The Influence of Microphytobenthos on the Northern Adriatic Ecosystem: A Modelling Study

Whilst studies have demonstrated that unicellular phytobenthic organisms can be locally important, little is known of their influence on their ecosystem, especially in terms of modifying benthic trophic dynamics and influencing the coupling between the benthos and pelagos. It may be hypothesized that the controlling influence on microphytobenthos would vary seasonally, with incident light, shading, nutrient depletion and grazing all playing a role. In order to elucidate some of these questions a theoretical model of microphytobenthos has been added to the European Regional Seas Ecosystem Model (ERSEM), coupled to a 1D vertically resolved water column model. Several water columns, extending in depth from 5 to 25 m have been simulated along an offshore transect at approximately 44 18 N. The microphytobenthos are predicted to contribute in excess of 50% of primary production in shallow (<5 m) depths, with light limitation reducing the potential growing season to zero at around 25 m. Light availability is the key factor limiting microphytobenthos, with self-shading dominating this effect in established populations. Grazing is shown to be a significant control on microphytobenthic populations. Nutrient stress is not a major limiting factor of microphytobenthic populations due to the availability of benthic nutrient pools. Although nutrient uptake and cycling via the microphytobenthos is not significant compared with regional inputs, the microphytobenthos significantly impact nutrient regeneration rates, aerobic layer processes and benthic trophic dynamics. Effects on the pelagic ecosystem are minimal.