Feeding of plankton in turbulent oceans and lakes

Abstract

Analytical models for the statistical distribution of the gut content of fish larvae in a turbulent ocean environment are compared to data obtained in a field experiment. The proposed model allows the nutrition state and thereby the survival probability of plankton populations to be estimated for given conditions and parameters characterizing their environment, i.e., prey concentrations and turbulence levels. These parameters are all available in the field data. Other parameters such as the capture range and fields of view together with a characteristic time for digesting prey are assumed to be known. The analysis allows an estimate for the probability density of the gut content of plankton in terms of the number of nauplii in the gut. In particular, the analytical results give a basis for evaluating the average gut content of a given plankton population on the basis of basic information concerning the prey concentration and the turbulence intensity. Also analytical models for the prey capture rates are compared with results based on the field data. The analysis emphasizes the effects of turbulence. MethodsThis study summarizes data from a field experiment and compares them with analytical results and models.

Feeding of Plankton in a Turbulent Environment: A Comparison of Analytical and Observational Results Covering Also Strong Turbulence

“…Encountered and captured prey contributes to the gut content of the predator, and will remain detectable until it is digested after some time ("gut clearance rate"), here denoted τ d . A simple model was proposed [18] for the gut content in form of a time series containing integers, N = 1, 2, . .…”

“…The maximum gut capacity has only little consequence for the data presented in the following, but the general results can be useful for other data. A relatively simple analysis [18] including a finite gut capacity gave the result…”

“…In reality we can have many small or a few large samples of prey in a full gut. This question was discussed elsewhere [18] with an assumed probability density for prey sizes. The result indicated that if the number of prey in the gut is large, some will be small, some large, so the actual net gut content would be close to the one obtained by assigning all prey the same size.…”

“…Our observational data are based on samples collected at Lofoten, Norway in April-May 1995 [18,48]. During this campaign data were collected at 5 sites, labeled Station I, II, III, IV and V, all located in shallow waters, see Figure 6.…”

“…In the present study we compare analytical results with results obtained by analyzing field data of the gut content of fish larvae collected in the shallow waters near Lofoten, Norway. Additional material is presented elsewhere [18]. Predators (in the present case cod larvae, Gadus morhua L.) were sampled by two different methods: 1) an ichthyoplankton net moved slowly from the seabed to the surface, thereby vertically integrating the larval samples, and 2) a high-capacity submersible pump (HUFSA) at selected positions 5, 10, 15, 20, 25 and 30 m below the surface.…”