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Stranger than Fiction: The Secret Lives of Freshwater Mussels
Anne Kinsinger: Good
evening. I'm Anne Kinsinger, Associate Director for Ecosystem Science
Geological Survey, and I want to thank you for coming tonight and
welcome to our evening lecture series, which showcases the work of USGS
scientists both locally and around the world. The Science in Action
Series is intended to give you a better understanding of the
science-based issues that affect your daily lives.
Our speaker tonight is Heather Galbraith, Fisheries Research
Biologist at the USGS Leetown Science Center in West Virginia. In her
present role, Heather studies Aquatic Ecology and Conservation
with an emphasis on the reproduction biology of freshwater mussels.
Heather's current research projects include studying the
conservation genetics of eastern elliptio mussel, ecological flow
requirements of the federally endangered dwarf wedgemussel, and
American eel restoration in the Susquehanna River Basin.
Heather received her Master's and her Ph.D. in Zoology from
the University of Oklahoma. She continued as a postdoctoral researcher
at the Trent University and Ontario Ministry of Natural Resources,
her research focus was on conservation genetics of endangered
Ladies and gentlemen, Heather Galbraith, "Stranger than
Fiction: The Secret Lives of Freshwater Mussels".
Heather Galbraith: Thank you
so much. Can everybody hear me? No, you can't hear me. Now just a
second, we're trying to get this up closer. Better
or worse? Better? OK, so everybody can hear me now? Perfect. OK.
Thank you for that nice introduction and thank you to all of
you for coming out in less-than-ideal weather conditions.
I'm going to be talking to you tonight about some work that
I've been doing since I started work with the USGS about a year ago. I
want to start out by actually acknowledging my co-author on the talk,
Bill Lellis. Much of the work that I'm going to talk to you about
Bill's been working on for probably 20 years. So Bill's been doing this
research for a really long time. He couldn't be here tonight, so he
sent me in his place.
Like I said, I just recently started working for the USGS
about a year ago, and Bill is moving on to bigger and better things and
I've been fortunate enough to inherit a lot of Bill's research
projects. I'm really excited to be continuing his work and starting
to develop my own work.
With that, I'm going to go and get started. Just to give you a
about who we are and where we're located, we are under the Mission Area
of ecosystems and our lab is actually in Wellsboro, Pennsylvania,
which is way up here in Northcentral Pennsylvania.
We are part of the Leetown Science Center, but our lab is
actually located up here in Northcentral Pennsylvania. We're a really
small lab; there are only about 15 of us in the building. We're
located right here at the foot of the Appalachian Mountains, so it's
absolutely beautiful there.
For those of you who are unfamiliar with the research goals of the USGS under the Ecosystem Mission Area, one of our goals is to conduct research to support the DOI lands, which accounts for about a fifth of the United States. We are also interested in studying priority ecosystems, and one of the major ones of interest to us is the Chesapeake Bay and the Chesapeake Bay Watershed. We're also interested in Trust species, which includes endangered, migratory, interjurisdictional and invasive species as well as species of importance to Native Americans.
At NARL, which is our lab, Northern Appalachian Research
Laboratory, we do have a whole suite of different research projects
ranging from environmental nutrition, so we do projects on the role of
vitamins in animal health, the effects of climate and land use changes
on freshwater ecosystems, the effects of energy development on stream
ecosystems, and mainly what I'm going to be talking to you about
tonight is our work with endangered species, and in particular we've
been recently interested in endangered freshwater mussel species.
What I'm going to do is I'm going to give you guys some
introduction to what freshwater mussels are, for those of you who are
unfamiliar, and then try and highlight a couple of the different
research projects that we've been working on related to freshwater
mussels. Depending on how fast or how slow I talk, I guess, dictates
how many projects I get to talk to you about.
When I say 'mussels', the first thing that probably pops into
your mind are actually saltwater bivalves, so these are the things that
probably familiar with eating, 'bivalves' being something that has two
two shells. So these are the common blue mussel or clams that you would
expect to see on your dinner plate.
Or if you are familiar with freshwater mussels, you probably
are most familiar with the invasive species, which include the zebra
mussel and the Asiatic clam. But related to those different species are
another group of organisms that belong to the family Unionidae, and
these are the
freshwater mussels that I'm going to be focusing on this evening.
