Apparent differential phenotypic responses by kelp forest grazers to disease-driven removal of sea star predators; [Data: Tegula shell morphology, GSI, stable isotope analysis]

The potential for aquatic gastropods to display phenotypic plasticity in response to predator cues is well documented in experimental settings. However, long-term physiological responses to predator exposure are difficult to evaluate at large scales in the field. Thus, it is currently unclear (a) the extent to which comparatively dilute predator cues experienced by natural snail populations influence morphometric development and (b) whether energetic costs associated with defensive morphology have allometric impacts on other life history characteristics (e.g., reproduction). The 2013 sea star wasting disease outbreak in central California, USA provided a unique framework for a large-scale natural predator removal experiment, comparing shell morphometrics and gonadosomatic index of subtidal Tegula turban snail populations at kelp forest sites where local predatory sea stars were completely absent (SS-) with paired sites maintaining low predator densities (SS+). All three snail species displayed significantly higher proportional allocation to shell mass at SS+ locations and concomitantly higher reproductive allocation with predators absent (SS-). Dietary stable isotope analysis suggests this may be partially an energetic consequence of behavioral grazing shifts displayed by snails following predator release. Interestingly, morphometric shifts in shell structure differed among the three Tegula species, and appeared closely related to species-specific predator avoidance strategies.

Methods
Dataset includes shell morphometric measurements and tissue (C & N) stable isotope analysis from subtidal Tegula turban snails (T. brunnea, T. montereyi, T. pulligo; total N = 300)  collected from three regions along the central California coast. Field collections were conducted in 2014-2015 after the widespread outbreak of sea star wasting disease, and snails were collected haphazardly by divers on SCUBA from paired sites within each region, selected based on the presence (SS+) and absence (SS-) of predatory sea stars. Detailed methods for data collection and processing are published in Wetmore & Anderson (2024).