Marine Biology

Abstract Marine vegetated habitats such as seagrass, mangroves, and macroalgae are common along tropical coastlines globally and provide habitats for a diversity of fishes, including juvenile fish and species found on coral reefs. Understanding the use of these habitats by different fish species and life stages is fundamental to spatial planning, fisheries management, and conservation. While previous studies have focused on the habitat potential of seagrass, macroalgae, or mangroves for coral reef fish independently, it is important to consider their combined roles, as tropical seascapes are often mosaics of such habitats. In this study, we evaluated habitat associations across life stages for fish species in coral reefs, seagrasses, macroalgae, and mangroves in Saudi Arabia’s central Red Sea. Through in situ visual surveys, we documented 36% of local coral reef fish species in one or more vegetated habitats, with the fraction of coral reef species utilizing macroalgae or seagrass much greater than that of mangroves (29%, 18%, and 6%, respectively). Mangroves hosted mainly juvenile fish (83% of observed population) and macroalgae hosted the largest proportion of herbivores (39% of observed population), suggesting that each environment offers different combinations of resources (food and shelter), and a mix of these habitats could support biological connectivity across a seascape. Species targeted by local fisheries made up 37% of the species documented in vegetated habitats. The use of multiple habitat types by juvenile and commercially important fishes in the Red Sea underscores the need for a holistic approach to habitat protection. Graphical abstract

Abstract Sacoglossa are known for stealing photosynthetically active chloroplasts from their macroalgal food and incorporating them into their cytosol. The nutritional support these alien organelles (kleptoplasts) provide to the slugs is still debatable. Comparing slugs starved in continuous darkness (non-photosynthetic condition) and light (photosynthetic condition) is often used to understand the contribution of the kleptoplasts to the slugs' metabolism. Here, we examined the slugs' side of starvation in darkness to better understand the effects of darkness on the slugs. We compared the gene expression profile and digestive activity of Elysia viridis, starved for one week under ambient light and continuous darkness. Starvation in darkness led to the up-regulation of genes related to glucose deficiency, while genes involved in the development, cellular organization, and reproduction were down-regulated. This specific gene expression may counteract reduced nutrient availability under non-photosynthetic conditions. Under photosynthetic conditions, kleptoplasts may have a higher nutritional value and may be able to support some metabolic processes. It appears that the slugs can only access kleptoplast photosynthates through autophagy during starvation. Nevertheless, autophagy and length reduction in darkness are highly elevated compared to light conditions, suggesting that more slug tissue is needed to satisfy the nutritional demands under non-photosynthetic conditions. Since we did not detect a gene expression related to the export of photosynthates to the slugs, our results support the hypothesis that slugs use kleptoplasts as larders accessible via autophagy. As long as the kleptoplasts are functional, they provide an energetic support, helping the slugs to reduce starvation-induced stress.

Abstract The intensification of coastal development poses potential threats for coastal seabirds, and understanding their habitat use is a key factor to guide conservation and management. In sub-arctic areas, black guillemots (Cepphus grylle) use coastal habitats year-round, which makes them vulnerable to the increasing human activities in these areas. In mainland Norway, one of the species’ strongholds, black guillemots are red-listed after substantial population declines. However, their fine-scale foraging behaviour has received little attention to date. We collected and analysed GPS tracking data from adult black guillemots at three sites located over a latitudinal gradient of 250 km in central/northern Norway. Maximum foraging ranges of 33 km at Sklinna (65°12′N) for incubating birds, and 18 km at both Vega (65°34′N) and Sklinna for chick-rearing birds, are among the longest reported for this species. At all three sites, foraging probability was highest in shallow waters (< 50 m depth) close to the colony and declined with increasing water depth and distance from colony. However, birds from Vega also foraged over deeper waters. Kelp presence was of high importance at Sklinna, but apparently less important at Røst (67°26’N) and Vega. We also found distinct differences in foraging activity across the day and with tidal height among the sites. Inter-site differences in habitat use and foraging activity may be explained by differences in the availability of habitats and suitable prey. Our study highlights the importance of shallow marine areas for black guillemots and shows that habitat use can vary substantially between sites.

Abstract Coral propagation and out-planting are becoming commonly adopted as part of reef stewardship strategies aimed at improving reef resilience through enhanced natural recovery and rehabilitation. The coral microbiome has a crucial role in the success of the coral holobiont and can be impacted shortly after out-planting. However, long-term characterisation of the out-plant microbiome in relation to out-plant survival, and how these properties vary across reef sites, is unexplored. Therefore, at three reef sites on Opal Reef, Great Barrier Reef (Mojo, Sandbox and Rayban, 16°12′18″S 145°53′54″E), we examined bacterial communities associated with out-planted Acropora millepora coral and monitored coral survival over 12 months (February 2021–22). Bacterial communities of out-planted corals exhibited significant changes from donor colonies 7 days to 1.5 months after out-planting. Further, bacterial community composition differed for sites Sandbox and Rayban with low overall survival (0–43%) versus Mojo with higher overall survival (47–75%). After initial dissimilarity in bacterial communities of out-plants across sites at 1.5 months, and despite changes within sites over time, out-plants exhibited similar microbial communities across sites at 7 days and 6, 9 and 12 months. We hypothesise these trends reflect how bacterial communities are shaped by rapid changes in local environmental characteristics (e.g. from source to out-planting site), where out-plant bacterial communities ‘conform’ to out-planting site conditions. After initial changes, out-plant bacterial communities may then be under the influence of global environmental conditions—such as annual trends in temperature across seasons. Such outcomes indicate the importance of site selection in shaping initial coral bacterial communities and subsequent out-plant success. Importantly, continued differences in out-plant survival trajectory but similar bacterial communities across sites after 1.5 months indicate that other factors—apart from bacterial community changes—likely govern out-plant success in the longer term. Our research highlights the need to resolve drivers of small-scale site differences alongside higher resolution spatiotemporal monitoring of environmental conditions to distinguish key drivers of (i) microbial change during out-planting and (ii) out-plant survival to subsequently inform out-plant site selection to optimise future restoration efforts.

Abstract This study conducted stable isotope analysis (δ13C, δ15N, and δ34S) on the epidermis and two skeletal elements (rib and squamosal bones) of Hawaiian green turtles (Chelonia mydas) and putative diet items obtained from two neritic sites: the Kona/Kohala coast and Oahu. Turtle tissues were collected in 2018–2020 and diet samples in 2018, 2019, and 2021. The effect of body size and sampling locality on individual bulk tissue isotope values was evaluated, and stable isotope mixing models based on δ13C, δ15N, and δ34S values from those tissues and four groups of food sources were used to reconstruct diet histories of the turtles. Mixing models indicated that green turtles along the Kona/Kohala coast consumed an omnivorous diet, whereas those from Oahu had an herbivorous diet. These diet make-ups are consistent with published gut content analyses. However, mixing models using the stable isotope ratios in rib and squamosal bone failed to yield reasonable diet histories, probably due to inadequacies of the applied trophic discrimination factor (TDF), a key model parameter. These results further establish that stable isotope ratios in the epidermis can be used effectively to study green turtle diet, but also reveal that more validation—and establishment of appropriate TDFs—is needed before bone can be used reliably to assess green turtle diet.