Aquatic connectivity: challenges and solutions in a changing climate.

The challenge of managing aquatic connectivity in a changing climate is exacerbated in the presence of additional anthropogenic stressors, social factors, and economic drivers. Here we discuss these issues in the context of structural and functional connectivity for aquatic biodiversity, specifically fish, in both the freshwater and marine realms. We posit that adaptive management strategies that consider shifting baselines and the socio-ecological implications of climate change will be required to achieve management objectives. The role of renewable energy expansion, particularly hydropower, is critically examined for its impact on connectivity. We advocate for strategic spatial planning that incorporates nature-positive solutions, ensuring climate mitigation efforts are harmonized with biodiversity conservation. We underscore the urgency of integrating robust scientific modelling with stakeholder values to define clear, adaptive management objectives. Finally, we call for innovative monitoring and predictive decision-making tools to navigate the uncertainties inherent in a changing climate, with the goal of ensuring the resilience and sustainability of aquatic ecosystems.

Cuttlefish adopt disruptive camouflage under dynamic lighting.

Many animals avoid detection or recognition using camouflage tailored to the visual features of their environment.1,2,3 The appearance of those features, however, can be affected by fluctuations in local lighting conditions, making them appear different over time.4,5 Despite dynamic lighting being common in many terrestrial and aquatic environments, it is unknown whether dynamic lighting influences the camouflage patterns that animals adopt. Here, we test whether a common form of underwater dynamic lighting, consisting of moving light bands that can create local fluctuations in the intensity of light ("water caustics"), affects the camouflage of cuttlefish (Sepia officinalis). Owing to specialized pigment cells (chromatophores) in the skin,6 these cephalopod mollusks can dynamically adjust their body patterns in response to features of their visual scene.7,8,9 Although cuttlefish resting on plain or patterned backgrounds usually expressed uniform or disruptive body patterns, respectively,10,11,12 exposure to these backgrounds in dynamic lighting induced stronger disruptive patterns regardless of the background type. Dynamic lighting increased the maximum contrast levels within scenes, and these maximum contrast levels were associated with the degree of cuttlefish disruptive camouflage. This adoption of disruptive camouflage in dynamically lit scenes may be adaptive, reducing the likelihood of detection, or alternatively, it could represent a constraint on visual processing.

The presence of territorial damselfish predicts choosy client species richness at cleaning stations.

Mutualisms are driven by partners deciding to interact with one another to gain specific services or rewards. As predicted by biological market theory, partners should be selected based on the likelihood, quality, reward level, and or services each partner can offer. Third-party species that are not directly involved in the interaction, however, may indirectly affect the occurrence and or quality of the services provided, thereby affecting which partners are selected or avoided. We investigated how different clients of the sharknose goby (Elacatinus evelynae) cleaner fish were distributed across cleaning stations, and asked what characteristics, relating to biological market theory, affected this distribution. Through quantifying the visitation and cleaning patterns of client fish that can choose which cleaning station(s) to visit, we found that the relative species richness of visiting clients at stations was negatively associated with the presence of disruptive territorial damselfish at the station. Our study highlights, therefore, the need to consider the indirect effects of third-party species and their interactions (e.g., agonistic interactions) when attempting to understand mutualistic interactions between species. Moreover, we highlight how cooperative interactions may be indirectly governed by external partners.

Consistency in mutualism relies on local, rather than wider community biodiversity.

Mutualistic interactions play a major role in shaping the Earth's biodiversity, yet the consistent drivers governing these beneficial interactions are unknown. Using a long-term (8 year, including > 256 h behavioural observations) dataset of the interaction patterns of a service-resource mutualism (the cleaner-client interaction), we identified consistent and dynamic predictors of mutualistic outcomes. We showed that cleaning was consistently more frequent when the presence of third-party species and client partner abundance locally increased (creating choice options), whilst partner identity regulated client behaviours. Eight of our 12 predictors of cleaner and client behaviour played a dynamic role in predicting both the quality (duration) and quantity (frequency) of interactions, and we suggest that the environmental context acting on these predictors at a specific time point will indirectly regulate their role in cleaner-client interaction patterns: context-dependency can hence regulate mutualisms both directly and indirectly. Together our study highlights that consistency in cleaner-client mutualisms relies strongly on the local, rather than wider community-with biodiversity loss threatening all environments this presents a worrying future for the pervasiveness of mutualisms.

To clean or not to clean: Cleaning mutualism breakdown in a tidal environment.

