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Dayton, PK, Jarrell SC, Kim S, Parnell PE, Thrush SF, Hammerstrom K, Leichter JJ.  2019.  Benthic responses to an Antarctic regime shift: food particle size and recruitment biology. Ecological Applications. 29   10.1002/eap.1823   AbstractWebsite

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.

Hewitt, JE, Thrush SF, Dayton PD.  2008.  Habitat variation, species diversity and ecological functioning in a marine system. Journal of Experimental Marine Biology and Ecology. 366:116-122.   10.1016/j.jembe.2008.07.016   AbstractWebsite

The expectation that long-term, broad-scale changes in the relative abundance of species, homogenisation of habitats and decreases in diversity will affect ecosystem function has led to an increasing number of studies on functional diversity and composition. Such studies frequently consider the effect of environmental gradients and anthropogenic impacts, but rarely the effect of biogenic habitat variation. In marine soft-sediment systems, habitat variability is likely to be of particular importance because of the strong link between habitat and species diversity. In this study we examine the link between functional trait diversity (as richness and evenness) and composition, and habitat variation in two locations with different regional species pools. We found similar functional traits occurring in the two locations, but differences between habitats within the locations. High evenness within traits was apparent (across both locations and habitats) reflecting the potential for the maintenance of function with the loss of individual species. Between-habitat differences in functional traits were driven by differences in organism densities rather than the presence/absence of individual traits, emphasising the importance of density shifts in driving function. Furthermore, our demonstration of habitat variation as a driver of functional composition and diversity suggests that habitat heterogeneity should be explicitly included within studies trying to predict the effect of species loss on ecosystem function. (C) 2008 Elsevier B.V. All rights reserved.