Seasonal distribution and reproductive strategy of seahorses

The unique morphology and life history characteristics make seahorses excellent flagship species for marine ecosystems. The ecological rarity of seahorses has made it difficult to address fundamental demographic processes of seahorses, such as seasonal migration and ecological characteristics. This 3-year investigation evaluated, for the first time, the seasonal distribution of a wild seahorse, Hippocampus mohnikei, and its ecological significance. The results revealed a significant difference in the abundance of wild H. mohnikei populations between warm and cold seasons, indicating that seahorses might undertake a seasonal inshore-offshore migration every year. A total of 42 794 samples were taken during the 3-year survey in the Laizhou Bay, and migratory seahorses had the highest reproductive rates from July to September each year, suggesting that seahorse reproduction might be an important trigger for variation in distribution and migration. Moreover, water temperature might also affect the temporal and spatial abundance of migratory seahorses. There was no genetic subdivision among the different geographical populations of H. mohnikei along China's coast. In conclusion, this study confirmed that large-scale seasonal seahorse migrations occur periodically and that reproduction is one of the important drivers, suggesting that closed-season fishing of breeding grounds is essential and applicable for seahorse conservation.