As orange sunlight begins to creep over the shallow seabed and scatter across the tropical water, seahorses emerge from their hiding spots within the gently-swaying marine vegetation. Before long, they wriggle toward one another, pairing up at predetermined rendezvous points and begin swimming up and down, tails oscillating side to side. The ritual dances have begun.
Seahorses make great parents. Male seahorses are famous for their unusual strategy of carrying developing embryos and birthing the fry. What isn’t as well known, however, is what comes before: an elegant, ritualized courtship dance.
The dance opens in lights, with paired seahorses rising and falling in the water column. They rapidly change their luminance, shining bright pale yellow and silver and then dimming to a dark gray, then repeating the pattern. Next, the tempo accelerates. They will often link tails and swim around in parallel circles as the dance intensifies. When one breaks loose, this signals that the dance may be over [1]. Their partner will have to wait till tomorrow.
The charismatic lined seahorse (Hippocampus erectus) is thought to be monogamous (like many other seahorse species) and they perform this ritual dance every morning at dawn to reestablish the pair bond with their single mate [2,3]. It’s also believed that these daily greetings help synchronize the two partners’ breeding cycles [1,4]. After their daily greetings, they either mate or separate, and each return home. Many seahorses will stay faithful, dancing only with their partner and ignoring solicitations from strangers. It’s only until their mate fails to appear at their special sites after several days that a seahorse decides to move on and find a new dance partner [5].
So why do we study the intricacies of seahorse mating rituals?
Fish from all over the globe are becoming increasingly threatened by human-induced changes to our oceans. Seahorses, with their unique life histories and eye-catching shapes, are among many species whose numbers are dwindling. All 33 recognized seahorse species (genus Hippocampus) are restricted from fishers and pet sellers due to overexploitation of wild populations. The World Conservation Union lists 3 species as endangered and 17 as vulnerable [6,7].
This reduction in numbers is likely due to vanishing habitat and global trade of seahorse products. Seahorses’ habitats are disappearing due to human development, ocean pollution, and climate change. Seahorses inhabit shallow coastal areas which are more affected by global warming than open ocean habitats [8]. Despite trade restrictions, many seahorses end up as accidental by-catch in trawl fisheries and as purposeful catch for aquariums [6].
Seahorse numbers are also dwindling due to their use in traditional medicine, most commonly in Southeast Asia [6]. The global trade of seahorses as medicine, ornamentals and curios was estimated by researchers to be at least 20 million seahorses a year with at least 50 nations and territories around the world buying and selling seahorses [6]. Considering these threats, conservationists have pondered ways to protect seahorses in the wild. There has been growing interest in culturing and breeding seahorses in many countries to reduce the pressure on wild stocks, though problems with successfully breeding them have made this option less viable [9]. Seahorses find a lab or aquarium very different from their ocean homes, and this has made aquaculture difficult. [4]. Studying how seahorses mate and their elaborate courtship rituals may be the key to solving this problem.
Every facet of an animal’s behavior tells a story. The seahorse courtship dance doesn’t just tell us how these fish form deep, long-term relationships; it is an essential part of their life cycle, and studying it can tell researchers a great deal about what seahorses need for their health and wellbeing. By keeping seahorse dancing grounds preserved, and by helping create new ones, we’ll ensure that these dances at dawn continue for all the mornings to come.
Written by: Sabrina Mederos (she/her) is a 3rd year Ph.D Candidate in the Animal Behavior program. She is in Dr. Bales’ lab where she studies the neurobiology and epigenetics of pair bond formation and maintenance in seahorses and prairie voles. She currently is interested in the characteristics of pair bonding and what underlying mechanisms are associated with it. When she’s not in the lab, she loves fostering kittens, archery, and playing video games.
References
[1] Vincent, A. C. J. 1995. A role for daily greetings in maintaining seahorse pair bonds. Animal Behaviour 49(1):258–260.
[2] Lin, T., X. Liu, D. Zhang, and S. Li. 2021. Female lined seahorses (Hippocampus erectus) recognize their mates based on olfactory cues. Behavioural Processes 189:104419.
[3] Sogabe, A., and Y. Yanagisawa. 2007. The function of daily greetings in a monogamous pipefish Corythoichthys haematopterus. Journal of Fish Biology 71(2):585–595.
[4] Faleiro, F., L. Narciso, and L. Vicente. 2008. Seahorse behaviour and aquaculture: How to improve Hippocampus guttulatus husbandry and reproduction? Aquaculture 282(1):33–40.
[5] Vincent, A. C. J., K. L. Evans, and A. D. Marsden. 2005. Home range behaviour of the monogamous Australian seahorse, Hippocampus whitei. Environmental Biology of Fishes 72(1):1–12.
[6] Vincent, A. C. J., S. J. Foster, and H. J. Koldewey. 2011. Conservation and management of seahorses and other Syngnathidae. Journal of Fish Biology 78(6):1681–1724.
[7] Foster, S. J., and A. C. J. Vincent. 2004. Life history and ecology of seahorses: implications for conservation and management. Journal of Fish Biology 65(1):1–61.
[8] Faleiro, F., M. Baptista, C. Santos, M. L. Aurélio, M. Pimentel, M. R. Pegado, J. R. Paula, R. Calado, T. Repolho, and R. Rosa. 2015. Seahorses under a changing ocean: the impact of warming and acidification on the behaviour and physiology of a poor-swimming bony-armoured fish. Conservation Physiology 3(1).
[9] Woods, C. M. C. 2000. Preliminary observations on breeding and rearing the seahorse Hippocampus abdominalis (Teleostei: Syngnathidae) in captivity. New Zealand Journal of Marine and Freshwater Research 34(3):475–485.
[Edited by Jacob Johnson]
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