Abstract
Simple SummaryPopulations of many marine species are threatened by a number of interacting factors, including anthropogenic activities, climate change, and biodiversity loss. The assessment of the conservation status of such populations relies heavily on several types of data, such as large-scale geographical and ecological distribution. Seahorses are charismatic fish sensitive to environmental pressures, and according to the IUCN directive 95/2020, they should be considered a model for environmental quality assessment. As in many other areas, the data on seahorse ecological distribution in Europe are scattered, patchy, and mainly focused on small-scale studies. Therefore, we undertook a systematic review using the PRISMA protocol to identify the current knowledge status, detect gaps, and propose future research priorities. We analyzed 32 years of published studies and described the distribution of Hippocampus guttulatus and H. hippocampus across 176 sites in the Atlantic Ocean, Mediterranean Sea, and Black Sea as a function of habitat, depth, and degree of confinement. The applied method evidenced the overall lack of a detailed habitat description in published studies. Seahorse conservation would benefit from an analytical description of habitats, such as data on the depth, nature of the substrate, and associated biological communities, as well as the use of a standardized habitat classification system, such as formally recognized EUNIS habitat codes.Human pressures on marine ecosystems have caused extensive degradation of marine habitats and several local extinctions. Overexploitation and destructive fishing practices are responsible for biodiversity loss in many coastal ecosystems. The definition of conservation programs in marine fish requires comprehensive knowledge on large-scale geographical distribution, while considering distribution/abundance patterns in relation to key environmental variables. Due to their life-cycle traits, the two European seahorses (Hippocampus guttulatus and H. hippocampus), as with other congeneric species, are particularly sensitive to the effects of anthropogenic activities and habitat changes. However, information on the ecological distribution of these two species is scattered, patchy, and mainly focused on small-scale studies. In this paper, we followed an international standard protocol for systematic reviews (the PRISMA protocol) to provide a detailed assessment of the two species’ geographical distribution in relation to the environmental characteristics. According to the 134 analyzed studies, Hippocampus guttulatus is more common in confined areas, while H. hippocampus is found in marine shelf waters. With several interspecific differences, seagrasses were the most used holdfasts of both species. The EUNIS codes (European nature information system) referring to a specific and unique habitat were discussed as a potential tool for defining the ecological distribution of the two species. The obtained results and their future implementation could help plan conservation actions.
Highlights
Worldwide, human pressures on marine ecosystems have caused extensive degradation of marine habitats, and by impacting many communities, have caused several local extinctions [1,2]
The success of specific conservation actions will rely heavily on the quantity and quality of data available on the large-scale geographical and ecological distribution, as well as on the environmental drivers that underlie the ecological dynamics of communities [9,10]
An analysis of the bibliographic sources from alternative search engines and referred to the data-poor regions revealed six peer-reviewed publications, two technical reports, and one congress paper, accounting for 134 studies used for the distribution analysis
Summary
Human pressures on marine ecosystems have caused extensive degradation of marine habitats, and by impacting many communities, have caused several local extinctions [1,2]. Overexploitation of fish and other seafood resources, coupled with destructive fishing practices, pollution, introductions of alien species, and climate change, are mainly responsible for biodiversity loss in coastal ecosystems [3] In this scenario, species with unique life-cycle traits (such as low swimming capacities, mate fidelity, lengthy parental care, and high site fidelity) and close trophic relationships with local communities seem much more sensitive to environmental changes, and this could especially refer to seahorses [4–8]. The exact causes remain unknown, there are some indications of a decrease in suitable habitats [20] or even illegal trafficking [20,21] Such a status for the two species, indicates the urgent need for specific conservation actions to preserve populations. By providing data on spatial distribution and its correlation with environmental features, the results of this study will help with better conservation of the two seahorse species
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