P. Caparroy et F. Carlotti, A MODEL FOR ACARTIA-TONSA - EFFECT OF TURBULENCE AND CONSEQUENCES FORTHE RELATED PHYSIOLOGICAL PROCESSES, Journal of plankton research, 18(11), 1996, pp. 2139-2177
A mathematical model of the energy budget of the copepod Acartia tonsa
is proposed. It takes into account the processes of ingestion (encoun
ter, capture, ingestion sensu stricto), digestion (assimilation, gut t
ransit and egestion), catabolic expenses and biomass production. In or
der to represent the potential effects of small-scale turbulence on th
e whole physiological processes of a copepod, some process submodels a
lready published are combined. A major assumption of the model is a sa
tiety effect resulting from midgut filling, which leads to a decrease
in the feeding activity. The model permits the simulation of the short
-term dynamics of ingestion under different food and turbulence condit
ions, as well as an integrated physiological balance over 24 h. The mo
del is validated through comparison with data at both scales. Simulati
ons show that turbulence increases ingestion rates and gut contents, a
nd causes a decrease in gut passage time and assimilation efficiency.
As a consequence, the dependent physiological processes are affected d
ifferently by turbulence. which preferentially increases egestion and
egg-production rates. Simulated daily ingestion rates of A.tonsa, for
suspension feeding on Thalassiosira weissflogii and for ambush predati
on on Strombidium sulcatum, are in good agreement with the available e
xperimental observations. The concurrent direct effect of turbulence o
n the copepod's metabolism, due to increased escape reactions, is also
simulated. Results of the model show that a switch from suspension fe
eding on diatoms in calm conditions, to ambush predation on ciliates i
n turbulent conditions, might allow A.tonsa to maintain its gross grow
th efficiency at the same level. It is suggested that a dynamic repres
entation of processes occurring over a time scale of a few seconds is
necessary to obtain, once integrated over 24 h, the correct simulation
of the effect of microscale turbulence on ingestion and the related p
hysiological processes.