Zebra Mussels

Invasive species have earned their bad reputations. English sparrows compete with native birds from Newfoundland to South America. Australian brown tree snakes are well on their way to exterminating every last bird from the forests of Guam. And I don’t think anyone can fully predict how Columbia’s rivers will change in response to drug lord Pablo Escobar’s escaped hippopotamus population.

While our climate protects us from rampaging hippos, the Northeast has plenty of exotic species in its waterways, including some that cause serious damage. Zebra mussels are possibly the most familiar of these. They were first discovered in Lake Champlain in 1993 by a precocious 14 year old, Matthew Toomey, who recognized one based on an identification card he’d received at school. Since then, the mussels have spread throughout the lake and their effects have been well chronicled. They kill native mussels; coat surfaces with razor-sharp shells; foul anchor chains; block water intake pipes; and steal plankton and other food from native fish.

With all of the negative press regarding the species, you might find it jarring to read anything positive about zebra mussels, particularly anything written by a biologist. Discussing positive effects of invaders is practically taboo. We don’t speak ill of the dead; we never praise invasive species. I’m certainly not advocating zebra mussel propagation, but like them or not, they are here to stay. These mussels are an important part of European ecosystems, and it’s interesting to consider what native organisms benefit from their presence.

Zebra mussels are voracious filter feeders. A single mussel can suck a liter of water through its body daily. All of this filtration removes plankton and particles from lake waters, but these particles don’t just disappear. The phrase immortalized in Minna Unchi’s children’s book Everyone Poops applies. Along with excrement, unpalatable particles rejected by zebra mussels are mixed with mucus and dropped on the lake floor. Mussel excrement and mucus might not sound appetizing, but it’s a smorgasbord for lake floor invertebrates and fish.

In addition to covering rocky surfaces, zebra mussels often carpet lake floor sand and silt. Formerly soft sediments that provided foraging grounds for sturgeon and other fish can become a tangled mess of living and dead mussels several inches thick. Not surprisingly, fish such as log perch, bullhead, and sculpins have difficulty finding their insect prey amongst the clutter of shells layered over their sandy habitats. When given the choice, juvenile sturgeon avoid zebra mussels and spend their time on sandy or rocky areas.

What’s bad for these predators may be good for their prey. To figure out just how good or bad zebra mussels could be for Lake Champlain invertebrates, we ran experiments under 30 feet of water in sandy areas of Appletree Bay. When my colleagues Ellen Marsden, Mark Beekey, and I fenced off lake floor patches with and without zebra mussels, twice as many invertebrates colonized areas with zebra mussels. More species also moved in. After a month, the number of species in experiments with added mussels doubled and included some species more typical of rocky lake floors. Nooks and crannies between zebra mussel shells seem to act like very small, natural shark cages that protect tiny insects from hungry fish. And when we placed insects and fish in aquariums, far more invertebrates survived with zebra mussels than without.

On balance, I would rather have a lake without zebra mussels than with them. But unless ways are found to eliminate them, it will remain important to understand how they affect native species. In Lake Champlain, the zebra mussel population grew rapidly and has since fallen below peak numbers, as often happens with this species in a new location. This month, for the first time in recent years, we pulled up a lake floor sample in Burlington Bay that entirely lacked zebra mussels. Perhaps we are reaching a new equilibrium?

Declan McCabe teaches biology at Saint Michael’s College. His work with student researchers on insect communities in the Champlain Basin is funded by Vermont EPSCoR’s Grant EPS-1101317 from the National Science Foundation.

This article was written for Northern Woodlands Magazine's Outside Story and first published on October 5 2015

The photograph of zebra mussels was downloaded from Wikimedia Commons under a CC BY-SA 3.0 Creative Commons license.

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Keeping it clean downstream

In peaceful streams, aquatic macroinvertebrates such as crayfish, stoneflies, and caddisflies travel over and under submerged rocks, foraging for other invertebrates, leaves, and algae. When rain falls, their world turns upside down.  At first only the surface is disturbed, but before long, runoff reaches the stream and increases its flow many fold. Silt and sand blast every exposed rock surface. At peak flow, boulders are propelled downstream by powerful currents.

