Sea Surface Temperature Variability in the Florida Keys and Its Relationship to Coral Cover

The hypothesis that moderate variability in Sea Surface Temperature (SST) is associated with higher coral cover and slower rates of decline of coral cover within the Florida Keys National Marine Sanctuary (FKNMS) was examined. Synoptic SST time series covering the period 1994–2008 were constructed for the FKNMS with the National Oceanic and Atmospheric Administration Advanced Very High Resolution Radiometer satellite sensors. The SST data were compared with coral-cover time-series data from 36 sites monitored by the Coral Reef and Evaluation Monitoring Program. Sites that experienced moderately high SST variability relative to other sites showed a trend toward higher percentage coral cover in 2008 and relatively slower rates of decline over the 14-year study period. The results suggest that corals at sites that are continuously exposed to moderate variability in temperature are more resilient than corals typically exposed either to low variability or to extremes

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

Quantification of Two Decades of Shallow-Water Coral Reef Habitat Decline in the Florida Keys National Marine Sanctuary Using Landsat Data (1984-2002)

The loss of coral reef habitats has been witnessed at a global scale including in the Florida Keys and the Caribbean. In addition to field surveys that can be spatially limited, remote sensing can provide a synoptic view of the changes occurring on coral reef habitats. Here, we utilize an 18-year time series of Landsat 5/TM and 7/ETM+ images to assess changes in eight coral reef sites in the Florida Keys National Marine Sanctuary, namely Carysfort Reef, Grecian Rocks, Molasses Reef, Conch Reef, Sombrero Reef, Looe Key Reef, Western Sambo and Sand Key Reef. Twenty-eight Landsat images (1984-2002) were used, with imagery gathered every 2 years during spring, and every 6 years during fall. The image dataset was georectified, calibrated to remote sensing reflectance and corrected for atmospheric and water-column effects. A Mahalanobis distance classification was trained for four habitat classes (\u27coral\u27, \u27sand\u27, \u27bare hardbottom\u27 and \u27covered hardbottom\u27) using in situ ground-truthing data collected in 2003-2004 and using the spectral statistics from a 2002 image. The red band was considered useful only for benthic habitats in depths less than 6 m. Overall mean coral habitat loss for all sites classified by Landsat was 61% (3.4%/year), from a percentage habitat cover of 19% (1984) down to 7.6% (2002). The classification results for the eight different sites were critically reviewed. A detailed pixel by pixel examination of the spatial patterns across time suggests that the results range from ecologically plausible to unreliable due to spatial inconsistencies and/or improbable ecological successions. In situ monitoring data acquired by the Coral Reef Evaluation and Monitoring Project (CREMP) for the eight reef sites between 1996 and 2002 showed a loss in coral cover of 52% (8.7%/year), whereas the Landsat-derived coral habitat areas decreased by 37% (6.2%/year). A direct trend comparison between the entire CREMP percent coral cover data set (1996-2004) and the entire Landsat-derived coral habitat areas showed no significant difference between the two time series (ANCOVA; F-test, p = 0.303, n = 32), despite the different scales of measurements

Influence of Water-Temperature Variability on Stony Coral Diversity in Florida Keys Patch Reefs