There are actually over 300 species of Unionids or
freshwater mussels in North America. The hotspots of diversity are in
the central part of the U.S. and down near the Gulf. We're not doing
too shabby over here on the East Coast with about 56 different species.
But I would say that the majority of research to date has
actually focused on the processes that are going on in mussel
communities in the center of the United States, with actually limited
research on the East Coast in the Atlantic slope. So that's one
particular area that we're really interested in.
In Pennsylvania, where I work, there are actually 65
different species. The majority of the species richness is over here in
part of the state. These are mainly the two drainages that we've
been working in lately, the Susquehanna Drainage and the Delaware River
which have substantially lower species richness, but like I said, we're
still trying to get a handle on how processes that go on in freshwater
mussel communities differ in this area.
Mussels are extremely diverse. As you can see from this
photo, they range in size from very, very tiny, so about the size of
the tip of your finger, up to, we've seen mussels that are the size of
dinner plate. So they vary in their size. They obviously vary in their
shell morphology. Some are smooth, some have ridges, some have pimples,
these big wings, so they look very unique.
Rhey can also exist in these really dense congregations called 'mussel beds'. You can get mussel beds comprised of one or multiple species, depending on where you are.
Freshwater mussels are actually of interest to us because they
are highly imperiled. So this is a graph, and you can see it's the
percentage of species on the X axis here that are either vulnerable,
imperiled, critically imperiled, or presumed extinct, and freshwater
mussels are up here on the top with almost 70% of all species listed as
threatened, and this is compared to the things that we hear about most
in the media, which I guess are probably mammals and birds and
charismatic megafauna. It's actually freshwater mussels that are
most critically imperiled organisms, and they're also ones we know very
Some suggested reasons as to why they are imperiled, there's a
whole list of them that includes climate change, habitat alteration,
pollution, invasive species such as the zebra mussel, water management
Actually, this picture here is really interesting. There's
been a historical mussel harvesting industry throughout the United
States. It's declined a lot recently because of their imperiled status,
but freshwater mussels used to be harvested. These people are actually
sitting on a giant mound of freshwater mussel shells. They used to be
harvested and their shells were used in
making buttons or as seeds for the pearl industry.
harvesting industry, like I said, has declined recently, but it still
does exist, particularly in the Midwestern U.S.
We're thinking that mussels are particularly susceptible to a lot of these threats for a variety of different reasons.
First of all, they are generally sessile. They don't move
very far. They can move, they do have a foot, but in general, they can
only move a couple of meters to, maybe in some really highly mobile
species, 50 to 100 meters. But in general they can't move very far.
They're not like a fish that just get up when things get difficult and
swim away. So basically they have to sit there and tolerate any
disturbances that come their way.
They have a complex life cycle, which I'm going to talk to you
more about here in just a few minutes. It depends on their
larvae-parasitizing host fish, so basically, anything that happens to
host fish affects freshwater mussel success.
They're also extremely long-lived. You can see from this photo here that mussels put down annual, just like trees do, so they lay down growth rings every single year. So we have the ability to thin-section their shells and figure out how old they are. Some mussels can actually live upwards of 100 years.
So one of the problems we have with mussels is because they
long, you can go out to mussel beds and there are these relict
populations that have been living there for a really long time, and you
can't really tell that anything's wrong because you can't monitor their
reproduction particularly easily. So it's really hard to tell when
freshwater mussel communities are in trouble. You get these
One thing that's really interesting about freshwater
mussels is their life cycle, so I wanted to spend a little bit of
time talking to you folks about freshwater mussel life cycle and
showing you some pretty cool pictures and some videos about how mussels
reproduce and how they're really unique. I'm just going to start off
and sort of work my way around how the mussel life cycle plays out.
Male mussels are broadcasters, so they broadcast their gametes
into the water column in these sperm balls. It's a ball that's
covered in probably several thousand different sperm. They broadcast
out into the water column. The females, which are filter feeders,
filter in the sperm. So actually fertilization in mussels is internal,
unlike most marine bivalves.
Here's a close-up picture of one of those sperm balls that I
was just telling you about. Sorry, I've got to get out of my PowerPoint
presentation to show you this.
This is some video footage we have of a male mussel releasing its gametes. You can see all of these teeny tiny little white dots are just millions and millions and millions of those sperm balls. So there's really a huge energetic investment on the part of the male and the female as well that goes into freshwater mussel reproduction. This particular individual mussel was released like this for probably 20 minutes to 45 minutes, so it's a really massive investment.
