef Watch (NOAA CRW) program provides daily global monitoring at 5 km resolution-at or near the scale of most coral reefs. In this paper, we introduce two new monitoring products in the CRW Decision Support System for coral reef management: Regional Virtual Stations, a regional synthesis of thermal stress conditions, and Seven-day Sea Surface Temperature (SST) Trend, describing recent changes in temperature at each location. We describe how these products provided information in support of management activities prior to, during and after the 2014 thermal stress event in the Commonwealth of the Northern Mariana Islands (CNMI). Using in situ survey data from this event, we undertake the first quantitative comparison between 5 km satellite monitoring products and coral bleaching observations. Analysis of coral community characteristics, historical temperature conditions and thermal stress revealed a strong influence of coral biodiversity in the patterns of observed bleaching. This resulted in a model based on thermal stress and generic richness that explained 97% of the variance in observed bleaching. These findings illustrate the importance of using local benthic characteristics to interpret the level of impact from thermal stress exposure. In an era of continuing climate change, accurate monitoring of thermal stress and prediction of coral bleaching are essential for stakeholders to direct resources to the most effective management actions to conserve coral reefs.

The vertical zonation of dominant megabenthic, photosynthetic taxa suggests that differential photosynthetic capabilities enable specialized, low-light zooxanthellate corals to dominate at depths where shallow-water corals become light limited. This study examines the ecophysiology of deep-water (68−113 m) Leptoseris spp. and shallow-water (2−15 m) Porites spp. zooxanthellate corals from Hawai'i by comparing spectral absorbance properties and photosynthetic pigment concentrations to the available light spectra in their respective environments. Photo synthetically active radiation reaching Leptoseris spp. was 3 to 11% of surface irradiance compared to 41 to 90% reaching Porites spp. Optical measurements indicated that Leptoseris spp. exhibited lower reflectance (i.e. higher absorptance) compared to Porites spp. and were chromatically adapted to the wavelengths of photons available at depth. Despite the decreased spectral reflectance, deep-water Leptoseris spp. exhibited significantly lower areal photosynthetic pigment concentrations than did shallow-water Porites spp. Based on morphological comparisons of the skeletons of both coral genera, we hypothesize that Leptoseris spp. skeletons may cause incident light to travel through the coral tissue several times, thereby increasing photon-pigment interactions without increasing pigment concentrations. This superior light harvesting efficiency exhibited by Leptoseris in an energy limited environment (enabled by skeletal design rather than pigment physiology) may in part explain why the dominant genus of reef-building corals in Hawai'i cannot compete successfully with specialized low-light corals at extreme depths. KEY WORDS: Photobiology · Mesophotic · Coral ecology · Ecophysiology · LeptoserisResale or republication not permitted without written consent of the publisher

Monitoring variability in coral reef primary production and calcification is needed to understand changes over time and between reef systems, which helps separate differences due to natural and/or anthropogenic factors happening now and in the future. This study measured net productivity and calcification for two reef systems at Shark Bay, Heron Reef in the southern Great Barrier Reef and Saipan Lagoon, Commonwealth of the Northern Mariana Islands. Net primary productivity and calcification were strongly correlated for reef flats with an adjusted R2 = 0.66. Night time dissolution occurred at Shark Bay reef flat with an average of −12.66 mmol CaCO3 · m−2 · hr−1, while calcification increased at night for the Saipan reef flat. For both reef flat sites, net productivity from oxygen flux was much lower than rates calculated from change in dissolved inorganic carbon. This study provided the first baseline estimates of net productivity and calcification for a reef flat and seagrass community in Saipan Lagoon. The seagrass community had the lowest productivity of all sites. However, the high presence of calcareous algae at the site highlights the need for more research on the carbonate chemistry of these habitats. All sites had high net productivity that was most likely associated with the dominant presence of algae.

Ocean warming is increasing the incidence, scale, and severity of global-scale coral bleaching and mortality, culminating in the third global coral bleaching event that occurred during record marine heatwaves of 2014-2017. While local effects of these events have been widely reported, the global implications remain unknown. Analysis of 15,066 reef surveys during 2014-2017 revealed that 80% of surveyed reefs experienced significant coral bleaching and 35% experienced significant coral mortality. The global extent of significant coral bleaching and mortality was assessed by extrapolating results from reef surveys using comprehensive remote-sensing data of regional heat stress. This model predicted that 51% of the world’s coral reefs suffered significant bleaching and 15% significant mortality, surpassing damage from any prior global bleaching event. These observations demonstrate that global warming’s widespread damage to coral reefs is accelerating and underscores the threat anthropogenic climate change poses for the irreversible transformation of these essential ecosystems.