Plankton at Gantry State Park

After a long cold snap at the end of the winter, and a pretty rainy spring, this week has finally brought in some sunny and warm days. I happen to be on spring break this week from one of the institutions I call home, so I took the time off to go fishing.  It’s not commonly known, there’s a pretty sizable community of people who fish in NYC and a number of piers where it’s not only legal, but encouraged. One excellent pier is in Gantry State Park in Queens.

Gantry State Park

The park was built on the site of a dockyard, and actually still features the old gantry cranes that used to be used there. More importantly for my purposes, it also features a pier that juts out fifty feet into the water, perfect for fishing off of. When I arrived a young guy was already there with his fishing lines cast off. He’d caught a perch. I congratulated him and found a spot to cast off my own line. Of course, I was looking for smaller fare.

A note on my equipment and my methods. Since I was looking for plankton, I needed a plankton net. There’s a pretty good tutorial on how to make a plankton net here. I followed it pretty much to the letter, with one or two exceptions. The first being that I turned the stocking inside out, which stretched the fabric a bit and made the conical shape stand out. The second being that rather than making my own wire ring, I upcycled a part from an outdoor lamp my father didn’t want. For the bottle, I chopped the top off of a restaurant style squeeze bottle. The end result looks like this:

Plankton Net

It’s not the fanciest piece of equipment in the world, but it does the trick marvelously. The hose is a bit delicate and can be prone to runs, but on the other hand, it costs very little money to replace.

The best time of day to gather plankton with a net like this (which is to say, from a stationary point) is at the turn of high tide. A plankton net needs to drag through the water in order to really do its work, because the idea is to drag a large volume of water, catch the plankton in that area, and discard the excess liquid. If you have a boat, you can accomplish this by dropping the net in and motoring/rowing some distance away, and then pulling the line in when you’re done. Since I don’t have a boat, I need to rely on the current, which, in an intertidal creek like the East River, is dictated by the tides.

In theory, you can do this at either tidal shift, but I choose high tide because it’s an old fishing trick. When the tide comes in, it drags with it many creatures from out in the ocean. They swim around for a while, and then the tide pulls them out.  In addition, high tide just gives my net more depth to work with, so I don’t have to worry about dredging the bottom or snagging on a rock.

This was all something of an experiment for me, and I honestly couldn’t have been more thrilled with the results.

This is the result of my first drag of about a half hour. Subsequent drags pulled in even more and more varied forms of creatures than this. Even here, though, you can see the water is dense with motion. Many of them are the familiar forms. Copepods are common in this sample, identifiable by their swift motion, their jerking. I managed to catch one that, to the naked eye, appeared to have a swollen tail. Under the microscope, it was revealed to be egg sacs.

If I am very lucky, I will be able to catch one again at a later stage of development and see the naupilii swimming around in the eggs.

The creatures I’ve found range toward more exotic things, though. Or at the very least, exotic to me. While looking over my sample at home, I noticed a globule bump in the water. At first, I assumed it was a barnacle cyprid, which I’ve noticed tend to get stuck in the surface tension.

But it was the wrong shape, its motion different than the cyprids I’ve seen. They tend to speed along the surface, driven by some motor I can’t figure out. This was swimming with a pair of legs, like a water beetle.

At first, I couldn’t figure it out, but have since narrowed it down. Normally, my process for this involves a  lot of Google image searching and guesswork. For this, I also recruited this guide to plankton. As the file name indicates, it’s a cladoceran (a water flea), but not the normal sort you see when you image search for this. A little further research told me that marine cladoceran species are few, so narrowing that down further, I’ve concluded it’s from the family evadne.

Sometimes it isn’t the creature that seems strange and interesting, but the behaviors I’ve been able to observe with them. Polychaete worms have become a staple of my catches over the last few months, but the ones I catch are never free swimming. Most bore or build tubes (I had the pleasure of watching one do this in one of my tanks recently; they’re incredibly clever about hiding their locations), but free-swimming polychaetes normally are in a reproductive stage. Still, I was surprised to find this one.

The bundle in the middle is its eggs. I discovered this when I noticed the worm swimming from point to point with a little sphere tucked under its belly. It would swim a few centimeters, and then settle, curled around the eggs like a dragon protecting its horde. This sort of prosocial behavior comes as a surprise to me in a worm. I have a strong affection for the polychaetes (they’re sort of gross seeming, but really interestingly adapted to the environment; plus, as the fishermen pointed out, they make excellent bait), but it never occurred to me one would protect its eggs so vigorously.

My favorite catch was the comb jellies. For reasons unknown even to me, comb jellies fascinate me. Most are fairly macro sized and highly visible to the naked eye.

Though they look like jellyfish, they’re actually a separate thing altogether, unrelated to jellyfish. Their motion comes about because of the movements of vast numbers of cilia moving along their body. You can see them when the animal is filmed in slow motion here.

What appears to be bioluminescence on them is actually a side effect of this cilia movement. The cilia catches the light, breaks it, and as a result, you get these iridescent pulses. The larger jellies are delicate creatures and much too large for a foldscope, but along with them, I also caught a few larvae, small enough to look at under the microscope.