How do small creatures survive such crushing chaos? They hunker down. Water-filled nooks and crannies extend deep below streambeds and far beyond river banks. These deep interstices provide a safe haven even while turbulent water pulverizes the riverbed, comparable to a storm cellar in a tornado.

Storm water has great destructive potential, but it also flushes and cleans aquatic habitats. Riverbeds are rejuvenated when sediment is flushed from the bottom and deposited on flood-plains. Algae and bacteria grow back rapidly on the scoured rocks. Macroinvertebrates climb out of their cellars and return to foraging. The cycle of storm, recovery and regrowth is the natural state.

You can see the effects of this cycle yourself by looking at river rocks. In a healthy stream, you’ll find rocks perched on other rocks, with the streambed visible under the water, and little silting. Although, just after a storm, the rocks may be scoured clean, they’ll soon develop a slimy covering of algae, and host a diversity of tiny creatures.

In polluted streams, however, you’re likely to find something different. River rocks may be embedded in silt, and when you pick them up, you’ll find that they’re wearing bath tub rings, with algae only growing on the upper half.

Poorly planned development disrupts the cycle of streambed renewal. Where stream banks are bare, erosion can be a big problem. Soil lost from over-grazed or over-cropped land ends up in the water, where it plugs the streambed nooks and crannies. Imagine a concrete truck unloading through your window, and filling your home with a solidifying mess. Only the hardiest of invertebrates survive these conditions, and the whole riverine food chain can be affected.

Traditional paving and buildings also create problems, as impervious surfaces dramatically increase the volume of water sent straight to streams. Formerly small, cool, perennial streams can become torrents of unnaturally warm water. Channels become deeper and eroded materials are deposited in stream beds. Since rain doesn’t reach the ground underneath the pavement, ground water can become depleted, and the streams may run dry between rain storms.

Farming or urbanization won’t disappear, but there are ways to intelligently develop landscapes to better protect streams. For example, St. Michael’s College, where I work, has installed a system of curbed parking lots connected to rain gardens. These are shallow, gravel-lined depressions, strategically planted with vegetation that tolerates occasional submersion. The rain gardens easily absorb water from typical rainstorms and can even contain all of the water dropped during 100-year storm events. St. Michael’s has also replaced many impervious sidewalks with attractive, pervious, bricked footpaths. Roof water from the gymnasium runs into deep gravel beds. Runoff from recently constructed roads collects in an underground tank. All of these systems drain gradually into the ground, drastically reducing the downstream potential for erosion. The recharged groundwater keeps a small perennial stream flowing to the Winooski River even during dry spells.

There is no doubt that people affect stream macroinvertebrates and the fish that they sustain. We do, however, have the choice to protect our streams by thoughtfully managing our impacts and reducing erosion in urban and agricultural settings. With respect to Joni Mitchell, there’s a lot of room for ingenuity between paradise and a paved parking lot.

Declan McCabe teaches biology at Saint Michael’s College. His work with student researchers on insect communities in the Champlain Basin is funded by Vermont EPSCoR’s Grant EPS-1101317 from the National Science Foundation.

This article was written for Northern Woodlands Magazine's Outside Story and first published on August 3 2015

The stonefly was photographed at Saint Michael's College by Erin Hayes-Pontius and is available from Wikimedia Commons under a CC BY-SA 3.0 Creative Commons license.

© by the author; this article may not be copied or reproduced without the author's consent.

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Flat Stanley and the Centipede

Biologists sometimes field questions about a “huge scary bug” that appeared in someone’s home or worse yet on their person. Most turn out to be benign organisms that ended up in the wrong place. For me, the most common questions come in July, when male dobsonflies emerge from the Winooski River and often end up crashing into windows on the Saint Michael’s College campus where I teach. The males have impressive mandibles that look scary but are harmless to people.
Recently however, one of these questions did actually involve something dangerous. One morning I received a call from a friend and grade school teacher, who explained that she had managed to corral a very large and intimidating centipede in a plastic container at her school. I immediately emailed her a photograph of a house centipede, fully expecting that to be the end of the discussion. House centipedes commonly attract the attention of teachers and home owners. They frequently get trapped in the sink at my children’s school, and I discreetly liberate them so that they can eat real pests. However, in this case, “house centipede” was not the correct answer. I asked if the arthropod was slow moving and dark, thinking that perhaps she had found a stranded hellgrammite. No, she said, it was fast. This was getting interesting!

