2008 NORTHEASTERN NATURALIST 15(4):589–594
Adult Zebra Mussels (Dreissena polymorpha) Avoid
Attachment to Mesh Materials
Ashley E. Porter1,2 and J. Ellen Marsden3,*
Abstract - Dreissena polymorpha (Zebra Mussel) is capable of attachment to a wide
range of natural and man-made materials, but individuals tend to attach to hard,
solid substrates. The effects of mesh substrates on Zebra Mussel attachment has not
been studied. This study examined the attachment of adult Zebra Mussels to mesh
substrates. Zebra Mussels >5 mm shell length were placed on trays constructed of
mesh of different hole size and material, and a hard substrate (PVC) control. Their
attachment choice was recorded after a 14-d period. The results indicated that Zebra
Mussels do not tend to attach directly to mesh, and instead will move towards the
closest hard substrate, usually another mussel. There was no significant difference
between numbers of mussels attached to different mesh material types and mesh pore
sizes. This study furthers our understanding of Zebra Mussel attachment and their
preferences when attaching to substrata and has implications for fisheries biologists,
aquarists, and others who use nets, mesh, or screens in fresh water.
Introduction
Dreissena polymorpha (Pallas) (Zebra Mussel) was first detected in North
America in 1989, and since then, the rapid expansion of its abundance and
distribution has had severe negative effects on native species, ecosystems,
and human activities (Claudi and Mackie 1994). Zebra Mussels are a biofouling
organism; they secrete proteinaceous adhesive byssal threads that create
a strong attachment to substrates (Eckroat et al. 1993). They adhere to a wide
range of materials, including rocks, sediments, water intake pipes, boat anchors
and hulls, navigation buoys, and other man-made underwater structures
(Ackerman et al. 1993, Claudi and Mackie 1994). The problems caused by
biofouling have stimulated research on factors that affect Zebra Mussel attachment,
such as substrate material, texture, orientation, and illumination
(Kobak 2004, Marsden and Lansky 2000), with a focus on development of antifouling
materials (e.g., de Lafontaine et al. 2002, Mussalli and Tsou 1990).
Settlement can be deterred by use of toxic coatings such as copper, tin, or zinc,
and removal of mussels can be facilitated with ablative paints and silicone
coatings that reduce the attachment strength. However, use of such coatings is
not applicable in all situations (e.g., paint cannot be applied to some research
equipment), and toxic coatings are banned in some inland waters. Fouling
of sampling and fishing nets or aquaculture pens is a particular concern, as
1Department of Biology, University of Vermont, Burlington, VT 05405. 2Current
address - Oceanographic Center, Nova Southeastern University, 8000 North Ocean
Drive, Dania, fl33004. 3Rubenstein School of Environment and Natural Resources,
81 Carrigan Drive, Aiken Center, University of Vermont, Burlington, VT 05405.
*Corresponding author - ellen.marsden@uvm.edu.
590 Northeastern Naturalist Vol. 15, No. 4
this equipment is expensive, cannot readily be coated with antifouling material,
and is challenging to scrub clean. Underwater screens used in a variety
of applications, particularly water intake pipes, are also vulnerable to Zebra
Mussel colonization. Fouling by settling juvenile mussels occurs over a period
of weeks; however, adult mussels will voluntarily detach and relocate to
new substrates in less than a day (J.E. Marsden, pers. observ.; Sandy Brown,
Bellows Free Academy, Fairfax, VT, and Declan McCabe, Saint Michael’s
College, Colchester, VT, unpublished data).
While holding adult Zebra Mussels in the laboratory, we noted that mussels
in shallow trays with a fiberglass mesh floor did not attach to the mesh,
but clustered in a mass in which they were attached to each other. Here, we
examine whether mussels preferably attach to solid or mesh substrates and
investigate which characteristics of mesh affect attachment; specifically,
we tested three types of mesh material and mesh with two sizes of holes. We
hypothesized that mussels would attach more readily to solid than to porous
(mesh) substrates, irrespective of the mesh material; we did not have a priori
hypotheses about the effect of hole size.
Methods
Mussels were collected from a near-shore area in Lake Champlain, VT,
approximately one week prior to initiation of the experiments, and held in
aerated lake water. The mussels were manually removed from their attachment
to the tank or each other just prior to use in the experiment; when
possible the byssal mass was left attached to the mussel to avoid harming
the mussel. Experiments were conducted in 1.3-m diameter, 1900-L
circular static tanks filled with dechlorinated, aerated water; water temperature
ranged from 18 to 20 °C. Tanks were exposed to ambient fluorescent
laboratory lighting for eight hours of each day, and indirect sunlight for the
remaining daylight hours. Circular, flat, wooden floating “trays,” 30 cm in
diameter, were constructed using mesh as the base (Fig. 1a). The sides of
the trays were 1 cm tall to confine mussels within the trays. The trays were
uncovered, and floated at the surface of the tank at a depth sufficient to just
immerse the mussels. Twenty mussels, picked randomly with respect to size,
but all between 6 and 26 mm in length, were placed on each tray so they
were approximately equidistant from each other and from the sides of the
tray. The average size of all mussels in the experiment was 18.5 ± 3.4 mm;
the average size of mussels in each tray ranged between 18 and 19 mm. At
the end of two weeks, individual mussel response was recorded as attachment
to the substrate, the wooden sides of the tray, another mussel, or no
attachment. Each substrate was replicated twice in each of two tanks. The
entire experiment was conducted three times over six weeks, but only one
tank was used in the third period, resulting in a total of 10 replicates. Each
mussel was used only once. A replicate included aluminum window screen
(1 mm holes; Fig. 1b), fiberglass window screen (1 mm holes), Ace knotless
nylon mesh with small holes (1 mm; Fig. 1c), Ace knotless nylon mesh with
large holes (2 mm; Fig. 1d), gray polyvinyl chloride (PVC) alone, and PVC
2008 A.E. Porter and J.E. Marsden 591
covered with a layer of fiberglass screen. Four comparisons were of interest:
attachment to (1) PVC versus mesh (nylon, aluminum, and fiberglass) material;
(2) mesh with small versus large holes; (3) mesh of different materials
(aluminum and fiberglass); and (4) solid substrate (PVC) versus PVC with
a layer of fiberglass mesh over it. The final comparison examined whether it
is the presence of mesh, or the absence of a hard underlying substrate, that
is most important in the attachment of Zebra Mussels. PVC was used for
the hard substrate control because Zebra Mussels will readily attach to this
material (Kilgour and Mackie 1993, Marsden and Lansky 2000).
