16 Paleontology of North America

Added from Discipline submissions.

Monday, 9 March 2026
1:30 PM - 4:30 PM
RCC, 106

Live-Dead Mollusk Assemblage Comparisons Reveal Spatial Homogenization and Declining Mollusk Biodiversity across Northern Tampa Bay, Florida

Paper number: 16-6
Program: Technical Sessions
Time: 3:00 PM – 3:15 PM

Authors

Abstract

Seagrass cover in Tampa Bay had declined significantly from the 1950s to 1982 as a result of extensive dredging and filling operations as well as abnormally high total nitrogen loads from insufficient wastewater treatment. Improved wastewater treatment and seagrass restoration efforts have proven successful, with seagrass cover more than doubling between 1982 and 2016. With different parts of Tampa Bay having various histories of seagrass disruption and recovery, we aimed to explore how these histories affected localized mollusk assemblages. We sampled four sites with differing histories of seagrass coverage: (1) Bahia Beach (recovery since 1990s); (2) Pelican Cove (persistent); (3) Davis Island (never established); (4) Courtney Campbell Causeway Trail (established prior to 1980s) to evaluate whether these short term changes in seagrass cover are captured in the live and dead mollusk assemblages. Surface (0-10 cm benthic depth) and subsurface (15-25 cm benthic depth) sediments were sampled and sieved through a 1 mm mesh. All mollusks were sorted by live/dead and identified to the lowest taxonomic level possible. Three sample sets (live surface, dead surface, dead subsurface) were compared against each other using non-metric multidimensional scaling (NMDS) to evaluate differences in spatial composition between each of the sites using Bray-Curtis distances. Preliminary results show that surface and subsurface dead assemblages at each site cluster close with one another, with larger distances observed between clusters representing each locality. Live mollusk compositions cluster close together regardless of locality, suggesting the homogenization of live mollusk composition across study sites across northern Tampa Bay. Consistently with the NMDS analysis, beta diversity of live assemblages is significantly lower relative to dead assemblages. Rarefied species richness plots reveal a significant decrease in live assemblage alpha diversity across all observed sites in comparison to their respective dead assemblages. Live-dead fidelity remains low across all observed sites with rho values ranging between 0.122 – 0.292. These preliminary comparisons of live assemblages with dead assemblages, which likely predate the major human impacts, suggest notable changes in mollusk communities in the northern Tampa Bay area. These changes include spatial faunal homogenization, decline in biodiversity, and changes in faunal composition. Historical archives provided by the dead assemblages can provide a useful baseline for conservation assessment, habitat management, and restoration.

Keywords: Seagrass, Mollusks, Community composition

Geological Society of America Abstracts with Programs. Vol. 58, No. 1

doi: 10.1130/abs/2026SE-411751

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