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

Abstract

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 ρ = 1, P = 0.002), and repair frequency was not affected by gastropod size in either 2013 (Spearman's ρ = 0.14, P = 0.80) or 2015 (Spearman's ρ = 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.

Killer whale predatory scarring on mysticetes: A comparison of rake marks among blue, humpback, and gray whales in the eastern North Pacific

“…We found evidence of species‐specific hunting approaches by killer whales though this finding needs to be considered in the context of the approach we used. While our study was limited to assessing killer whale attacks on survivors using photographs of flukes, previous studies have used similar findings in other species as an index of predation rates (Cockroft et al, 1989; Kröger, 2011; Ramsay et al, 2000; Stafford et al, 2015; Tyler et al, 2019). Our approach is also consistent with accounts that most baleen whale's rake marks should be located on the tail fluke, because it is often used for defense and located at the rear end of the whale's body (Ford & Reeves, 2008; Rice & Wolman, 1971).…”

Predation Scars Reveal Declines in Crab Populations Since the Pleistocene

“…Given that gastropod shells grow by accretion, sampling of repairs scars can be considered to be on the scale of the animals' lifespan. Furthermore, repair scar frequencies on T. funebralis are not impacted by short term, but extreme, environmental disturbances, indicating that T. funebralis repair scar patterns in the modern are operating on at least the decadal scale (Tyler et al, 2019). Thus, repair scar patterns can be considered to capture more robust biological signals "time averaged" over the lifespan of the organism, as is also an advantage of more time averaged fossil assemblages (Kowalewski et al, 1998;Kidwell, 2013), and useful when comparing sampling efforts between live or recent samples versus death assemblages (Powell et al, 2020).…”

“…Crab predation scars (repair scars) on mollusks have been used to assess patterns as broad as the development of antipredatory adaptations and mollusk diversity through time (Schindel et al, 1982;Vermeij, 1982c;Alexander and Dietl, 2003;Dietl et al, 2010;Mondal et al, 2014;Mondal and Harries, 2015), to variation in predation in modern ecosystems (Vermeij, 1982a,b;Schmidt, 1989;Schindler et al, 1994;Cadée et al, 1997;Alexander and Dietl, 2001;Dietl and Alexander, 2009;Molinaro et al, 2014;Stafford et al, 2015b). Predation traces also provide useful information on how crabs and their ecosystems are affected by environmental disturbances (Tyler et al, 2019). Most importantly for stock assessments, repair frequencies accurately track crab abundances in modern coastal studies (Schindler et al, 1994;Molinaro et al, 2014;Stafford et al, 2015b), especially when limited to repairs found on a single, common prey species.…”