Like I said, the female mussels then filter in the sperm
and fertilization is internal. And actually, the females brood their
larvae inside their gills. Mussel larvae is called glochidia. This
picture down here are the females' gills inflated, really filled up
with all of these larval glochidia.
The females brood the glochidia for several weeks, and then
the glochidia are released and they have to spend a portion of their
life as a
parasite on a particular host fish in order for them to successfully
turn into adult mussels.
For the most part, glochidia attach to the gills of fish.
There are some species, though, attached to the skin or to the fins,
but for the most part, it usually happens on the gills.
species they use varies according to what mussel species are these.
mussel species are specialists and their glochidia can only attach to
one species or one or two species. Other freshwater mussels are
generalists and their glochidia can use a variety of different host
So you can see this picture right here is actually a picture
of a fish's gill that's just loaded down with glochidia.
Now, mussels have evolved some really cool strategies for
getting their glochidia attached to their host fish. Some mussels just
basically release their glochidia out en masse. They broadcast their
glochidia or release them out in these mucus strands, which you can see
right here. I think this is an eastern elliptio mussel. The glochidia
through the water column until they come in contact with their
particular host fish.
The viability of the glochidia, I guess, varies, but usually
for a couple of days, they are viable.
So if they don't come into contact with the fish, then they generally
There are other species that actually climb up onto the bank and spit their larvae onto the water surface. I guess that's still broadcasting; it's just a unique take on that strategy.
This is where it starts to get cool. Some mussels package
their glochidia in these packets called 'conglutinates'. Now, some
conglutinates are just sort of
run-of-the-mill packets, but others have evolved to look like food
items or invertebrates that live in the streams. Believe it or not,
this is a package of larval mussels, not a bug.
I've got some close-ups here. This is a female mussel that
has just released lots and lots of conglutinates. I say down here at
the bottom that "a single female can produce between 200,000 and 17
million glochidia per breeding season," so, again, the energetic
investment that goes into reproduction in mussels is just incredible.
Here is one of those conglutinates that looks like a little invertebrate with its eye spots that's broken open and you can see all of these individual glochidia that are spilling out of it. Again here's another close-up of all those individual glochidia, and you can actually see the hooks on the glochidia here for attaching onto the host fish.
This is my favorite. Some other mussels have evolved these
mantle lures for attracting the host fish towards the mussel. This
right here is not a fish. It's actually a piece of the freshwater
mussel. It is its mantel, so it's the little flap of skin inside its
shell that helps to create the shell. Oh, sorry about that.
This right here is a modified piece of its mantle, and the mussel will wave this in the water column to try and attract a fish towards it. And then when the fish strikes that, thinking that it's a prey item or a competitor, the mussel's gills are sticking out right in here and the fish ends up getting a big biteful of glochidia.
I've got a couple of videos here of some different mussel
lures. This is the black sandshell and this is, I guess, maybe you
say a relatively primitive lure. Basically it's just the mussel waving
its mantel trying to attract a fish towards it.
Those things that are waving, like I said, are a piece of
the skin or the tissue that lines the inside of the shell, and those
white things that look like teeth in the middle are each of the
individual gill filaments that's just filled up with all of the larvae
This is an image of the rainbow mussel. I'll play this one a couple of times because it's relatively quick. Its lure actually looks like a crayfish moving. I think this one is really cool because it's not just the mussel waving its lure. There's an actual behavior there. I mean, that mussel is pulling itself forward with its foot to try and mimic a crayfish's behavior there.
This is a video of yellow lampmussel. Its mantel lure
looks like a fish swimming in the water there. You can see, again,
these right here are the mussels' gills, so anytime a fish comes in and
tries to strike at that lure, it's going to get a mouthful of glochidia
from that mussel's gills.
This is the orange nacre mussel, and this is actually a little bit different. This is a super conglutinate. Basically, what this mussel does is it sends out a big, long fishing line. At the end of that fishing line is a giant package of glochidia called a 'super conglutinate'. So it waves it out in the water. Again, it looks like a fish or maybe a worm. It's got eye spots there, so it's designed to attract a host fish.
And then the final mechanism that mussels have evolved for
transferring their glochidia to a host fish is this host capture
mechanism where the mussel actually physically grabs a hold of the
fish, holds onto it, and off-loads its glochidia onto the fish.
