PEELING OUT PREDATION INTENSITY: DOES REPAIR SCAR FREQUENCY SHIFT DURING MODERN ECOLOGICAL DISTURBANCE?

Predation is an influential process within most ecosystems, however tracking predation intensity in the fossil record can be challenging. Previous modern work has shown that repair scar frequency can be a useful proxy for comparing predation intensity among prey populations. However, little is known of whether repair frequencies change in relation to short-term ecological disturbance over time. This is problematic; if ecological disturbances significantly alter predation intensity, and therefore repair frequency, even over a few years, then interpretations of predation in fossil assemblages affected by time-averaging could be suspect.

To determine if repair frequencies shift as a result of ecological disturbance, live specimens of the gastropods Chlorostoma funebrale, Nucella ostrina, and N. lamellosa were examined for Caedichnus repair scars at seven sites along a well-established gastropod/crab predation gradient near Bamfield, B.C., Canada in 2015, and the results compared to data from 2013 and earlier. All three gastropod species are common in the intertidal of the Pacific northwest, and all are frequent prey of the red rock crab Cancer productus. Since the summer of 2013, the Bamfield area has experienced significant ecological disturbance in the form of surface-temperature spikes, multiple red tides, and severe sea star population decline. This study aims to determine whether these disturbances have affected repair scar frequencies, or whether the signal from repairs over a shell’s life is strong enough to overcome that of short-term environmental perturbations.

There is no significant difference in repair scar frequencies on C. funebrale between 2015 and the earlier studies, despite the ecological disturbances (Pearson's r = 0.98, p << 0.001). Inclusion of the Nucella species into the data set further strengths this conclusion (Pearson's r = 0.99, p << 0.001), and also indicates that the previously observed repair frequency gradient of C. funebrale also holds true for species of Nucella. These findings indicate that short-term ecological disturbances likely do not affect repair scar frequencies in gastropod/crab predation systems, implying that repair scar frequencies are accurate proxies for the predation intensity experienced by gastropods throughout their life history.