Monday, October 19, 2015

The Hand of Man - Part II

The previous hand of man posting discussed how human activity has changed the Ozarks waters through the introduction of the zebra mussel, and its effects on our lakes and streams.  The other part of the picture above was sent to me as a challenge to identify it.

Chris Barnhart had sent me this picture from Bull Shoals.  This had been underwater until the lake level had dropped, leaving several of these high and dry.  The twig indenting the side showed that it was flexible.  It resembled a spotted salamander egg mass but wasn't transparent and there were no eggs to be seen.  I finally gave up and he identified it as the magnificent bryozoa,  Pectinatella magnifica.  I was somewhat relieved to discover that no less than scientists at the Virginia Institute of Marine Science were equally puzzled when first faced with a similar glob.  Here is their description.
"The object is about 4 feet in diameter. It has moved about 6 feet down the shoreline in the last 24 hours. It 'jiggles' when the waves in the lake hit it… when we prod it, it seems to be spongy feeling… The texture appears to be that of a rock with algae spots on it -- it is brown and yellow, with a pattern of some type."
Bryozoans are single celled microscopic aquatic invertebrates that live in colonies.  These colonies can form round jelly-like masses or even form irregular colonies resembling moss (bryozoa means "moss animal").  P. magnifica  forms round masses, sometimes up to six feet in diameter.  Missouri Department of Conservation describes the animals like this.
Click to enlarge -
"Each tiny individual bryozoan (zooid) is attached to a surface at its base. Its body has an outer sleevelike structure (cystid) and a mass of organs (polypide) that moves within it. An opening at the top of the cystid permits the polypide to slide outward toward the water, exposing a headlike structure (lophophore) crowned with tentacles, which filter food from water. At the slightest disturbance, the polypide and tentacles retract instantly."
A community of rosettes - CB
This animal is a basic as it gets.  They are found in the fossil record 500 million years ago, unchanged from today's structure.  Immersed in water, they absorb algae, surviving without a respiratory, circulatory or excretory system.  They cluster together, 12-18 zooids (animals) forming each rosette within the jelly-like mass which is 99% water.  The rosettes form a community in their jelly-like blob which usually is attached to a structure but can be free floating.  Although they seem to be entirely passive, one study showed that small colonies could move by coordinated pulses of the individual animals.  Imagine a tiny rowing team of single celled animals with no nervous system!

Now the hand of man throws the community a curve.   For millions of years they have been living in bodies of water that may slowly rise and fall.  Now they are faced with sudden changes in the water level as man-made dams contain and then suddenly release water, leaving them suspended in the air.  They must be looking at each other in their rosettes, scratching their head-like lophophores with their tentacles, asking why man has done this to them.

"Hey guys, what's going on?" - CB

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