A synthesis of European seahorse taxonomy, population structure, and habitat use as a basis for assessment, monitoring and conservation

Abstract

Accurate taxonomy, population demography, and habitat descriptors inform species threat assessments and the design of effective conservation measures. Here we combine published studies with new genetic, morphological and habitat data that were collected from seahorse populations located along the European and North African coastlines to help inform management decisions for European seahorses. This study confirms the presence of only two native seahorse species (Hippocampus guttulatus and H. hippocampus) across Europe, with sporadic occurrence of non-native seahorse species in European waters. For the two native species, our findings demonstrate that highly variable morphological characteristics, such as size and presence or number of cirri, are unreliable for distinguishing species. Both species exhibit sex dimorphism with females being significantly larger. Across its range, H. guttulatus were larger and found at higher densities in cooler waters, and individuals in the Black Sea were significantly smaller than in other populations. H. hippocampus were significantly larger in Senegal. Hippocampus guttulatus tends to have higher density populations than H. hippocampus when they occur sympatrically. Although these species are often associated with seagrass beds, data show both species inhabit a wide variety of shallow habitats and use a mixture of holdfasts. We suggest an international mosaic of protected areas focused on multiple habitat types as the first step to successful assessment, monitoring and conservation management of these Data Deficient species.

Fig. 1

Locations of seahorse tissue collection, population demography and environmental data, including site codes. Filled shapes are sites with new data and open shapes are sites with published data

Fig. 2

Phylogenetic tree of the relationship among Hippocampus species, constructed from Cytochrome b using MrBayes (GTR + γ) and shows posterior probability. Shaded labels are those generated in this study, and H. hippocampus from Senegal are denoted by bold text

Fig. 3

Standard length of H. guttulatus (squares) and H. hippocampus (circles) including new data and that from published studies, when n > 10. Filled in shapes are new data and open shapes are data from previous studies (Table 1 for site code details). Sites are grouped by region and are ordered from north to south or west to east depending on location

Fig. 4

Holdfast substrate types utilized by H. guttulatus (a) and H. hippocampus (b). Blues Organic, Browns Inorganic, Orange Artificial, Green No holdfast (swimming)