Nest watch – 2
Nests in aquatic environments
Geetha Iyer
Nests of birds are the most visible, easily observable and built by organisms that humans in general like. But nests are built by diverse organisms and for purposes that are sometimes not limited to raising the young. Imagine building in water! It requires a lot more engineering skill than building on land. Animals that live in water have needs similar to those of the avian community. How do they build? What are the materials they use? Is it possible to observe them build? I share with you some of the interesting nests built in watery habitats.
If nest immediately evokes images of birds, water naturally brings to mind the fish and then perhaps whales and dolphins. But the aquatic medium is home to diversity beyond our imagination. With deep sea submersibles and advance photographic systems, scientists and researchers are beginning to discover a whole new world of organisms deep down in the oceans and equally bizarre structures built for their use. Organisms found in both fresh and marine environments build structures, the largest among them is the coral reefs. Since it is easier to study fish and insect for a classroom project I confine this article to these two groups.
Fish are found in the marine, freshwater and estuarine regions. Each of these habitats present challenges the fish has to deal with and ensure that they are not only able to build but retain the nest till the purpose is achieved. Ocean currents, tides, wind, sand particles, viscosity of the mud are all factors to be taken into account and the only tools they have are their fins and mouths. With the help of the fins they build by excavating, piling or finding ways to glue materials together. One or a combination of these techniques are used. Here are three examples from bizarre to easily observed in homemade aquariums.
Puffer fish
Year 1995. On a seabed at the Amami-Oshima island of Japan, a circular structure approximately 2m in diameter caught the interest of divers and scientists. Divers came across this structure frequently and not knowing its origin named it mysterious circles. The mystery was solved in 2011 by marine scientists from Japan who discovered that it was a nest built by the male puffer fish. A fish which is no bigger than 12 cms long creates a nest that is 2 metres wide. Fascinating! The process of creating a geometric structure in the sands of the sea bed requires talent especially when the tools available for the job are just fins. The blueprint resides within the fish’s brain. Imagine the kind of abstract thinking and spatial reasoning needed for such a venture. This is intelligence of a very high order. How does it manage those circles and radials? Something else is new here. Once the female has inspected the nest and approved it, he then remodels it so that she can lay her eggs and he can fertilize them. Very rare are examples of nest modifications. The entire process is very detailed, too large for this article. Do read the detailed description of how they created this amazing structure in this paper available on the Internet. The video presentation is worth using when you teach reproduction; your class would not only be an instant hit with the students, it will also effortlessly make them think, connect, raise questions, etc.
The male puffer fish is the architect and his work continues much after the female has laid her eggs and left. He fertilizes them and then takes care of them till they hatch, as the nest he built with such care disintegrates slowly around him. There are many other fish architects in the ocean such as the gobies, sticklebacks, etc.
Mudskippers4
Mudskippers are air breathing fishes that belong to the family of gobies. They can be seen on coastal mudflats moving quite unlike other fish. They jump and skip using their tail fin or move (called crutching) by rotating their pectoral fins, reminding you of a ‘fish out of water’ (pun unintended). Mudflats are coastal wetlands that lie in the intertidal zones.
The amphibious mudskippers, one of the few vertebrate to thrive here has to adjust to periodic flooding and draining, oxygen shortage, dislodgement by currents, siltation and predation. Come reproduction time, eggs too need to be protected from these extreme conditions. So they dig burrows into which they retreat during high tides, and when the time comes, keep the eggs safely. But their burrows are not just simple excavations.
Using their mouths to dig, the males make their burrows on elevated sloping parts of the mudflats. The burrow has a vertical shaft that could be up to 2m deep, which then turns to continue horizontally. They may have a single opening leading into a J shaped tunnel or two openings in some species forming a Y shaped vertical shaft that then merge into a single one. The horizontal part of the excavated tunnel/shaft is expanded into a chamber where eggs are laid. The eggs are generally attached to the roof of the chamber.
They stay in this burrow during high tides and come out during low tides to graze and quickly retreat into the burrow in case of perceived danger. Two species of Periophthalmus build turrets at their entrance, perhaps using it to survey the land before exiting their burrow. Some believe that it may be a resting place to sun themselves and become warm before stepping out – a fish sauna.
During high tide the burrows are filled with hypoxic water. The eggs laid in these chambers need oxygen for their development. The male mudskippers that guard these egg chambers deposit mouthful of fresh oxygen during each low tide. The eggs are spawned and developed within this air containing space of the burrow. This behaviour has been documented in detail for the Japanese mudskipper Periophthalmus modestus and the scientists describe this as the ability to maintain an air-phase in the burrow. Mudskippers are also territorial about their burrows. In the face of competition they build small walls to mark their boundaries. In a mudflat thickly populated by them, the area appears like a polygonal/hexagonal mosaic of enclosures. Each could be a meter wide and several inches high.
