Invasions and declines of submersed aquatic macrophytes


Chambers, P., J. W. Barko, and C. S. Smith, Co-chairs. 1993.
Evaluation of invasions and declines of submersed aquatic
macrophytes.  Journal of Aquatic Plant Management 31:218-220.
Reprinted by the National Biological Service, Environmental
Management Technical Center, Onalaska, Wisconsin, May 1995.  LTRMP
95-R003.  3  pp.  (NTIS #PB95-232617


ABSTRACT

During the past 60 yr, sightings of aquatic macrophyte species in
geographic regions where they had previously not been found have
occurred with increasing frequency, apparently due to both greater
dispersal of the plants as a result of human activities as well as
better documentation of plant distribution. Intercontinental
invasions, such as Myriophyllum spicatum and Hydrilla into North
America, Elodea canadensis into Europe and Elodea nuttallii,
Egeria densa and Cabomba caroliniana into Japan, have generally
been well documented. However, the spread of an exotic species
across a continent after its initial introduction (e.g.,
Potamogeton crispus in North America) or the expansion of a
species native to a continent into hitherto unexploited territory
(e.g., the expansion of the North American native Myriophyllum
heterophyllum into New England) have received little attention.
Natural declines in aquatic macrophyte communities have also
received little scientific study although there are many accounts
of macrophyte declines. The best-documented example comes from the
marine literature where extensive declines of eelgrass (Zostera)
occurred in the 1930s along the Atlantic coast due to a pathogenic
marine slime mold ("wasting disease").

The aim of this workshop was to identify examples of invasions or
natural declines of aquatic macrophyte species throughout the
world and assess the importance of environmental factors in their
control. Forty-five scientists and aquatic plant managers from ten
countries participated in the workshop. Eleven of the participants
contributed written evaluations of species invasions and declines
in their geographic region. These were distributed to registered
participants prior to the meeting and served as the starting-point
of workshop discussions. To address the topics raised in the
working papers, the participants divided into four working groups
to evaluate:  1. Environmental controls of species invasions.  2.
Biotic controls of species declines.  3. Abiotic controls of
species declines.  4. Impact of management practices on macrophyte
invasions or declines.  Each working group was asked to identify
existing evidence, the need for additional evidence and management
implications of their topics and then requested to discuss their
findings with the entire workshop at the conclusion of
discussions.


KEYWORDS

submersed macrophytes, macrophyte declines, environmental factors,
biotic factors, invasions and declines