Coexistence of deep- and shallow-water foraminiferal faunas off Panama City, Florida

Abstract

Benthic box core sampling along a transect off Panama City, Florida, in the vicinity of the DeSoto Canyon, from 37-m to 200-m depths, were run throughout the Bureau of Land Management's Outer Continental Shelf environmental assessment program for the Mississippi-Alabama-Florida (MAFLA) area from 1974 through 1978. Seasonal samples were taken and analyzed for benthic distribution, abundance, diversity, and faunal affinities. The most striking feature brought out by foraminiferal analyses was the mixture of foraminifera from different depth zones. Species normally found in abundance only at depths of > 100 m in adjacent areas were living at all shallower depths, including 37 m. Coexisting with the deeper assemblage were all of the species normally encountered at the shallow depths. Species diversity, normally showing a progressional increase from inner to outer shelf, either remained constant or decreased due to the decrease of shallow-water species with depth. Along with this mixed assemblage, there was a planktonic foraminiferal content in the shallowest assemblage of as much as 25%. Normally, planktonic percentage of similar water depths is 0%. Seasonality had minor effects on the assemblages. The planktonic content is attributed to Loop Current water providing open-Gulf water to the inner shelf. Because the Loop Current is intermittent, the consistently high percentages of deeper-water species on the inner shelf must be attributed to up-welling currents providing cooler, deeper water to the inner shelf. However, since this deeper water did not restrict survival of shallow-water species, multiple factors must be considered for controlling benthic foraminiferal distribution.