Data from: Indirect legacy effects of an extreme climactic event on a marine megafaunal community

While extreme climactic events (ECEs) are predicted to become more
frequent, reliably predicting their impacts on consumers remains
challenging– particularly for large consumers in marine environments. Many
studies that do evaluate ECE effects focus primarily on direct effects,
though indirect effects can be equally or more important. Here, we
investigate the indirect impacts of the 2011 “Ningaloo Niño” marine
heatwave ECE on a diverse megafauna community in Shark Bay, Western
Australia. We use an 18 year community level dataset before (1998-2010)
and after (2012-2015) the heatwave to assess the effects of seagrass loss
on the abundance of seven consumer groups: sharks, sea snakes (multiple
species), Indo-pacific bottlenose dolphins (Tursiops aduncus), dugongs
(Dugong dugon), green turtles (Chelonia mydas), loggerhead turtles
(Caretta caretta), and pied cormorants (Phalacrocorax spp.). We then
assess whether seagrass loss influences patterns of habitat use by the
latter five groups, which are under risk of shark predation. Sharks catch
rates were dominated by the generalist tiger shark (Galeocerdo cuvier) and
changed little, resulting in constant apex predator density despite heavy
seagrass degradation. Abundances of most other consumers declined markedly
as food and refuge resources vanished, with the exception of generalist
loggerhead turtles. Several consumer groups significantly modified their
habitat use patterns in response to the die-off, but only bottlenose
dolphins did so in a manner suggestive of a change in risk-taking
behavior. We show that ECEs can have strong indirect effects on megafauna
populations and habitat use patterns in the marine environment, even when
direct effects are minimal. Our results also show that indirect impacts
are not uniform across taxa or trophic levels and suggest that generalist
marine consumers are less susceptible to indirect effects of ECEs than
specialists. Such non-uniform changes in populations and habitat use
patterns have implications for community dynamics, such as the relative
strength of direct predation and predation risk. Attempts to predict
ecological impacts of ECEs should recognize that direct and indirect
effects often operate through different pathways and that taxa can be
strongly impacted by one even if resilient to the other.