Project Title

Linking spatial distributions of injury on seagrass blades of Thalassia testudinum to sea urchin Lytechinus variegatus grazing patterns

Presenters

Academic department under which the project should be listed

CSM - Ecology, Evolution, and Organismal Biology

Faculty Sponsor Name

Dr. Joseph M. Dirnberger

This project does not use human subjects for research. Therefore this step was not required in the completion of this project. However, this project was approved by both the EEOB Department as well as the Graduate College at Kennesaw State University.

Abstract (300 words maximum)

Patterns of injury to plants can yield information on herbivore activity and impact that would be otherwise difficult to observe directly. However, it is often difficult to attribute injury to specific herbivores. Here, we examine injury to Turtlegrass, Thalassia testudinum, across various spatial scales to access whether patterns in injury can inform us on grazing behaviors of the Green (or Variegated) Urchin, Lytechinus variegatus. Urchin densities at 7 sites along St. Joeseph Bay (Florida, USA) increased dramatically from inshore to offshore (from 0 urchins inshore to as much as 570 individuals/100m2 500 m from shore). Blades with injury tended to be distributed in a similar pattern along the bay. Along blades, injury was more frequent on older, distal portion of blades, than the more recently produced basal portions. The type of tissue grazed by urchins (live tissue or senesced tissue) was visually assessed by gently turning over individual urchins in situ. Urchins that were feeding consumed senesced tissue more frequently (>2X) than live tissue. Relative availability of tissue types within the seagrass bed, as well as seagrass cover and various physical parameters were also assessed and compared to visual measurements of grazing, fecal content and urchin spatial distributions. Based on these results, assessment of blade injury can be used to compliment more labor-intensive methods in evaluating the way in which L. variegatus grazes on T.testudinum in situ.

Project Type

Oral Presentation (15-min time slots)

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Linking spatial distributions of injury on seagrass blades of Thalassia testudinum to sea urchin Lytechinus variegatus grazing patterns

Patterns of injury to plants can yield information on herbivore activity and impact that would be otherwise difficult to observe directly. However, it is often difficult to attribute injury to specific herbivores. Here, we examine injury to Turtlegrass, Thalassia testudinum, across various spatial scales to access whether patterns in injury can inform us on grazing behaviors of the Green (or Variegated) Urchin, Lytechinus variegatus. Urchin densities at 7 sites along St. Joeseph Bay (Florida, USA) increased dramatically from inshore to offshore (from 0 urchins inshore to as much as 570 individuals/100m2 500 m from shore). Blades with injury tended to be distributed in a similar pattern along the bay. Along blades, injury was more frequent on older, distal portion of blades, than the more recently produced basal portions. The type of tissue grazed by urchins (live tissue or senesced tissue) was visually assessed by gently turning over individual urchins in situ. Urchins that were feeding consumed senesced tissue more frequently (>2X) than live tissue. Relative availability of tissue types within the seagrass bed, as well as seagrass cover and various physical parameters were also assessed and compared to visual measurements of grazing, fecal content and urchin spatial distributions. Based on these results, assessment of blade injury can be used to compliment more labor-intensive methods in evaluating the way in which L. variegatus grazes on T.testudinum in situ.