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Kim, S, Hammerstrom K, Dayton P.  2019.  Epifaunal community response to iceberg-mediated environmental change in McMurdo Sound, Antarctica. Marine Ecology Progress Series. 613:1-14.   10.3354/meps12899   AbstractWebsite

High-latitude marine communities are dependent on sea ice patterns. Sea ice cover limits light, and hence primary production and food supply. Plankton, carried by currents from open water to areas under the sea ice, provides a transitory food resource that is spatially and temporally variable. We recorded epifaunal abundances at 17 sites in McMurdo Sound, Antarctica, over 12 yr, and found differences in communities based on location and time. The differences in location support patterns observed in long-term infaunal studies, which are primarily driven by currents, food availability, and larval supply. The temporal differences, highlighting 2004 and 2009 as years of change, match the altered persistence of sea ice in the region, caused by the appearance and disappearance of mega-icebergs. The temporal changes were driven by changes in abundance of species that filter feed on large particulates. The shift in current patterns that occurred due to mega-icebergs decreased the normal food supply in the region. In addition to the decrease in food availability, we suggest that the reduced light resulting from thicker-than-normal sea ice resulted in a shift to smaller phytoplankton. A change in food quality as well as quantity may have influenced the temporal change in epifaunal communities.

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.

Abrams, PA, Ainley DG, Blight LK, Dayton PK, Eastman JT, Jacquet JL.  2016.  Necessary elements of precautionary management: implications for the Antarctic toothfish. Fish and Fisheries. 17:1152-1174.   10.1111/faf.12162   AbstractWebsite

We review the precautionary approach to fisheries management, propose a framework that will allow a systematic assessment of insufficient precaution and provide an illustration using an Antarctic fishery. For a single-species fishery, our framework includes five attributes: (1) limit reference points that recognize gaps in our understanding of the dynamics of the species; (2) accurate measures of population size; (3) ability to detect population changes quickly enough to arrest unwanted declines; (4) adequate understanding of ecosystem dynamics to avoid adverse indirect effects; and (5) assessment of the first four elements by a sufficiently impartial group of scientists. We argue that one or more of these elements frequently fail to be present in the management of many fisheries. Structural uncertainties, which characterize almost all fisheries models, call for higher limit points than those commonly used. A detailed look into the five elements and associated uncertainties is presented for the fishery on the Antarctic toothfish in the Ross Sea (FAO/CCAMLR Area 88.1, 88.2), for which management was recently described as highly precautionary'. In spite of having features that make the Ross Sea fishery ideal for the application of the precautionary approach, gaps in our knowledge and failure to acknowledge these gaps mean that current regulation falls short of being sufficiently precautionary. We propose some possible remedies.

Konotchick, T, Parnell PE, Dayton PK, Leichter JJ.  2012.  Vertical distribution of Macrocystis pyrifera nutrient exposure in southern California. Estuarine Coastal and Shelf Science. 106:85-92.   10.1016/j.ecss.2012.04.026   AbstractWebsite

We examined water column temperature time series profiles for several years at two locations in a single kelp (Macrocystis pyrifera) forest to characterize the alongshore variability of the nutrient climate that giant kelp is exposed to and compare it to the response of giant kelp. The differences in nutrient climate are due to differential alongshore vertical variations in temperature, a well-established proxy of nitrate, due to the topographically induced internal wave dynamics within the kelp forest. We observed the greatest temperature variability during summer and most of this variability occurred near the surface. The 14.5 degrees C isotherm, indicating the presence of nitrate, ranged the entire vertical extent of the water column, and was shallowest during the winter and in the southern portion of the kelp forest. Predicted water column integrated nitrate varies from 0 mu mol NO3-/m(2) to 431 mu mol NO3-/m(2) yielding a time series daily average of 0.12 gN/m(2)day (North La Jolla) and 0.18 gN/m(2)day (South La Jolla). Redfield conversion of these values puts the time series daily average for carbon production (upper limit) between 0.8 and 1.2 gC/m(2)day for the north and south parts of the bed respectively, and shows considerable variation at several time scales. Giant kelp in the southern portion of the forest exhibited greater stipe densities (a proxy for kelp production) than individuals in the northern portion, corresponding with the alongshore nutrient climate variability. The depth of the nutricline varied by up to 10 m over time scales as short as hours. Variability was greatest at diurnal and semi-diurnal frequencies, with shallower water column depths showing greatest variability. These depth-specific variations in temperature and nutrient exposure may have biologically important consequences for M. pyrifera especially during low nutrient seasons. (C) 2012 Elsevier Ltd. All rights reserved.

Levin, LA, Dayton PK.  2009.  Ecological theory and continental margins: where shallow meets deep. Trends in Ecology & Evolution. 24:606-617.   10.1016/j.tree.2009.04.012   AbstractWebsite

Continental margins, where land becomes ocean and plunges to the deep sea, provide valuable food and energy resources, and perform essential functions such as carbon burial and nutrient cycling. They exhibit remarkably high species and habitat diversity, but this is threatened by our increasing reliance on the resources that margins provide, and by warming, expanding hypoxia and acidification associated with climate change. Continental margin ecosystems, with environments, constituents and processes that differ from those in shallow water, demand a new focus, in which ecological theory and experimental methods are brought to bear on management and conservation practices. Concepts of disturbance, diversity-function relationships, top-down versus bottom-up control, facilitation and meta-dynamics offer a framework for studying fundamental processes and understanding future change.