Understanding Seahorse Distribution and Ecology in Malta through Citizen Science.

Abstract

Two seahorse species (Hippocampus guttulatus and Hippocampus hippocampus) are frequently encountered on the Maltese archipelago. Both species are considered to be endangered and are globally data deficient. They are under-studied in Maltese waters when compared to data published from Mediterranean studies. Seahorses are sporadically encountered by the public (particularly by scuba divers) in Maltese waters and as Malta is considered a centre for recreational Scuba diving in Europe, it was deemed a good candidate for a sub-aquatic citizen science initiative. In this study, citizen science approaches were compared to systematic surveys. The surveys found very few seahorses, whereas, once well publicised, records of seahorses from citizen scientists were relatively frequent in the summer months. Citizen science surveys were used to discover the population composition of those seahorses reported and observed in terms of species, sex and gravidity in relation to environmental factors. Citizen science can confirm the long-term presence of both species in Maltese waters. The nature of the data collected by citizen science allows for some comparative work between species. For example, a significant shift in species composition over time was observed which may indicate the decrease of H. hippocampus in Maltese waters. However, opportunistic citizen science data has limits. For example, whilst sea temperatures are correlative to this apparent decline in H. hippocampus, the data is less abundant for months where scuba diving and particularly tourist scuba diving is less common and the correlation could therefore be a result of more records occurring when the water is warmer. Nevertheless, it could be concluded both species of seahorse are present in Maltese waters and that pregnant males for H. guttulatus were observed with relative frequency indicating that Maltese waters are active breeding sites for at least one of the seahorse species in the Mediterranean.