|Title||Benthic responses to an Antarctic regime shift: food particle size and recruitment biology|
|Publication Type||Journal Article|
|Year of Publication||2019|
|Authors||Dayton PK, Jarrell SC, Kim S, Parnell P.E, Thrush S.F, Hammerstrom K, Leichter J.J|
|Type of Article||Article|
|Keywords||bivalves; bryozoans; climate; climate-change; communities; echinoderms; ecosystem; Environmental Sciences & Ecology; episodic events; feeders and plankton particulate size; filter; ice; mcmurdo-sound; oceanography; population-structure; Regime shift; ross sea; scaling space and time; southern-ocean; Sponges; variability; west side|
Polar ecosystems are bellwether indicators of climate change and offer insights into ecological resilience. In this study, we describe contrasting responses to an apparent regime shift of two very different benthic communities in McMurdo Sound, Antarctica. We compared species-specific patterns of benthic invertebrate abundance and size between the west (low productivity) and east (higher productivity) sides of McMurdo Sound across multiple decades (1960s-2010) to depths of 60 m. We present possible factors associated with the observed changes. A massive and unprecedented shift in sponge recruitment and growth on artificial substrata observed between the 1980s and 2010 contrasts with lack of dramatic sponge settlement and growth on natural substrata, emphasizing poorly understood sponge recruitment biology. We present observations of changes in populations of sponges, bryozoans, bivalves, and deposit-feeding invertebrates in the natural communities on both sides of the sound. Scientific data for Antarctic benthic ecosystems are scant, but we gather multiple lines of evidence to examine possible processes in regional-scale oceanography during the eight years in which the sea ice did not clear out of the southern portion of McMurdo Sound. We suggest that large icebergs blocked currents and advected plankton, allowed thicker multi-year ice, and reduced light to the benthos. This, in addition to a possible increase in iron released from rapidly melting glaciers, fundamentally shifted the quantity and quality of primary production in McMurdo Sound. A hypothesized shift from large to small food particles is consistent with increased recruitment and growth of sponges on artificial substrata, filter-feeding polychaetes, and some bryozoans, as well as reduced populations of bivalves and crinoids that favor large particles, and echinoderms Sterechinus neumayeri and Odontaster validus that predominantly feed on benthic diatoms and large phytoplankton mats that drape the seafloor after spring blooms. This response of different guilds of filter feeders to a hypothesized shift from large to small phytoplankton points to the enormous need for and potential value of holistic monitoring programs, particularly in pristine ecosystems, that could yield both fundamental ecological insights and knowledge that can be applied to critical conservation concerns as climate change continues.
The spatial and temporal changes at a regional scale across McMurdo Sound are interesting, in part, because the oceanography of the region was long thought to be highly stable and predictable (Littlepage 1965, Dayton et al. 1974), but this view was modified by observations of decadal changes (Dayton 1989, Dayton et al. 2016b, Schine et al. 2016). We focus on decadal-scale change in major components of the two very different benthic communities. These shifts offer a unique opportunity to evaluate the ecological legacies of two different communities following a substantial climate-driven environmental change and offer insights into the resilience of this system to future changes.