GCRC Project Summary |
Dynamics of Benthic Marine Invertebrate Communities on Temperate Offshore Reefs of Georgia
PIs: Daniel Gleason, Department of Biology, GA Southern University
Support: Georgia Sea Grant College Program
Timeframe: 2/1/08-1/31/2009
Project Objectives:
A) To determine if the sequential change in non-mobile, bottom-dwelling invertebrate species (e.g., sponges and corals) that occurs on newly exposed surfaces on temperate hard bottom reefs is predictable and always culminates in the same mix of species.
B) To determine if the composition of established non-mobile, bottom-dwelling invertebrate communities present on single hard bottom reefs varies both spatially and through time.
C) To determine if sedimentation is a structuring force in the development and maintenance of subtidal hard bottom reef communities of coastal Georgia.
Progress and Findings:
Benthic plots established in June 2004, were monitored photographically in late spring, summer, fall, and winter of 2008. These photographs were combined with those taken in previous years and all were processed for percent cover and species diversity. Analysis of these data suggest that predictable seasonal variation in both percent cover and species diversity occurs for sessile benthic invertebrate populations on reefs off the Georgia coast, but that these patterns can be partially disrupted by stochastic events such as tropical storms.
At a single reef site, three permanent transect lines were established at various distances away from the reef scarp to encompass the gradations in community composition that occur across reef ledges. In addition, instantaneous meaures of species diversity and percent cover were taken at six other reef sites within Gray's Reef National Marine Sanctuary. Combined, these data indicate that the changes in benthic species morphological types (e.g., encrusting, upright branching) that occur from the reef scarp to the flat top plateau at a single ledge site are similar among physically separated ledges. However, the benthic species making up the community is highly variable among ledges.
Sediment traps have been deployed along the same three transect lines used to address Objective B. Sediments captured by these traps are processed for total weight, grain size distribution, and organic content. Preliminary data analysis indicates that there is significant variability in sedimentation rates spatially (across a single ledge) and temporally (among seasons). Sedimentation rates appear to be lower during the summer months and higher in the late fall. This variability in sedimentation rates appears to have significant negative impacts on the survival and growth of invertebrates inhabiting the benthos.
Publications:
Benthic Monitoring Module. Developed in collaboration with Elizabeth McGovern (Countryside High School, Clearwater, FL) and Kathryn Kornberg (Southeast Whitfield County High School, Dalton, GA), this module allows advanced high school students to determine species abundance and diversity of sessile benthic invertebrates. The photographs used for this purpose originated from the currently funded Sea Grant project. This module was class-tested successfully in Fall 2008.
Introduction to Population Ecology: Dispersion and Survivorship of Recruits of the Coral, Oculina arbuscula. This is a laboratory exercise for students in college-level introductory biology major classes that allows them to assess patterns of dispersion and also develop life tables for coral recruits. I developed this laboratory during Fall 2008 and the photographs used as the basis for the lab originated from the currently funded Sea Grant project. This laboratory was class-tested successfully with approximately 150 students in Fall 2008.
Planned publications:
Gleason, Daniel F., Leslie R. Sutton, and Lauren M. Divine. Recruitment dynamics of the temperate scleractinian coral, Oculina arbuscula, on reefs of the South Atlantic Bight, U.S.A. To be submitted August 2009 to Marine Ecology Progress Series.
Gleason, Daniel F. and Kenan O. Matterson. Dynamics of sessile benthic marine invertebrate communities on temperate offshore reefs of Georgia, U.S.A. To be submitted September 2009 to Marine Ecology Progress Series.