Thursday 18th Feb - Day Five: Dredging in the D'Entrecasteaux Channel

 

There couldn’t have been a more perfect day to coast down a channel and search through sea floor for tiny, wonderfully weird looking invertebrates and plants. The sun was out for most of the time, there was barely a wind to create even the smallest of waves and we were feeling good about the prospect of being elbow deep in seaweed, algae and things that clamp around your fingers.

Dredging is fascinating. The boat has a winch that has a rope attached to a large, metal sieve-like basket. You can see it in the picture below. A camera on a long, optical fibre was lowered into the water so that the scientists could get an idea of what’s on the sea floor.

The skipper of the boat lowered the basket into the water until it hits the bottom (about 14m) and moved the boat forward slowly for about 3 minutes. Then, the boat was stopped and the winch hoisted the basket onto the boat. The boat crew tipped the contents of the basket on to a table and, using forceps (tweezers identical to the ones in our School lab), we picked out all the obvious invertebrates (Fiona, who I’ve written about on previous days, picked out the seaweed she wanted to study – one was gorgeous with fractal patterns!). We found a range of onrganisms. There were sea urchins, sea stars, hermit crabs, Great Spider crabs, decorated crabs, prawns, sea cucumbers, sponges, brittle sea stars and much much more. Have a look at the photos below and then read on.

By the way, if you go to Woodbridge in Tasmania, go and see the Marine Discovery Centre. It's amazing! Andrew, who is the primary school teacher there, Skyped our year three boys today! He found an undiscovered jellyfish on his own a few years ago.

 

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Tomorrow, being the last school day that I’m on this expedition, is when I assist the arachnologist, Dr Robert Raven (also known as ‘Spider Man’ here. In case you don’t see this blog on Saturday, I have some photos of Dr Raven below. He set up some traps a few days ago, which I peeked into yesterday and saw that it had caught a spider. After yesterday’s field work, I came back to the lab to see the other scientist working. Dr Raven showed me how to identify male and female spiders. He is quite meticulous and pays a lot of attention to detail to be able to tell spiders apart. He drew me a diagram to show the different shapes of the pedi palps, which are reproductive organs once the spider has fully matured into an adult. A male will have palps similar to large boxing gloves with hairs. A female will have one that looks similar to a leg. Spiders of different species have different shaped palps, which is how Dr Raven tells them apart. I was quite fascinated when Dr Raven showed me a trap door spider he found and casually let it crawl over his hands.

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I can’t wait to work with him tomorrow to catch intertidal spiders, which is considered a very cool discovery.