The dynamics and prevalence of mutualistic interactions, which are responsible for the maintenance and structuring of all ecological communities, are vulnerable to changes in abiotic and biotic environmental conditions. Mutualistic outcomes can quickly shift from cooperation to conflict, but it unclear how resilient and stable mutualistic outcomes are to more variable conditions. Tidally controlled coral atoll lagoons that experience extreme diurnal environmental shifts thus provide a model from which to test plasticity in mutualistic behavior of dedicated (formerly obligate) cleaner fish, which acquire all their food resources through client interactions. Here, we investigated cleaning patterns of a model cleaner fish species, the bluestreak wrasse (Labroides dimidiatus), in an isolated tidal lagoon on the Great Barrier Reef. Under tidally restricted conditions, uniquely both adults and juveniles were part-time facultative cleaners, pecking on Isopora palifera coral. The mutualism was not completely abandoned, with adults also wandering across the reef in search of clients, rather than waiting at fixed site cleaning stations, a behavior not yet observed at any other reef. Contrary to well-established patterns for this cleaner, juveniles appeared to exploit the system, by biting ("cheating") their clients more frequently than adults. We show for the first time, that within this variable tidal environment, where mutualistic cleaning might not represent a stable food source, the prevalence and dynamics of this mutualism may be breaking down (through increased cheating and partial abandonment). Environmental variability could thus reduce the pervasiveness of mutualisms within our ecosystems, ultimately reducing the stability of the system.

Cleaner personality and client identity have joint consequences on cleaning interaction dynamics.

Mutualistic interactions involve 2 species beneficially cooperating, but it is not clear how these interactions are maintained. In many mutualisms, one species interacts with multiple species, and since partners differ in terms of the commodities they trade, partner identity will directly influence the decisions and behaviors of interacting individuals. Here, we investigated the consequences of within and between-species diversity on a model cleaner-client interaction in a natural environment, by quantifying the behavior of both partners. We found that the predominant Caribbean cleaner fish, the sharknose goby (Elacatinus evelynae), shows personality variation as we documented repeatable individual differences in activity, boldness, and exploratory behaviors. Personality variation was associated with cleaner-client interactions: cleaner boldness and activity were significantly related to posing by clients and cleaning, respectively. Cleaner personality variation was also associated with the functional identity (sociality, mobility, body size, and trophic level) of clients posing and being cleaned. We thus demonstrate that partner identity can have consequences on mutualistic outcomes which will contribute to the context-dependency and highly heterogeneous patterns we observe at a population level. We also suggest that within- and between-species differences have consequences on partner choice, a feature that has been previously thought to be absent from these cleaner-client interactions.

The selective cleaning behaviour of juvenile blue-headed wrasse (Thalassoma bifasciatum) in the Caribbean.

Through the removal of parasites, dead skin and mucus from the bodies of visiting reef fish (clients), cleaner fish have a significant ecosystem function in the ecology of coral reefs. Cleaners gain nutrition from these interactions and through offering a 'service' are afforded protection from predators. Given these benefits, it is unclear why more fish do not engage in cleaning, and why part-time cleaning strategies exist. On coral reefs, dedicated species clean throughout their life, whereas some species are facultative, employing opportunistic and/or temporary cleaning strategies. Here, we investigate the cleaning behaviour of a facultative species to assess the relative importance of this interaction to the cleaner. Using a combination of focal and event sampling from a coral reef in Tobago, we show that cleaning is not an essential food source for facultative juvenile blue-headed wrasse (Thalassoma bifasciatum), as cleaning rate was unrelated to their foraging rate on the substrate. These wrasse displayed two cleaning strategies: stationary versus wandering cleaning, with cleaning frequency being highest for stationary cleaners. A specific cleaning location facilitated increased cleaning frequency, and wrasse cleaning rate decreased as cleaner or client abundance increased. We also compared juvenile blue-headed wrasse cleaning behaviour to a resident dedicated cleaner, the sharknose goby (Elacatinus evelynae), and showed that, in comparison, juvenile wrasse clean a narrower client range, predominately cleaning three species of gregarious free-ranging surgeonfish (Acanthurus spp.). The wrasse, however, frequently approached these clients without cleaning, which suggests that their selective cleaning strategy may be driven by the acquisition of a particular parasitic food source. Juvenile blue-headed wrasse are generalist foragers, and may thus be limited in their cleaning behaviour by their nutritional requirements, the availability of a suitable cleaning site, and fish density, which ultimately means that they do not adopt more dedicated cleaning roles within the reef community.