# 2.4. Biotic ressources¶

Biotic resources such as phytoplankton and zooplankton are not explicitly modelled in Osmose but are essential to take into account are they constitute the base of the trophic chain. They are considered as an input of the model, spatially explicit and varying with time.

In this section, the way LTL biotic resources are defined is described

## 2.4.1. Osmose <= 4.2.0¶

In the Osmose versions prior to 4.2.0, the biotic resources were defined as follows:

 plankton.name.plk# Name of the plankton group. plankton.TL.plk# Trophic level of the plankton group. plankton.size.min.plk# Minimum size of the organisms in the plankton group (centimeters). plankton.size.max.plk# Maximun size of the organisms in the plankton group (centimeters). plankton.accessibility2fish.plk# Fraction of the plankton biomass that is accessible to the fish, ranging from zero to one.

The plankton.accessibility2fish.plk# parameter accounts for many biological processes that are not explicitly represented in Osmose and basically says that only a small fraction of the plankton in the water column is effectively available to the fish for preying upon. Plankton accessibility is generally completely unknown and, just like larval mortality, it should be estimated in the calibration process.

## 2.4.2. Osmose >= 4.3.0¶

Since Osmose 4.3.0, plankton groups are defined using the same parameters, except that they have different names.

 species.name.sp# Name of the plankton group. species.TL.sp# Trophic level of the plankton group. species.size.min.sp# Minimum size of the organisms in the plankton group (centimeters). species.size.max.sp# Maximum size of the organisms in the plankton group (centimeters). species.accessibility2fish.sp# Fraction of the plankton biomass that is accessible to the fish, ranging from zero to one. species.type.sp# Type of the species. Must be resource for biotic resources

An additional argument, species.type.sp#, must be defined and set to resource for biotic resources.