Assessing the Distribution of Patch Reef Morphologies in the Lower Florida Keys, USA, using IKONOS Satellite Imagery

As live coral cover continues to decline in the Florida Keys, it becomes increasingly important not only to determine the location and abundance of live coral remaining, but also to understand why certain areas possess higher coral cover than others. At present, coral cover tends to be highest at shallow inshore patch reefs. Our study has two objectives: 1) to determine, to the full extent visible by satellite imagery, the number and characteristics of patch reefs that could be recognized using IKONOS imagery; and 2) to test the assumption that various morphological groups of patch reefs occupy distinct cross-shelf zones in the Lower Keys. Two previous survey efforts using aerial imagery and reported 420 and 750 patch reefs, respectively, from Big Pine to the Marquesas Keys. By performing a visual assessment on IKONOS satellite imagery, we were able to delineate 2,251 patch reefs for this region. These patch reefs vary in their overall morphology (i.e., shape) and are spatially distributed in several cross-shelf bands. Patch reef classes identified were Aggregate, Atom, Colony, Crescent and Dome. Aggregate patch reefs are very numerous, relatively small, and dominantly located either shallow-midshelf or offshore. Dome, Colony and Crescent patch reefs are larger in area and are most common in the shallow-midshelf or offshore zones. This study represents an important first step in understanding the factors that may be controlling the distribution and shape of patch reefs along the Florida Keys Reef Tract and, subsequently, relating this to living coral cover on modern reefs

Synoptic Water Clarity Assessment in the Florida Keys Using Diffuse Attenuation Coefficient Estimated from Landsat Imagery

The diffuse attenuation coefficient, K (m-1), is a measure of the effective attenuation of light in the water column. It characterizes water clarity and is used as a proxy for water quality. Mapping of shallow water benthic habitats using optical means, including daytime visible satellite imagery, requires knowledge of K to correct for water column effects such as light absorption and scattering. Traditionally, K is derived from imagery using a priori knowledge of bottom types at different depths and specific locations, and assuming that light attenuates exponentially with depth. This technique is applied to three Landsat 7 satellite images (February, May, and July 2000) from the Florida Keys Reef Tract between Key Largo and Key West. Interpolated depth data, initially from NOAA vector chart data, with uncertainties of ±0.5 m, were draped over 30 m spatial resolution Landsat satellite imagery. K was derived for 27 sites where bright sand could be observed at depths between 3 and 20 m. The blue and green bands (Landsat bands 1 and 2 at 450-520 nm and 520-600 nm, respectively) provided K values consistent with time and location. Average K values for bands 1 and 2, respectively, were 0.029 and 0.043 m-1 (Lower Keys), 0.050 and 0.072 m-1 (Middle Keys), and 0.063 and 0.082 m-1 (Upper Keys). The red band (band 3, 630-690 nm) provided more ambiguous and erroneous results with several negative K values, attributed primarily to three factors: use of a simple atmospheric correction, the high absorption and rapid attenuation of red light in water, and low radiometric sensitivity of the Landsat ETM+ sensor. Despite the fact that these observations were a snapshot in time, trends were observed for the Upper, Middle, and Lower Keys, possibly due to the influence of more turbid Florida Bay waters

Coral Reef Change Detection Using Landsats 5 and 7: a Case Study Using Carysfort Reef in the Florida Keys

Landsats 5 and 7, with the Thematic Mapper (TM) and Enhanced Thematic Mapper Plus (ETM+) sensors provide the longest time series of satellite observations available for coastal researchers. A Mahalanobis distance classification was carried out to identify four benthic classes: coral-dominated , sand , algae , and substrate . The results were compared to an in situ database, which included transect and monitoring station data, as well as an aerial photograph

Detection of Changes in Coral Reef Communities Using Landsat-5 Tm and Landsat-7 Etm+ Data

Satellite remote sensing is increasingly used to map and monitor coral reefs. From 1984 to the present, Landsat-5 thematic mapper (TM) and Landsat-7 enhanced thematic mapper plus (ETM+) images provide the longest time series available for change detection analysis over coral reefs. A time series of four Landsat-5 images and one Landsat-7 image spanning 1984‐2000 was analyzed to detect changes in coral-dominated , sand , algae , and substrate benthic classes for Carysfort Reef in the Florida Keys. To properly analyze this time series, a set of corrections was undertaken, which included noise-reduction correction, atmospheric correction, and TM‐ETM+ data normalization. All images were classified with a Mahalanobis distance classifier using statistics from the 1984 image to identify the four benthic classes. The results were compared with historical ground-truthing data, a combination of high-resolution aerial photography and Ikonos satellite data, and results from a temporal texture change detection analysis. All data sets provided consistent results, with an extreme loss in coral cover between 1982 and 2000. The Landsat time series provided across-time progression and locations of the coral-dominated zones for all of Carysfort Reef. This study demonstrates the feasibility and utility of combining Landsat-5 TM and Landsat-7 ETM+ images for coral reef community scale change detection studies at a decadal scale. It opens the possibility of a cost-effective larger scale study, which could include an entire reef tract

