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Objectives
Our primary objective is to determine the impact of the invasive,
Ponto-Caspian colonial hydroid, Cordylophora caspia on
benthic invertebrate communities in southern Lake Michigan. We
propose to address two fundamental questions related to the
presence of Cordylophora in southern Lake Michigan: 1)
What is the predatory role of this hydroid in Lake Michigan
macrobenthic communities?, and 2) Does the filamentous structure
of this hydroid enhance macroinvertebrate abundances in zebra
mussel colonies?
More specifically, we will determine how this benthic invertebrate
influences prey availability for fish. We propose a project examining
three objectives involving field and laboratory research to assess the
effects of Cordylophora on benthic invertebrates in southwestern
Lake Michigan: 1) document specific locations and diets of
Cordylophora (specifically at sites where it is associated with
zebra mussel colonies); 2) characterize feeding preferences of
Cordylophora on common Lake Michigan benthic invertebrates using
laboratory feeding experiments; 3) compare species composition and
abundances of invertebrates present in mussel colonies with and without
Cordylophora to assess the impact of this hydroid as a predator
that decreases fish food availability and/or as a filamentous substratum
that enhances invertebrate densities in freshwater benthic invertebrate
communities.
Methodology
Objective 1: Assessing Cordylophora locations and diets
Zebra mussel colonies will be assessed at numerous locations in
southwestern Lake Michigan for the selection of sites where
Cordylophora co-occurs with zebra mussels. At two to three of these
sites, rocks with coexisting zebra mussels and hydroids will be
collected from two depths at each site because non-mussel invertebrate
community structure has been found to differ depending on water depth.
Samples of comparable rocks/mussel colonies with Cordylophora
will be collected at < 10m and > 15 m. During Year 1 of funding, we will
use SCUBA to conduct bi-monthly field sampling in June, July and August
of 2006. Ten rocks with zebra mussels and associated Cordylophora
will be sampled from each depth for a total of 20 rocks at each site;
rocks with mussels will be placed into individual Ziploc® bags. The
samples will be preserved by adding 95% ethanol to the bags upon
returning to the surface; samples will be returned to the laboratory for
sorting and identification of invertebrates. From each sample, 200
Cordylophora hydranths (minimum) will be dissected to assess prey
items consumed by the hydroid. Comparisons of hydroid hydranth contents
and benthic invertebrates from mussel colonies will allow us to
determine to what extent hydroid diets reflect fish prey availability at
each site.
Objective 2: Hydroid Feeding Preferences in the Lab
Assessing the preference for different benthic prey will allow
us to address the hydroid's preference for and ability to consume prey
that also serve as fish food. In order to assess feeding preferences,
live hydroids from Lake Michigan sites sampled in Objective 1 will be
transported to the Folino-Rorem laboratory at Wheaton College.
Facilities at Wheaton for culturing hydroids are well established and
are ideal to assess feeding preferences. We will use various benthic
invertebrate prey types found in hydranths of hydroids collected in
Objective 1 (2-3 chironomid species, amphipods, and isopods). These prey
items are common in Lake Michigan and are important prey of benthivorous
fish. Individual hydranths or feeding polyps of Cordylophora will
be cultured on microscope slides in the laboratory aquaria with Lake
Michigan water according to a successfully established protocol.
Hydranths will be starved 24 hours before each trial, and we will
control for prey size of a given prey type (± 0.5 mm). Two aspects of
feeding will be assessed: 1) is the prey item caught by the hydranth's
tentacles, and 2) is the prey item consumed by the hydranth. One must
consider how prey density may create a confounding effect in predation
experiments. Because Cordylophora is a passive predator (contact
with prey is necessary for predation to occur), prey will be kept in
suspension using a bubbler to facilitate encounters between hydranth
tentacles and prey or prey will be delivered to the hydranth using a
pipette. All possible pair wise combinations of prey will be
administered to at least 20 individual hydranths (n = 20). Lastly, we
will expose a given hydranth to prey (prey combinations) for 30 mins (Folino-Rorem
laboratory: this is ample time for prey capture and the initiation of
consumption of prey). If a given hydranth does not capture and/or
consume a prey item, it will be fed brine shrimp, Artemia (the
laboratory food item for Cordylophora) to ensure feeding.
Objective 3: Cordylophora effects on non-mussel invertebrates in
mussel colonies
To further identify the effect of Cordylophora predation
on benthic invertebrate communities, we will address how the presence
and absence of hydroid colonies affects benthic invertebrate community
composition in zebra mussel colonies. We will establish mussel colonies
with and without hydroids. The mussel colonies will be deployed at the
two to three locations at a single depth designated in Objective 1 in
Lake Michigan. To control for mussel colony size, we will establish
zebra mussels on 10 X 10 cm unglazed ceramic tiles attached to bricks.
For each site, we will establish 8 replicates of mussels that will be
void of the hydroid Cordylophora (non-hydroid treatments),
whereas 8 replicates will have the hydroid (hydroid treatment). We will
deploy mussel colonies at the beginning or middle of June through July
and August when colonization rates of most macroinvertebrates are high
(M. Berg, pers. obs.). The colonies will be assessed weekly to
bi-monthly to prevent hydroid colonization on non-hydroid treatments;
hydroids will be removed if present on non-hydroid treatments. After
allowing 2-3 months for invertebrate colonization, the colonies and
associated non-mussel invertebrates will be collected and analyzed for
macroinvertebrate differences between treatments.
Rationale
The ecological ramifications for this research are significant
because a largely unstudied Ponto-Caspian invasive species is being
investigated. A better and more thorough understanding of the ecological
role of the invasive hydroid, Cordylophora caspia, and its
association with zebra mussels in Lake Michigan will help elucidate the
potential development of a Ponto-Caspian food web. Our findings will be
important because few scientists have assessed the ecological impacts of
this invasive hydroid on benthic invertebrate species composition and
abundances in southwestern Lake Michigan and the ultimate effects on
food-web dynamics. Our results will clarify the indirect effects of yet
another invasive species on bottom-dwelling fish in the Great Lakes. If
this hydroid is an important predator on macroinvertebrates that are
common prey for fish, then this hydroid could have localized effects on
fish prey with ramifications throughout benthic aquatic food webs in the
Great Lakes.
The information obtained from this study will be presented to
colleagues at conferences (North American Benthological Society,
International Invasive Species Conference) and to those at interested
organizations such as the GLIN (Great Lakes Information Network), Great
Lakes Commission, Illinois Natural History Survey and others that would
benefit from information on the distribution and impact of
Cordylophora on fish prey availability in Lake Michigan. Two
manuscripts on various aspects of the proposed research will be written
and submitted to peer-reviewed journals (Journal of North American
Benthological Society, Journal of Great Lakes Research, Biological
Invasions and/or Freshwater Biology). |