Statistical analysis
Initially, possible effects due to tank or experimental period were tested
using one-way analysis of variance (ANOVA). For each comparison listed
above, the response variable was the proportion of Zebra Mussels that attached
to the substrate, each other, the side of the tray, or did not attach. All
comparisons of interest were examined with ANOVA.
Results
Of 1184 Zebra Mussels, 70% formed an attachment to either a substrate
or another mussel; only 3% of all mussels attached to mesh. Results were
Figure 1. Experimental apparatus at the beginning of an experiment, and the three
mesh types used in the experiments, showing mussels clustered on each substrate at
the termination of an experiment. a = experimental tray, with floats around the edge;
b = 1 mm fiberglass screening; c = 1 mm Ace mesh; and d = 2 mm Ace mesh.
592 Northeastern Naturalist Vol. 15, No. 4
consistent among tanks and experimental periods. Sixteen mussels were
not accounted for at the end of the experiments, and likely crawled off the
trays. There was no difference in attachment of Zebra Mussels between
mesh with small and large holes (Fig. 2), between aluminum and fiberglass
mesh (Fig. 2), or between the PVC and the PVC with an overlying layer of
fiberglass mesh (Fig. 3). There was a significant difference in the proportion
of mussels attached to all mesh substrates (nylon, aluminum, and fiberglass)
versus solid substrate (PVC) (df = 5, F = 102.7, P < 0.0001; Fig. 2). Among
all substrate types, there was no difference in proportion of mussels attached
to the wooden sides of the trays (average per treatment 1–4 mussels, SD
1.1–3.3) and that did not form any attachment (average 4.2–7.7, SD 2.3–3.8;
Figs. 2 and 3). However, the number of mussels attached to the substrate
versus to other mussels varied inversely, and was related to substrate; significantly more mussels attached to each other on mesh substrates (50.7%)
than on solid substrates (7.9%; P < 0.001). We did not measure attachment
strength quantitatively; however, attachment to the solid PVC was detectably
stronger than attachment to mesh substrates.
Discussion
This study demonstrates that adult, detached Zebra Mussels >5 mm shell
length avoid re-attachment to mesh substrates. This avoidance was not affected
by mesh material or the pore size of mesh. Byssal threads are produced
from a gland in the foot, and are attached to substrate by an adhesive plaque
at the terminal end of the thread (Eckroat et al.1993). The mussels may be
Figure 2. Attachment of Zebra Mussels to four types of mesh vs. hard substrate
(PVC). Bars are the mean of 10 replicates ± 1 standard deviation.
2008 A.E. Porter and J.E. Marsden 593
unable to achieve a secure attachment of their byssal threads to the porous
materials. Mussels would tend to encounter voids as they began to establish
their initial attachment on mesh, and this may be sufficient to stimulate them
to find a better location.
In the presence of solid material, the majority of Zebra Mussels attached
to the substrate; on mesh substrates, mussels tended to attach to each other
rather than the sides of the containers. This result may be simply a consequence
of encounter rate; mussels in the center of the trays would likely
find another mussel before they reached the edge of the tray. It could also
indicate a tendency toward conspecific attraction (Cawein 1993); Wainman
et al. (1996) noted that dreissenid larvae showed a preference for initial attachment
to dreissenid shells in preference to other materials.
Our study only examined the attachment tendencies of adult Zebra
Mussels that had been detached from their substrate. A future study should
examine preferences of settling juveniles, which are more numerous and
can cause much greater fouling. Our observations suggest that juveniles also
avoid mesh substrates. In an unrelated experiment, we left Ace mesh bags
containing stainless steel mesh containers suspended underwater in Lake
Champlain; after approximately three months, from June to September,
the lines holding the bags were heavily colonized with newly settled Zebra
Mussels, but there were few mussels on the mesh bags and none on the mesh
portion of the steel containers.
From a practical standpoint, these results suggest that mesh materials
used for a variety of scientific, fishery, and industrial applications are
Figure 3. Attachment of Zebra Mussels to hard substrates vs. hard substrate with
mesh. Bars are the mean of 10 replicates ± 1 standard deviation.
594 Northeastern Naturalist Vol. 15, No. 4
unlikely to become badly fouled by Zebra Mussels. Moreover, the composition
of the fabric is not important. The meshes we used were at the small end
of the range of those used in most fishery work; gill nets and trap nets, for
example, generally have meshes with holes from 1.3 to 15.2 cm.
Acknowledgments
We thank Kathy Chiang, who first noticed the phenomenon of mesh avoidance,
and Declan McCabe, who assisted with data analysis. This study was conducted at
the Rubenstein Ecosystem Science Laboratory at the University of Vermont.
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