Doctor of Philosophy (PhD)


Biological Sciences

Document Type



Phytoplankton and benthic microalgae (BMA) may both contribute to the sediment organic matter pool available to benthic consumers. Recent studies have highlighted the presence and ecological roles of benthic microalgae (BMA) on the continental shelf but studies from the north-central Gulf of Mexico are limited. Here we use photosynthetic pigment analysis and microscopic examination of sediment microalgae to investigate how the biomass, composition, and degradation state of sediment-associated microalgae varies along the Louisiana inner shelf across a continuum of water column and sediment conditions. The contribution of microalgae to higher trophic levels was also examined. Three sandy shoals and surrounding muddy sediments with depths ranging from 4 to 20 m were studied. Light levels (< 1 to 30% of surface PAR) were sufficient for benthic photosynthesis although likely limiting at most locations. Sediment chlorophyll a concentrations ranged from 8 to 77 mg m-2 with no significant differences among locations. Pigment data suggested that sediment microalgae were primarily diatoms at all locations. Epipelic pennate diatoms, (considered indicative of BMA) made up a significantly greater proportion of sediment diatoms at sandy (50% to 98%) compared to muddy stations (16 to 56%), and sediment total pheopigment concentrations on the sandy stations (<20 mg m-2) were significantly lower than concentrations at nearby muddy stations (>40 mg m-2) suggesting that BMA predominate in shallow sandy sediments and that phytodetritus predominates at muddy stations. Our results also suggest that the relative proportion of phytodetritus in the benthos was highest where phytoplankton biomass in the overlying water was greatest, independent of sediment type. Stable isotopes indicated that, I found BMA was the primary basal resource for infauna where BMA was consistently predominant in the sediment algae. In sediments containing a mix of BMA and phytoplankton, isotope data indicated both resources were important to infauna. Our study demonstrates that, when available, BMA is utilized by shelf infauna that, in turn, support higher trophic levels.



Document Availability at the Time of Submission

Student has submitted appropriate documentation to restrict access to LSU for 365 days after which the document will be released for worldwide access.

Committee Chair

Fleeger, John W.