Mammoth grazers on the ocean's minuteness: a review of selective feeding using mucous meshes

Abstract

Mucous-mesh grazers (pelagic tunicates and thecosome pteropods) are common in oceanic waters and efficiently capture, consume and repackage particles many orders of magnitude smaller than themselves. They feed using an adhesive mucous mesh to capture prey particles from ambient seawater. Historically, their grazing process has been characterized as non-selective, depending only on the size of the prey particle and the pore dimensions of the mesh. The purpose of this review is to reverse this assumption by reviewing recent evidence that shows mucous-mesh feeding can be selective. We focus on large planktonic microphages as a model of selective mucus feeding because of their important roles in the ocean food web: as bacterivores, prey for higher trophic levels, and exporters of carbon via mucous aggregates, faecal pellets and jelly-falls. We identify important functional variations in the filter mechanics and hydrodynamics of different taxa. We review evidence that shows this feeding strategy depends not only on the particle size and dimensions of the mesh pores, but also on particle shape and surface properties, filter mechanics, hydrodynamics and grazer behaviour. As many of these organisms remain critically understudied, we conclude by suggesting priorities for future research.

Rewiring and indirect effects underpin modularity reshuffling in a marine food web under environmental shifts

“…In the course of green-blue transitions in GoN plankton community (D'Alelio, Libralato, et al, 2016), Appendicularia can feed in the main energetic module of the food web, including either surface or deep unicellular nodes, based on their relative availability: To this respect, Appendicularia may behave as "couplers" sensu Rooney et al (2008) (Figure 6c). This hypothesis is in line with field observations: Like zooplankton of similar size, appendicularians perform vertical migrations throughout the water column following higher food concentrations (Ursella, Cardin, Batistić, Garić, & Gačić, 2018) and this strategy can be at the base of the explosive demographic increases observed for these and other pelagic tunicates (e.g., Conley, Lombard, & Sutherland, 2018).…”

Spring distribution of shelled pteropods across the Mediterranean Sea

“…The majority of pteropods belong to the Thecosome order and have a unique feeding method involving the production of a large mucous web that is suspended in the water column, which passively entraps organic particles and motile organisms, enabling them to filter water at high rates (Conley et al, 2018). To ingest the material collected by the mucous webs, they draw the webs into their mouth via ciliary action, a feeding method that may allow them to overcome low food condition due to their ability to capture and filter through relatively large amounts of organic matter (Hamner et al, 1975).…”

“…Thecosome pteropods are holoplanktic mollusks found in all major world oceans (Bednaršek et al, 2012). This organism plays an important role in the biogeochemical cycle (Manno et al, 2019) and in ocean food webs as bacterivores, (predominantly) herbivores, and as pray for higher trophic levels (Conley et al, 2018). Pteropods are very susceptible to changes in carbonate saturation state (Ω) due to their aragonite shell, which is a comparatively highly soluble form of calcium carbonate (Mucci et al, 1989), and they therefore represent an excellent sentinel for indicating the impacts of ocean acidification (OA) (Bednaršek et al, 2016;Manno et al, 2017).…”

Prey taxonomy rather than size determines salp diets

“…Coulter counters also grouped different particle types together into a single "size" category, thus providing limited and potentially distorted information of the retained particles (Rosa et al 2015). Deibel (1985) stated another disadvantage of Coulter counters: they discriminate between prey types based on volume, whereas planktonic grazers sometime discriminate between prey types on the basis of their linear dimensions (i.e., length, width, or diameter) as recently demonstrated by Conley and Sutherland (2017) and Conley et al (2018). Estimation of prey size from gut content samples suffers from differential preservation of prey in the gut (Kremer and Madin 1992), and therefore, prey size quantification from gut content often miss the smallest and less armored cells.…”