Fear-induced behavioural modifications in damselfishes can be diver-triggered

Abstract

Fear is a short-term response arisen from the way an animal perceives its environment when some threat makes it insecure. Thus, the risk perception of predation shapes the cost-benefit decisions associated with food and safety in animal communities. Even non-consumptive human-related activities such as ecotourism may influence species behavioural traits. Marine wildlife tourism might produce different impacts on organisms, stressing and modifying (directly or indirectly) species behaviour, physiology and habitat use. Understand the effects of human presence on site-attached fish’ behaviour is crucial to elucidate how dive-tourism could shape their limited-range seascape. Given the importance of the territorial damselfishes as reef farmers and ‘ecosystems engineers', here we investigated if the presence of SCUBA divers and snorkelers can disrupt the foraging and territorial defence of the Dusky damselfish, Stegastes fuscus. Experimental approaches (diver presence and absence) were applied in 30 territories of S. fuscus using underwater remote video cameras. Behavioural responses were analysed by considering the frequency of refuge, foraging and chase behaviours. Both recreational dive activities had an analogous role in frighten and disturb the Dusky damselfish activities. Considering the frequency of behaviours displayed in diver's absence vs presence, S. fuscus increased its refuge times from approximately 2% to 50% on SCUBA diver presence and from 9% to 43% in snorkeler presence. It is directly linked to the missed feeding opportunities, which reduced by half during both diver's presence. Damselfish's aggressiveness proportionally dropped (0.3%) during SCUBA diver presence but increased (2.4%) while snorkeler was present. However, the average frequency of chase behaviour reduced with both divers' approach. Interruptions in damselfish behaviour may modify the resource monopolization and productivity inside their territories, affecting its relationships with other species beyond the boundaries of their territoriality, and leading a possible change on its functional role in the reef community. Territorial reef fish behaviour and their relationship with divers' presence can provide a more holistic comprehension regarding the seascape of fear concept and could be useful as an indicator of human disturbances.