Patterns in morphology, pigment concentration, and light saturation kinetics of Ecklonia radiata reveal great morphological and physiological variability among individuals from sites spanning strong gradients in topographic shading and wave exposure among the 14 fjords in southwestern New Zealand. Morphology of E. radiata varies from relatively narrow (85 6 4.7 mm) (mean 6 standard error), thick (3.2 6 0.30 mm) blades from the well-illuminated, wave-exposed outer coast sites to wide, undulate (460 6 36.8 mm,) and thin (0.46 6 0.059 mm) blades from quiescent, topographically shaded inner fjord sites. Chlorophyll a (Chl a) concentration of blades (0.084-1.34 mg g 21 of tissue) and the ratio of fucoxanthin to Chl a (0.33 to 0.56) also increased along this gradient, indicating photoacclimation within the inner fjord populations. In situ measurements of light saturation kinetics indicate maximum photosynthetic rates at lower irradiance (I max 5 43.7 vs. 257 mmol quanta m 22 s 21 ) for algae at inner fjord sites relative to well-lit outer fjord locations. Individuals exhibiting characteristically photoacclimated relative electron transfer rate curves had more deplete d 13 C (213.35% to 222.35%) than individuals with higher I max . There was no significant association between the kelp morphology or geographic location and the observed recombinant DNA diversity of ITS sequences that would indicate the presence of two Ecklonia species in the fjords. E. radiata occupies a wide range of habitats in Fiordland and displays variability in morphology and photo-physiological responses to low light that coincide with gradients in wave exposure and topographically shaded light conditions.

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Organic matter produced by the sea ice microbial community (SIMCo) is an important link between sea ice dynamics and secondary production in near-shore food webs of Antarctica. Sea ice conditions in McMurdo Sound were quantified from time series of MODIS satellite images for Sept. 1 through Feb. 28 of 2007-2015. A predictable sea ice persistence gradient along the length of the Sound and evidence for a distinct change in sea ice dynamics in 2011 were observed. We used stable isotope analysis (δ C and δ N) of SIMCo, suspended particulate organic matter (SPOM) and shallow water (10-20 m) macroinvertebrates to reveal patterns in trophic structure of, and incorporation of organic matter from SIMCo into, benthic communities at eight sites distributed along the sea ice persistence gradient. Mass-balance analysis revealed distinct trophic architecture among communities and large fluxes of SIMCo into the near-shore food web, with the estimates ranging from 2 to 84% of organic matter derived from SIMCo for individual species. Analysis of patterns in density, and biomass of macroinvertebrate communities among sites allowed us to model net incorporation of organic matter from SIMCo, in terms of biomass per unit area (g/m ), into benthic communities. Here, organic matter derived from SIMCo supported 39 to 71 per cent of total biomass. Furthermore, for six species, we observed declines in contribution of SIMCo between years with persistent sea ice (2008-2009) and years with extensive sea ice breakout (2012-2015). Our data demonstrate the vital role of SIMCo in ecosystem function in Antarctica and strong linkages between sea ice dynamics and near-shore secondary productivity. These results have important implications for our understanding of how benthic communities will respond to changes in sea ice dynamics associated with climate change and highlight the important role of shallow water macroinvertebrate communities as sentinels of change for the Antarctic marine ecosystem.

Omnivores play an important role in the routing and distribution of organic matter across food webs. We demonstrate a novel approach to quantifying the coincidence of landscapescale nutritional gradients with niche breadth in terms of variability in trophic level and use of basal organic matter sources. We provide an example of the links between individual variability in resource use and habitat of a broad-spectrum omnivore, the red rock lobster Jasus edwardsii. Information on the co-occurrence of J. edwardsii with kelp bed habitats Ecklonia radiata and with their preferred prey Mytilus edulis galloprovinciallis were collected at 60 sites across Fiordland, southwest New Zealand. Analysis of distance-based linear models (DISTLM) indicated that the presence of mussels was the best predictor of lobster occurrence in the model set. At a subset of sites, we collected lobster muscle for stable isotope analysis and measured 3 demographic parameters from the lobsters: relative abundance, sex and carapace lengths. We characterised habitats with surveys of common kelp and mussels. Using stable isotope signatures (δ 13 C and δ 15 N), we calculated individual-based estimates of trophic level and the mixture of organic matter sources, i.e. phytoplankton and macroalgae. Using DISTLM, lobster and mussel densities best explained variability in lobster diet. Variability in resource use was distinct inside and outside of kelp bed habitat. In kelp beds, lobsters fed at a higher average trophic level, with low variability among individuals in trophic level and use of organic matter sources. Outside kelp beds, individual variability indicated broad trophic diversification. These patterns indicate a strong influence of the nutritional landscape at the scale of the metapopulation, which has important implications for understanding dietary influences on population structure. KEY WORDS: Food web · Omnivory · Stable isotopes · Jasus edwardsii · Kelp forestResale or republication not permitted without written consent of the publisher

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