Abstract
The western Antarctic Peninsula is experiencing strong environmental changes as a consequence of ongoing regional warming. Glaciers in the area are retreating rapidly and increased sediment-laden meltwater runoff threatens the benthic biodiversity at shallow depths. We identified three sites with a distinct glacier-retreat related history and different levels of glacial influence in the inner part of Potter Cove (King George Island, South Shetland Islands), a fjord-like embayment impacted since the 1950s by a tidewater glacier retreat. We compared the soft sediment meio- and macrofauna isotopic niche widths (δ13C and δ15N stable isotope analysis) at the three sites to investigate possible glacier retreat-related influences on benthic trophic interactions. The isotopic niches were locally shaped by the different degrees of glacier retreat-related disturbance within the Cove. Wider isotopic niche widths were found at the site that has become ice-free most recently, and narrower niches at the older ice-free sites. At an intermediate state of glacier retreat-related disturbance (e.g. via ice-growler scouring) species with different strategies could settle. The site at the earliest stage of post-retreat development was characterized by an assemblage with lower trophic redundancy. Generally, the isotopic niche widths increased with increasing size spectra of organisms within the community, excepting the youngest assemblage, where the pioneer colonizer meiofauna size class displayed the highest isotopic niche width. Meiofauna at all sites generally occupied positions in the isotopic space that suggested a detrital-pool food source and/or the presence of predatory taxa. In general ice scour and glacial impact appeared to play a two-fold role within the Cove: i) either stimulating trophic diversity by allowing continuous re-colonization of meiofaunal species or, ii) over time driving the benthic assemblages into a more compact trophic structure with increased connectedness and resource recycling.
Highlights
The West Antarctic Peninsula (WAP) has been one of the Earth’s most rapidly warming regions over recent decades [1,2,3,4,5], with obvious consequences such as ice-sheet thinning [6], widespread retreat of glacier fronts [7], retreat and collapse of ice-shelves [8,9] and acceleration of snow melting [10])
Isla D station records the highest sediment accumulation rates of the three study sites, and is likely to continue to be strongly affected by ice impact as reflected in the patchy distribution of the endobenthic assemblage [44]. Focusing on these known sites within Potter Cove, in this study we investigated whether the local glacier retreat had detectable effects on trophic interactions in the benthic assemblage, through applying techniques to describe their isotopic niche distribution in order to identify the positions of different organisms within the food web
The most depleted δ13C (-34.9‰) as well as δ15N (-2.6‰) values were recorded for the harpacticoid copepod MT2 which was the taxon present at Isla D colonized by epibionts. δ15N values of consumers showed a similar pattern with deposit feeder/omnivore holding an intermediate position in the trophic level bi-plot (Fig 3) representing all the consumer trophic levels and showing the widest range of δ15N signatures
Summary
The West Antarctic Peninsula (WAP) has been one of the Earth’s most rapidly warming regions over recent decades [1,2,3,4,5], with obvious consequences such as ice-sheet thinning [6], widespread retreat of glacier fronts [7], retreat and collapse of ice-shelves [8,9] and acceleration of snow melting [10]). In the Antarctic, one of the major structuring forces involved in shaping the shallow benthos is ice scouring [21,22,23,24,25,26,27,28,29], including the formation of anchor ice [30,31,32] Other factors such as sedimentation have been seen to affect Arctic meio- and macrobenthos distribution [33,34,35,36], Antarctic soft coral survival (after a slumping event, [29]), and the physiology and survival of Antarctic key species such as the bivalve Laternula elliptica, ascidians and the sea-pen Malacobelemnon daytoni [35,37]. Not unique in the history of the WAP [5], the present rate of environmental changes can be considered to be a greater disturbance to shallow marine communities than any previously identified Such changes, constitute potential stress factors that may alter community composition and species interactions
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