And I've got a video of that. This is the northern riffleshell
mussel. So there's the mussel just hanging out in the sediment there,
and siphoning. There's its host fish, which I believe has a lot of
Heather Galbraith: And there
we go. So it clamps down on the fish's head, and you can watch
in slow motion as that mussel just starts pumping glochidia out onto
Now I can't imagine that the fish likes it, but they survive.
I don't know that I want to say it doesn't hurt the fish necessarily,
the fish does survive.
Heather Galbraith: And
that's done, the mussel lets go, and the fish is free
Heather Galbraith: A
little shell-shocked, but he's free to go, right?
Actually, if you did catch
it... Let me go back. Check out the teeth on that guy. The mussel
shell actually has these spikes on it to help hang on to the fish and
hold it there while it's off-loading its glochidia.
So those are just some of the unique strategies that mussels
have for infecting their host fish with glochidia.
Now, the glochidia spends several weeks to several months
attached to their host fish. As of right now, we don't know of any
necessarily negative effects that glochidia have on the host fish. When
people think of parasites, they think, 'Oh, that's going to hurt
the fish,' but to our knowledge right now, there are no necessarily
detrimental effects to the host fish of having mussel glochidia
After the glochidia have spent their requisite time attached
their host fish, they then drop off as these microscopic juvenile
mussels, I don't know, maybe about 150 microns, so they're still really
at this stage. They drop off and they live in the sediments.
very little about what happens to juvenile mussels until they
eventually grow up into this adult stage, so what habitat they prefer,
whether or not they're actually living in and amongst adult mussel
beds, we really know very little about this whole juvenile stage in
You're probably thinking at this point, 'OK, mussels,
they are threatened, they do lots of cool things to have babies, but
really cares?' Well, mussels are actually considered by some to be
ecosystem engineers, so they actually do really important things in
First of all, they're very powerful filter feeds, which you
can see up here in this picture. This tank has turbid water in it with
no mussels. This tank had the same turbid water in it with mussels, and
in about 55 minutes those mussels were able to filter all of the
particulate matter out of that water. So they are extremely strong
They do move around, so they help oxygenate the sediment to prevent anoxia and hypoxic conditions. They excrete nutrients, which helps facilitate local algal communities. They biodeposit feces and pseudofeces, so they're contributing organic matter to the ecosystem, which actually serves as the basis for food webs.
Their shell also provides unique habitat to algal species
and macroinvertebrates. And when I say 'unique', I mean a different
of rocks. If you compare the invertebrate and algal communities
on a freshwater mussel, they actually differ from the algal and
invertebrate communities on rocks. So freshwater mussels are doing
something different in the ecosystem.
As far as what mussels do is concerned, we know two things. We
know that mussel diversity is important and mussel biomass is
important. So as you increase the number of mussel species in a
community, which is species richness here on the X axis, the things
they do in the ecosystem actually increases.
Here, this is algae on the mussel shells. This is bugs on
the mussel shells. And you can see, as you increase the number of
species, the algal biomass increases and the invertebrate biomass
species diversity is important in mussel beds. But biomass is also
important. As you increase mussel biomass,
the nutrients that they contribute to the ecosystems also increases.
So this is just an example of the kind of biomass of
freshwater mussels you can see in a community. This is one of the
mussel beds that we worked in while I was doing my graduate work in
Oklahoma, and in a 300-square-meter stretch of river, there was the
equivalent of about four elephants' worth of mussels sitting there. So
the biomass can be extremely high in these mussel beds, which makes you
think that the effects that they're having on freshwater ecosystems can
also be really large.
One of the mussel species that we've been doing a lot
of our research with is the eastern elliptio mussel, Elliptio
complanata. It's highly
abundant. It has extremely high biomass. It's mainly found along the
Coast of the U.S. It's actually not considered imperiled, to my
knowledge, along most of its range. It's fairly abundant.
But I want to tell you kind of a cool story that goes along
elliptio. In some freshwater mussel surveys that we did in the
Delaware River about 10 years ago, we did snorkel surveys of about 120
miles of the entire Delaware River, which, I think, to my knowledge, is
the largest freshwater mussel survey that's been done to date. I
might just be making that up. But I'm pretty sure it is.
So we did this freshwater mussel survey in the Delaware River,
and this is just to illustrate how abundant the eastern elliptio mussel
can be. This is the list of species that we found in our survey. The
eastern elliptio comprised about 98% of all the freshwater mussels
in the Delaware River.