It pulses, trying to move through the water, its little tendrils dangling from it. A good closeup shot of one reveals the rows and rows of stinging cells.

I was so ecstatic at catching the comb jellies, I showed them to the other fisher. He was less impressed with them than me, but that led to a conversation about the different creatures I was catching. As the day went on, he shared things he didn’t want with me.

Protip: tell the other people fishing around you what you’re up to, and they may actually help you out with some cool things. For instance, he reeled in an empty line at one point, but snagged on the line was a hairy mass that looked like grey seaweed. He offered it to me, and I gratefully took it, recognizing it as something much more interesting.

Under the microscope, it’s clear they’re not seaweed, but actually hydroids, relatives of jellyfish that have evolved a sessile and colonial existence. They drift through the water with their fronds open, feeding on creatures that come through. You can see the mouth of one in this video, moving around as it waits to eat, and the same stinging cells on its tentacles as you see on the comb jelly. Unlike the comb jelly, they’ve grown structures of calcium around them to keep them still. For reproduction, they make buds, like this one (I think) that hatch further polyps.

Hydroid Polyp 2

Taking advantage of the free ride and the great infrastructure, multiple colonies of vorticella also grow on the surface of this structure created by the hydroids.

(UPDATE: In addition to the vorticella, a tiny skeleton shrimp also was taking advantage of the structure of this colony!)

I’m really just getting started with the two jars of seawater I brought home from this last trip. This is to say nothing of the other cnidarians I found, or the free swimming prawn larva or the crab zoea and the marvelous colors the foldscope exposes on each of these.

This sample alone will keep me busy for a week before I have to send them back. But there’s more in this tank to be seen and over the summer, I plan to sample more creatures from different points around the city. Maybe this will provide a picture for me of what the map of the city looks like from watery space around it.

10 Comments Add yours

  1. laksiyer says:

    @Matt. Reading your post needs one to curl with a cup of hot chocolate and watch. What exquisite detail, what diversity. Really enjoyed reading and re-reading your post and seeing the movies.

  2. Uma Krishnan says:

    This is such an interesting post! I had no idea one could discover such interesting finds in a single sample of seawater! I didn’t even realize the time passing by as I read the post and watched the videos. Wow it was so cool seeing all those creatures that live in what, at first, appears to be simply water. This was great!

  3. Matthew Rossi says:

    @Uma, oh yeah! I think I could spend literally another month looking through this sample discovering new things. Granted, this amounted to about a half gallon of seawater, all told, but the diversity of life in the water is enormous.

    @Laks hot chocolate actually sounds pretty good right about now…

  4. laksiyer says:

    @Matt. I know you have a special slide set up for wet samples to keep critters alive. I have a few tadpoles that I want to look at. We tried the ziplock method, but killed one tadpole :(. If you have a previous post, could you point me to it?

  5. Matthew Rossi says:

    @Laks I haven’t been able to develop a method that keeps them alive for longer than a few minutes. I use one of two methods: for smaller creatures, like copepods, I actually use the method you championed a while back. I post a slide cover on four corners with some sticky wall putty, drop my sample onto that, and then fasten a well slide to it with the concave side facing the drop.

  6. laksiyer says:

    @Matt… thanks… Sometimes one needs to be told that it is that simple. I should go back to the cavity slides. I have been thinking of rubber band stuck with nail polish with a thin cover slip. I found these plastic coverslips that are much thinner and can take a lot of pressure. However, I should just try this with the cavity slides.

  7. Matthew Rossi says:

    @Laks let me know about the plastic slips. I’m constantly breaking cover slips, which is annoying. Depending on how big the tadpole is, you might think of filling a petri dish with a little water and then using a macro lens and a top light to film it. I’ve had good luck using the main lens from an old digital camera tacked to my phone as a macro lens. There’s good detail in that and not too much cost most of the time.

    @manu I noticed you have a post in which you discussed building a plastic box to catch plankton over a longer period of time. I wonder whether you have any instructions on making one of those. I’d love to compare the difference between using one of those and using a plankton net.

    1. Saad Bhamla says:

      @matt and @laks..
      Lately i’ve been using plastic coverslips from amazon (1000 for $30). I use a paper-punch ($2 from amazon) to make different size holes in it and use it as a ‘jail’ for microorganisms.

      So: glass slide + plastic coverslip with punch-hole + full plastic/glass coverslip taped down to hold in place = good sealing+jail for an hour or so of imaging.

      This is how I was able to do live demo’s as well – as you can make these slides and carry them in your pocket…

      @matt -beautiful beautiful post. I am slowly going through all of them in small bite sizes 🙂


  8. laksiyer says:

    @Matt, I am going to do the same with my macro lens. I had it stored away as I found it to be of little use, but now you have given me a great idea. BTW the thin coverslips I bought were
    but I noticed the same one that Saad writes about and that is really cheap. @Saad that is a brilliant brilliant idea. I need to try it tonight.

  9. Matthew Rossi says:

    Incidentally, as a follow up expedition, I plan to add a light to the front opening of my rig and try again at night. Plankton are incredibly light sensitive and photophilic. When I shine a flashlight into my holding tank, they swarm toward it like mosquitoes toward a camp light. I wonder what doing this at night would bring to the sample.

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