Gourami
From sea to the coastal mudfl ats and now to freshwater. Goruamis are a group of freshwater fishes that are commonly found from Pakistan, India, and Malayan archipelago up to Korea. These are among the easier fish to keep in a freshwater aquarium. They are mouth brooders and not all species build nests. The Siamese fighter fish and the dwarf gourami build nests. They are also common in most aquariums. They build bubble nests and observing them make their nest will help us learn not just about fish but also about concepts in physics.
Bubble nests are built also by frogs and an insect called froghopper. If you have seen what looks like a spit among stalks of herbaceous plants or grasses, it is the nest of the larvae of froghopper, commonly known as spittle bug. The bubble foam created by the frogs are better known to many than the bubble nests built by the fish.
The fish build their bubbles under/near a floating vegetation. It’s the male fighter fish that builds these bubble nests. He does that even if the femaleis not around. It appears that blowing bubble is almost a hobby for this fish.
The description of the nests in water would be quite inadequate without a mention of the underwater architects of the insect world – the caddisflies. They are master craftsmen who use anything available in water – sand, algae – and build a variety of structures embellishing them with any and every material they find in water. There are three kinds of builders. The portable case makers who carry their cases with them. The retreat making ones which make nests to retreat into; they could be like hammocks, domes, funnels, sacks, trumpets etc. The simplest retreat is a long tube of sand and organic material glued together with silk7. The third group are the closed cocoon making kinds who build not for themselves but for their next stage of life when they turn into cocoons. The cocoons develop into adults in the safety of these cases. The cases may be of any shape – long tubes, coiled shell like structures and even fine meshed nets. But they will happily accept any material available to build with. French artist Hubert Duprat has made jewellery8 from caddisfly cases. He harvested caddisfly larvae from their natural environment and kept them in glass tanks at home. He carefully removed the sand debri and provided them with precious rubies, gold, pearls, etc. They built their cases using these materials and he then used them as jewellery pieces. The caddises vacate their case soon after pupation when they metamorphose into adults.
The natural world is filled with architects who have learnt to build a variety of structures from small to big, tiny to large, simple to the bizarre. I shall conclude this series in the next article where I hope to share with you the nests built by other creatures.
For the classroom5,6
Set up a fresh water aquarium in a small glass tank that can hold 30L of water. Do not use plastic plants, but obtain live green aquatic plants like Hydrilla, Cabomba or Pistia.
Introduce a fighter fish pair. Do not have more than one male as they will fight vigorously. You can have more than one female to ensure that the male is encouraged to build a nest. Apparently if the male is happy in its tank then it will build a nest irrespective of the presence or absence of females, but don’t take a chance. Keep a female. If you see a series of bubbles floating up, then it is a sign of building. You can also introduce a dwarf gourami pair.
They too build bubble nest. Unlike the fighter fish, the dwarf gourami incorporates decorations to its bubble nest by adding leaf bits, twigs and other debris found to hold the nest together firmly. Having built the nest he will actively court the female. Observe and you will be able to see the eggs laid, how they enter the bubble nest, what happens if the eggs fl oat away in water and finally how the male adds to the bubble nest to keep the eggs safe. Spawning may take up to 3 hours during which time nearly 600 eggs are laid. They take anywhere between 12-24 hours to hatch. Now remove the adults from the tank for there is a high chance that some of the fries that emerge from the nest after 3 days may be eaten up by their parents.
This project and its observations can lead to discussions, questions and can be used to teach about floatation, density, air (bubbles), eggs, reproduction, mating, parental care, gender issues, etc. The choice of what you want to discuss is entirely up to you as a teacher. Simply put, this could be part of your nature club/hobby activity – to watch, enjoy and learn informally what each student wants to.
References
- https://www.flickr.com/photos/oceanexplorergov Deep sea organism. http://oceanexplorer.noaa.gov/facts/life. html – Check this site for lessons on deep sea organisms
- Role of Huge Geometric Circular Structures in the Reproduction of a Marine Pufferfish by Hiroshi Kawase, Yoji Okata & Kimiaki Ito – http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3696902/pdf/srep02106.pdf
- https://www.youtube.com/watch?v=BRQpqSI_krQ – Video of Pufferfish construction up till egg care
- Mudskippers – http://www.mudskipper.it/Intro.html
- How to take care of a dwarf gourami – http://www.wikihow.com/Care-for-a- Dwarf-Gourami
- How to take care of a fighter fish – http://www.wikihow.com/Take-Care of-a-Betta-Fish
- The Weavers-The curious world of insects by Geetha Iyer. Harper Collins Publishers, India Ltd. Pages 34-41
- Jewellery from the structures built by caddisfl ies – http://www.treehugger.com/culture/hubert-duprat-jewelrycreated-by-living- larvae.html
- Mudskippers brood their eggs in air but submerge them for hatching-Atsushi Ishimatsu et al. The Journal of Experimental Biology; http://www.ncbi.nlm.nih.gov/pubmed/17981862
The author is a consultant for science and environment education. She can be reached at scopsowl@gmail.com.