My friend described a centipede that was black and orange at the front, with a forked “tail” and yellow legs. Its most surprising feature was its size, a full six inches long. At this point, I asked for a photograph because the insect sounded like nothing I had encountered in Vermont. From the photograph, I determined that it was most likely a giant desert centipede (Scolopendra heros). That settled the first question, but left still many others unanswered. The school principal wanted to know if the centipede was dangerous. Were there likely to be more lurking about? Should he shut down the classroom? How does a desert centipede end up in Vermont?

I reassured them that it was unlikely to find even one such centipede in Vermont (and then less reassuringly suggested that, because one was found, they keep their eyes open). I informed the state entomologist and sent him photographs. I learned that desert centipedes give particularly nasty bites. In some cases, they can cause renal failure and even death. While death by centipede isn’t a common way to go, even in the desert, this species was certainly due some respect.

I guessed that the centipede may have come up from the desert southwest in packaging material, or perhaps through the pet trade. The truth was more surprising.  The school in question, like many Vermont schools, uses a children’s book called Flat Stanley to combine reading skills with art, geography, and just plain fun. Because Stanley is flat, he can be mailed in an envelope, and many children in schools across the world make their own Flat Stanleys and send them to friends in other places. Their friends photograph Stanley in interesting locations and return him along with local souvenirs. When my son did this, we sent Stanley to Ireland, Cyprus, and Australia.

Stanley was sent by my friend’s student to an aunt in Texas, and she mailed him back with Texas souvenirs.  The package included a map of Texas, a length of rope representing the horn span of a Texas longhorn, a piece of prickly pear cactus, and a Ziploc® bag with a hole chewed in the corner labeled, “DO NOT TOUCH – CENTIPEDE.”  Why one sends a dangerous centipede (or any centipede) through the mail is a mystery, but it certainly happened. While I can’t imagine that this centipede would establish in Vermont even if dozens were sent, it underscores the continuing need to educate the public about the dangers of moving species to new locations.

On a positive note, the school has added the now dead, preserved centipede to its invertebrate collection for classroom use. I think that speaks very well for the school that the students will learn valuable lessons from Flat Stanley’s travel companion. Perhaps it will inspire some budding entomologists?

Declan McCabe teaches biology at Saint Michael’s College. His work with student researchers on insect communities in the Champlain Basin is funded by Vermont EPSCoR’s Grant EPS-1101317 from the National Science Foundation. This article was adapted from the Newsletter of the Vermont Entomological Society and most recently circulated by Northern Woodlands Magazine's outside story.

New semester; snorkeling; insect identification; and statistics!

A new semester; new students; and an 85 F temperature forecast for lab.  It seemed like a perfect opportunity to really experience Lake Champlain.  I bought out all of the remaining masks and snorkels from a certain local store and we were ready to go.

My customary first lab in Community Ecology has been to test the species area relationship.  It seems like a simple enough concept: bigger area - more species, but the concept underlies important conservation biology topics such as reserve design.  The lab also provides an ideal entry point to community ecology.  Bigger areas do tend to have more species, but also a mathematical inconvenience: there are also more individual organisms.  Imagine any community with some finite number of species.  We sample 1 individual and we automatically have sampled 1 species.  As we sample more individuals we also sample more species.  Therein lies the mathematical problem: do larger areas have more species for some biological reason.....or is it just because we sampled more individuals?

On cool September days we typically wade into Lake Champlain in chest waders.  But the warm weather this year was perfect for snorkeling.  So in we went!  Snorkeling or wading, the procedure is simple enough: Find submerged rocks of diverse sizes, net them, measure them, and identify all of the attached invertebrates.

