Goatfishes (Mullidae) as indicators in tropical and temperate coastal habitat monitoring and management

This review investigates if goatfishes qualify as habitat indicators and play a role as key species for use in coastal ecosystem monitoring and management, emphasizing major gaps of knowledge in goatfish ecology and systematics. Currently, 66 species of goatfishes are known, the family occurring widely in tropical, subtropical and temperate habitats from the upper littoral down to the upper slope. Studies of goatfish occurrence and abundance in natural habitats have documented general preferences for sand-associated bottoms after post-larval settlement that goes hand in hand with the development of the characteristic barbels. Species, populations and later life-history stages may, however, differ significantly from each other in habitat use. Some species are more restricted to hard bottoms, others separate mainly by depth. Goatfishes respond to human-induced factors such as fisheries and habitat modification, as reflected by abundance, size, or weight changes, or changes in their distributional ranges. Temperature increase may lead to increased reproductive or growth rates and longer warming periods may induce goatfishes to migrate to higher latitudes, as exemplified by striped red mullet (Mullus surmuletus) in the North Sea. Isolated occurrences of this species in the Norwegian Sea at 60°N have been documented. Goatfishes may act as allochthonous ecosystem engineers through their vigorous foraging behaviour with barbels and mouth, which leads to the stirring-up of sediments and associated detritus particles high into the water column. Goatfishes play a key role in the formation of multi-species foraging associations as nuclear species that are followed by many other species. The role of goatfishes in food webs has been rarely evaluated and the many interactions goatfishes may be involved in have not yet been sufficiently considered. There is also a considerable lack of basic systematic and taxonomic knowledge, new species still being described and intraspecific morphological variation and genetic differentiation requiring more detailed studies. Goatfishes clearly deserve more attention in future coastal habitat exploration, monitoring and management efforts.