Perhaps of interest to the biologists among us. Big brown jelly fish.

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William_H

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Here in the Swan River in summer we get a huge amount of these ugly creatures. Often 20cms across and 15cm deep body. In quiet conditions you can feel the rudder hit them on my little boat. When swimming you tend to do breast stroke. Totally harmless the kids are often terrified of them. I was led to this story or research on them and found it fascinating. Takes a bit to read it all though. Turns out they give up their stinging carnivorous ways when tiny juveniles attached to rocks and about 1mm sized. They become homes to and live on algae that provide food and oxygen from sun light. Makes me quite fond of them. Ugly is beautiful. ol'will
https://docs.google.com/presentatio...pWe-/pub?start=false&loop=false&delayms=60000
 
When we stayed over on Fremantle for a few days on our way to the GP in melbourne we were also amazed by the sheer quantity floating the ferry from Fremantle to Perth.

Yes Ugly but beautiful in a strange way.

Thls for the link
 
Thanks for the interesting link.

On a rather different scale, I was long ago fascinated by the description and simple line drawing in Sir Alister Hardy’s The Open Sea, Its Natural History of a ubiquitous appendicularian called Oikopleura. Tadpole-shaped but just a few millmetres long, it synthesizes around itself (and discards, as often as every 4 hours) a complex but very delicate filtering ‘house’ to capture bacteria and phytoplankton. I’m sure I must have missed appendicularians in natural history TV programmes, but here is a video of a giant species and its ‘house’. https://www.youtube.com/watch?v=L1wFb_ShW7k
 
Rogershaw said:
When I encountered the jelly fish on the swan river It was not the size it was the quantity that intrigued me.
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I remember many years ago seeing a similar phenomenon in the Beaulieu River (Hampshire UK). The water was more like Moon Jellyfish soup. These were small 3 - 4 cm. I did try to research how it was possible for, presumably, a swarm of adults to navigate up the river in order to reproduce and create this swarm of young going the other way. Never did find a convincing explanation.
Has anyone seen this in the Beaulieu river in recent years or was it a one-off?
 
I recall that when sampling the front to the south of the IoM in the mid ‘70s, we knew how well-defined it was only from our physico-chemical monitors. So it was startling to have it suddenly manifest in the davit floodlight at dead of night, by the sudden appearance of a mass of jellyfish (and attendant garfish) with a leading edge as sharp as guardsmen on parade. There has since been quite a bit of research on jellyfish aggregation at discontinuities, and both physical movement by the water and/or wind, and active swimming, may be involved.
 
lampshuk said:
Do they go around together?
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They were possibly simply attracted to similar prey - the enhanced primary production in the front would have resulted in high zooplankton levels (we were measuring chlorophyll, but not doing biological sampling). Making water bottle casts in the early hours was sleepily boring, so the sudden appearance of the jellyfish and garfish had a memorably magical air, and I apologise for the purely poetic ‘attendant’. :culpability:
 
We were up the Beaulieu River on Tuesday near Buckler's Hard. Guess what, thousands of moon jellyfish floating/swimming upriver with the tide. They varied in size from a couple of centimeteres to about 9 cm. At a very rough estimate there was one per square metre visible from the surface. Not quite the soup I remembered from previous years but that must still add up to several hundred thousand. Maybe they live their whole life in the river just going up and down with the tidal flow and up and down the water column depending on food/light/temperature/salinity etc etc?
 
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