Different feeding strategies in Antarctic scavenging amphipods and their implications for colonisation success in times of retreating glaciers

Abstract

BackgroundScavenger guilds are composed of a variety of species, co-existing in the same habitat and sharing the same niche in the food web. Niche partitioning among them can manifest in different feeding strategies, e.g. during carcass feeding. In the bentho-pelagic realm of the Southern Ocean, scavenging amphipods (Lysianassoidea) are ubiquitous and occupy a central role in decomposition processes. Here we address the question whether scavenging lysianassoid amphipods employ different feeding strategies during carcass feeding, and whether synergistic feeding activities may influence carcass decomposition. To this end, we compared the relatively large species Waldeckia obesa with the small species Cheirimedon femoratus, Hippomedon kergueleni, and Orchomenella rotundifrons during fish carcass feeding (Notothenia spp.). The experimental approach combined ex situ feeding experiments, behavioural observations, and scanning electron microscopic analyses of mandibles. Furthermore, we aimed to detect ecological drivers for distribution patterns of scavenging amphipods in the Antarctic coastal ecosystems of Potter Cove. In Potter Cove, the climate-driven rapid retreat of the Fourcade Glacier is causing various environmental changes including the provision of new marine habitats to colonise. While in the newly ice-free areas fish are rare, macroalgae have already colonised hard substrates. Assuming that a temporal dietary switch may increase the colonisation success of the most abundant lysianassoids C. femoratus and H. kergueleni, we aimed to determine their consumption rates (g food x g amphipods−1 x day−1) and preferences of macroalgae and fish.ResultsWe detected two functional groups with different feeding strategies among scavenging amphipods during carcass feeding: carcass ‘opener’ and ‘squeezer’. Synergistic effects between these groups were not statistically verified under the conditions tested. C. femoratus switched its diet when fish was not available by consuming macroalgae (about 0.2 day−1) but preferred fish by feeding up to 80% of its own mass daily. Contrary, H. kergueleni rejected macroalgae entirely and consumed fish with a maximal rate of 0.8 day−1.ConclusionThis study reveals functional groups in scavenging shallow-water amphipods and provides new information on coastal intraguild niche partitioning. We conclude that the dietary flexibility of C. femoratus is a potential ecological driver and central to its success in the colonisation of newly available ice-free Antarctic coastal habitats.Electronic supplementary materialThe online version of this article (10.1186/s12983-017-0248-3) contains supplementary material, which is available to authorized users.

Can mandible morphology help predict feeding habits in Antarctic amphipods?

“…Such species' molars therefore do not have a grinding function, but can serve to push pieces of food into the stomodeum when the mandible is adducted (Steele & Steele 1993). Members of the second functional group have a continuous and less rapid feeding behaviour and probably do not survive long starvation periods (Seefeldt et al 2017). The mandibles of these usually smaller species bear a slender incisor process and a triturative molar (Sainte-Marie 1984, Momo et al 1998, Arndt et al 2005, Seefeldt et al 2017).…”

“…The development of the molar suggests that these animals rely on a broader dietary regime (Sainte-Marie 1984). This group would therefore be composed of more facultative scavengers that could also act as predators and/or deposit feeders (Seefeldt et al 2017).…”

“…some cnidarians, sponges, holothurians or polychaetes) appear to share an absent or greatly reduced molar (Coleman 1989a, 1989b, 1990, Watling 1993, Guerra-García & Tierno de Figueroa 2009), whereas a broader and triturative molar is presumably used to crush more rigid food items, such as crustacean exoskeletons (Caine 1974, Sainte-Marie 1984, Haro-Garay 2003). Highly adapted scavenger species generally combine wide, sharp and toothless shearing incisors (to bite off large pieces of carrion) with tall, conical, posteriorly projecting, non-triturative molars, which push pieces of food into the stomodeum without chewing (Dahl 1979, Sainte-Marie 1984, Steele & Steele 1993, Watling 1993, Arndt et al 2005, Seefeldt et al 2017). Facultative scavengers often show some degree of omnivory and appear to have a somewhat distinct mandible morphology compared to exclusive scavengers, characterized by a slender incisor and a lower triturative molar process (Dahl 1979, Momo et al 1998, Arndt et al 2005, Seefeldt et al 2017).…”

A biodiversity survey of scavenging amphipods in a proposed marine protected area: the Filchner area in the Weddell Sea, Antarctica

“…A recent study on subterranean amphipods has shown that morphologically cryptic species in fact occupied very distinct feeding niches ranging from predation to filter-feeding (Fišer et al 2015). Furthermore, also within the scavenging guild, distinct succession patterns linked to feeding strategies (carcass "openers" vs. "squeezers") and morphological adaptations to opportunistic or obligate carrion-feeding, may allow niche partitioning amongst closely related lysianassoids (Seefeldt et al 2017b). In this context, in-depth morphological investigations based on scanning electron microscopy of the feeding apparatus (e.g., a mouthpart-atlas, Arndt et al 2005), as well as feeding experiments characterizing feeding rates and preferences (Seefeldt et al 2017b), can elucidate subtly different feeding methods within the scavenging guild.…”

Citizen-Science for the Future: Advisory Case Studies From Around the Globe

“…They dwell in sheltered sites, almost exclusively under flat, loose stones, making specimens readily available to volunteers at low tide. Scientists had previously conducted research demonstrating that the two species compete for space (Weslawski, 1990). However, in that study only a single fjord was investigated.…”