The zonation of macrobenthic infauna on the South Texas Outer Continental Shelf is related to water depth and sediment facies. Five zones can be defined by species distribution and density, diversity, equitability, and biogenic sedimentary structures.
The numbers of species and individuals per unit area correlate locally with substrate characteristics (particularly sand-to-mud ratios). Sandier substrates have more species and individuals than muddier ones. In the study area, sand-to-mud ratios generally decrease as water depth increases. Consequently, the numbers of species and individuals decrease away from land.
Diversity (H") is higher in sandier substrates than in muddier substrates. Overall diversity decreases in a seaward direction. Equitability increases as sand-to-mud ratios decrease and thus tends to increase as water depth increases.
Biogenic sedimentary structures on the South Texas Outer Continental Shelf result from the interaction of biologic and geologic processes. The zonation of the structures is useful in overall environmental interpretations of Holocene events and processes. The zonation can be defined in terms of diversity, density, and distribution.
Zonation of biogenic sedimentary structures parallel macrobenthic infaunal zonation. Substrates with diverse and dense biogenic sedimentary structures are associated with diverse, dense macrobenthic infaunal assemblages. The distribution of biogenic sedimentary structures is similar to the distribution of sediment types. Diversity and density of biogenic sedimentary structures decrease away from land. Locally, individual biogenic sedimentary structures become more obvious and distinct in finer sediments and deeper water.
