Use of two spatially explicit models to determine the effect of injury geometry on natural resource recovery

1. Disturbance to sessile communities has been evaluated in a wide variety of terrestrial and marine settings, but, to our knowledge, recovery has not explicitly considered the effects of injury shape, except in an exploratory fashion. Therefore, we have developed a simple, but spatially explicit relationship between the geometry of a disturbance and the recovery rate in the context of natural resource damage assessment. 2. Here, grounding of motor vessels in shoalgrass (Halodule wrightii), manatee grass (Syringodium filiforme), and turtlegrass (Thalassia testudinum) habitats results in a variety of injury shapes whose recovery must be evaluated to assign penalties and restoration costs to the party responsible. 3. We developed two spatially explicit, cellular automata modelling techniques to evaluate injury recovery trajectory. Techniques in both SAS(R) and ArcINFO(R) were developed and applied to injuries of varying perimeter but fixed area. 4. The SAS method utilized either a simple Boolean or probabalistic interrogation of the status of adjacent pixels using the matrix language component of the software. ArcINFO utilized a cost/ distance module to evaluate proximity of unfilled to filled (colonized) pixels and then applied a decision rule that governed conversion from unfilled to a filled state. As expected, the greater the perimeter/area ratio, the faster the recovery; and modelling approaches yielded almost identical results. 5. A case study involving similar to 1200 m(2) of almost monotypic T. testudinum revealed that both models predicted that 100% recovery of above-ground components of the injury would not occur for approximately 60 years. This model is now being used routinely in the assessment of vessel groundings in seagrass beds within the Florida Keys National Marine Sanctuary and has been used successfully by the Government to prevail in US Federal Court challenges. Both methods have substantial, untapped capabilities to explore the effect of numerous ecological effects on the processes influencing recovery from disturbance. Published in 2004 by John Wiley Sons, Ltd.