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.