Qualitative and Quantitative Study of Wound Healing Processes in the Coelenterate,Plexaurella fusifera:Spatial, Temporal, and Environmental (Light Attenuation) Influences

Abstract

Following injury, the Caribbean soft coral,Plexaurella fusifera,forms an epithelial front containing amoebocytes and zooxanthellae, a photosynthetic endosymbiont. Amoebocytes may be responsible for extruding the connective mesogleal fibers necessary for regeneration of tissue and zooxanthellae may provide the energy for repair. This study examined the effects of time, space, and environment (light attenuation) on wound healing in this coral species and quantitatively confirmed the increase of amoebocyte concentrations in the injured area. A wound was made on coral branchlets by removing ∼4.5 mm of coenenchyme. At assigned times after injury, samples were collected for gross morphological and histological evaluation, in which amoebocytes and zooxanthellae concentrations were quantified within 0.009 mm3of tissue. Overall amoebocyte numbers within uninjured and wounded tissue were similar. However, when numbers of amoebocytes per area of injured tissue were calculated and compared to those of uninjured tissue, 82.4% more amoebocytes occurred at distances 0–0.5 mm from the wound edge, while areas of tissue >2 mm from the wound edge were occupied by fewer amoebocytes. Overall increases in concentrations of zooxanthellae also occurred within wounded coral, but no apparent temporal, spatial, or light-related pattern was detected. Therefore, this study supports the conjecture that amoebocyte accumulation at a wound site is an effect of cells migrating from uninjured tissue adjacent to the wounded edge. In addition, this movement occurs regardless of light attenuation. Light, which in this study was confined to ranges between 70 and 545 μE s−1m−2, did not significantly affect the wound healing process in regard to either closure or cellular concentrations.