Abstract
In southern Patagonia, the Beagle Channel shows very low production during winter but simultaneously sustains very dense aggregations of the pelagic stage of squat lobster (Munida gregaria), a benthic decapod whose pelagic juveniles have the largest body size within the chitinous pelagic community. To assess the coexistence of the mesozooplankton community and the pelagic M. gregaria stage under the harsh feeding winter conditions, we conducted a research cruise at two locations connected to the Beagle Channel, Yendegaia Bay (land terminating-glacier) and Pia Fjord (marine-terminating glacier). Our results showed that the zooplankton communities were similar in these two fjords, that a single pelagic group dominated in terms of biomass (pelagic Munida gregaria), and that differences in vertical distribution existed between most of the principal crustacean zooplankton and pelagic M. gregaria. All groups showed consumption of terrestrially derived organic matter, as revealed by their δ13C values. However, the isotopic composition, trophic positions (TP), and isotopic niche areas of the groups separated pelagic M. gregaria, presenting some of the lowest δ15N and the highest δ13C values, and the narrowest isotopic niche width. Pelagic M. gregaria was dominated by a single body size class along the 0–100 m water column, with no diel changes in vertical distribution, remained mostly in the upper layers (0–50 m), and benefited from the slightly higher phytoplankton concentrations at shallower depths as revealed by their higher δ13C values and low trophic position. In contrast, the other groups, including zoea M. gregaria stages, developed changes in distribution between day and night or remained deeper in the water column. These groups showed higher δ15N values, higher TP, and lower δ13C values, most of which probably fed on a nanoheterotrophs and terrestrial particulate organic matter mixture at deeper layers. Thus, the different vertical distributions, different trophic level food sources, and slightly different organic carbon sources apparently reduced any potential competence for food resources and form part of the feeding strategy that may facilitate the coexistence of the different large pelagic crustaceans under harsh feeding winter conditions in this high latitude austral region.
Highlights
Austral Patagonia has recently received attention with regard to global climate change because it contains some of the largest freshwater reserves in continental areas in the form of extensive ice fields and glaciers (González et al, 2016; RGI, 2017)
The objectives of the present study were to assess (a) whether the largest body size and more abundant zooplankton crustacean groups were the same in different fjords, (b) whether their organic carbon source was primarily of marine origin or terrestrially derived, (c) whether the trophic positions and isotopic niche widths differed among crustacean groups, and (d) to evaluate whether potentially different feeding behavior along with potential differences in vertical distributions might constitute a way of partitioning the environment to facilitate the maintenance of different groups within this low winter production high-latitude system
The general objective of this study was to assess how the dominant chitinous zooplankton groups in the Beagle Channel (BC) survive during the winter low production season in this high latitude region
Summary
Austral Patagonia has recently received attention with regard to global climate change because it contains some of the largest freshwater reserves in continental areas (other than Antarctica) in the form of extensive ice fields and glaciers (González et al, 2016; RGI, 2017). Recent reports have documented the retrieval of these ice masses during the last two decades associated with changes in nival and rain precipitation (Climate Change, 2007, 2013; Rivera et al, 2007; Casassa et al, 2010; Marín et al, 2013) These variations, in turn, have induced changes in the amount of water received in the coastal and fjord environments and the amount of terrestrial originated debris conducted toward the adjacent marine system (Dussaillant et al, 2009; Meerhoff et al, 2019; Ross et al, 2020). Most recent studies carried out in spring on the Atlantic side of the Beagle Channel (BC; 55◦S) report that the carbon flux in the area is based on combined marine phytoplankton, macroalgae, and terrestrially derived plant debris with the largest fraction provided by these latter two sources that reach the higher trophic levels of the food web (Riccialdelli et al, 2017)
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