First records of Hippocampus algiricus in the Canary Islands (north-east Atlantic Ocean) with an observation of hybridization with Hippocampus hippocampus

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

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.

Molecular phylogeny and patterns of diversification in syngnathid fishes

The family Syngnathidae is a large and diverse clade of morphologically unique bony fishes, with 57 genera and 300 described species of seahorses, pipefishes, pipehorses, and seadragons. They primarily inhabit shallow coastal waters in temperate and tropical oceans, and are characterized by a fused jaw, male brooding, and extraordinary crypsis. Phylogenetic relationships within the Syngnathidae remain poorly resolved due to lack of generic taxon sampling, few diagnostic morphological characters, and limited molecular data. The phylogenetic placement of the threatened, commercially exploited seahorses remains a topic of intense interest, with conflicting topologies based on morphology and predominantly mitochondrial genetic data. In this study, we integrate eight nuclear and mitochondrial markers and 17 morphological characters to investigate the phylogenetic structure of the family Syngnathidae at the generic level. We include 91 syngnathid species representing 48 of the 57 recognized genera, all major ocean basins, and a broad array of temperate and tropical habitats including rocky and coral reefs, sand and silt, mangroves, seagrass beds, estuaries, and rivers. Maximum likelihood and Bayesian analyses of 5160bp from eight loci produced high congruence among alternate topologies, defining well-supported and sometimes novel clades. We present a hypothesis that confirms a deep phylogenetic split between lineages with trunk- or tail-brood pouch placement, and provides significant new insights into the morphological evolution and biogeography of this highly derived fish clade. Based on the fundamental division between lineages - the tail brooding "Urophori" and the trunk brooding "Gastrophori" - we propose a revision of Syngnathidae classification into only two subfamilies: the Nerophinae and the Syngnathinae. We find support for distinct principal clades within the trunk-brooders and tail-brooders, the latter of which include seahorses, seadragons, independent lineages of pipehorses, and clades that originated in southern Australia and the Western Atlantic. We suggest the seahorse genus Hippocampus is of Indo-Pacific origin and its sister clade is an unexpected grouping of several morphologically disparate Indo-Pacific genera, including the Pacific pygmy pipehorses. Taxonomic revision is required for multiple genera, particularly to reflect deep evolutionary splits in nominal lineages from the Atlantic versus the Indo-Pacific.