The mechanisms of intertidal fish coexistence: a model

Research into the ecology of intertidal fishes of the U.K. appears to be lacking, reportedly due to the mobility and cryptic nature of the more common species. However, some intertidal fishes contribute to the diets of commercially important species such as cod (Gadus morhua), haddock (Melanogrammus aeglefinus) and near-threatened European otter (Lutra lutra). The current study contains the first comprehensive research into the ecology of intertidal fishes from the English, Yorkshire coast and Welsh, Anglesey coast, identifying and addressing the mechanisms which allow for their coexistence. Seven mechanisms were identified which promote interspecific fish coexistence. It was found that coexistence can occur when: (I) fish diversity on a shore is low, thus minimising high degrees of co-occurrence within pools, (II) co-occurrence on shores (at tidal height level) is minimal and when fishes do co-occur, they are of similar sizes thus reducing size-dominated hierarchies, (III) the significant variables which predict fish presences differ, (IV) there is an abundance of shelter/protection readily available, which reduces the competition to access such features, (V) morphology is such, that for the majority of the year, it is more profitable for the piscivorous fishes to predate on food items other than fish, (VI) competition for prey items is reduced, when variability of resources is high, and (VII) there is a difference in the most targeted prey items between fish species, despite some overlap in targeted prey items.