Tag Archives for Seahorses

Pregnant male seahorses support up to 1,000 growing babies by forming a placenta


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Jessica Suzanne Dudley, Macquarie University and Camilla Whittington, University of SydneySupplying oxygen to their growing offspring and removing carbon dioxide is a major challenge for every pregnant animal. Humans deal with this problem by developing a placenta, but in seahorses — where the male, not the female, gestates and gives birth to the young — exactly how it worked hasn’t always been so clear.

Male seahorses incubate their embryos inside a pouch, and until now it was unclear how the embryos “breathe” inside this closed structure. Our new study, published in the journal Placenta, examines how pregnant male seahorses (Hippocampus abdominalis) provide oxygen supply and carbon dioxide removal to their embryos.

We examined male seahorse pouches under the microscope at different stages of pregnancy, and found they develop complex placental structures over time — in similar ways to human pregnancy.

Male pot-bellied seahorses have large fleshy pouches where embryos develop during pregnancy.
by Aaron Gustafson



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A pregnant dad gestating up to 1,000 babies

Male pregnancy is rare, only occurring in a group of fish that includes seahorses, seadragons, pipehorses and pipefishes.

Pot-bellied seahorse males have a specialised enclosed structure on their tail. This organ is called the brood pouch, in which the embryos develop.

The female deposits eggs into the male’s pouch after a mating dance and pregnancy lasts about 30 days.

While inside the pouch, the male supplies nutrients to his developing embryos, before giving birth to up to 1,000 babies.

Male pot-bellied seahorse filling his pouch with water in a mating display.
by Kymberlie R. McGuire

Embryonic development requires oxygen, and the oxygen demand increases as the embryo grows. So too does the need to get rid of the resulting carbon dioxide efficiently. This presents a problem for the pregnant male seahorse.

Enter the placenta

In egg-laying animals — such as birds, monotremes, certain reptiles and fishes — the growing embryo accesses oxygen and gets rid of carbon dioxide through pores in the egg shell.

For animals that give birth to live young, a different solution is required. Pregnant humans develop a placenta, a complex organ connecting the mother to her developing baby, which allows an efficient exchange of oxygen and carbon dioxide (it also gets nutrients to the baby, and removes waste, via the bloodstream).

Placentae are filled with many small blood vessels and often there is a thinning of the tissue layers that separate the parent’s and baby’s blood circulations. This improves the efficiency of oxygen and nutrient delivery to the fetus.

Surprisingly, the placenta is not unique to mammals.

Some sharks, like the Australian sharpnose shark (Rhizoprionodon taylori) develop a placenta with an umbilical cord joining the mother to her babies during pregnancy. Many live-bearing lizards form a placenta (including very complex ones) to provide respiratory gases and some nutrients to their developing embryos.

Our previous research identified genes that allow the seahorse father to provide for the developing embryos while inside his pouch.

Our new study shows that during pregnancy the pouch undergoes many changes similar to those seen in mammalian pregnancy. We focused on examining the brood pouch of male seahorses during pregnancy to determine exactly how they provide oxygen to their developing embryos.

A Pot-belly seahorse (Hippocampus abdominalis) floats in water
By viewing the seahorse pouch under the microscope at various stages of pregnancy, we found that small blood vessels grow within the pouch.
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What we found

By viewing the seahorse pouch under the microscope at various stages of pregnancy, we found that small blood vessels grow within the pouch, particularly towards the end of pregnancy. This is when the baby seahorses (called fry) require the most oxygen.

The distance between the father’s blood supply and the embryos also decreases dramatically as the pregnancy goes on. These changes improve the efficiency of transport between the father and the embryos.

Interestingly, many of the changes that occur in the seahorse pouch during pregnancy are similar to those that occur in the uterus during mammalian pregnancy.

We have only scratched the surface of understanding the function of the seahorse placenta during pregnancy.

There is still much to learn about how these fathers protect and nourish their babies during pregnancy — but our work shows the morphological changes to seahorse brood pouches have a lot in common with the development of mammalian placentae.



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The Conversation

Jessica Suzanne Dudley, Postdoctoral Fellow, Macquarie University and Camilla Whittington, Senior lecturer, University of Sydney

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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To save these threatened seahorses, we built them 5-star underwater hotels



Two adult seahorses living on the seahorse hotels four months after the hotels were deployed.
Author provided

David Harasti, Southern Cross University; Michael Simpson, University of Sydney; Rebecca L. Morris, University of Melbourne, and Ross Coleman, University of Sydney

Venture beneath the ocean and you’ll see schools of fish and other alien-like species that may take your breath away. But one species in particular is an enigma in the marine world: the shy, elusive seahorse.

Approximately 50 species of seahorse are found worldwide, and Australia’s waters are home to at least 17 of them.

However, seahorses are considered threatened around the world, largely from over-harvesting for traditional Chinese medicines, unintended capture in fish trawl nets, and the loss of natural habitats such as seagrasses and mangroves.