Prediction of Coral Bleaching in the Florida Keys Using Remotely Sensed Data

Shallow water tropical coral reefs may bleach due to extremes in a variety of environmental factors. Of particular concern have been temperature, ultraviolet radiation, and photosynthetically available radiation. Satellite observation systems allow synoptic-scale monitoring of coral environments that can be used to investigate the effects of such environmental parameters. Recent advancements in algorithm development for new satellite data products have made it possible to include light availability in such monitoring. Long-term satellite data (2000–2013), in combination with in situ bleaching surveys (N = 3,334; spanning 2003–2012), were used to identify the environmental factors contributing to bleaching of Florida reef tract corals. Stepwise multiple linear regression supports the conclusion that elevated sea surface temperature (SST; partial Radj 2 = 0.13; p \u3c 0.001) and high visible light levels reaching the benthos (partial Radj 2 = 0.06; p \u3c 0.001) each independently contributed to coral bleaching. The effect of SST was modulated by significant interactions with wind speed (partial Radj 2 = 0.03; p \u3c 0.001) and ultraviolet benthic available light (partial Radj 2 = 0.01; p = 0.022). These relationships were combined via canonical analysis of principal coordinates to create a predictive model of coral reef bleaching for the region. This model predicted ‘severe bleaching’ and ‘no bleaching’ conditions with 69 and 57 % classification success, respectively. This was approximately 2.5 times greater than that predicted by chance and shows improvement over similar models created using only temperature data. The results enhance the understanding of the factors contributing to coral bleaching and allow for weekly assessment of historical and current bleaching stress

Change Detection in Coral Reef Communities Using Ikonos Satellite Sensor Imagery and Historic Aerial Photographs

For decades, aerial photographs have been the only source of very high spatial resolution data for coral reef researchers. With the launch of the Ikonos satellite in 1999, imagery with a 4 m spatial resolution in multispectral mode can now be combined with historical aerial photographs for change detection. We demonstrate this potential by combining two aerial photographs (1981 and 1992) and an Ikonos image (2000) to detect change in the coral reef communities for Carysfort Reef, Florida, USA. The results show a loss of \u27coral-dominated\u27 bottom from 52% (1981) to 16% (1992) to finally 6% (2000), a trend similar to in situ observations

Strange Bedfellows—a Deep-water Hermatypic Coral Reef Superimposed on a Drowned Barrier Island; Southern Pulley Ridge, SW Florida Platform Margin

The southeastern component of a subtle ridge feature extending over 200 km along the western ramped margin of the south Florida platform, known as Pulley Ridge, is composed largely of a non-reefal, coastal marine deposit. Modern biostromal reef growth caps southern Pulley Ridge (SPR), making it the deepest hermatypic reef known in American waters. Subsurface ridge strata are layered, lithified, and display a barrier island geomorphology. The deep-water reef community is dominated by platy scleractinian corals, leafy green algae, and coralline algae. Up to 60% live coral cover is observed in 60–75 m of water, although only 1–2% of surface light is available to the reef community. Vertical reef accumulation is thin and did not accompany initial ridge submergence during the most recent sea-level rise. The delayed onset of reef growth likely resulted from several factors influencing Gulf waters during early stages of the last deglaciation (∼14 kyr B.P.) including; cold, low-salinity waters derived from discrete meltwater pulses, high-frequency sea-level fluctuations, and the absence of modern oceanic circulation patterns. Currently, reef growth is supported by the Loop Current, the prevailing western boundary current that impinges upon the southwest Florida platform, providing warm, clear, low-nutrient waters to SPR. The rare discovery of a preserved non-reefal lowstand shoreline capped by rich hermatypic deep-reef growth on a tectonically stable continental shelf is significant for both accurate identification of late Quaternary sea-level position and in better constraining controls on the depth limits of hermatypic reefs and their capacity for adaptation to extremely low light levels

Alternative spatially enhanced integrative techniques for mapping seagrass in Florida\u27s marine ecosystem.

Seagrass is an important component of coastal marine ecosystems. Seagrass mapping provides a means for assessing seagrass health by monitoring the spatial distribution and density of seagrass habitat in coastal waters. Recent image processing and satellite technologies present the opportunity to leverage quantitative techniques that have the potential to improve upon traditional photo-interpretation techniques in terms of cost, mapping fidelity, and objectivity. Integrated spatial and spectral processing techniques were identified as an alternative method for mapping seagrass extent and density from an IKONOS satellite image of Springs Coast, Florida. These spatially enhanced integrative mapping techniques objectively standardize seagrass-monitoring efforts and enhance mapping capabilities by characterizing spatial seagrass density gradients. A combination of water column correction, pixel classification, and image segmentation techniques provided a seagrass density index map that represented seagrass density and distribution with high spatial detail and overall accuracy (77%) comparable to photo-interpretation techniques. Satellite imagery-based spatially enhanced image processing techniques were found to provide a consistent, quantitative, and cost-effective alternative for seagrass mapping in Springs Coast with the potential to be transferred to other parts of the world. A cost savings analysis concluded that there was a 13% cost saving using satellite photo-interpretation and a 47% cost saving using enhanced satellite classification when compared to aerial photo-interpretation