Geology topics

Research about Crocker Reef

Source-linked reports with geographic coverage including Crocker Reef.

2 recordsLinked to original sources

USGS2018

Hydrodynamics and sediment mobility processes over a degraded senile coral reef

Coral reefs can influence hydrodynamics and morphodynamics by dissipating and refracting incident wave energy, modifying circulation patterns, and altering sediment transport pathways. In this study, the sediment and hydrodynamic response of a senile (dead) barrier reef (Crocker Reef, located in the upper portion of the Florida Reef Tract) to storms and quiescent conditions was evaluated using field observations and the Coupled Ocean-Atmosphere-Wave-Sediment Transport model. Waves, circulation, and resultant sediment mobility were modeled across different reef zones. Sediment mobility during quiescent periods and the passage of far-field storms are driven by nonbreaking waves and, to a lesser degree, regional circulation. Spatial variability in these processes produces the present-day distribution of sediment grain size at Crocker Reef, wherein finer-grain material along a shallow central ridge is frequently mobilized (43% to 62% of the time), winnowed away, and deposited along the lower-energy flanks and in the fore reef where sand mobility occurs less frequently (32% to 43% and 1% to 22% of the time, respectively). Analysis of wave conditions for the period of 2006–2014 supports that wave heights rarely exceed the threshold for breaking (0.1% and 0.3% at the reef crest and at the reef flat, respectively), predominantly during the passage of tropical storms. There is a shift to a wave-breaking regime during near-field storms, creating the potential for mobilization of larger material and enhanced reef degradation. Sediment mobility can be enhanced due to wave skewness or the generation of free infragravity waves during periods of depth-induced wave breaking.

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USGS2015

Seasonal microbial and environmental parameters at Crocker Reef, Florida Keys, 2014–2015

Crocker Reef, located on the outer reef tract of the Florida Keys (fig. 1), was the site of an integrated “reefscape characterization” effort focused on calcification and related biogeochemical processes as part of the U.S. Geological Survey (USGS) C oral R eef E cosystem ST udies (CREST) project. It is characterized as a senile or dead reef, with only scattered stony coral colonies and areas of sand and rubble. It was chosen as an end-member for later comparison to sites with a healthy, growing reef framework. The CREST reefscape characterization included two intensive seasonal sampling trips to capture summer (July 8–17, 2014) and winter (January 29–February 5, 2015) conditions. This report presents water column microbial and environmental data collected for use as metadata in future publications examining reef metabolic processes via metagenomes derived from water samples and fine-scale temporal and spatial carbonate chemistry measurements. Microbial measurements included enumeration of total bacteria, enumeration of virus-like particles, and plate counts of Vibrio spp. colony-forming units (CFU). These measurements were intended to give a sense of any seasonal changes in the total microbial load and to provide an indication of water quality. Additional environmental parameters measured included water temperature, salinity, dissolved oxygen, and pH. Four sites (table 1) were intensively sampled for periods of approximately 48 hours during summer (July 2014) and winter (January–February 2015), during which water samples were collected every 4 hours for analysis, except when prevented by weather conditions.

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