Epiphytes compete with the eelgrass for light and nutrients. Epiphytes attach to the shoot leaves, so if they cover too much of the leaf, then shoots die because they won't get enough light. This then causes the epiphytes to die because they lost their "home." Light restrictions are calculated in the global input sector.
Epiphytes grow through a random seeding function as well as through primary production. Primary production is limited by nutrients, light, and water temperature. Epiphyte biomass is lost through respiration, grazing, and mortality.
* Note: only spatial movement to the north is portrayed here for the sake of simplicity. Movement to the south, east, and west is calculated in the same manner.