Bill Banta on Bryozoa

         Subject: Re: Egg Mass, or Bryozoan Colony
             Date: Tue, 12 Aug 1997 16:49:18 -0400
            From: WC Banta <wcbanta@american.edu>
 Organization: American University
                To: Dick and Jill Miller <DMiller@ziplink.net>
 
First, regarding the reference - yes it is available online at
http://gurukul.ucc.american.edu/banta/PHY_REP.TXT
accessed through:
http://gurukul.ucc.american.edu/banta/WQ_BIO.HTML

Byron will probably answer your questions soon, but there is little
doubt that the bryozoan is Asajirella (=Pectinatella) magnifica. Here is
the relevant part from our little report:

"Pectinatella magnifica.  This is the most common of the
lophopodid phylactolaemates in the United States.  One reason it is
so commonly reported is that it is very conspicuous.  The massive
gelatinous colonies may measure up to half a meter in diameter.  It
prefers highly eutrophic waters with abundant phytoplankton
populations.

       P. magnifica grows between 20 and 28C and reportedly
degenerates rapidly at temperatures less than 20C.  This narrow
temperature tolerance is in keeping with its preference for
shallow, slowly flowing waters, which are generally warm.

       The species is thought to be intolerant to pollution of all
kinds and is reportedly absent from "uncontaminated" areas.  We
know of no data about the sorts of pollutants to which it is
sensitive.  It invariably is found in highly eutrophic waters, with
abundant phytoplankton populations, which apparently are necessary
to support the densely packed colonies.  Klemm et al. (1990) rate
P. magnifica as "sensitive" to heavy metals and "facultative" (3)
in its tolerance to organic wastes.

       We have not collected massive colonies from waters where
there is more than a barely perceptible water flow.  However,
relatively small colonies may be encountered under rocks in rapidly
flowing water.  These sites, including the bypass channel at Lock
6, are characterized by highly eutrophic water with dense
phytoplankton populations.  The species is seasonal but locally
abundant in shallower parts of the C&O Canal.  Massive colonies
occur mostly in late summer and early fall.  We dredged it by the
barrel-full from the tidal Potomac at least until 1985.
Unfortunately, the lack of a boat and dredging materials prohibited
us from collecting in this area during this study.  Nothing is
known about its abundance downstream.

       The sites where P. magnifica is abundant are consistent with
their requirements for warm, highly eutrophic waters.  It seems to
be absent from streams which directly drain urban areas, the
Potomac population excepted.  Presumably, the substances to which
P. magnifica is sensitive are sufficiently diluted by the waters of
the lower Potomac."

One good recent reference to the freshwater Bryozoa is:

WOOD TS (1989)  Ectoproct bryozoans of Ohio.  Bulletin of the Ohio
Biological Survey, New Series 8(2), 70 p.

Freshwater bryozoans have an extensive literature. The literature cited
by Wood is a good start.

Information about the group can be found in most good Biology texts, and
at the Bryozoa home page:
http://www.civgeo.rmit.edu.au/bryozoa/bryozoa.html

The black structures you found were statoblasts, asexually-produced,
multicellular clones of the adults, which hatch under suitable
circumstances to produce a new (clonal) colony. Statoblasts are released
when the colony dies and disintigrates. The spines are apparently to
assist in dispersal by clinging to feathers of waterbirds.

Please write if I can be of any more help.
------------------------------
WC Banta, Professor of Biology
American University
Washington DC 20016-8007
202/885-2181w
301/718-4217h
202/885-6797 fax - if no answer 2182
wcbanta@american.edu or bantawc@aol.com
http://gurukul.ucc.american.edu/banta/banta.html
 
 

         Subject: Re: Egg Mass, or Bryozoan Colony
             Date: Wed, 13 Aug 1997 15:04:31 -0400
            From: WC Banta <wcbanta@american.edu>
 Organization: American University
                To: Dick and Jill Miller <DMiller@ziplink.net>
 
Thanks for the note. Regarding the observation of "highly eutrophic," I
would not put so much faith in that statement that you are surprised by
its presence in water that is less than 'highly' eutrophic. If there are
a lot of hedge words in a report of this sort, that is one of the
reasons.

You are quite right about the typo: "The species is thought to be
intolerant to pollution of all kinds and is reportedly absent from
"uncontaminated" areas," the last word should be "contaminated." Your
suggestion that filter-feeding invertebrates may contribute
substantially to the clarity of the water is probably correct. A good
deal of research has been done, for example, on the contribution of the
introduced Asian Clam, Corbicula, to increased water clarity and
reappearance of submerged aquatic vegetation in the Chesapeake area. The
jury is still out, but results look promising. If you are interested in
the topic, contact Dr. Harriette Phelps at hphelps@hers.com.

About the hazards of Asijirella: some marine gelatinous bryozoans are
known to cause a serious dermatitis and it is possible that the jelly
may affect some people. I don't know of other dangers, but if you are
planning to dine regularly on the stuff, I suggest you find an
alternative food source, because it could be toxic.

Regarding the dietary requirements of A. magnifica, it is not
necessarily the case that if the water is clear that there is not a good
deal of productivity going on. Cloudiness is evidence of a high standing
stock of phytoplankton; productivity is the rate of reproduction.
Surprising productivity can take place in relatively clear waters. Water
clarity, moreover, is a relative value. On the other hand 4m secci disk
readings are pretty high for "eutrophic" fresh waters. The main growth
of the colony could have taken place earlier in the season when there
were more cells available. I seem to remember something about symbiotic
zoochlorellae in this species, which would add another complication.
Admittedly, the statement about eutrophic waters may be an
overgeneralization. If so, I can claim the error: the generalization was
assembled from literature references. By the way, there are many
hundreds of records of the animal from all over the world.

Byron Backus is a real authority on freshwater bryozoans and can give
you a better answer. Citations of some of his papers are available at
http://gurukul.ucc.american.edu/banta/BACKUS.HTML

Best wishes.
------------------------------
WC Banta, Professor of Biology
American University
Washington DC 20016-8007
202/885-2181w
301/718-4217h
202/885-6797 fax - if no answer 2182
wcbanta@american.edu or bantawc@aol.com
http://gurukul.ucc.american.edu/banta/banta.html
 
 

         Subject: Re: Moss Animals Invade Lake Cochituate
             Date: Thu, 14 Aug 1997 13:04:12 -0400
            From: WC Banta <wcbanta@american.edu>
 Organization: American University
                To: Dick and Jill Miller <DMiller@ziplink.net>

I saw your article on the bryozoans - well done. I have only one
comment.

It has not been shown that A. magnifica is an "invader" - a term used
for an organism that turns up in a place for the first time because its
propagules (eggs, etc.) got there for the first time. Since there was no
systematic survey mentioned, it could have been there all along, but not
noticed or reported until this year, when it became more abundant than
usual.
------------------------------
WC Banta, Professor of Biology
American University
Washington DC 20016-8007
202/885-2181w
301/718-4217h
202/885-6797 fax - if no answer 2182
wcbanta@american.edu or bantawc@aol.com
http://gurukul.ucc.american.edu/banta/banta.html