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Throughout the world, anthropogenic pressure on natural ecosystems is intensifying, notably through urbanisation, economic development, and tourism. Coral reefs have become exposed to stressors related to tourism. To reveal the impact of human activities on fish communities, we used COVID-19-related social restrictions in 2021. In French Polynesia, from February to December 2021, there was a series of restrictions on local activities and international tourism. We assessed the response of fish populations in terms of changes in the species richness and density of fish in the lagoon of Bora-Bora (French Polynesia). We selected sites with varying human pressures-some dedicated to tourism activities, others affected by boat traffic, and control sites with little human presence. Underwater visual surveys demonstrated that fish density and richness differed spatially and temporally. They were lowest on sites affected by boat traffic regardless of pandemic-related restrictions, and when activities were authorised; they were highest during lockdowns. Adult fish density increased threefold on sites usually affected by boat traffic during lockdowns and increased 2.7-fold on eco-tourism sites during international travel bans. Human activities are major drivers of fish density and species richness spatially across the lagoon of Bora-Bora but also temporally across pandemic-related restrictions, with dynamic responses to different restrictions. These results highlight the opportunity provided by pauses in human activities to assess their impact on the environment and confirm the need for sustainable lagoon management in Bora-Bora and similar coral reef settings affected by tourism and boat traffic., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

How vocal organisms share acoustic space has primarily received attention in terrestrial environments. Comparable studies in marine environments, however, remain rare. By recording sounds on a coral reef in French Polynesia for 48 h and 24 h, this study provides first insights on how different sound types are distributed within the acoustic space and may create acoustic niches optimizing acoustic communication within a highly diverse community containing numerous soniferous fish species. Day-time was dominated by two to six sound types, while recordings performed at night revealed a more diverse vocal community made of up to nineteen sound types. Calling activity was distributed over time allowing each sound type to dominate the soundscape sequentially. Additionally, differences in the acoustic features of sounds occurring during the same period were observed. Such partitioning in time and acoustic spaces would reduce potential overlaps of sounds produced by vocal species living in sympatry in coral reefs.

In fishes, sonic abilities for communication purpose usually involve a single mechanism. We describe here the sonic mechanism and sounds in two species of boxfish, the spotted trunkfish Ostracion meleagris and the yellow boxfish Ostracion cubicus. The sonic mechanism utilizes a T-shaped swimbladder with a swimbladder fenestra and two separate sonic muscle pairs. Extrinsic vertical muscles attach to the vertebral column and the swimbladder. Perpendicularly and below these muscles, longitudinal intrinsic muscles cover the swimbladder fenestra. Sounds are exceptional since they are made of two distinct types produced in a sequence. In both species, humming sounds consist of long series (up to 45 s) of hundreds of regular low-amplitude pulses. Hums are often interspersed with irregular click sounds with an amplitude that is ten times greater in O. meleagris and forty times greater in O. cubicus. There is no relationship between fish size and many acoustic characteristics because muscle contraction rate dictates the fundamental frequency. We suggest that hums and clicks are produced by either separate muscles or by a combination of the two. The mechanism complexity supports an investment of boxfish in this communication channel and underline sounds as having important functions in their way of life.