On average, we found about 165 eastern elliptios per hour of
search time. What that translates to is if you were to just drive
over the Delaware River right now, pick any random spot in the river
and get in, it would take you about 22 seconds to find an eastern
elliptio mussel. So they are that common.
Now compare that to the next most-common mussel, it would take you 24 minutes. So, I mean, really they are almost an order of magnitude, more abundant. And then if you look at the dwarf wedgemussel, which is one of the endangered species that we've been working with in our lab, it would take three weeks to find them. So there are elliptios all over the place.
What we did then is we translated our survey effort into an
estimate of what elliptios are contributing to the ecosystem in the
Delaware River. We figured that, based on our numbers, there are
approximately two million eastern elliptio mussels per mile. Now if you
translate that into biomass, that's 32 elephants
per mile of river.
If you look at the filtration capacity, so you multiply all those mussels by the volume of water that the eastern elliptio can filter, we're looking at 16 to 48 million gallons per mile per day of water filtered by freshwater mussels. Basically, every drop of water in that Delaware River is passing through a mussel's gills at some point.
We translated that into sediment removal capacity. They
have the potential to remove over a half of ton of sediment per mile
per day. So this is a really phenomenal contribution to river
in ecosystems. Like I said, elliptios are dominant and abundant in the
Now, Pine Creek is the creek that runs right outside our lab
in Willsboro and it's part of the Susquehanna River Basin. We also have
eastern elliptio in Pine Creek as well. While we were doing this
we started to notice that in the Delaware, we were finding a lot of
baby eastern elliptio mussels, and it dawned on us that we spend a
lot of time in Pine Creek and I don't think we have ever seen a baby
eastern elliptio mussel.
So we went and looked at some survey data that we had from
Pine Creek, and that's what this graph is here. This is mussel length
along the X axis and the percentage of the population on the Y axis.
And you can see the Delaware River, which is this blue line
here, you get a pretty wide distribution of size ranges in elliptio in
the Delaware. There are small individuals, but most of them are
larger, and then few are really, really big individuals.
If you look in Pine Creek, though, all of the mussels are big.
You're missing all of these small mussels. So we started wondering, 'Is
there a recruitment issue? Are mussels not reproducing in Pine Creek?
Does this go farther than Pine Creek?'
So what we did is we did some mussel survey work in 2008,
so about two years ago, and we picked 13 different sites throughout the
Susquehanna Drainage that have historically had abundant elliptio
populations. We went to each of those 13 sites and we collected mussels
and we thin-sectioned them to age them and we did detailed quantitative
survey work to try and determine if there were small elliptios in each
of these beds.
And what we found out, we found the exact same thing as we did
in Pine Creek. At each of these 13 historically abundant eliptio sites,
there weren't any babies. So we started scratching our head and saying,
is this happening?" Elliptio is so abundant in the Delaware River. Why
are there no babies in the Susquehanna Drainage?
So we started thinking that maybe it was a function of their host fish and maybe the host fish that elliptio is using is not in the Susquehanna Drainage anymore.
So what we did is we tested 38 different species of fish. We
put the fish in buckets, dumped in a bunch of elliptio glochidia,
them all around, and then monitored them. Everyday we would siphon out
the bottoms of the buckets looking for either glochidia that had
off or juveniles that had transformed, trying to identify what the host
fish that elliptio is using.
We tested all of these fish and had no successful
transformation. The only fish that we tested where we actually
successfully got juvenile mussels were these fish listed here, the
American eel, lake trout, brook trout, and then two species of sculpin.
We know that lake trout are not native to the Susquehanna, so it doesn't make sense to us that the lake trout would be the natural host fish species for elliptio in the Susquehanna Drainage. So in our mind, we've kind of moved the lake trout out.
We also know that although brook trout were historically
abundant and sculpin are still abundant, they're not found in locations
where freshwater mussels are found. These are typically more headwater
species, and their ranges don't seem to overlap with eastern elliptio
Which basically leaves us with the American eel, so right now
our working hypothesis/theory is that eastern
elliptio uses the American eel as its host fish or historically has
the American eel as its host fish.
For those of you who are unfamiliar with the American eel and its life cycle, eels used to be highly abundant along the entire Atlantic coast. They accounted for upwards of 25% of the fish biomass in a lot of rivers along the East Coast.
