Abstract
We studied the population dynamics and parasite load of the foraminifer Cibicides antarcticus on its host the Antarctic scallop Adamussium colbecki from three localities differing by sea ice cover within western McMurdo Sound, Ross Sea, Antarctica: Explorers Cove, Bay of Sails and Herbertson Glacier. We also estimated CaCO3 biomass and annual production for both species. Cibicides populations varied by locality, valve type, and depth. Explorers Cove with multiannual sea ice had larger populations than the two annual sea ice localities, likely related to differences in nutrients. Populations were higher on Adamussium top valves, a surface that is elevated above the sediment. Depth did not affect Cibicides distributions except at Bay of Sails. Cibicides parasite load (the number of complete boreholes in Adamussium valves) varied by locality between 2% and 50%. For most localities the parasite load was < 20%, contrary to a previous report that ~50% of Cibicides were parasitic. The highest and lowest parasite load occurred at annual sea ice localities, suggesting that sea ice condition is not important. Rather, the number of adults that are parasitic could account for these differences. Cibicides bioerosion traces were categorized into four ontogenetic stages, ranging from newly attached recruits to parasitic adults. These traces provide an excellent proxy for population structure, revealing that Explorers Cove had a younger population than Bay of Sails. Both species are important producers of CaCO3. Cibicides CaCO3 biomass averaged 47-73 kg ha-1 and Adamussium averaged 4987-6806 kg ha-1 by locality. Annual production rates were much higher. Moreover, Cibicides represents 1.0-2.3% of the total host-parasite CaCO3 biomass. Despite living in the coldest waters on Earth, these species can contribute a substantial amount of CaCO3 to the Ross Sea and need to be incorporated into food webs, ecosystem models, and carbonate budgets for Antarctica.
Highlights
Parasites are emerging as important ecological agents for structuring plant and animal communities, signifying the vitality or degradation of ecosystems [1,2,3]
We examined the relationship between the parasitic foraminifer Cibicides antarcticus and its host, the Antarctic scallop Adamussium colbecki, which live in the coldest waters on Earth near the freezing point of seawater (-1.97 °C)
Despite the death of its host, Cibicides continued to live on the top valve until it was retrieved from the seafloor a year later
Summary
Parasites are emerging as important ecological agents for structuring plant and animal communities, signifying the vitality or degradation of ecosystems [1,2,3]. Parasitic biomass often exceeds that of top predators in marine systems, affecting ecosystem function [4]. Despite their importance, the majority of food web topologies exclude parasites [5,6]. Foraminifera are diverse and abundant in marine ecosystems [8] They enter into marine food webs at multiple trophic levels, including suspension feeding, grazing, predation, and parasitism [9,10,11,12,13,14,15]. Thereby, a single species enters into a food web at multiple levels, with implications for ecosystem function Of these trophic modes, parasitism is the least well understood
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