Prediction of ecological niches and carbon export by appendicularians using a new multispecies ecophysiological model

We developed, calibrated and validated an ecophysiological model that represents food consumption, growth and production of faecal pellets and discarded houses during the life cycle ofOikopleura dioica,O. longicauda,O. fusiformisandO. rufescens, which are among the most abundant appendicularian species in the ocean.

The forcing variables of the model are temperature (T) and food concentration. We calculated the growth rates of the 4 species and predicted the dominant species as a function of environmental conditions on 3 ecological applications. Firstly, we used the seasonal changes inTand chlorophylla(chla) in the English Channel to predict the seasonal succession of the 4 species.

Secondly, using sea surfaceTand chladata from the MODIS satellite, we determined the dominant appendicularian species over the World Ocean, thus providing a first-ever description of appendicularian biogeography over the 4 different seasons. Thirdly, we applied our model toin situobservations performed with the Underwater Video Profiler during the POMME 3 cruise in the Northeastern Atlantic in 2001.

In areas of high appendicularian concentrations (135 ind. m–3), the appendicularians grazed daily only 0.6% of the stock of total particulate carbon. Of this grazed material, 21% was used for growth, 14% was respired and 65% was lost as detritus. Based on our model predictions, we concluded that at 2 of the 4 sampling stations, the integrated mass of detritus produced by the appendicularian population equalled or exceeded the carbon flux recorded in sediment traps at 200 m depth.

This indicated high rates of disaggregation and/or consumption of these particles during their transit to depth.