Repair scars preserve decadal‐scale patterns of predation intensity despite short‐term ecological disturbances

Recent ecological disturbances have dramatically altered the composition of rocky intertidal Pacific coast communities of North America, particularly top invertebrate predators. Predation is an important regulatory force on intertidal gastropod communities, and the depletion or loss of predators is therefore likely to have a considerable community-wide short-term impact. However, assessing the magnitude and nature of the resulting ecological changes may be problematic in the absence of data recording pre-disturbance conditions. Here, the effectiveness of traces of unsuccessful crab predation on gastropod shells at providing a long-term, decadal record of predation intensity in Barkley Sound (Vancouver Island, British Columbia) was evaluated subsequent to multiple large-scale ecological disturbances, including sea star wasting disease, abnormally high sea surface temperatures, and harmful algal blooms. The frequency of failed crab attacks recorded by repair scars on six populations of the intertidal gastropod Tegula funebralis were surveyed to compare spatial patterns in predation intensity before and after disturbance (2013 and 2015 respectively). The repair frequency gradient observed in 2013 was also recorded by repair scars in 2015 (Spearman's rho = 1, P = 0.002), and repair frequency was not affected by gastropod size in either 2013 (Spearman's rho = 0.14, P = 0.80) or 2015 (Spearman's rho = 0.66, P = 0.18). These findings are consistent with the hypothesis that repair frequency provides decadal records of predation intensity and may be effective to establish persistent levels of predation intensity prior to disturbances in rocky intertidal habitats.