Regional estimates of reef carbonate dynamics and productivity using Landsat 7 ETM+, and potential impacts from ocean acidification

摘要

Using imagery at 30 m spatial resolution from the most recent Landsat satellite, the Land-sat 7 Enhanced Thematic Mapper Plus (ETM+), we scale up reef metabolic productivity and calcification from local habitat-scale (10~(-1) to 10~0 km~2) measurements to regional scales (10~3 to 10~4 km~2). Distribution and spatial extent of the North Florida Reef Tract (NFRT) habitats come from supervised classification of the Landsat imagery within independent Landsat-derived Millennium Coral Reef Map geomorphologic classes. This system minimizes the depth range and variability of benthic habitat characteristics found in the area of supervised classification and limits misclassification. Classification of Landsat imagery into 5 biotopes (sand, dense live cover, sparse live cover, seagrass, and sparse sea-grass) by geomorphologic class is > 73 % accurate at regional scales. Based on recently published habitat-scale in situ metabolic measurements, gross production (P= 3.01 × 10~9 kg C yr~(-1)), excess production (E = -5.70 × 10~8 kg C yr~(-1)), and calcification (G = -1.68 × 10~6 kg CaCO_3 yr~(-1)) are estimated over 2711 km~2 of the NFRT. Simple models suggest sensitivity of these values to ocean acidification, which will increase local dissolution of carbonate sediments. Similar approaches could be applied over large areas with poorly constrained bathymetry or water column properties and minimal metabolic sampling. This tool has potential applications for modeling and monitoring large-scale environmental impacts on reef productivity, such as the influence of ocean acidification on coral reef environments.