The lab has all of the ingredients necessary for an excellent learning experience: field work; sampling real communities; insect identification; data generation; analysis; writing; and the opportunity to get wet in Lake Champlain on the second day of a new semester was icing on the cake.  This year yielded a bumper crop of very tiny zebra mussels along with 24 other invertebrate species.  

By now there are 22 students writing lab reports based on the data set.  They have learned how to deal with the mathematical sampling issue using rarefaction, how and why to log transform their data set, and how to use linear regression to measure the strength of the relationship between rock area and the number of species sampled.

I'm looking forward to reading the lab reports and moving on to another successful semester in Community Ecology!

Aquatic insect identification......in your pocket

Science teachers are always on the lookout for the next idea to immerse students in hands-on science.  Collecting, identifying, and analyzing macroinvertebrate communities in streams may well be one of the most accessible and fun ways to literally immerse students in science.  Streams are ubiquitous habitats and students are often surprised to see the fascinating organisms that can be see by just picking up a rock or two.  And who doesn't enjoy cooling their feet in stream water on a hot day?

Figure 1.  Screen shot from Iphone app.         

Simply sorting invertebrates into ice-cube trays by type and quickly estimating the number of species is an easy way to get started.  Number of species is the first component of diversity.  Comparing the number of species found in two streams provides an excellent ecological lesson or could be the basis for a science fair project.    Saint Michael's College Biology students in my Community Ecology class take it several steps farther than that.  And of course they should take it farther; they are in an upper-level biology course.

Many students are interested in identifying the organisms they collect and professional taxonomic keys are readily available.  Comprehensive family-level keys designed for the mid west can be downloaded for free and work reasonably well for fauna of the north east.

Vermont EPSCoR has made an even easier tool to help with identification. Most streams and ponds host only a small subset of the organisms found in the comprehensive keys.  Using comprehensive keys requires long hours of reading detailed descriptions of arcane morphological descriptions to eliminate the large majority of organsism found in the key....but absent in your specific samples. The new tool focuses only on the organisms previously found in specific streams.  This means that a high school student collecting macroinvertebrates for the first time can identify them more accurately and in a fraction of the time it would take using traditional keys.

Figure 2.  An organism found in Brewster River.

We started by making web sites tailored to the few streams and ponds where we and our collaborating high schools sampled.  The list of streams and ponds has since expanded to include 78 sites in Vermont, New York, and Puerto Rico.  Each web site contains roughly 10 to 20 organisms making it possible to identify 95% of the organisms found at a particular site.  

Computer Science students at the University of Vermont have taken the tool one step further by developing an Iphone app.  The app can be synchronized before field work to load images from the web directly onto an Iphone.  The app can then be used at remote fields sites with or without a cellphone signal.

Students can collect an organism from Brewster River in Jeffersonville Vermont for example, pull out their cell phones or Ipads, and compare the catch of the day to a gallery of photographs of organisms found at that site (Figure 1).  A quick click on an organism's photograph reveals it's name and identification tips (Figure 2).

The web pages and Iphone app are based on a series of 138 mini web pages called templates that represent 138 different organisms that we have found in our stream and pond study sites.  The templates are like Lego bricks that can be used and reused in different stream and pond web sites.  At this point the bulk of the work has been done and it takes little time to create a new web page for a freshly sampled stream.  We can also rapidly add organisms to existing stream sites.  All new information is passed onto Iphones by synchronizing with the web sites.

I hope that this new tool can lower the taxonomic barriers a little bit and make working with macroinvertebrates in aquatic habitats a little easier for a tech-savvy generation. 

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Making trees: how are mammals related?

Figure 1.  An 1837 sketch from Charles Darwin's notebooks.

How do scientists tell what organisms are related to other organisms?  It's not easy to go back in time and visit with the common ancestor of chimpanzees and humans for example, so we need some approaches to place organisms into natural groups.  This was precisely what the Swedish biologist Carl Linnaeus first attempted in a 12 page publication called  Systema Naturae in 1735.  By 1758, the tenth edition included descriptions of 12,100 plants and animals.