Eels are in trouble, mainly because of
impoundments and their complicated life cycle. All eels reproduce in
the Sargasso Sea, so the adults migrate from freshwater down to the
Sargasso Sea. They have these leptocephalus larvae that floats at sea
about a year until they drift into the estuaries as these glass eels.
The glass eels then migrate up into freshwater systems. They
develop into this yellow eel phase and they live in freshwater for
about 15 to 20 years until they become reproductive silver eels again
make their migration back to the Sargasso Sea.
Unfortunately, a lot of the impoundments in some of the major
rivers have decimated eel populations along the East Coast. The
glass eels are unable to migrate out over these giant dams, so they
get upstream, and any adults that are already upstream end up getting
killed in the hydroelectric turbines on their way back into the
Sea. So basically eels have been essentially eliminated from the
So our working hypothesis right now is that because
the eels have been eliminated from the Susquehanna, there is no host
elliptio's glochidia to attach to, and therefore we are losing out on
We have been working on an experimental eel reintroduction project. We've been working with the U.S. Fish and Wildlife Service and the Audubon Society, and we've been reintroducing American eels in two rivers in the Susquehanna Drainage.
We've been introducing all different life stages. We've been
collecting adults. Fish and Wildlife Service is really good
at this. They do most of our eel collection for us. They collect
adults for us down in the lower Susquehanna Drainage. We bring them
lab and we've been PIT-tagging them, so we put these little electronic
tags under their skin. They each have a unique identifier in them, so
if anybody catches an eel, we can scan that tag and figure out which
eel it was, how much it used to weigh, how long it was, etcetera. So
we're stocking tagged eels.
They're also collecting elvers at the base of the Conowingo Dam on the Susquehanna in these eel traps, and then they're trucking the elvers up into Buffalo Creek and Pine Creek and we're releasing elvers. And then they've also been collecting glass eels down near Ocean City and bringing them to us up in our lab, and we've been rearing them up to the elver stage and then stocking them in Buffalo Creek and Pine Creek. This past year, I think we raised about 100,000 glass eels in our lab and stocked those between the two different creeks.
We've had a lot of public involvements. We've had some press
releases. The folks in and around these creeks are really excited about
this. We get lots of stories about how they remember when they were
kids they used to catch eels and they remember there being historical
abundant mussel populations.
So the public's actually been really
good and really fired up about our introduction efforts. We've been
handing out these little cards with fishing
licenses, telling fishermen, 'Please, if you catch an eel, give us a
call. Let us know where you caught it, if it had a tag on it...' So
been a lot of fun.
Our goal for this project was to introduce about 45,000 eels
into Buffalo Creek, 50,000 eels into Pine Creek, and then to do this
over the course of three years. Right now, I think we just completed
our second year of eel-stocking, so we have one more year to go. I
think we're fairly close to reaching our stocking goals.
So what we've been doing is we've been monitoring both the
fish communities and the mussel communities, and this is a long-term
project that's expected to go for 10 years. We're interested in how
reintroducing the eels is going to change the native fish
communities that are in these rivers, but we're also really interested
in whether or not stocking the American eel is going to help facilitate
freshwater mussel reproduction in these rivers.
Like I said, we've nearly reached our stocking goal and we're
only in the second year. This past summer, we went into both of the
rivers and did some electrical shocking, and we shocked up quite a few
eels. Some of them, actually, their gills were infected with
elliptio glochidia, which was promising to us, so we're really hopeful
and really excited about that.
We had barely high eel recapture success, which was
pleasantly surprising to us. I mean, these are migratory species, so we
weren't really sure what was going to happen when we dumped a bunch of
eels in the river, if they were all going to head north or if they
were all going to head south. But it seems that they're actually
staying put for the most part. We had shocked a 75-meter stretch of
Buffalo Creek and actually
came up with about 400 eels in 75 meters. So they're staying where we
put them, which is right over the top of the mussel beds, which is
I guess what our big question is, can we restore successful elliptio reproduction in these experimental rivers? And then we need to start thinking about, OK, well, long term, this is not necessarily sustainable, hauling eels from below the Conowingo Dam up here. Is there a more sustainable way to reintroduce the eel back into its natural habitat to help facilitate freshwater mussel reproduction?
