Estimating digestion time in gelatinous predators: a methodological comparison with the scyphomedusa Aurelia aurita
In order to quantify the trophic impact of gelatinous predators, digestion time estimates are commonly applied to counts of prey in the guts. Three primary approaches are used, the Manual-feeding, Natural-feeding and Steady-state methods; these differ in methodology and their underlying assumptions. The criteria used to define the end-point of digestion, and the resolution at which digestion progress is observed, also vary across studies. To understand the impact of such differences, we estimate digestion times of the scyphomedusa Aurelia aurita fed adult females of the copepod Acartia tonsa using these various approaches. We find ~fourfold differences which can be attributed to bias towards the slowest rates of digestion by some end-point criteria, and overestimation from low observation resolution. Artificial manipulation and the degree to which swimming and feeding behaviour are natural may also influence estimates. We provide recommendations for those quantifying digestion times of Aurelia aurita medusae and gelatinous predators.
KeywordsPrey Item Prey Type Digestion Time Complete Digestion Gastric Cavity
We wish to thank all staff at the Horniman Museum, London, for their help with the supply of Aurelia aurita. Hoba Saleh and Jack Forster provided invaluable assistance with the experimental work and we are grateful to Guillaume Drillet (DIFR) for the supply of Acartia tonsa eggs. Comments and suggestions by Mike Dawson, Jennifer E. Purcell and anonymous referees have greatly improved this manuscript. This study was funded by the Natural Environment Research Council, Grant number NE/G005516/1, to AGH and CHL.
Conflict of interest
The authors declare that they have no conflict of interest.
We declare the experiments comply with the current laws of the country (UK) in which they were performed.
- Baars MA, Helling GR (1985) Methodical problems in the measurement of phytoplankton ingestion rate by gut fluorescence. Hydro Bull 19:81–88Google Scholar
- Guillard RRL (1975) Culture of phytoplankton for feeding marine invertebrates. In: Smith WL, Chanley MH (eds) Culture of Marine Invertebrate Animals. Plenum Press, New York, pp 26–60Google Scholar
- Martinussen MB, Båmstedt U (1995) Diet, estimated daily food ration and predator impact by the scyphozoan jellyfishes Aurelia aurita and Cyanea capillata. In: Skjoldal HR, Hopkins C, Erikstad KE, Leinaas HP (eds) Ecology of fjords and coastal waters. Elsevier, Amsterdam, pp 127–145Google Scholar
- Martinussen MB, Båmstedt U (2001) Digestion rate in relation to temperature of two gelatinous planktonic predators. Sarsia 86:21–35Google Scholar
- Mayer AG (1910) Medusae of the World, III: the Scyphomedusae. Carnegie institution, Washington, p 735Google Scholar