Modern biologists are just as concerned with appropriately grouping related organisms as was Linnaeus.  Since the time of Darwin we have used tree diagrams to represented the relationships among related organisms (Figure 1).  Humans and chimpanzees for example can be placed on the tips of branches that can be followed back to a larger branch that represents the ancestor we share in common.  To see how we are related to monkeys, bats, dogs, or sharks, we'd have to track back closer and closer to tree trunk and then trace paths back out along more distant branches.  The length of that branch-tracking journey represents the distance of the relationship between any two organisms on the tree.

When I started teaching evolution at Saint Michael's College I wanted an authentic activity that students could complete to make an actual evolutionary tree.  It's quite frankly boring to simply study trees completed by others and memorizing the branching patterns seems utterly pointless.  My quest was for a prepared procedure that would walk students through the actual process used by evolutionary biologists to make the trees that we call phylogenies.

Figure 2.  Data from 2015 Saint Michael's College students.

My quest was fruitless and so I wrote my own student-accessible procedure based on the techniques used by professional biologists.  My students use a collection of real and replica mammalian skulls.  They come up with a laundry list of observable skull characteristics: canine teeth, forward facing eyes, snouts, notches, grooves, and whatever traits they can come up with and clearly communicate to their class mates.  Each skull is then scored for each trait: "1" represents "present"; "0" represents "absent".  A subset of this year's data is shown in Figure 2 and from it you can see that bobcats, and lynx have tiny molars and Y-shaped premolars that are not found in the other organisms on this subset of the larger list.  These unique traits together with many others can be used to infer that bobcats and lynx are related.

Figure 3.  The arbitrary starting tree; click to enlarge.

This year we measured 46 traits from 26 mammals and then placed the mammals on an arbitrarily drawn tree (Figure 3).  I describe the starting tree as "arbitrary" because no attempt was made to place related organisms on adjacent branches: bobcats share a branch with polar bears and sheep for example.  Obviously this is not ideal and more importantly, it suggests that tiny molars evolved bobcats, and again in lynx, and evolved independently three more times in lions, cougars, and Bengal tigers.  It makes more logical sense that tiny molars evolved in some ancient cat and that the trait was passed down to modern cats.  If this is true we should expect to see this traits in other cats and indeed we do see exactly that in the two other species we have in our collection: house cat and caracal cat.  Scientists call this "the principle of parsimony": why invoke 5 evolutionary events when just 1 is needed to explain the data.

We refer to the gain or loss of traits as "transitions" and we used software to count the 251 transitions needed to explain the arbitrary tree.  My students then move branches around on the tree and the software automatically recalculates the number of transitions.The goal is to generate the most parsimonious tree, or the tree with the smallest number of transitions.  This becomes competitive as student groups report out on their shorter and shorter trees during the lab session.  As a homework assignment, the students compare their trees to trees published by evolutionary biologists.  This places their work in the larger context and I have found that the comparisons generally fare very well.  As a result of writing this blog I think I'll ask my students to use their trees, together with published trees to write several hypotheses about the traits of skulls they have not yet seen.  Sounds like a whole new lab!

Figure 4.  A tree made based upon the observed skull traits.

What I don't tell my students is that the software has a feature that does the work automatically.  The software is unbiased; it won't place the polar bears near the brown bears just because that might make most sense.  Instead, the software makes groups that minimize the number of transitions and generates a tree based solely on the data (Figure 4).  This data-based tree requires 121 transitions and places organisms together in ways that very closely match the tree of life, a phylogeny generated by professional biologists.

Importantly, 15 students dreamed up 46 traits without consulting published work and without reference to what some other biologist might think of as a 'good trait'.  They worked in groups and the only criteria for choosing traits were: that they could communicate the trait to their peers; the trait should occur in at least 2 skulls; the trait could not occur in every skull.

