IDENTIFICATION AND ECOLOGICAL IMPACT OF DREDGE AND FILL DEPOSITION SURROUNDING THE PINELLAS BAYWAY BRIDGE IN BOCA CIEGA BAY, FLORIDA

In Boca Ciega Bay, located north of Tampa Bay in Florida, dredge and fill operations have been used to significantly modify coastal geography to fulfill the demand for bayside property. The Pinellas Bayway Bridge, originally constructed in 1961 and then rebuilt with a parallel footprint in 2021, connects Isla Del Sol to Tierra Verde and was made possible using dredge and fill deposition. Though common, dredge and fill deposition has been shown to have negative environmental impacts, such as diminishing biological resources, degrading water quality, and altering chemical and physical processes. Our multidisciplinary approach aims to identify potential sedimentological and ecological impacts on seagrass habitats caused by the dredge and fill operations used during the bridge construction. We collected 15 vibracores along transects to the west and east of the bridge as well as west of Indian Key, a control site. Visual descriptions and quantitative sedimentological analyses were used to define the lithological units. Mollusk shells were taken from sediment samples, identified, quantified, characterized by ecological preference. This data was interpreted in the context of the lithological units to quantify ecological patterns and potential impacts. Sedimentary units suspected to be fill deposits were identified in nearly all cores near the bridge and were defined by a) spikes in gravel concentrations, b) relatively high abundances of mollusk shells, and c) a decrease in molluscan species primarily found in seagrass habitats as compared with other units.These three characteristics are absent in the control site core. Molluscan assemblages in the suspected fill sediments increase in shell abundance and are primarily composed of species found in sand habitats. In comparison, the sediments before and after the suspected fill units, have a lower overall shell abundance and have a more equal distribution of sand and seagrass species.These findings suggest that the ecosystem was able to recover after the deposition. This project provides insights into the ecological adaptability of seagrass habitats in response to dredge and fill operations. In doing so, it offers a context for potential consequences of future dredge and fill operations as well as how past operations may have affected coastal marine ecosystems.