Pelagic Tunicates: Why Gelatinous?

Jelly-falls historic and recent observations: a review to drive future research directions

“…For thaliaceans, there is evidence that high concentrations of particles and suspended organic matter [e.g. chlorophyll a[1 mg m -3 ; Perissinotto & Pakhomov (1998)] clog their feeding apparatus causing death (Acuña, 2001) despite food being abundant (Harbison et al, 1986;Zeldis et al, 1995). This explains the salp jelly-fall studied by Duggins (1981) in the subtidal zone in Alaska and the beaching of salps reported by Pakhomov et al (2003) in the Southern Ocean.…”

Copepoda – Cladocera – Tunicata: The role of three major mesozooplankton groups in pelagic food webs

“…Harbison (1992) pointed out that due to reduced gravitational 166 U. Sommer and H. Stibor stresses the gelatinous morphotype can develop large feeding structures. Recently, Acuna (2001) supported these ideas in an elegant study using a semi-empirical approach including filtration theory and physiological allometry to show that pelagic tunicates are normal animals that mimic giants to endure food dilution. The whole filter architecture and functioning is tuned for survival at extremely low food concentrations by increasing the body size and the supportive structure for the filter while maintaining a low carbon content.…”

“…Salps, for example, have approx. 5 m 3 body volume/kg body carbon (Acuna 2001) as opposed to about 0.0079 m 3 body volume/kg carbon for average non-gelatinous zooplankton (Hansen et al 1997). All pelagic tunicates are filter feeders filtering the entire size range from very small colloids to large phytoplankton chains in the case of salps and doliolids, while smaller appendicularians are usually considered microphageous.…”

“…There are also specialized predators of gelatinous zooplankton and recent research indicates that tunicates may be a good food resource for some fish (Harbison 1998). Alternatively, the success of gelatinous zooplankton might also be explained by a bottom-up hypothesis: A gelatinous body may allow survival at low food concentrations that are typical for open oceans (Harbison 1992;Acuna 2001). Pelagic tunicates have successfully colonized ultra-oligotrophic areas of the oceans where concentrations of seston are extremely low.…”

Cladocerans versus copepods: the cause of contrasting top–down controls on freshwater and marine phytoplankton

“…''Herbivorous'' crustaceans are now acknowledged as omnivores, with their individual feeding modes and food size spectra being considered more important for selectivity than the auto-or heterotrophic nature of their prey. In addition to crustaceans and protozoans, marine ecologists began to become aware of the functional importance of pelagic tunicates (Deibel 1992;Acun˜a 2001), a group which is entirely lacking in freshwaters.…”