Dear Polychaete people:
Many new species have in recent decades been introduced into the
Baltic Sea area, most likely via transport in ship ballast water (See
Essink, 1988 in Proceedings of the Symposium on the Ecology of the North
Sea). One of these organisms is the estuarine polychaete Marenzelleria
viridis. The presence of aloctone species in an area can have great
implications on the local communities (many cases can be outlined, the
algae Caulerpa taxifolia in Western Mediterranean, the Ctenophore
Mnemiopsis leidyi in the Black Sea, ...). Ecological effects of
anthropogenic activities can led to long-term alterations of marine
systems. Changes associated to the introduction of a new species in one
particular habitat can have ecological important implications and this is
something that should be carefully followed.
Concerning the case recently outlined in this electronic list, I
had the opportunity to work in the past with field populations of
Marenzelleria viridis in Southern New England (USA) (see J. mar. biol.
Ass. U.K., 1995. 75, 725-738). In this area, the Production estimates
and P/B of this species was considerably high and it did not match with
indirect estimates of production based on similar polychaete fauna.
We believed that M. viridis in favorable conditions can behave as
an opportunistic species capable of rapid reproduction and growth. In
our area, during the winter of 1987, the sediments of the marsh were
frozen for 45 days and the fauna living in the upper centimeters of the
sediment was killed. M. viridis is a cold water spawner and it was the
first polychaete to settle after thawing, exploiting the available and
defaunated sediments. Then, in May and June the sediments contained
great quantities of juveniles of M. viridis and the presence of other
polychaetes as C. capitata or N. arenaceodonta was low. In 1988, marsh
sediments were frozen only during few days, the recruitment of M. viridis
was six times lower and this year the presence of C. capitata and N.
arenaceodonta was much higher. We do not known if the high recruitment
of M. viridis was as a consequence of a good year for the species or if
it was dependent on the defaunated sediments, but the rapid growth of M.
viridis this year yield this high production values, and competitive
interactions with the remaining fauna.
I have been following the work of the Baltic researchers, Essink
pointed out the effects of M. viridis on populations of N. diversicolor.
Papers have been published by Bochert (larval ecology & reproduction),
Bastrup (genetics) and Atkins et al, and Zettler & Bick (population
dynamics) among others. I think that the invasive case of M. viridis in
the Baltic Sea should be followed closely and it is a good example for
polychaete people to learn about the biotic mechanisms between estuarine
species.
Best regards from Blanes (Catalunya, Spain)
RAFAEL SARDA
<sarda at azathoth.ceab.es>
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