Read more:
Flash photography doesn’t harm seahorses – but don’t touch

To help seahorse populations bounce back while their natural habitats recover, we created new artificial habitats, called “seahorse hotels”. Our recent research showed how these hotels gave the Australian endangered White’s seahorse (Hippocampus whitei) – also known as the Sydney seahorse – a safe place to come together and call home.

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Seahorse hotels are magnets for marine growth.

Species under threat

Hippocampus, the entire genus (category) for the species, is listed on Appendix II of the Convention on International Trade in Endangered Species (CITES) of Wild Fauna and Flora. This means nations that have signed up to the convention must ensure harvesting seahorses – such as for traditional medicines – is done in a sustainable way.

Unfortunately, the CITES listing hasn’t been enough, and several seahorse species are still experiencing population declines.

Fourteen seahorse species are officially listed as endangered or vulnerable, and these species are considered at risk of becoming extinct in the wild. White’s seahorse is among them. It is one of the two seahorse species listed as globally endangered.

White’s seahorse hiding among sponges.
Author provided

The first Australian seahorse under threat

First discovered in Sydney Harbour, White’s seahorse is native to the east coast of Australia and has been spotted from Hervey Bay in Queensland to the New South Wales south coast.

It grows up to 16 centimetres long and is found in shallow water bays and estuaries, where it lives among its natural habitats of sponges, soft corals and seagrasses. Marine biologists have also shown the species “falls in love” – pairings of males and females mate for life.



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But over the past decade, White’s seahorse populations declined by up to 97% at some sites in Port Stephens. It’s now considered “endangered” under the NSW Fisheries Management Act.

White’s seahorse hiding in their natural soft coral cauliflower habitat.
Author provided

The primary cause is the loss of natural habitats across their range in eastern Australia. In fact, within Port Stephens, more than 90% of soft coral and sponge habitats declined over 10 years at sites where the seahorse was once abundant.

These habitats were destroyed through the installation of boat moorings, anchoring of boats, and the inundation of habitats by sand moving into the Port Stephens estuary.

A home away from home

We devised seahorse hotels to help reverse the decline in White’s seahorse populations. And we named them so because we considered them to be a temporary residence while their natural habitats recovered.



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The idea was born after we saw discarded or lost commercial fisher traps that, when rediscovered, had become heavily covered in marine growth such as sponges and corals.

These lost traps over time become magnets for marine growth which naturally starts to occur within days. As the growth increases over time, fish and invertebrates would move onto these new artificial homes. A few seahorses were even spotted living on them.

An old discarded fish trap that gave David Harasti the idea to develop seahorse hotels.
Author provided

We built on past research, which had also shown White’s seahorse will use artificial habitats if they were available, such as using protective swimming nets found around Sydney.

After we first deployed our 18 hotels, we found it only took within two months for seahorses to start using them. Over time, the numbers of seahorses using the hotels gradually increased: we recorded at least 64 different individuals over the next 12 months of 2018.

Seahorses hold onto the hotels by curling their long tail around the frame, the algae and the sponges, which holds them in place and stops them from being swept away by the waves and currents. By marking each seahorse with small fluorescent tags inserted just beneath the skin (called elastomer), giving each a unique ID, we’re able to track each seahorse.

A baby seahorse clinging to the hotel after months of marine growth.
Author provided

Seahorse babies

We found some seahorses maintained a strong attachment to the hotels – they were spotted regularly on the monthly surveys. One seahorse was even sighted using the hotels in 12 different surveys.



Read more:
Curious Kids: Is it true that male seahorses give birth?

What’s more, the seahorse hotels help White’s seahorses breed. We saw this when breeding season began in October, finding that 13 males living in the hotels had become pregnant. This gives us hope for the local population size to increase.

Excitingly, our seahorse hotel study has had international interest too, with more hotels trialling in places like Gibraltar, Greece, the United States, Philippines and Indonesia.

A pregnant male seahorse found living on the seahorse hotels for a few months. Look closely and you can spot the fluorescent orange tag just beneath its skin.
Author provided

While we must do what we can to help conserve the natural habitats of seahorses, we at least know we can use the seahorse hotels to recover these elusive populations. Their success in attracting seahorses and helping them come together to mate seems to follow the simple concept of: “If you build it, they will come!”.The Conversation

David Harasti, Adjunct assistant professor, Southern Cross University; Michael Simpson, PhD candidate, University of Sydney; Rebecca L. Morris, Research Fellow In Ecological Engineering, University of Melbourne, and Ross Coleman, Professor, University of Sydney

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Flash photography doesn’t harm seahorses – but don’t touch


Maarten De Brauwer, Curtin University; Benjamin John Saunders, Curtin University, and Tanika Cian Shalders, Curtin University

We all enjoy watching animals, whether they’re our own pets, birds in the garden, or elephants on a safari during our holidays. People take pictures during many of these wildlife encounters, but not all of these photographic episodes are harmless.

There is no shortage of stories where the quest for the perfect animal picture results in wildlife harassment. Just taking photos is believed to cause harm in some cases – flash photography is banned in many aquariums as a result.

