Meeting Abstract
Rocky intertidal organisms experience varying levels of environmental stress along elevational (tide height) and oceanographic (geographic) gradients with implications for survival and patterns of abundance and distribution. Given potential changes in food availability and physical stress under climate change, it is important to determine how the physiological conditions of intertidal species are affected by environmental stressors. Mussels are critical foundation species in rocky intertidal ecosystems, as they are a trophic link between primary production and predators and provide habitat to associated intertidal organisms. We determined mussel condition across multiple stress gradients in New Zealand, where four co-occurring mussel species (Aulacomya maoriana, Perna canaliculus, Mytilus galloprovincialis, and Xenostrobus pulex) comprise a uniquely diverse intertidal assemblage. We measured three metrics of mussel condition (growth rate, gonadosomatic index [GSI], and tissue C:N ratio) across two stress gradients (temperature represented by tide height and food availability represented by chlorophyll concentration). We hypothesized that as stress increased, condition would decrease. We found that growth rate was the only metric that varied in the expected direction, indicating that GSI and tissue C:N ratio are likely influenced by other factors. A temporal difference may also help explain our results: growth rate was measured – and integrated environmental impacts – over a year while GSI and C:N ratio were measured only once as “snapshots” of mussel condition. Our results suggest measurements that describe organismal performance over longer time scales (e.g. annual growth rates) are better indicators of potential impacts of climate change on these marine species.
