Document Type
Thesis
Abstract
The Chesapeake Bay faces a myriad of anthropogenic problems, including over-fishing, nutrient pollution, and increased turbidity. Restoration of Bay benthic communities requires accurate estimates of mollusk diversity and abundance throughout the Holocene; however, studies of molluscan paleoecology and taphonomy have not yet been undertaken. This research quantifies preservational bias in Chesapeake Bay benthic mollusk communities using a live/death assemblage analysis. This analysis involved collecting one to two years of data on the molluscan death assemblage from sites in the mainstem of the Chesapeake Bay. These data were then compared to molluscan live community data collected by the Chesapeake Bay Program over the past 19 years from the same sites or nearby. Samples were collected according to the Chesapeake Bay program benthic sampling protocol, mainly via Young’s modified grab samplers and stored in rose bengal and formalin solution. The Chesapeake Bay Program collected live data from each sample. The remaining material was transported to William and Mary and the death assemblage was sieved four fractions. Mollusks were sorted according to species and valve, and identified to species level wherever possible. I analyzed the 4mm, 2mm, Imm, and 0.5mm sieve size fractions. Previous studies have shown that including size fractions smaller than 2mm introduces a bias in the live/death agreement. However, the live data was collected as the size fraction greater than 0.5mm. I assessed the correlation between the live and the dead assemblage including the smaller than 2mm sieve fractions and the correlation when only the greater than 2mm sieve fractions were included. This study focuses specifically on the composition, abundance, diversity, and evenness of the live versus death assemblages. Composition was calculated as: the percentage of live species in the death assemblage, the percentage of dead species in the live assemblage, and the percentage of individuals of species found in the death assemblage also found in the live community. Abundance was quantified using raw, rank, and proportional metrics. Diversity metrics were used to compare the number of species, and evenness metrics were used to compare species dominance in the live community versus the death assemblage. When the live community data was standardized to two sampling events per year, 83% of the species in the live community were also found in the death assemblage, 40% of the species in the death assemblage were also found in the live community, and 90% of the individuals of species that were found in the death assemblage were also found in one year of the live community.
Date Awarded
2004
Department
Geology
Advisor 1
Rowan Lockwood
Recommended Citation
Chastant, Lisa R., "Taphonomic Bias in Chesapeake Bay Mollusks: The effects on species composition, diversity, and abundance" (2004). Geology Senior Theses. William & Mary. Paper 127.
https://scholarworks.wm.edu/geologyseniors/127
