The Environmental Science Graduate Students at Watlings Castle, San Salvador, Bahamas.(TME 98)
The Seahorse, Hippocampus Ramulosus, is a remarkable member of the vast marine biodiversity. Seahorses are bony fishes and members of the family syngnathidae (Tudge, 2000). There are about 35 know species (Zubi, 2004). These animals have a very distinct and characteristic body pattern, unlike that of any other marine inhabitant. Seahorses also boast a rather unique quality shared only with a handful of other bony fishes—that is, male brooding. In addition, unlike other bony fish they maintain monogamous relationships between males and females during courtship and mating. These attributes might offer evolutionary advantages to success for the Seahorse as a whole.
The common Seahorse has a long and narrow snout and no teeth. Their extended bodies are surrounded by bony rings with small gill slits (Zubi, 2004). Their fin patterns and distributions are different than those for other bony fish. They have no pelvic fins, small pectoral fins, and one dorsal fin (Zubi, 2004). The pectoral fins turn the Seahorse and aid in steering, while the dorsal fin moves it forward. The coronet of the Seahorse is its most distinctive feature, helping in identification as the thumbprint does for humans (Zubi, 2004). Seahorses are similar to chameleons in that each eye can move independently of the other. The ability of independent eye movement is common to all Syngnathids (Zubi, 2004). The tail of the Seahorse is prehensile, similar to that of a monkey in the rainforest. The prehensile tail allows the Seahorse to hold itself to the underlying substratum and sea grasses and weeds (Tudge, 2000). The male Seahorse has a brood pouch on its ventral surface (Dando, 1996). Depending on the species, Seahorses range in size from 1/4 inch to a foot long (Zubi, 2004). The common Seahorse is 15cm from the crown of its head to the tip of the tail (Dando, 1996).
The common Seahorse is found in the majority of the world’s temperate and tropical coastal waters (Kingdom, 1997). Their favorite areas to inhabit are coral reef systems and adjoining sea grass beds (Zubi, 2004). Although the majority prefer saltwater, a few species inhabit brackish or freshwater. They like sheltered and hidden areas, where they spend most of their time (Zubi, 2004). This fact relates form and function; with the prehensile tail of the Seahorse functioning to help keep the Seahorse adhered to its preferred habitats. The only place that Seahorses are rare is in Northern European waters (Dando, 1996).
Seahorses eat using their long snouts much like a vacuum cleaner (Tudge, 2000). They swim along in an upright position with their tails pointed down. The Seahorse sits and waits for its prey to float or swim by (Zubi, 2004). Aiding in their feeding strategy is the ability of the Seahorse to change its body color to camouflage itself with the surrounding environment (Zubi, 2004). In general they feed on small crustaceans, such as brine shrimp (Dando, 1996). Each day a Seahorse can consume up to 3,000 brine shrimp (Zubi, 2004). Because the Seahorse has no teeth, food is swallowed whole (Zubi, 2004).
Reproduction in Seahorses is their most intriguing quality. The male, not the female, plays the primary role in carrying the developing babies and then later caring for the young. This male behavior is atypical when we as humans think about it, because we are mammals and automatically relate prenatal and postnatal care primarily with the female mother. Among fish, however, it is quite common for the male to be the primary caretaker of the eggs. The male guards the eggs and keeps them clean until they hatch (Kingdom, 1997). The Seahorse takes male parenting to an extreme. The male Seahorse not only guards the eggs but also carries them “inside” himself. The male Seahorse has a brood pouch on his ventral side where, following courtship, the female deposits her eggs (Kingdom, 1997). The male then fertilizes the eggs that he is now carrying and incubates them until it is time for them to hatch. A capillary network is set up between the male and the eggs to provide the eggs with oxygen and nutrients that are transferred from the male to the eggs (Kingdom, 1997). The male Seahorse also controls the environment of the pouch to make it increasingly more like that of the seawater, in order to prepare the eggs for their future environment (Kingdom, 1997). On average, pregnancy lasts two to three weeks dependent upon the species (Zubi, 2004). After the determined pregnancy period, the male then gives birth to the hatched babies. He usually becomes pregnant again right away (Zubi, 2004).
During the courting phase before the female deposits her eggs into the male’s brooding pouch, both male and female are able to undergo body color transformations to either attract or repel possible mates (Kingdom, 1997). During the courting time, the male and female participating in the courtship are monogamous (Kingdom, 1997). They remain interested or attracted to only each other during the entire, lengthy courtship and mating (Kingdom, 1997). This aspect of Seahorse reproduction is truly unique from that of other bony fishes and most other types of animals as well.
Through the course of evolution, traits and events in an animal’s life are carried from generation to generation. Those traits that are carried on tend to be advantageous to that animal species. There is a major evolutionary purpose that monogamy provides for the Seahorse. The longer amount of time an act is practiced, then the more perfected it will become. This is just the case in Seahorse reproduction. The longer that a male and female Seahorse stay monogamous with each other, the more perfected their act of reproduction becomes, and the more successful the mother/father team is at producing babies (Kingdom, 1997).
A baby Seahorse begins its life with a disadvantage. On average only two of the thousands of babies that a male and female Seahorse produce will survive to maturity (Kingdom, 1997). Male pregnancy helps to ensure the future for the babies, by making only a few stronger, more developed babies as opposed to countless underdeveloped weak offspring (Kingdom, 1997).
The future of the Seahorse as an animal is uncertain. Seahorses are being exploited in numerous and devastating ways. In nature, a Seahorse must contend with its predators, such as rays, skates, crab and tuna (Zubi, 2004). A Seahorse’s most devastating natural adversary is storms. Adult Seahorses are extremely vulnerable to the waves and tides generated by strong storms. Seahorses are torn away from their holdfasts. They then are washed to shore, dry out, and die, or they die from exhaustion (Zubi, 2004). In addition to the natural problems that Seahorses face, humans are adding to the depletion of the Seahorse population around the world. Seahorses have been used in Chinese medicine for 500 years. Today approximately 20 million Seahorses are used each year for medicine (Zubi, 2004). The Seahorse is said to cure impotency, effectively treat asthma, prevent arteriosclerosis, and lower cholesterol (Zubi, 2004). Seahorses also increasingly are being used in aquariums and as souvenirs (Zubi, 2004).
In addition to direct exploitation, the Seahorse is indirectly affected by habitat loss. Coral bleaching, pollution and eutrophication all lead to a loss in the substratum and environment that a Seahorse calls home. In the Central Philippines alone the Seahorse population declined by 70% from 1985 to 1995 (Zubi, 2004). The Seahorse has been placed on the “red list” by the International Union for the Conservation of Nature, warning that species are at risk (Kingdom, 1997). Much more can be done to preserve this intriguing animal. For example, never buy Seahorse souvenirs and don’t attempt to raise a Seahorse in a home aquarium.
There is much that is still unknown about Seahorses. It is not known how long they live. In addition, differences between female and male eating patterns and how Seahorses choose their mating partners are poorly understood (Kingdom, 1997). Research on these fascinating creatures has begun only relatively recently. It is up to our generation to ensure that they survive and thrive for future study.
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Dando, Marc, Burchett, Michael. Sealife; A Complete Guide to the Marine Environment. Ed. Geoffrey Waller. Washington, D.C.:Smithsonian Institute Press, 1996
“Kingdom of the Seahorse.” NOVA. 1997. PBS Online.
Zubi, Teresa. “Seahorses.” 26 Dec. 2004
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