SCUBA diver and submersible observations were used to characterize tropical reef fish assemblages on the hard banks of the northwestern Gulf of Mexico, which have been relatively unstudied due to their remoteness and depth. Four assemblages were distinguishable: coral reef, mid-shelf, algal-sponge, and drowned reef zones in the order of their species richness. These tropical communities are limited to the intermediate and outer shelf by winter cooling of inner shelf waters and high turbidity associated with discharge of the Mississippi/Atchafalaya and other rivers. These communities exhibit seasonal stability and annual persistence over the length of the study (ca. 10 yrs). High reef fish diversity at the Flower Garden banks is due to the variety of habitats and insular environmental conditions. Some Caribbean species are not established in the northwestern Gulf due to the lack of habitat diversity rather than temperature tolerance. Similarities in reef fish species composition on widely scattered banks is due to similar crest depths and hydrographic conditions which result in similar epibenthic communities. The nepheloid layer was the most important environmental factor in determining composition of reef fish assemblages, by producing low species richness and abundance. Limited food resources may also play a role in determining reef fish abundance and species composition on deeper reefs. The scarcity of hard substrate and the presence of the nepheloid layer combine to limit the distribution and abundance of tropical reef fish in the northwestern Gulf of Mexico. Species composition of tropical reef fish assemblages indicate an ecotone between western Atlantic continental and insular tropical faunas in the northwestern Gulf of Mexico.

Depth range
20- 180 m

Mesophotic “mentions”

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Classification
* Presents original data
* Focused on 'mesophotic' depth range
* Focused on 'mesophotic coral ecosystem'

Fields
Community structure
Fisheries
Long-term monitoring
Biodiversity
Ecology

Focusgroups
Fishes
Overall benthic (groups)

Locations
USA - Gulf of Mexico

Platforms
Manned Submersible
SCUBA (open-circuit or unspecified)