Eat and run: anoxic feeding and subsequent aerobic recovery by Orchomene obtusus in Saanich Inlet, British Columbia, Canada

Abstract

The lysianassid amphipod Orchomene obtusus (Sars) is known as an epibenthic scavenger, but it is abundant in the water column of Saanich Inlet, British Columbia, a temperate fjord with poorly oxygenated deep water. Sampling with vertically-stratified nets and baited traps indicates that O. obtusus is abundant within the oxycline at 100 to 140 m, is present in anoxic deep waters at low abundances, and is also abundant in the anoxic benthic environment. Shipboard incubations revealed that O. obtusus can survive between 10 and 33 h of anoxia at in situ conditions. Stable isotope and gut fluorescence measurements suggest that these amphipods feed on material produced in surface waters, and not on the isotopically dissimilar suspended detrital material present in the vicinity of the oxycline. The amphipods do not enter surface waters, and it appears that O. obtusus has adapted to oxygen gradients in this environment by feeding on surface-water-derived material in the food-rich and predator-poor anoxic benthos and subsequently migrating into the water column to conduct aerobic respiration. These vertical excursions are probably a modification of the swimming behavior exhibited by hyperbenthic amphipods in well-oxygenated environments, and may constitute an important mechanism for benthic-pelagic coupling.

Comparison of Faunal Scavenging of Submerged Carrion in Two Seasons at a Depth of 170 m, in the Strait of Georgia, British Columbia

“…to bait odors, increased respiration rates and elevated oxygen consumption was recorded for up to eight hours [34], so it is very probable that the amphipods create a localized anoxia, repelling larger crustaceans. This is unlikely to affect the feeding amphipods as O. obtusa has been experimentally shown to survive 10–33 h of anoxia [35]. In these experiments, the optodes were not close enough to the carcasses to measure a localized drawdown and the numbers of amphipods were much fewer than those seen at 300 m, so may not have produced the same levels of hypoxia.…”

Are Organic Falls Bridging Reduced Environments in the Deep Sea? - Results from Colonization Experiments in the Gulf of Cádiz

“…Sulphide concentrations at different experimental locations may also provide an explanation for differences in lysianassid colonization as they were only dominant in the alfalfa assemblages at Mercator MV where the seepage is mild [35]. Although lysianassids can tolerate reduced environments, they require daily migrations to better oxygenated waters for recovery of routine metabolic rates and removal of sulphide and acidic end-products of anaerobic metabolism [73]. The 2 mm mesh net enclosing the experimental substrata is an obstacle for such migrations and would probably affect their survival under higher local sulphide concentrations.…”

Ecology of Benthesicymus tanneri Faxon, 1893 (Dendrobranchiata: Benthesicymidae) from the Mexican Pacific slope

“…Some specimens (9%) of B. tanneri were nevertheless collected in shallower, less oxygenated waters. These vertical migrators (Heffernan and Hopkins, 1981) probably entered the OMZ temporarily for feeding, avoiding predators, or diapausing, a pattern that has been reported in the upper (e.g., De Robertis et al, 2001;Hidalgo et al, 2005;Werner and Buchholz, 2013) and lower (Escribano et al, 2009;Gooday et al, 2009) boundaries of the OMZ. Vertical migration by B. tanneri is supported by the absence of a bathymetric size-structure of the population.…”