Separate Feeding Between the Pelagic Stage of the Squat Lobster Munida gregaria and the Larger Sized Zooplankton Crustacean Groups in the Beagle Channel as Revealed by Stable Isotopes

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.

Vertical distribution of macrobenthic communities from a shipwreck in the Strait of Magellan

“…Finally, omnivores monotonically increased with depth (z= 2.35, P = 0.02, pseudo-R 2 = 0.34). The squat lobster Munida gregaria, an abundant species in Patagonia fjords (Castro et al 2021), accounted for most of the abundance of omnivore organisms (Table 1) (Pérez-Barros et al 2010). In addition, the benthic life phase of M. gregaria seems to be unable to cope with low-salinity shallow waters in fjords, which could explain the patterns observed in this study (Betti et al 2020).…”

Approaching the Ecological Role of the Squat Lobster (Munida gregaria) and the Fuegian Sprat (Sprattus fuegensis) in the Francisco Coloane Marine Area (Magellan Strait, Chile) Using a Pelagic Food Web Model

“…The oceanographic conditions are determined by complex marineterrestrial-atmospheric interactions that result in unique marine ecosystems with high biological production [21][22][23]. In the Magallanes region, the squat lobsters Munida gregaria and M. surugosa are the dominant group in terms of biomass [24,25]. Due to their abundance; their importance as prey for various predators such as cephalopods, fish, birds, and marine mammals [26]; and their direct connection between lower and higher trophic levels, Munida spp.…”