Natural dimethyl sulfide gradients would lead marine predators to higher prey biomass

Abstract

Finding prey is essential to survival, with marine predators hypothesised to track chemicals such as dimethyl sulfide (DMS) while foraging. Many predators are attracted to artificially released DMS, and laboratory experiments have shown that zooplankton grazing on phytoplankton accelerates DMS release. However, whether natural DMS concentrations are useful for predators and correlated to areas of high prey biomass remains a fundamental knowledge gap. Here, we used concurrent hydroacoustic surveys and in situ DMS measurements to present evidence that zooplankton biomass is spatially correlated to natural DMS concentration in air and seawater. Using agent simulations, we also show that following gradients of DMS would lead zooplankton predators to areas of higher prey biomass than swimming randomly. Further understanding of the conditions and scales over which these gradients occur, and how they are used by predators, is essential to predicting the impact of future changes in the ocean on predator foraging success.

Olfactory epithelium and ontogeny of the nasal chambers in the bowhead whale (Balaena mysticetus)

“…For example, mysticetes might use dimethyl sulfide (DMS) as an olfactory indicator of their prey (Bouchard et al, 2019). Zooplankton biomass is spatially correlated to natural DMS concentrations in air, suggesting that particularly over broad geographic scales, DMS could act as a useful foraging cue for zooplankton predators, like mysticetes (Owen et al, 2021). Marine plastic can also emit DMS (Savoca, Wohlfeil, Ebeler, & Nevitt, 2016), which might disturb their foraging attempts.…”

A field study of chemical senses in bottlenose dolphins and pilot whales

“…There is a growing body of evidence that the olfactory sense is still functional in mysticetes but that it has partly been lost in odontocetes. A recent oceanographic survey in North Atlantic waters interestingly confirmed that DMS a and DMS g would accurately lead zooplankton predators such as mysticetes towards prey aggregations over long distances (Owen et al, 2021). The authors of the study however found no correlation between DMS (in air or in seawater) and fish biomass, possibly due to time lags between DMS production and the buildup of fish biomass.…”

“…The presumed short-scale attraction of the dolphins toward the DMS diffuser would however more likely be a curiosity response than a foraging behavior. The DMS test solution was much more concentrated than natural seawater (0.2 M vs. less than 20 nM, Turner, Malin, Nightingale, & Liss, 1996;Owen et al, 2021). We chose this concentration as it was previously shown to attract seabirds in the wild (Dell'Ariccia et al, 2014;Nevitt et al, 1995;Wright, Pichegru, & Ryan, 2011) and to induce an acoustic reaction in humpback whales (Bouchard et al, 2019).…”

“…At a larger scale, marine predators might also find their foraging grounds in the open ocean by following chemical indicators of highly productive zones such as dimethyl sulfide (DMS), a molecule produced by phytoplankton when grazed by zooplankton (Cantin, Levasseur, Gosselin, & Michaud, 1996;Dacey & Wakeham, 1986). DMS, both in the air (DMS g ) and seawater (DMS aq ), is spatially correlated to zooplankton biomass (Owen et al, 2021). Several experimental studies have shown that DMS g attracts seabirds and turtles and that DMS aq attracts whale sharks (Dove, 2015;Endres & Lohmann, 2012;Nevitt & Bonadonna, 2005).…”

“…We focused on these two species because they can be found in similar areas but show very distinct feeding ecologies: while bottlenose dolphins mainly hunt teleost fish within the first 100 m under the surface, pilot whales almost exclusively feed on cephalopods during dives reaching more than 800 m (Blanco, Raga, & Salom on, 2001;Canadas & Sagarminaga, 2000;Heide-Jørgensen et al, 2002). As DMS is a marker of surface productivity (produced within the oceanic mixed layer at a depth less than 50-100 m, Royer et al, 2016) correlated with higher surface prey biomass (Owen et al, 2021), we can expect that it would be more attractive for bottlenose dolphins than pilot whales. This first behavioral exposure experiment in odontocetes thus allowed us to test whether chemical cues could play a role in their foraging ecology.…”