Affiliation:
1. Lake Michigan Ecological Research Station, United States Geological Survey, Porter, Indiana 46304
Abstract
ABSTRACT
Each summer, the nuisance green alga
Cladophora
(mostly
Cladophora glomerata
) amasses along Lake Michigan beaches, creating nearshore anoxia and unsightly, malodorous mats that can attract problem animals and detract from visitor enjoyment. Traditionally, elevated counts of
Escherichia coli
are presumed to indicate the presence of sewage, mostly derived from nearby point sources. The relationship between fecal indicator bacteria and
Cladophora
remains essentially unstudied. This investigation describes the local and regional density of
Escherichia coli
and enterococci in
Cladophora
mats along beaches in the four states (Wisconsin, Illinois, Indiana, and Michigan) bordering Lake Michigan. Samples of
Cladophora
strands collected from 10 beaches (
n
= 41) were assayed for concentrations of
E. coli
and enterococci during the summer of 2002. Both
E. coli
and enterococci were ubiquitous (up to 97% occurrence), with overall log mean densities (± standard errors) of 5.3 (± 4.8) and 4.8 (± 4.5) per g (dry weight).
E. coli
and enterococci were strongly correlated in southern Lake Michigan beaches (
P
< 0.001,
R
2
= 0.73,
n
= 17) but not in northern beaches (
P
= 0.892,
n
= 16). Both
E. coli
and enterococci survived for over 6 months in sun-dried
Cladophora
mats stored at 4°C; the residual bacteria in the dried alga readily grew upon rehydration. These findings suggest that
Cladophora
amassing along the beaches of Lake Michigan may be an important environmental source of indicator bacteria and call into question the reliability of
E. coli
and enterococci as indicators of water quality for freshwater recreational beaches.
Publisher
American Society for Microbiology
Subject
Ecology,Applied Microbiology and Biotechnology,Food Science,Biotechnology
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