|A weedy seadragon feeding. Photo: Keith Martin-Smith/Project Seahorse|
As part of our "Year of the Water Dragon" feature, I sat down with Dr. Keith Martin-Smith, a former research fellow and honorary research associate with Project Seahorse, to talk about his work on the beautiful and elusive seadragon. His scholarly articles and photographs have been published in Oryx, Fish Biology, and on BBC Nature, among other places. See also our gallery of seadragon images, fun facts page, and a recent scholarly article.
First of all, what makes seadragons unique?
Seadragons are arguably the most charismatic members of the seahorse family, primarily because of their outrageous colour patterns in the weedy seadragon and their amazing camouflage for the leafy seadragon. They have extremely brightly coloured eggs that they carry underneath the tail and which gradually become covered in algae over the course of their development.
Weedy seadragons gather in large groups of 20 or more individuals to breed, akin to ‘lekking’ behaviour in some land animals. They also have a fascinating ‘mirroring’ behaviour during courtship where the male and female hold their bodies in identical postures but in mirror image of each other. I have also occasionally seen female-female pairs performing the same display. Whether this is competitive behaviour or mistaken identity I’m not sure!
What is the connection between seahorses and seadragons?
Seahorses and seadragons are all in the same family of fishes, the Syngnathidae, and share a number of common features such as the long, tubular snout, reduced fins, male pregnancy and hard, external body plates. They live in similar, shallow coastal habitats and are similar ecologically, feeding on small crustaceans and with restricted home range.
How many species of seadragon are there and what differentiates them?
There are two species of true seadragon – the weedy or common seadragon, Phyllopteryx taeniolatus, and the leafy seadragon, Phycodurus eques. The weedy seadragon has a complex pattern of purple stripes on the ‘neck’ region and hundreds of yellow spots on the side of the abdomen, the head, the snout and the tail while the leafy seadragon is mostly brown and green with white stripes on the abdomen when living in shallow water or reddish in deeper water. The leafy has many frondose appendages while the leafy has simpler appendages. A third species, the ribboned pipefish, Haliichthys taeniophorus, is sometimes called the ribboned seadragon or tropical seadragon. Confusingly, the pipehorses, Solegnathus spp., are known as hai long or sea dragons in traditional Chinese medicine.
|Click the image to watch weedy seadragons disappear into their habitat. Video: Keith Martin-Smith/Project Seahorse|
How did you come to study these animals?
I’ve been working with seadragons since 2001 at sites in southern Tasmania. Initially, with some students, we developed techniques for tagging seadragons with visible implant fluorescent elastomer (VIFE), a coloured substance injected under the skin in a variety of body locations to uniquely identify individuals. We also used surface-towed GPS units in waterproof housings to establish the home range of individuals. Then, in 2004-05, I collaborated with Jaime Sanchez-Camara, a seadragon researcher from Spain who had been working on weedy seadragons around Sydney.
We used our combined data to show that seadragons in colder waters grow more slowly, breed later in the year and live longer than individuals in warmer waters. In 2009, on a recreational dive, I noticed that one of the seadragons that I’d seen still had VIFE tags from 2004. This re-stimulated my interest in seadragons and I began a study to see if we could use the spot patterns on the abdomen to uniquely identify individuals — something that I have since confirmed over a period of three years.
In fact, I’m still regularly seeing the first individuals that I photographed and I can identify all of the seadragons at my regular dive sites. Some of these individuals still have their VIFE tags from 2004-05 in 2012, seven or eight years later, which suggests that they can live a long time. My data predicts that they can live more than 12 years in the wild. I’ve also found that the males carry two broods a year here in Tasmania and all of them start the first pregnancy at the same time.
|A pair of male seadragons. Eggs are visible on their brood patch on their tails. Photo: Keith Martin-Smith/Project Seahorse|
Where are they found, geographically, and in what kinds of habitats?
Leafy seadragons have a very restricted distribution, only found on the southern coast of Australia in the states of Western Australia, South Australia and Victoria while the weedy seadragon has a wider distribution extending from Perth in Western Australia to Sydney in New South Wales and around Tasmania. They both live in similar habitats - namely shallow, algae-covered rocky reefs down to perhaps 30 m.
What threats do they face and what is their IUCN Red List status?
The major threat to both species of seadragon is habitat loss from activities such as coastal development, pollution, dredging etc. An unknown, but potentially serious threat, is related to climate change where warmer ocean conditions are allowing the spread of barren-forming sea urchins which graze large seaweeds and inhibit regeneration of kelp forests. Both species are listed as Near Threatened on the IUCN Red List.
What can seadragons tell us about evolutionary biology? What other scientific insights can they yield?
The reproductive biology of seadragons may provide insight into the evolution of male pregnancy as they have the simplest form of reproduction in the family with eggs just embedded in spongy tissue on the tail. Other reproductive aspects of seadragons remain enigmatic such as sex roles and whether they are monogamous within and between pregnancies. The extreme camouflage of the leafy seadragon is also a fascinating evolutionary development.
Finally, the growth of algae on the eggs during development but not on the body of the seadragon is a promising area for investigation – how do the seadragons remain free of fouling growth and which genes are switched on/off in the eggs?
Why do we rarely see them in aquariums? Can they be bred in captivity?
We rarely see them in aquariums for a number of reasons – they are difficult to maintain, requiring live food; the export trade from Australia is tightly controlled and they are very expensive to purchase costing many hundreds or even thousands of dollars. There is only a single individual in Australia who captures a few brooding male seadragons each year and raises the offspring for sale soley to public aquariums. Captive breeding has proved difficult but I think that there has been some recent success at the Aquarium of the Pacific in Long Beach, CA.
How can we protect seadragons?
Seadragons are protected by strong federal and state laws in all locations in Australia where they occur so the major contribution to protection that is needed is to ensure that habitat loss is minimised through sensitive coastal development. Marine protected areas where intact habitat is preserved and protected can obviously help.