Dayton PK et al. (2019), Benthic responses to an Antarctic regime shift:...

ECB-ART-46861

Ecol Appl 2019 Jan 01;291:e01823. doi: 10.1002/eap.1823.

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Benthic responses to an Antarctic regime shift: food particle size and recruitment biology.

Dayton PK , Jarrell SC , Kim S , Ed Parnell P , Thrush SF , Hammerstrom K , Leichter JJ .

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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.

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Genes referenced: abcc3a LOC100887844 LOC100893907 LOC115925415

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	Figure 1. Map of the study sites in McMurdo Sound, Antarctica: Cape Armitage, Explorers Cove, and Salmon Bay.
	Figure 2. (a) Representative photo of the sponge habitat at Cape Armitage at 45 m depth. The yellow line visible at the top was placed in 1975, 35 yr previously. These transect lines were almost completely buried by the growth of the sponges and bryozoans. (b) A photo of the soft bottom habitat in Explorers Cove in 1975 at 45 m depth. The white figures are sponges being carried by the urchin Sterechinus neumayeri. Almost no urchins were observed in 2010.
	Figure 3. (a) Photo of the brackish moat at Salmon Bay with the ice wall on the left. The sea ice floats up during high tides allowing the productive water in the moat to escape over the ice wall into the study site. The “bridge” was designed to allow divers and tenders to access the dive site from shore. (b) Divers at Salmon Bay accessing the dive hole over difficult multi‐year sea ice characterized by layers of windblown gravel that absorbs solar energy and melts about 1 m into the ice, leaving a pool of water covered with thin ice.
	Figure 4. Percent cover of all sponges vs. Bryozoa/Hydrozoa patches. Curves indicate second‐order polynomial fits to the data.
	Figure 5. Mean densities of bivalves Laternula elliptica, Adamussium colbecki, and the crinoid Promachocrinus kerguelensis along the depth gradient at Explorers Cove in 1974–1977, a transect for Adamussium in 1985, and 2010. The circles and solid lines represent pooled data from 1974 to 1979 and × and dashed lines represent data from 2010. The triangles represent poor photo transects for 1985. The error bars represent standard error.
	Figure 6. Mean densities of the deposit‐feeding sea urchin Sterechinus neumayeri and the heart urchin Abatus nimrodi across the depth gradients at Explorers Cove. The circles and solid lines represent pooled data from 1974 to 1977 and x and dashed lines represent data from 2010. The triangles represent poor photo transects from 1985. The error bars represent standard error.
	Figure 7. Mean densities of the polychaetes Perkinsiana littoralis and Serpula narconensis across the depth gradients at Explorers Cove in the 1970s and 2010. The circles and dashed lines represent pooled data from 1974 to 1979 and × and dashed lines represent data from 2010. The error bars represent standard error.
	Figure 8. Mean densities of predators (Ophionotus victoriae, Parborlasia corrugatus, Ophiosparta gigas, and Ctenocidaris perrieri) at Explorers Cove, New Harbor with the data for 1974–1979 summed. The circles and dashed lines represent pooled data from 1974–1979 and × and dashed lines represent data from 2010. The triangles represent poor photo transects for 1985. The error bars represent standard error.
	Figure 9. Mean density of an opportunistic sponge, Homaxinella balfourensis, and two unidentified Bryozoa, Camptolites sp. and Hornera sp. The × and dashed lines represent data from 2010 and triangles and dotted lines represent the lack of individuals in 1988. The error bars represent standard error.
	Figure 10. Densities of bivalves (Laturnula elliptica and Adamussium colbecki) across a depth gradient at Salmon Bay. The triangles and dotted lines represent transects in 1988 and the × and dashed lines represent data from 2010. The error bars represent standard error.
	Figure 11. Densities of deposit feeders Sterechinus neumayeri and Abatus nimrodi across a depth gradient at Salmon Bay. The triangles and dotted lines represent transects in 1988 and the × and dashed lines represent data from 2010. The error bars represent standard error.
	Figure 12. Density of polychaetes Perkinsiana littoralis and Serpula narconensis across a depth gradient at Salmon Bay. The triangles and dotted lines represent transects in 1988 and the × and dashed lines represent data from 2010. The error bars represent standard error.
	Figure 13. Density of carnivores (Ophionotus victoriae, Ophiosparte gigas, Parborlasia corrugatus, and Psilaster charcoti) across a depth gradient at Salmon Bay. The triangles and dotted lines represent transects in 1988 and the × and dashed lines represent data from 2010. The error bars represent standard error.

References [+] :

Barnes, Disturbance, colonization and development of Antarctic benthic communities. 2007, Pubmed