Annual surveys conducted by the Coral Reef Evaluation and Monitoring Project (CREMP) reported that average benthic cover of stony corals in the Florida Keys National Marine Sanctuary, USA declined from ∼13% in 1996 to 8% in 2009. Keys-wide, mean species richness (SR) declined by ∼2.3 species per station. Stress due to temperature extremes is suspected to be a major driver of this trend. We tested the potential for sea surface temperature (SST) variability and acute warm-temperature events (assessed with Degree Heating Weeks) to affect stony coral diversity in the Florida Keys. Benthic cover of 43 stony coral species was examined with respect to SST variability and habitat type (patch, offshore shallow, and offshore deep reefs). For each CREMP site, SST annual variance was classified as low (\u3c7.0°C2), intermediate (7.0 to 10.9°C2), or high (≥11.0°C2). Nonparametric MANOVA analyses showed that in the Upper, Middle, and Lower Keys regions, massive-type stony coral species (e.g. Siderastrea siderea, Pseudodiploria strigosa, Orbi-cella annularis complex, Montastraea cavernosa, and Colpophyllia natans) were prevalent in the patch reef habitats exposed to intermediate to high SST variability. Intermediate SST variability was also correlated with higher Shannon diversity means in patch reefs in the Upper Keys and higher SR means in the Middle Keys, indicating either that the stony coral species in these habitats are adapted to an intermediate temperature range or that individual colonies have acclimatized to that range. No significant relationships were found between stony coral diversity and SST variability in the Dry Tortugas region

Variable Thermal Stress Tolerance of the Reef-Associated Symbiont-Bearing Foraminifera \u3cem\u3eAmphistegina\u3c/em\u3e Linked to Differences in Symbiont Type

Adaptation, acclimatization and symbiont diversity are known to regulate thermal tolerance in corals, but the role of these mechanisms remains poorly constrained in other photosymbioses, such as large benthic foraminifera (LBFs), which are known to bleach at temperatures that are likely to be exceeded in the near future. LBFs inhabit a broad range of shallow-water settings. Within species, differences in thermal tolerance have been found among populations from different habitats, but it is not clear whether such differences occur among LBFs inhabiting similar habitats, but differing in other aspects, such as symbiont type. To this end, we compared responses to thermal stress in specimens from a population of Amphistegina lessonii, an abundant Indo-Pacific species, to specimens of Amphistegina gibbosa, its Atlantic counterpart, from a similar environment but two different water depths (5 and 18 m). Test groups of each species were exposed in a common experiment to three thermal stress scenarios over a four-week period. Growth, respiration, mortality and motility were measured to characterize the holobiont response. Coloration, photosynthesis and chlorophyll a content were measured to determine the response of the endosymbiotic diatoms. The photosymbionts were characterized by genetic fingerprinting. Our results show that, although groups of A. gibbosa were collected from different habitats, their responses were similar, indicating only marginally higher tolerance to thermal peaks in specimens from the shallower site. In contrast, species-specific differences were stronger, with A. lessonii showing higher tolerance to episodic stress and less pronounced impacts of chronic stress on motility, growth and photosymbiont performance. These interspecies variations are consistent with the presence of different and more diverse symbiont assemblages in A. lessonii compared with A. gibbosa. This study demonstrates the importance of considering symbiont diversity in the assessment of intra- and interspecific variations in stress responses in LBFs

Molecular Identification of Algal Endosymbionts in Large Miliolid Foraminifera: 1. Chlorophytes

Large miliolid foraminifers bear various types of algal endosymbionts including chlorophytes, dinoflagellates, rhodophytes, and diatoms. Symbiosis plays a key role in the adaptation of large foraminifera to survival and growth in oligotrophic seas. The identity and diversity of foraminiferal symbionts, however, remain largely unknown. In the present work we use ribosomal DNA (rDNA) sequences to identify chlorophyte endosymbionts in large miliolid foraminifera of the superfamily Soritacea. Partial 18S and complete Internal Transcribed Spacer (ITS) rDNA sequences were obtained from symbionts of eight species representing all genera of extant chlorophyte‐bearing Soritacea. Phylogenetic analysis of the sequences confirms the previous fine structure‐based identification of these endosymbionts as belonging to the genus Chlamydomonas. All foraminiferal symbionts form a monophyletic group closely related to Chlamydomonas noctigama. The group is composed of seven types identified in this study, including one previously morphologically described species, Chlamydomonas hedleyi. Each of these types can be considered as a separate species, based on the comparison of genetic differences observed between other established Chlamydomonas species. Several foraminiferal species share the same symbiont type, but only one species, Archaias angulatus, was found to bear more than one type