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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: 2/1/08-1/31/2010

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 at J-Y reef were monitored photographically in April, June, July, and October of 2009. These photographs were combined with those taken in previous years and all photos up through July 2009 have been processed for percent cover and species diversity. The resulting database represents 5 years of change in species diversity and percent cover. Diversity and percent cover of benthic invertebrates show close correspondence over time. This relationship between diversity and cover appears to be driven, at least partially, by predictable seasonal variation in the abundance of certain members of the benthos.

A surprising result has been the length of time that it is taking cleared plots, even though small, to recover in terms of both species diversity and percent cover. While cleared natural substrata and artificial substrata show similar increases in diversity and cover over time, only in the past year have both of these values began to approach those observed in unmanipulated plots. These results suggest that damage to reefs resulting from such anthropogenic impacts as dragging anchors or bottom trawls has long-range negative impacts on the benthos.

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. We conclude that there is no single climax species state that can be predicted to occur on hard-bottom reefs off the Georgia coast. Rather, there appear to be functional groups (e.g., large vase-like and amorphous sponges) that dominate in well-developed hard-bottom communities.

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. Data analysis to date indicates that the quantities of organic material falling out of the water column appear to be fairly constant, but that the quantities of inorganic sediments vary seasonally: highest in the fall and winter and lowest during the summer. However, this seasonal pattern of sedimentation rates can be disrupted by stochastic events such as storms with significant negative impacts on the survival and growth of invertebrates inhabiting the benthos.

Presentations:

Gleason, Daniel F. Are marine invertebrates meeting their recruitment goals? September 2009. Invited Seminar. University of Alabama-Birmingham, Department of Biology, Birmingham, AL.

Matterson, Kenan O. and Daniel F. Gleason. May 2009. The effect of settlement angle on juvenile chlorophyll concentrations in the temperate scleractinian, Oculina arbuscula. Symbiofest, University of Georgia, Institute of Ecology, Athens, GA.
Divine, Lauren M. and Daniel F. Gleason. May 2009. The effects of sediment on juveniles of the temperate scleractinian coral, Oculina arbuscula. Symbiofest, University of Georgia, Institute of Ecology, Athens, GA.

 

Teaching Tools:

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 Fall 2010 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 Fall 2010 to Marine Ecology Progress Series.

Divine, Lauren M and Daniel F. Gleason. The role of active and passive sediment shedding abilities in the survival and growth of juvenile Oculina arbuscula. To be submitted Spring 2011 to Journal of Experimental Marine Biology and Ecology.

Matterson, Kenan O. and Daniel F. Gleason. The effect of settlement angle on the survival and growth of juveniles of the temperate coral, Oculina arbuscula. To be submitted Summer 2011 to Marine Biology.


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This page was updated September 14, 2010