But it’s not always clear how bright camera flashes affect eyes that are so different from our own. Our latest research, published in Nature Scientific Reports, shows that flash photography does not damage the eyes of seahorses, but touching seahorses and other fish can alter their behaviour.



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Look but don’t touch

In the ocean it is often easier to get close to your subject than on land. Slow-moving species such as seahorses rely on camouflage rather than flight responses. This makes it very easy for divers to approach within touching distance of the animals.

Previous research has shown that many divers cannot resist touching animals to encourage them to move so as to get a better shot. Additionally, the high-powered strobes used by keen underwater photographers frequently raise questions about the welfare of the animal being photographed. Do they cause eye damage or even blindness?

A researcher photographing a ghost pipefish.
© Luke Gordon

Aquariums all around the world have taken well-meaning precautionary action. Most of us will have seen the signs that prohibit the use of flash photography.

Similarly, a variety of guidelines and laws exist in the scuba-diving community. In the United Kingdom, flash photography is prohibited around seahorses. Dive centres around the world have guidelines that include prohibiting flash or limiting the number of flashes per fish.

While all these guidelines are well-intended, none are based on scientific research. Proof of any damage is lacking. Our research investigated the effects of flash photography on slow-moving fish using three different experiments.

What our research found

During the first experiment we tested how different fish react to the typical behaviour of scuba-diving photographers. The results showed very clearly that touching has a very strong effect on seahorses, frogfishes and ghost pipefishes. The fish moved much more, either by turning away from the diver, or by swimming away to escape the poorly behaving divers. Flash photography, on the other hand, had no more effect than the presence of a diver simply watching the fishes.

For slow-moving fishes, every extra movement they make means a huge expense of energy. In the wild, seahorses need to hunt almost non-stop due to their primitive digestive system, so frequent interruptions by divers could lead to chronic stress or malnutrition.

Researchers tested the effect of high-strobe flashes on frogfish.
Author provided

The goal of the second experiment was to test how seahorses react to flash without humans present. To do this we kept 36 West Australian seahorses (Hippocampus subelongatus) in the aquarium facility at Curtin University. During the experiment we fed the seahorses with artemia (“sea monkeys”) and tested for changes in their behaviour, including how successful seahorses were at catching their prey while being flashed with underwater camera strobes.



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An important caveat to this experiment: the underwater strobes we used were much stronger than the flashes of normal cameras or phones. The strobes were used at maximum strength, which is not usually done while photographing small animals at close range. So our results represent a worst-case scenario that is unlikely to happen in the real world.

The conclusive, yet somewhat surprising, result of this experiment was that even the highest flash treatment did not affect the feeding success of the seahorses. “Unflashed” seahorses spent just as much time hunting and catching prey as the flashed seahorses. These results are important, as they show that flashing a seahorse is not likely to change the short-term hunting success (or food intake) of seahorses.

Scuba divers should always avoid touching animals.
sanc0460/Flickr, CC BY

We only observed a difference in the highest flash treatment (four flashes per minute, for ten minutes). Seahorses in this group spent less time resting and sometimes showed “startled” reactions. These reactions looked like the start of an escape reaction, but since the seahorses were in an aquarium, escape was impossible. In the ocean or a large aquarium seahorses would simply move away, which would end the disturbance.

Our last experiment tested if seahorses indeed “go blind” by being exposed to strong flashes. In scientific lingo: we tested if flash photography caused any “pathomorphological” impacts. To do this we euthanised (following strict ethical protocols) some of the unflashed and highly flashed seahorses from the previous experiments. The eyes of the seahorses were then investigated to look for any potential damage.

The results? We found no effects in any of the variables we tested. After more than 4,600 flashes, we can confidently say that the seahorses in our experiments suffered no negative consequences to their visual system.

What this means for scuba divers

A potential explanation as to why flash has no negative impact is the ripple effect caused by sunlight focusing through waves or wavelets on a sunny day. These bands of light are of a very short duration, but very high intensity (up to 100 times stronger than without the ripple effect). Fish living in such conditions would have evolved to deal with such rapidly changing light conditions.

This of course raises the question: would our results be the same for deep-water species? That’s a question for another study, perhaps.



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So what does this mean for aquariums and scuba diving? We really should focus on not touching animals, rather than worrying about the flash.

Flash photography does not make seahorses blind or stop them from catching their prey. The strobes we used had a higher intensity than those usually used by aquarium visitors or divers, so it is highly unlikely that normal flashes will cause any damage. Touching, on the other hand, has a big effect on the well-being of marine life, so scuba divers should always keep their hands to themselves.The Conversation

Maarten De Brauwer, PhD-candidate in Marine Ecology, Curtin University; Benjamin John Saunders, Lecturer / Research fellow in Marine Ecology, Curtin University, and Tanika Cian Shalders, Marine Scientist, Curtin University

This article is republished from The Conversation under a Creative Commons license. Read the original article.