Opportunities to scuba dive with, and closely study, wild seahorses are very few and far between. In fact, Gaye searched for seahorses on the Costa Brava for 15 years before discovering a location where both species of European seahorses, Hippocampus hippocampus and Hippocampus guttulatus, return to breed every summer.
Many volunteer divers and marine biology students have taken part in the Seahorse Project over the past three years. From 2016 Gaye will be concentrating on the July - August peak breeding season and accepting only a very small number of self-funding research assistants to join her for this unique fieldwork experience.
European Seahorses, Hippocampus hippocampus and Hippocampus guttulatus, living in the Mediterranean Sea have their preferred coastal habitats in Posidonia oceanica meadows. However, these seagrass meadows are being destroyed by coastal development and tourism in so many places. Even where seahorses still exist they are difficult to spot: they are small and able to camouflage themselves exceedingly well, changing colour to blend in with their environment.
Seahorses are amazing, cryptic creatures, unlike other fish. They don't have scales but skin covering bony plates, often with many frilly appendages that serve to increase their camouflage. The jaws are united together in a pipe snout, with a small toothless mouth. The family name Syngnathidae means "fused jaw". They feed on tiny Mysis shrimp and zooplankton, prey which are easily digestable as they have no stomach and cannot store food. An adult eats 65 to 70 shrimps per day while baby seahorses need to eat 3000 planktonic shrimps per day!
The seahorse´s typical horse-like head allows a greater range of movement than their pipefish cousins. The head is very mobile, with muscles in the neck which can be tensed and quickly released to catch passing prey. This evolutionary development, called pivot-feeding, gives seahorses a feeding advantage in terms of speed and stealth. There´s a great slow-mo video of pivot-feeding in action on YouTube.
Compared with the typical fish anatomy seahorses hardly look like fish at all, the difference is striking. Pelvic fins are missing, anal and caudal fins are very small or missing. The prehensile tail is long and can withstand considerable crushing, for example from a turtle's jaws, due to being articulated. During swimming, propulsion is given by dorsal fin movement, with the participation of the pectoral fins beating 35 to 70 times per second.Generally seahorses prefer to remain stationary, the tail gripping a holdfast of seagrass or algae, where they can be well hidden from predators whilst feeding.
The Seahorse Project has been researching the size of territory utilised by individuals and mating pairs, we have found that paired males keep to a small area of just a couple of square meters while their female partners have a larger, overlapping territory of around 10 square meters. Females visit their mates each morning for a greeting/bonding session.
Gaye was surprised to find that Danny, pictured above, who was pregnant five times during June to October 2014, could reliaby be located within his small territory almost every time she surveyed. It was a different story with unattached females. They travelled around a lot, presumably looking for a mate, with Topsey moving almost 100 meters from her original position over the course of two weeks. In 2014 volunteers studied 28 individual seahorses and in 2015 the number rose to over 50 catalogued into Gaye Rosier´s photo-base.
The seahorse reproductive system is unique: during mating females pass their eggs, via their ovipositor, to the male breeding pouch, the marsupium. Here the eggs are fertilized by the male and provided with oxygen and nourishment during their development. After 2 to 4 weeks, depending on the number of hours of daylight and sea temperature, the male gives birth to hundreds of baby seahorses. Birthing usually occurs at night, to avoid predators, as the young are released to form part of the zooplankton for several weeks. In the wild less that 1% survive this stage. Those that do, then settle down into the relative safety of a holdfast in the seagrass and by six months of age they can begin reproducing.