This is our third year running this experiment.  We use different skulls each year to keep it interesting.  The list of traits that students come up with changes each year also.  If other teachers would like to run this exercise on skulls or on other organisms you can find all of the needed information in this short paper.

Figure 1 from Wikimedia Commons.  Other figures generated at Saint Michael's College. 

Take only pictures; camera trapping!

As a child, I remember seeing photographs of startled birds and mammals in nature magazines and National Geographic.  Knowing how hard it was to observe even common mammals like badgers near my home town of Athlone in Ireland, I was enthralled by the idea that the animals could trigger cameras and capture their own images.  In our teens, a good friend and I spent a number of nights up in trees near badger setts trying to catch glimpses of these fascinating animals.  We knew that they were there; we had looped briars around the entrances to their underground setts to catch hairs.  We failed to catch hairs because the badgers removed the briars, and we failed to capture all but the briefest glimpses that left us wondering what we had really seen.

Camera traps were out of reach for the average Irish teen, and indeed 1970s versions were not exactly user friendly.  Early traps were single-shot film cameras used by professional wildlife biologists.  They were expensive, challenging to use, and required wait time while film was developed.  Many things are different in 2014 and camera traps have dropped in price, increased in sophistication, and are very very easy to use.

This evening I removed the chip from a camera I installed in August.  It has been clicking away at passing animals without much care or attention from anyone.  Similar cameras have revolutionized wildlife biology and made wildlife photography available to a far broader range of people.  It's hard to say that my little camera trapping adventure has revolutionized much of anything, but it's a lot of fun for my favorite 8 year old to see what comes through our back yard.

The camera is installed on the corner of our deck at about 4 feet off the ground and pointing down at a 45 degree angle.  I have tried various angles and placements, and this approach seems to eliminate false triggers by windblown tree branches, and distant photos of out-of-focus birds and joggers.  Most of the photographs are actually of the animals I'd like to see. 

Birds and mammals trigger the camera by movement and photographs are taken in natural day light or using an infra red flash at night time.  It runs on a dozen rechargeable double-A batteries and stores photos on an SD card that slots right into my computer.  As I write this I'm glancing through literally thousands of photographs of backyard wildlife.  It's a far cry from the days of single shot cameras.

My daughter and I strategically place left over food in the path of the camera to attract birds and mammals.  After an October apple picking adventure, we placed a pile of apple peelings in the yard.  An opossum, who seems to be one of our most frequent visitors, spent several hours on three successive nights gorging on apple peels and shared the night shift with a cottontail rabbit.  A chipmunk and several grey squirrels took over the day shift and were joined by cardinals and blue jays.

Wildlife biologists are regular users of camera traps and an array of scientific questions have been answered using very similar cameras.  European investigators used camera traps to see how many of the baits left out for foxes were actually consumed by foxes as compared to non-target animals.  It turned out that hedgehogs were regularly consuming the baits, but simply burying the bait or placing it nearer to fox dens drastically improved success.

 Even our simple back yard setup is generating data that could easily be used to address a number of questions.  For example, the published accounts of cotton tail rabbits suggest that they are most active near dawn and dusk.  But in my back yard, I most often photograph rabbits after mid night.  Quite obviously I may well be photographing the same midnight bunny on several nights, but it does suggest that I should repeat the experiment in a different location and capture evidence from one or several other rabbits.

Our yard is visited by skunks, racoons, opossums, rabbits, squirrels, chipmunks, and several different neighborhood cats.  We have also captured photographs of several birds including catbirds, grackles, cardinals, bluejays, sparrows, juncos, and robins. Skunks have distinctive coat patterns and there are at least two that visit our yard.

I can't recommend a specific camera brand because I have only tried one.  I can say that I'm very happy with the Reconyx camera that I'm currently using.  An available metal housing makes it possible to string a cable lock through the housing and the camera reducing the possibility of theft.  However, I can strongly recommend camera trapping as a fun family activity and a way to connect to seldom seen animals that quietly slip through our back yards.  Once could very easily craft a fascinating science fair project or indeed publishable study with the budding scientist in your life.

All photographs taken using a Reconyx HC600 Hyperfire