Microplastics are ubiquitous throughout the oceans, yet few studies have documented their occurrence in marine organisms associated with coral reefs. Four genera of adult fish were sampled (Myripristis spp., Siganus spp., Epinephelus merra and Cheilopogon simus) from different trophic guilds around the tropical island of Moorea, French Polynesia. Digestive tracts from 133 adult fish were surveyed and microplastics were found in 28 tracts (21%). Abundance of ingested microplastic pieces per individual fish varied from 1 to 3 pieces, with an average of 1.25 ± 0.13 ingested microplastic pieces. Microplastics size ranged from 0.031 to 2.44 mm and 70% of microplastics did not exceed 0.3 mm in size. Overall, this study shows that the number and size of microplastic ingested per trophic groups are independent of trophic guild. Additional studies are needed to sample in other tropical regions in order to have a better assessment of microplastic occurrence in coral reefs., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Dory, the animated surgeonfish created by the Pixar Animation studios, famously suffered from short-term memory loss leading to many adventures. In reality, many fishes have excellent cognitive abilities and are able to learn and retain important information such as the identity of predators. However, if and how cognition can be affected by anthropogenically altered oceanic conditions is poorly understood. Here, we examine the effect of a widely used pesticide, chlorpyrifos, on the retention of acquired predator recognition in post-larval stage of the surgeonfish Acanthurus triostegus. Through associative learning, post-larvae of A. triostegus were first observed to forage significantly less in the presence of conspecific alarm cues and alarm cues associated to a predator's odor. The retention of this anti-predator behavior was estimated to last between 2 and 5 days in the absence of pesticide. However, environmentally-relevant concentrations of chlorpyrifos (1 μg.L -1 ) induced the loss of this acquired predator recognition. This reduced ability to recognize learned predators is discussed as it may lead to more vulnerable fish communities in coastal areas subjected to organophosphate pesticide pollution., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Lateralization, i.e. the preferential use of one side of the body, may convey fitness benefits for organisms within rapidly-changing environments, by optimizing separate and parallel processing of different information between the two brain hemispheres. In coral reef-fishes, the movement of larvae from planktonic to reef environments (recruitment) represents a major life-history transition. This transition requires larvae to rapidly identify and respond to sensory cues to select a suitable habitat that facilitates survival and growth. This 'recruitment' is critical for population persistence and resilience. In aquarium experiments, larval Acanthurus triostegus preferentially used their right-eye to investigate a variety of visual stimuli. Despite this, when held in in situ cages with predators, those larvae that previously favored their left-eye exhibited higher survival. These results support the "brain's right-hemisphere" theory, which predicts that the right-eye (i.e. left-hemisphere) is used to categorize stimuli while the left-eye (i.e. right-hemisphere) is used to inspect novel items and initiate rapid behavioral-responses. While these experiments confirm that being highly lateralized is ecologically advantageous, exposure to chlorpyrifos, a pesticide often inadvertently added to coral-reef waters, impaired visual-lateralization. This suggests that chemical pollutants could impair the brain function of larval fishes during a critical life-history transition, potentially impacting recruitment success.

For marine fishes with a bipartite life cycle, pelagic larval dispersal can shape the distribution, connectivity, composition and resilience of adult populations. Numerous studies of larval dispersal, and associated settlement and recruitment processes, have examined the relationship between population connectivity and oceanographic features. However, relatively little is known about spatial and temporal variation in the abundance of larvae settling among different reefs and the extent to which the species assemblage of larvae settling at one location is reflective of the assemblage in neighbouring areas. Here, using crest nets, which provide a non-selective measure of the total abundance and assemblage of larvae settling to a reef (i.e. larval supply), we collected larval coral reef fishes at five locations surrounding two spatially disparate French Polynesian islands: Moorea and Nengo-Nengo. Overall, larval settlement patterns were correlated with the lunar cycle, with larval abundance peaking during the new moon. Although there were some spatial differences in larval supply among the five monitored sites, settlement patterns were largely consistent, even at the species level, irrespective of factors such as coastline orientation or distance between sites. This study provides further insights into the mechanisms driving patterns of dispersal and settlement of larval fishes over large spatial scales.

Aggressive interactions between animals often occur in the presence of third parties. By observing aggressive signalling interactions, bystanders may eavesdrop and gain relevant information about conspecifics without the costs of interacting. On the other hand, interactants may also adjust their behaviour when an audience is present. This study aimed to test how knowledge about fighting ability of an audience affects aggressive interactions in male Siamese fighting fish. Subjects were positioned between two dyads of non-interacting males and allowed to observe both dyads shortly before the view to one of the dyads was blocked, and the dyads were allowed to interact. Subjects were subsequently exposed to an unknown opponent in the presence of either the winner or the loser of the seen or unseen interaction. The results suggest a complex role of the characteristic of an audience in the agonistic behaviours of a subject engaged in an interaction. The presence of a seen audience elicited more aggressive displays towards the opponent if the audience was a loser. This response was different in the presence of an unseen audience. Subjects then directed a higher aggressiveness against their opponent if the audience was a winner. These results also suggest a potentially more complex and interesting process allowing individuals to gain information about the quality and threat level of an unknown audience while it is interacting with a third party. The importance of information acquisition for an individual to adapt its behaviour and the role of communication networks in shaping social interactions are discussed. [ABSTRACT FROM AUTHOR]