So we've really been thinking about this in relation to the
Chesapeake Bay and water quality. This is a publication that came
out on "6 Most Cost-Effective Ways to Reduce Nutrients" in the Bay, and
wastewater treatment plant upgrades, animal feed adjustments,
nutrient management and enhanced nutrient management, cover crops,
And what we're really interested in is, can we add a seventh item to this list, which is just simply restoring natural riverine ecological services. We don't know the answer to that, and our lab is trying to start to peel off the layers and address this question.
Actually, almost all the work that I just presented to you was
work that has been done in the last 10 years. So we've learned a lot of
stuff in just 10 years, and so we're hoping that as we slowly start to
figure out more about the host fish requirements of elliptio, more
nutrient dynamics in and around freshwater mussel beds, that we can
start to make better management recommendations regarding freshwater
mussel communities and American eels.
With that, I'm happy to take any questions.
Yes. Do I get to pick who...sorry. Yeah.
Audience 1: You were
saying that the dams are one of the impediments to the whole migration.
So is there any talk about somehow modifying the dams to allow the eels
to go back and forth?
Yeah. There are fish ladders in place in a lot of these dams for other
migratory fish like shad, and we don't know why, but eels don't seem to
This is a hot research area right now is trying to
figure out how to get eels up and how to get eels back down stream. A
lot of the dams on the Susquehanna are up for their re-licensing soon,
so there's talk about whether or not
it should be mandatory that they have to install eel ladders on their
dams for their re-licensing. It's sort of an up-in-the-air political
now. But that's a good question.
Yeah. Yeah, go ahead. Yes, you. Oh, sorry.
Audience 2: Mike Hamm.
I have a two-tier question.
You showed in your early slides harvesting of mussels, including the
if so, what are the chances of a shore introduction...? The
second question is, would it help clean up Chesapeake Bay by having a
greatly enhanced mussel populations in the feeder river?
Heather Galbraith: I'm
sorry, in what river?
Audience 2: In the
feeder river. In other words, by cleaning up particulate matter in the
tributary to Chesapeake, would that help reduce the... in the Bay?
Let's start with your first question, which was mussel harvest. The
mussels that have been typically harvested for the pearl and the
button industry are thick, heavy-shelled mussels, which probably would
include elliptio. A lot of the harvesting went on in the Mississippi
Drainage if elliptio does not occur in the Mississippi
What we do know, though, is that there was historical very
heavy Native American use of elliptio on the East Coast. There are a
of relict sites where you can go and just see these giant pits that
are aligned with eastern elliptio shells, so Native Americans used to
collect shells and line pits and then used them to drain their corn in
these pits. Whether or not they actually killed the mussels to do this
or they just collected already dead shells, I don't know if we know the
answer to that. We really don't have a good estimate of what historical
elliptio populations looked like.
Question about whether or not we can start restoring elliptio
populations in the tributaries to help Chesapeake Bay, I don't have an
answer to that. But that is what a lot of the research in our lab
is looking at.
Freshwater mussels are long-lived and they have a very slow
growth rate, so we have to try and figure out the best way that we
could sustainably burrow and then stock elliptios. And then trying to
figure out what their historical densities were that we would stock
them back to is another question.
Like I said, we're still trying to figure out the intricacies in our lab of what it is that elliptio is actually going to do as far as ecosystem contributions is concerned by restoring these populations.
We're pretty certain that freshwater mussels are going to
serve as a nutrient sink that we can use elliptios to help ameliorate
some of the nutrient problems. But, I mean, they also excrete
too, like any other living organism does, so we're really trying to get
at the nutrient dynamics question of what exactly is elliptio is
doing to nutrients in riverine systems.
I'm not sure if that answered your question or not. Yeah.
Audience 3: Hello.
Heather Galbraith: Hi.
Audience 3: In the planet Earth, Heather, 10% of the planet Earth is freshwater and 90% is saltwater. In realization due to what we've seen tonight, a species we saw tonight, is the rapid growing of species that transition from saltwater to freshwater. The evolution of this species has gone a long way, actually more quicker than saltwater, to make that major change.
Can this species unite with water pollution, 40% of the lakes
and rivers included in the United States, do you people see
what any change in the size of how these species will change
into a type to be able to live near deep?
Yeah. That's a whole other line of work that we're doing in our lab
that I didn't talk to you about tonight.
One thing that we're really interested in is the physiological requirements of freshwater mussels, how they tolerate stress, how they respond to stress, and then how we can manage our rivers to maximize human gain and minimize stress on aquatic organisms.
