Finding the Knysna Seahorse: Mini-blog 4

We are 5 days into sampling environmental DNA of the Knysna seahorse (Hippocampus capensis) and I continue to be impressed by the landscapes and nature of South Africa. After sampling at the southern Eastern Cape we traveled to the Knysna estuary in the Western Cape. We not only collected water samples along our way, but also passed through a national park to get a look at some of the wildlife.

ElephantAnd oh my, how lovely that was. I might be a marine scientist, but seeing the impressive wildlife here is pretty amazing as well. Obviously seeing elephants, zebras, lions and all the other cool animals roaming around is awesome, but there is so much more than that. There’s all the different kinds of gazelles, the warthogs (might be a personal favourite) and the very diverse birdlife. Unfortunately there won’t be enough time this trip to really experience it all, so I will just have to come back!

The focus of the trip is still very much on the endangered Knysna seahorse.  But what does it mean when we say that an animal is endangered? And why are the Knysna seahorse and the estuarine pipefish endangered?

The easiest way to explain what “Endangered” means, is that an animal or plant has a high chance of becoming extinct in the near future. This can be caused by directly killing the animals/plants, such as overfishing or hunting (think rhinos and the ivory trade), but also by more indirect threats. For example: if you cut down the rainforest, the animals that need the forest to live in will disappear as well, even if you do not kill the animal directly.

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Swartvlei estuary

In the case of the two species we are working on, two big factors are responsible for their high extinction risk. Both the Knysna seahorse and the Estuarine pipefish only occur in a very, very small area of the world. The seahorse only lives in 3 estuaries and the pipefish in 4 estuaries in the southern tip of South Africa. They do not live in the ocean or the rivers, but only in the small area of mix salt and fresh water where the rivers go into the ocean.

The other big factor is that both species only live in a particular habitat. That is, they don’t just live anywhere in those estuaries, that would be too easy! No no, the species we study aren’t happy anywhere else than in areas where there is enough seagrass. So even though there might be a lot of space in the estuaries they live, they only live in a very small area in that space.

Seahorse

Can you spot the Knysna seahorse (Hippocampus capensis) in the seagrass?

What this means is that small changes to the seagrass can have a very big effect on the seahorses or pipefishes. As you may or may not know, seagrass is disappearing all over the world, including South Africa. Some of the most important causes are poor water quality, coastal development, and climate change (Here is a great site for more info on threats to seagrass meadows).

For our two species, even a small, localised decrease of seagrass means they can go extinct in those estuaries where the seagrass is affected. The estuarine pipefish has in fact already disappeared from two estuaries where it used to live. This might also already have happened to the Knysna seahorse, but there is very little information about where it used to live and where it lives now, so it is hard to be certain about this.

Hopefully our work will help to protect these beautiful, but vulnerable animals. How the results of our research might help is for one of the next mini-blogs.

Sampling

Early morning water sampling

Little known facts about seahorses

I have been reading up about seahorses recently and discovered some interesting little bits of information I could not help but share. While seahorses seem to be a big favourite for divers and non-divers alike, we actually know surprisingly little about them. Some of their strange quirks are well known. The fact that the males get pregnant is probably one of the favourite and most retold bits of knowledge about them. I want to go a bit further and more interesting than that, so let’s get started.

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The fused jaw of a seahorse (Source)

Seahorses belong to the family of Sygnathidae, which  translates as “fused jaws”. What this means is that all seahorses and pipefishes have jaws that are stuck together, they can’t open them anymore. So if you were to imagine eating like a seahorse, try gobbling up your salad, steak, pizza, apple,… with clenched jaws, while only using your lips to help you suck the food in. A good thing seahorses do not have teeth, as that would make it even more difficult!

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Hippocampus taenopterus, getting ready to growl

Another quirky thing seahorses do, is that they make noise. They make two distinct types of sounds: “clicking” and “growling”. I absolutely love the idea of a growling seahorse! It seems they do this when they are stressed out and it might even be some sort of escape mechanism to startle predators. Most likely because those predators would be laughing too hard because a seahorse just growled at them… The clicking sounds are mostly used during courtship and mating, so not only do seahorses growl to chase away predators, they also serenade their partners to get them in the right mood. Strange little critters indeed.

To keep up with the strangeness, have you ever wondered how strange the tail of a seahorse actually is? Probably not, I definitely hadn’t before reading this article.  The tails of most animals are round, but nearly all seahorses have square tails. As it turns out, this square shape is better at grasping and holding items. At the same time it offers a higher resistance to crushing than a round tail would. So perfect for a camouflaged critter which spends most of its time clinging on to objects, pretending to be something it is not to avoid getting eaten by predators.

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Different 3D printed models of seahorse tails (Source)

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Hippocampus histrix

The objects seahorses hold onto can be anything, usually they cling on to objects like seagrass, algae, gorgonian seafans, etc. But they do not seem to be very picky at all. This article showed how seahorses living in areas with a lot of plastic actually use that plastic as camouflage. The seahorses even changed their colour to resemble the colour of the plastic and the spots on it. Unfortunately I cannot put the original pictures online due to copyright issues, so if you want to see them, follow this link. Since seahorses don’t really mind what they hold on to, artificial structures can be used to provide habitat for them when their natural habitat has been destroyed. This way populations can continue to exist until the natural vegetation has recovered.

Loss of habitat is one of the risks that endanger seahorses, the trade for traditional Chinese medicine is another big threat to them. IUCN has listed 7 species as Vulnerable and one species as Endangered, but most species have either not been assessed or we lack the data to assess whether or not they are endangered. To combat the illegal trade and offer some means of protection, all seahorses are listed with CITES, which means trading them is strictly controlled. One of the simple rules used to do this, is a size limit of 10cm. This size ensures that most traded seahorse species are mature individuals who can reproduce and that juveniles are left alone.

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Hippocampus pontohi

The fact that we don’t really know how many species of seahorses exist, makes protecting them hard. Estimates of the number of seahorse species range from 40 to 48 species. It is quite likely new species are still waiting to be discovered, though the opposite might happen as well. Two species of pygmy seahorses (Hippocampus severnsi and Hippocampus pontohi) were described in 2008. But recent genetic analyses showed that they are actually the same species which comes in different colour variations.

 

If you want to know more about seahorses or just have a good laugh, check out this great video from Ze Frank with some more true facts about seahorses.