Playback experiments have been a useful tool for studying the function of sounds and the relevance of different sound characteristics in signal recognition in many different species of vertebrates. However, successful playback experiments in sound-producing fish remain rare, and few studies have investigated the role of particular sound features in the encoding of information. In this study, we set-up an apparatus in order to test the relevance of acoustic signals in males of the cichlid Metriaclima zebra. We found that territorial males responded more to playbacks by increasing their territorial activity and approaching the loudspeaker during and after playbacks. If sounds are used to indicate the presence of a competitor, we modified two sound characteristics, that is, the pulse period and the number of pulses, in order to investigate whether the observed behavioural response was modulated by the temporal structure of sounds recorded during aggressive interactions. Modified sounds yielded little or no effect on the behavioural response they elicited in territorial males, suggesting a high tolerance for variations in pulse period and number of pulses. The biological function of sounds in M. zebra and the lack of responsiveness to our temporal modifications are discussed. [ABSTRACT FROM AUTHOR]

Abstract: While acoustic communication has been described in adults of various fish species, our knowledge about the ontogeny of fish sound production is limited. In adults, sound signals are known to be involved during aggressive interactions. However, aggressive behaviour may appear early in the life of fishes due to the possible competition for food and space. If acoustic signals are used to send information to competitors, sounds are likely to play a role during interactions between juvenile fish as well. The apparition and evolution of sound production were monitored in a group of juveniles of the cichlid fish Metriaclima zebra from hatching to 4months of age. In addition, the link between vocalizations and agonistic behaviour was studied during dyadic interactions at three different ages. Sounds production appeared to be present early in the development of this fish and increased along with the number of aggressive behaviours. Recorded sounds consisted, in juveniles, in isolated pulses showing a decrease in frequency and duration as the fish grew. In adults, sounds became bursts of pulses but the transition from isolated to repetitive pulses was not observed. These results are compared to the existing literature on sound production ontogeny in fishes. [Copyright &y& Elsevier]

Acoustic signals are produced in many fish species during agonistic or courtship interactions. A way to test the biological role of these sounds is the use of acoustic playback experiments. However, sounds are usually associated with visual displays and playback experiments performed in fish so far, often failed to match acoustic and visual stimuli. To avoid this mismatch issue, we experimentally separated or coupled visual and acoustic channels to test the role of sounds produced during male-male aggressive interactions in a cichlid fish, Metriaclima zebra. Results show that aggressive behaviour is based on visual stimuli and that acoustic signals alone never trigger aggression. Furthermore, the association between visual and acoustic channels lowers the level of aggressiveness found when fish can only interact visually. This suggests that acoustic signals used during a dispute may complement visual displays to modulate males' behaviour by reducing their aggressiveness and the risk of escalated fights. [ABSTRACT FROM AUTHOR]

The COVID-19 pandemic led to a global lockdown in mid-2020, leading to a rapid decline in international travel and tourism. In French Polynesia, marine-based tourism activities ceased in March 2020 with the suspension of international flights (i.e., 45 days - between 20th March and 04th May 2020), slowly restarting between May–July as domestic and international visitors returned. The impacts of this rapid change in human activity at reef tourism sites on associated reef fishes was examined at Bora-Bora Island through underwater surveys of five control and nine eco-tourism sites. Our results showed that fish density significantly increased from March to May (i.e., the overall density of fishes increased by 143% and harvested species by 215%), but returned to pre-lockdown levels by August 2020. At the usually busy eco-tourism sites, fish diversity, notably of piscivores, omnivores, and benthic feeders, was higher in the absence of tourists. The impact observed is almost certainly related to short term changes in fish behavior, as any density fluctuations at the population level are unlikely to have happened over such a short time frame. Overall, these findings highlight the influence of human activities on fish communities and underline the need for further research to evaluate the environmental impacts of eco-tourism. • Tourism can be a cause of coral reefs degradation but also an asset to their protection. • In 2020, the COVID-19 pandemic provided an opportunity to quantify these impacts. • Fish abundance increased in the absence of tourists as a result of changes in their behavior. • It returned to usual levels when human activity resumed. • Better eco-tourism practices should improve management and sustainable ecosystem use. [ABSTRACT FROM AUTHOR]