I don't know the answer to your question. I don't know if
we've pushed mussels beyond the point of recovery. I hope not, because
they're my favorite animal in the whole world. But they're resilient
and they've lasted a long time in
evolutionary history. Hopefully we'll be able to figure that out.
We're working with the federally endangered dwarf wedgemussel
right now, which is in the Delaware River.
That's a highly managed river. I mean, it can go from flood stage to
absolutely bone-dry in a matter of 24 hours.
There is a federally endangered mussel there, so what we're trying to do is figure out how it responds to flow stress, how it responds to temperature stress, and then manipulate the way that the water is managed in that river and make predictions about how that is going to affect the dwarf wedgemussel's habitat. So we are taking these things into account as far as water management is concerned.
Audience 4: How long
is a typical eel? And do they come in different colors?
Yeah. As they
grow, their color changes. As glass eels, they are clear. When they
transform into the elver stage, they're kind of just a plain brown. And
then they transform into the yellow stage, and they're actually yellow,
that's the stage that they spend most of their life in.
They vary in size, but they can get fairly large. I think
or four feet is probably maximum. I was in the Delaware River two weeks
ago and had one that was maybe two-and-a-half-feet swim right
me. That was a little scary, but it was pretty cool. It was the first
time that ever happened.
And then after the yellow phase, they transform into the
silver eel stage and they develop this really silver hue as they
migrate downstream. They vary in size. The glass eels are teeny, teeny
maybe two inches, and then they've got a fairly fast growth rate. Like
I said, they grow up to be about three feet.
Audience 5: Do you
have any information about mussel populations in the Potomac Watershed
or Roanoke, Virginia?
Heather Galbraith: Off
the top of my
head, I don't, but we've been working with Maryland's DNR and they've
got some crazy, crazy data on mussels and vertebrates, algae, you
name it, and they've got these long-term monitoring sites that they
track of. Do you know how far back their data is? Ten or 20 years.
I think they've got this rotation where they would have all these different sites and every year they'd pick different sites to monitor. So I would check out their website, because I bet you can get a lot of good information on the freshwater mussels in the Potomac.
Audience 6: Why do the
mussels, why do they need certain fish?
Audience 7: ...
Heather Galbraith: We
don't. That's another part of the freshwater mussel life cycle that I
think that's really understudied. We don't know what it is that makes
particular species specialists and others generalists. We're assuming
that there's some sort of recognition protein on the surface of the
fish that has to match up with something on the glochidia. I don't
we know the answer to that. That's a really good question.
Audience 8: But my
question is, more generally, what ... reaction do we get from
the fish to ensure...?
Heather Galbraith: I
don't even know if we know the answer to that question.
As far as I
know, there is no literature saying that anything actually transfers
from the fish to the glochidia. Now, that doesn't mean that it doesn't
happen. I don't think we know the answer to that. We just know that
they have to latch on, they have to spend a portion of their life
there, and doing so somehow triggers some sort of developmental gene so
that they make the transition from glochidia to juvenile.
Audience 9: Just
curious as to how the mussels tolerate high-intensity rain events like
we just had.
Yeah. Some do and some don't. Our little endangered dwarf wedgemussels,
which are maybe an inch long, they don't tolerate flow very well, so
they get very easily blown downstream.
Now, other species have very heavy shells and can bury way down into the sediment. I mean, we're talking like two feet. Some of these mussels can bury down really, really far. So those species tend to fair out fairly well.
It all depends
on microhabitat, too. I mean, if you're a little mussel and you're
lucky enough to find a nice flow refuge tucked underneath a rock, you
be OK. If you're laying out in a pile of sand, you're probably headed
Anne Kinsinger: OK.
Heather Galbraith: All
right. Thank you so much. This has been really enjoyable.
Title: Stranger than Fiction: The Secret Lives of Freshwater Mussels
Within the rivers, streams, and lakes of North America live over 200 species of freshwater mussels that share an amazing life history. To metamorphose from larvae to adult, the mussels must pass through a parasitic phase on the gills of freshwater fish. To trick the fish into accepting their larvae, female mussels have developed a complex array of lures and baits to attract and fool their unsuspecting hosts. This talk will explore the fascinating reproductive biology and ecological role of one of nature’s most sophisticated fishermen.
Location: Reston, VA, USA
Date Recorded: 9/7/2011
Audio Producer: Melanie Gade , U.S. Geological Survey
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