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Brian Lehrer: Brian Lehrer on WNYC, and for this membership drive we're handing most of our shows with a short deep dive into the marine life living right here in our listening area. We have picked six unique species that you might not have expected are in our waterways. We've partnered with our friends at the Billion Oyster Project, the New York City-based nonprofit that has the goal of restoring 1 billion live oysters to New York Harbor by 2035.

In this series we're going to talk about the technically edible but we don't recommend that black fish, the spider crab, the skillet fish, because it looks like a frying pan, and this thing called a sea squirt. Joining me now to talk about the lined seahorse, one of the more fragile species, but that keeps showing up more and more in our waterways, and what that indicates about water conditions around here, is Shinara Sunderlal, education outreach coordinator at the Billion Oyster Project. Shinara, welcome to WNYC.

Shinara Sunderlal: Thanks for having me, Brian. How are you?

Brian Lehrer: Good. I think I've only seen seahorses on fabric patterns, and probably a lot of our listeners have have too. Does a seahorse really have a head that looks like the head of a horse?

Shinara Sunderlal: It kind of does. I think it's really the snout that gives them that seahorse horse shape. Think five to six inches miniature, has a tail, has a mouth, tube-shaped snout there. They can get up to eight inches in New York, but really their bodies are covered in this body armor. When you see them, distinctly you can see some of those lines and they're contoured. That's where they get that name, the lined seahorse.

Brian Lehrer: I see the way they eat is pretty unique. Tell us about that.

Shinara Sunderlal: Correct. They don't have teeth. They basically are sucking in some animals like crustaceans, little shrimp, copepod. Think very microorganisms that you can find at the bottom off New York Harbor and other parts of the world. They are essentially having it whole and it goes through their digestive system. Again, toothless, which is amazing that they can eat little crustaceans.

Brian Lehrer: One of the unusual things about seahorses is that the male carries the eggs instead of the female?

Shinara Sunderlal: That is correct.

Brian: How do they mate? How do they breed, how do they brood?

Shinara Sunderlal: For females and males, first actually, even before getting to the mating, they really have this amazing courtship behavior where they will do this courtship dance with each other for sometimes up to eight hours. Then that leads to the female depositing her eggs in the male's pouch. The mating bearer basically intwine their tails, they align what we call this long tube from the female, an ovipositor, into the male's pouch. Then the eggs move through this tube into the male's. The male keeps them in his pouch for 10 to 25 days for the lined seahorse, but it can be a little longer for other species.

Then from there the father is carrying them, the eggs hatch in the pouch, and he's regulating the water salinity and everything in his pouch in there, which can be pretty costly energetically. From there, the male undergoes muscular contractions like a human woman would, and then the little babies are expelled, the young, which are called fry at that time. They usually have 1,000 in a brood and about fewer than 5 survive to adulthood.

Brian Lehrer: I see that these seahorses are monogamous, which is apparently rare among fish, and that some seahorse couples will even greet one another each morning with a little dance. Why do they partner up for life and why do other fish not?

Shinara Sunderlal: That's a good question. Scientists are still trying to figure this out more and more. We've really only seen this monogamous behavior with some species of seahorses. There are about 40, 45 in the world. Especially this Australian species, the hippocampus whitei, they are the ones that are really being seen as they can stick with a single mate for life. I think the speculations are that they're doing this so that breeding is more successful. The numbers of offspring that survive to adulthood are so low. That is one strategy to be able to make sure that you're having more offspring that are surviving.

Also thinking about abundance. These seahorses are tiny. They're at the bottom of the harbor, and it's hard to find each other when they're living amongst these reeds and eelgrass beds and oyster beds. We're thinking that it's nicer when they're able to have one mate for life. They communicate with them whether it's through dance or through clicks or sounds that they make. I think it really is a strategy to get more seahorses out there in our oceans and our estuaries.

Brian Lehrer: Now, one of the things that we're doing in this series about the marine life in our area is getting into some of the threats that are impacting each species in particular. I see that the lined seahorses in our area are extremely fragile and easily impacted by pollution in the water. Tell us more. What kind of pollutants, how's this species doing around here?

Shinara Sunderlal: It's interesting because a lot of us, at especially a Billion Oyster Project and through our partner organizations, we've been finding more of them. That could be because we're looking for them, but also because we are starting to see our water quality getting a little bit better with some of that nitrogen reducing in our waters which is coming from pollution, and more dissolved oxygen in our waters now, which our seahorses really, really want and need. With more dissolved oxygen comes more plants and more habitat for our seahorses to come back to in our harbor.

The increased numbers that we are observing may be a product of our oysters being the ecosystem engineers that they are, creating this habitat for them that we can now start seeing them. I think it also does pertain a lot to speak to our water quality in our harbor getting better with controlled pollution and in general being able to have more algae growth and more of that understory in our harbor start growing.

Brian Lehrer: Nice to hear a little environmental good news from New York Harbor and thereabouts. We thank Shinara Sunderlal, education outreach coordinator at the Billion Oyster Project. Tomorrow, another species from the local marine life. Tune in and find out what it is. Shinara, thanks a lot.

Shinara Sunderlal: Thanks for having me. Bye.

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