Meet Hip­pocam­pus erec­tus, the only sea­horse of the Bay


In the Lower Ch­e­sa­peake Bay, a small horse moves through the un­der­wa­ter beds of eel­grass look­ing for food. No, it’s not a pony like the fa­mous wild horses of As­sateague Is­land National Seashore. It’s a lined sea­horse (Hip­pocam­pus erec­tus), the only species of sea­horse, out of nearly 50, found in the Ch­e­sa­peake Bay.

The lined sea­horse in­hab­its a range from the north­ern point of Nova Sco­tia, Canada, to the south­ern area of Venezuela in South Amer­ica. Here­abouts, lined sea­horses are usu­ally found from the Lower to Mid Ch­e­sa­peake, although in drier, saltier years they may move as far north as Mary­land’s Bay Bridge.

Sea­horses are ver tebrate fish be­long­ing to the fam­ily Syn­g­nathi­dae. Other fam­ily mem­bers in­clude the sead­ragon, ghost pipefish, sea moth and pipehorse. The lined sea­horse is most closely re­lated to the pipefish: Both share the char­ac­ter­is­tic elon­gated tubu­lar jaw with a small tooth­less mouth at the end.

A sea­horse’s body is cov­ered with a kind of bony ar­mor of jointed rings. A dor­sal fin, made up of 16 to 20 rays, beats so rapidly that it ap­pears trans­par­ent. It also has an anal fin with three or four rays. The top of its head, the coro­net, is al­most as dis­tinc­tive in each an­i­mal as a hu­man thumbprint. Ma­ture lined sea­horses can reach a length of 6.7 inches. They range in color from pale yel­low to black and are marked lat­er­ally with dusky spots and lines.

The Ch­e­sa­peake’s un­der­wa­ter grass mead­ows are the lined sea­horse’s pre­ferred habi­tat. It swims erect, paus­ing to curl its tail around strands of grass to sta­bi­lize its body, then stay very still. This skill, com­bined with the crea­ture’s abil­ity to quickly change its color, cam­ou­flag­ing its skin to match the sur­round­ings, makes the sea­horse an am­bush preda­tor. It uses its long, tubu­lar snout to suck in tiny crus­taceans, plank­ton, worms and other in­ver­te­brates swim­ming by.

Ef­fec­tive cam­ou­flag­ing also helps to pro­tect the sea­horse from its po­ten­tial preda­tors, such as ray, fish, birds, crabs and sea tur tles — as well as peo­ple, who col­lect them for medicines, aquaria or sou­venirs. The sea­horses’ so­phis­ti­cated cam­ou­flage makes them hard to find, cre­at­ing a few prob­lems for sci­en­tists who want to learn more about the an­i­mals.

One of the most strik­ing char­ac­ter­is­tics of this species is its re­pro­duc­tive cy­cle. In many fish species, parental care of­ten falls to the male, which is re­spon­si­ble for fan­ning or guard­ing the eggs and mak­ing sure they re­main oxy­genated. Sea­horses takes this a step fur ther — the males ac­tu­ally guard and nur­ture the eggs in a pouch on their body.

Af­ter an elab­o­rate courtship, which the monog­a­mous pair may re­peat dur­ing a later re­pro­duc­tive cy­cle, the fe­male lays 200–300 eggs in the male’s pouch be­fore he fer­til­izes them. The male pro­vides oxy­gen and trans­fers nu­tri­ents to the de­vel­op­ing em­bryos through a net­work of cap­il­lar­ies in its pouch. The young re­main in the pouch for about two to three weeks, de­pend­ing on water tem­per­a­ture.

Af­ter a con­vul­sive “birth,” dur­ing which the male sea­horse’s body ex­pels the con­tents of the pouch, tiny ju­ve­nile sea­horses emerge. The male usu­ally be­comes preg­nant again al­most im­me­di­ately. De­spite the fre­quency of these preg­nan­cies and the vol­ume of young pro­duced, on av­er­age only two of the thou­sands of ju­ve­niles a pair pro­duces reach ma­tu­rity each breed­ing sea­son.

In sum­mer, the lined sea­horses in­habit shal­low waters, and it swims to water only a few feet deeper in win­ter. The weight of their body “ar­mor” and their erect habit makes them poor swim­mers.They spend most days feed­ing while at­tached by their tail to veg­e­ta­tion. And when they do swim, they use their dor­sal fin (which beats 20–30 times per sec­ond) to pro­pel them­selves for­ward, glid­ing slightly up and down through the water.

Lined sea­horse pop­u­la­tions were as­sessed by the In­ter­na­tional Union for Con­ser­va­tion of Na­ture in 2017. It was listed as a vul­ner­a­ble species be­cause of its prox­im­ity to the highly pop­u­lated coasts of North, Cen­tral and South Amer­ica. Spe­cific world­wide threats in­clude by­catch in shrimp trawl fish­eries and col­lec­tion for the aquar­ium trade, tourism cu­rios and cul­tural medicines.

In the Ch­e­sa­peake Bay, their pop­u­la­tion is con­sid­ered sta­ble. But the loss of their pri­mary habi­tat from shore­line de­vel­op­ment and nu­tri­ent pol­lu­tion could harm lo­cal pop­u­la­tions. Re­duc­ing nu­tri­ent and sed­i­ment pol­lu­tion and con­serv­ing our coastal shore­line habi­tats, par­tic­u­larly un­der­wa­ter grass beds, will help en­sure the con­tin­ued ex­is­tence of this unique sea­horse of the Ch­e­sa­peake Bay.


Hip­pocam­pus erec­tus

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