SEAHORSES – A curiosity of nature

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Seahorses are an iconic fish whose name is derived from the Greek word hippos which means horse. The scientific name Hippocampus combines horse with beast (kampos) to translate to horse beast. Interestingly, these are the mythological beasts that pulled Poseidon’s carriage.

Gibraltar is home to two known species of seahorses, Hippocampus hippocampus (short-snouted seahorse) and Hippocampus guttulatus (Long-snouted seahorse) and both are on the protected species list. Although seahorses are fish, they do not have scales like normal fish do. In fact, they have skin over some bony plates arranged in rings around their bodies and although cute, they certainly aren’t cuddly. They also have no caudal fin like most normal fish and swim with the beating of their dorsal fin which is pretty unusual.

Seahorses are known to be bad swimmers and tend to live in seagrass meadows in the demersal zone. Seagrasses weaken the flow of strong currents and this prevents the seahorses being swept away. The seagrasses also make a handy anchor for the seahorse to grab on to with their prehensile tail. Unfortunately, most of the native Gibraltar seagrass beds have disappeared due to commercial activities. On the upside, the Government is taking this very seriously and has declared a marine protected area around Seven Sisters where it is attempting to restore these habitats.

A common misconception is that seahorses mate for life. As with a few fish species, they tend to form pair bonds that last the breeding season but there are some species which form breeding groups. This helps to increase genetic diversity within populations which can often suffer from being isolated from neighbouring populations nearby.

Unknown to most people is the fact that seahorses can completely change the colour of their skin to increase camouflage. This does not happen instantly like with Octopus, but rather the change graduates over many days. The range of colours is also impressive too as they have been known to turn bright yellow and red to match debris in the sediment around their territory. Small, faster colour changes do also happen as part of the courtship display. Males and females often entwine tails and simultaneously change colours. This ritual can happen daily for weeks before mating will actually take place.

Once it has, the female passes the eggs to the male who take on complete single parent responsibility from this point on. Male seahorses brood their young in a pouch which provides the young eggs with oxygen and a protein called prolactin which is very similar to milk in mammals. All the eggs hatch inside the male’s pouch until the young have developed sufficiently and are released. This parental strategy ensures that baby seahorses have a relatively good survival chance. From each successful pairing, it is possible that around 1,500 fry are produced in a pouch with a volume of less than half a tablespoon.

But don’t let the cute demeanour fool you because these guys are highly veracious predators. A seahorse succeeds in devouring around 90% of its intended prey items. Compare that figure to the efficiency of a Great White Shark (Carcharodon carcharias) which only manages to eat about 55% of its target prey and you get an idea of the kind of deadly killers they actually are. They also have excellent eyesight and can move their eyes independently. This allows them to search for prey in front and behind them, simultaneously. They feed on tiny crustaceans called Mysis which are floating in the surrounding water. They have also been known to feed on small planktonic fish and have a distinct dislike for anything dead. This dislike extends so far that it is a huge endeavour to train seahorses to eat dead mysis in aquariums, making their presence pretty rare.

Irrespective of their hunting prowess, human impact has been highly detrimental to these beautiful creatures. Loss of habitat is the main culprit responsible for the decline in abundance locally. Plans to develop a known seahorse nursery site at Rosia Bay have been blocked out of protection concerns; an important first step in ensuring their continued presence along the Gibraltar coastline.

The next and most important step must be to successfully restore the seagrass beds which were commonly found within the bay. There is little hope of continuing to have these exceptional fish on our doorstep should we not succeed in this effort. One way would be to ban any activity which causes benthic disturbances like trawling or anchor drags within specific protected reserves. By simply allowing the grasses to re-establish themselves we would be increasing restored habitat range for the seahorses; their numbers should quickly increase.

Further, regular benthic surveys should help determine the rates of seagrass regrowth and identify any issues which may be hampering their establishment. This would also allow for constant tweaking of the protected area to maximise results.

It would be very sad to see such a flagship species completely disappear from our coastline due to indifference or negligence. But, unfortunately, as a species, humans have a pretty poor conservational track record, when cash is involved. This would essentially condemn seahorses, much like the Gods that once rode them, to be confined to a dusty book somewhere in a Mythology section of library.