Pulley Ridge

Pulley Ridge is a 100+km long series of N/S trending, underwater barrier islands on the SW Florida Shelf (approximately 250 km west of Cape Sable). A relatively healthy mesophotic (mid-light) coral ecosystem with an unusual mixture of corals, algae, and shallow- and deep-water species, it is home to groupers and snappers (important species in commercial and recreational fisheries). With the well-documented decline of Florida’s reefs, places like Pulley Ridge may serve as sources of larvae that can help sustain the Keys’ reef ecosystem and the tourism economy that is dependent on it.

The following descriptive paragraphs are quoted from USGS Coastal & Marine Geology Program archive:
“The ridge has been mapped using multibeam bathymetry, submarines and remotely operated vehicles, and a variety of geophysical tools. The ridge is a subtle feature about 5 km across with less than 10 m of relief. The shallowest parts of the ridge are about 60 m deep. Surprisingly at this depth, the southern portion of the ridge hosts an unusual variety of zooxanthellate scleractinian corals, green, red and brown macro algae, and typically shallow-water tropical fishes.

Pulley Ridge was mapped with the USF Kongsberg Simrad EM 3000 high-resolution multibeam sonar, which produces both bathymetry and backscatter. The multibeam mapping efforts were led by David Naar and Brian Donahue of USF, in coordination with Bob Halley and David Twichell of the USGS and by Bret Jarrett, Al Hine, and Stan Locker of USF. Kate Ciembronowicz of both USF and USGS completed the post-processing of several multibeam bathymetry data sets spanning 1999 to 2004. The raw data was processed in Caris and gridded to a 5 m resolution (black line indicates area believed to contain hermatipic coral cover).

The corals Agaricia sp. and Leptoceris cucullata are most abundant, and are deeply pigmented in shades of tan-brown and blue-purple, respectively. These corals form plates up to 50 cm in diameter and account for up to 60% live coral cover at some localities. Less common species include Montastrea cavernosa, Madracis formosa, M. decactis, Porities divaricata, and Oculina tellena. Sponges, calcareous and fleshy algae, octocorals, and sediment occupy surfaces between the corals. Coralline algae appear to be producing as much or more sediment than corals, and coralline algal nodule and cobble zones surround much of the ridge in deeper water (greater than 80 m).

In addition to coralline algae other abundant macro algae include Halimeda tuna, Lobophora variegata, Ventricaria ventricosa, Verdigellas peltata, Dictyota sp., Kallymenia sp., and particularly striking fields of Andaymonene menzeii. The latter algae covers many hectares at densities of tens of individuals per square meter, constructing regions that appear like lettuce fields growing in the dusk at this depth on the sea floor.

The fishes of Pulley ridge comprise a mixture of shallow water and deep species sharing this unusual habitat. More than 60 species have been identified. Commercial species include Epinephelus morio (red grouper) and Mycteroperca phenax (scamp). Typical shallow-water tropical species include Thalassoma bifasciatum (bluehead), Stegastes partitus (bicolor damselfish), Cephalopholis fulva (coney), Lachnolaimus maximus (hogfish), Pomacanthus paru (French angelfish), and Holacanthus tricolor (rock beauty). The deepwater fauna is represented by Chaetodon aya (bank butterflyfish), Sargocentron bullisi (deepwater squirrelfish), Bodianus pulchellus (spotfin hogfish), Pronotogrammus martinicensis (roughtongue bass), and Liopropoma eukrines (wrasse bass). Malacanthus plumieri (sand tilefish) and several other species construct large burrows and mounds that serve as refuge for multiple species. Mounds and pits larger than 1m2 are apparent on side-scan sonar images and have been counted in excess of 200/km2 for parts of the ridge.

The extent of algal cover and abundance of herbivores suggest benthic productivity is moderate to high on parts of the ridge. Such productivity is unusual, if not unique at this depth in the Gulf of Mexico and Caribbean. Several factors help to account for the existence of this community. First, the underlying drowned barrier islands provided both elevated topography and lithified substrate for the hard bottom community that now occupies the southern ridge. Second, the region is dominated by the western edge of the Loop Current that brings relatively clear and warm water to the southern ridge. Third, the ridge is within the thermocline, a water mass that is known to provide nutrients during upwelling to shallow reefs in Florida.

Notwithstanding the positive factors for reef growth listed above, this largely photosynthetic community appears to be thriving on 1-2% (5-30 microEinsteins/1m2/sec) of the available surface light (PAR) and about 5% of the light typically available to shallow-water reefs (500 – 1000 microEinsteins/1m2/sec). The corals generally appear to be healthy, with no obvious evidence of coral bleaching or disease. Although the community is clearly one adapted to low light conditions, the variety and extent of photosynthetic organisms between 60 and 70 meters depth is impressive.

Is southern Pulley Ridge the United State’s deepest coral reef? That depends, of course, on one’s preferred definition of a coral reef. There are deeper, ahermatypic coral buildups both in the Gulf of Mexico and Atlantic off Florida coasts. Classically, a coral reef is a wave resistant structure built by hermatypic corals and hazardous to shipping. From a geologist’s point of view, Pulley Ridge corals appear to have built a biostrome, an accumulation at least a few meters thick, although corals may not account for the bulk of the topography. From that of a biologist, the most abundant corals in the ridge are hermatypic corals but they are lying, mostly unattached, on the surface. Clearly a ship’s captain could not run his vessel aground on this reef, so mariners would not consider this a reef. Nevertheless, from the scientific perspective of a structure built from hermatypic corals, southern Pulley Ridge may well be the deepest coral reef in the United States.”

The Pulley Ridge Project (officially titled ”REPP–Connectivity–Pulley Ridge: Population connectivity of the Pulley Ridge–South Florida coral reef ecosystem: processes to decision-support tools”) was a NOAA-funded, multi-PI project, led by Dr. Robert Cowen (formerly at RSMAS, now at OSU’s Hatfield Marine Science Center). IDSC played a major part in this 5-year, $5M, multi-disciplinary project, and took the lead in the design, development, and deployment of the project’s Decision Support Resource (DSR). Project servers are hosted by IDSC, and a project website was created and supported (coastal.er.usgs.gov/pulley-ridge). The IDSC team was led by Software Engineering Director Chris Mader, and IDSC alum Felimon Gayanilo. [Now a Systems Architect with Harte Research Institute for Gulf of Mexico Studies at Texas A&M University in Corpus Christi, Dr. Gayanilo’s list of major projects includes the initiation of the design and development of Gulf of Mexico Research Initiative , and the Gulf of Mexico Coastal Ocean Observing System (GCOOS) Data Portal, which he began while at CCS. He also worked on the NIH-funded BAOSearch application.]

The project got underway in late November of 2011.