When More is not Merrier: Shifting Baselines and Invasive Species

Since the early 1980’s my family has been vacationing along the St. Lawrence River in upstate New   York. We’d head up year after year to relax in the beautiful wilderness, and though I was too young to know it at the time, I was witnessing one of the worst ecological invasions of our time. The dreaded zebra mussel, now in Massachusetts, was marching through the great lakes, clearing the water of its precious plankton and forever changing the ecosystem.

But for me, the zebra mussel was just a normal part of the river while I was growing up. I thought the environment seemed healthy enough – there were birds to be seen and fish to be caught. That was because I hadn’t seen the river before the zebra mussel, they’d always been there, that was my baseline. My parents certainly remember a different river, and from their time to mine the baseline had shifted.

It wasn’t until I was much older that I saw the effect of a new invasive species in that same river, the round goby fish. I’d cast a reel and catch this funny looking bottom-feeder on rare occasions. But lately I’ve caught more and more gobies. Now I just expect them as part of the ecosystem, and one day when my kids fish in the St. Lawrence, their baseline will be filled with gobies.

The trouble is that our shifting baselines are dangerous: they cloud our idea of what’s “normal”, and they don’t allow us to see the gradual decline in the environment around us. Be it climate change, ocean acidification, pollution, overfishing, or invasive species, it can be tough to tell what “normal” used to look like.

But invasive species actually provide us with an interesting case. On one hand, if they’ve been around long enough we way think of them as part of the native community (like I did with the zebra mussel). Take, for example, the common periwinkle, Littorina littorea, an invasive species that has been around since the mid 1800’s. They’ve been here so long and they are so ubiquitous that until recently scientists have even debated whether they’re native or invasive. Surely you’ve seen these snails blanketing our rocky shores, and you too may not have thought much of them. But what did our beaches look like before they were here?

On the other hand, some species invasions allow us to witness substantial environmental changes in just a few years, and they can demonstrate to us the fragility of our ecosystems. Like the European shrimp, Palaemon elegans, which was found in Salem Sound just a couple years ago. They eat a lot of other small crustaceans, potentially shifting community interactions, and they are likely to spread rapidly along the coasts. They have already been reported in Maine, Boston Harbor, and in Rhode Island. We’ll actually be able to witness the effects of this invader in just a short while, though we can’t yet predict the severity of the impact they’ll have on native species.

With all of this change it can be easy to lose track of what’s happening in our New England waters, which is why documenting species introductions and the distributional changes of those invaders is so important. A local scientist leading the effort to detect invaders is Dr. Judy Pederson from the MIT Sea Grant College Program. Every few years she and a team of scientists perform surveys to look at the organisms (mostly attached to docks) along New England coastlines. She notes the value of a citizen monitoring program that she says has worked very well for recording invasive species.

“Part of what we do is document the presence and absence of species and their movements up and down the coast,” she told me. “But once an invasive species is found in the marine environment, it’s almost impossible to eliminate.” Since they’re so tough to get rid of, Dr. Pederson also works on helping to control the initial introduction of invaders. The most widely reported vector for spreading invasive species is the discharge of ship ballast water from foreign ports. Microscopic larvae (part of the plankton) taken into ballast water across the ocean often get released into new coastal waters where they may metamorphose and ultimately thrive. But everyday ocean-using citizens spread organisms too, which is why Dr. Pederson has worked to educate divers and boaters about cleaning their equipment after using it, lest they involuntarily transfer species to new places.

It’s a noble effort, tackling such a daunting and complicated problem. Some invasive species are even displacing previous invaders. Remember the European green crab, Carcinus maenas, whose voracious appetite isn’t very easily satiated? Though they are a menace, in some areas even these crabs are being pushed around by a relatively new (1988) invader, the Asian shore crab, Hemigrapsus sanguineus. I can’t turn over a rock at low tide without finding a few of these pugnacious little guys.

In fact, Dr. Pederson had some sobering stats: “About 15% of the species we find during our surveys are non-native, but they can be 40% of the biomass at some locations.” And the increasing effects of climate change are not likely to ease the trouble. As we’ve seen recently, the distributions of native species have been shifting, introducing New Englanders to a host of new organisms. But invaders are on the move too. The devastating lionfish has been found as far north as Narragansett Bay, and is already on the way to becoming an ecological disaster. With no known predators and native communities that aren’t adapted to recognize them as a threat, lionfish can quickly wipe out the biodiversity of entire ecosystems.

Maybe we can’t get rid of the invasive species that have taken up residence here, but without the knowledge of what used to be, we may not notice the slow changes happening all around us. We need to stay vigilant, and you can help keep a watchful eye on our oceans to remind us of how our baselines are always changing.

Casey Diederich is a 5th year PhD candidate in Tuft’s University’s Biology Department, and is conducting his research on slipper-shell snails. We are thrilled to have Casey guest blogging for us about some of the more fascinating plants and animals in our ocean. – Ed.

Image via the National Center for Ecological Analysis and Synthesis

Citizen Plankton Science! Join the Secchi Disk Project (and be Extremely Awesome)

So, you want to be a marine biologist but you have no training? No problem, as long as you’ve been to the eye doctor lately. Don’t have all that expensive equipment? All you’ll need is little more than your smart phone. Forget the endless hours of studying and the late nights analyzing data… Dr. Richard Kirby is giving you an easy and fun chance to contribute, and on a really important project.

Dr. Kirby is a scientist across the pond at Plymouth University’s Marine Institute and he studies plankton. We’ve taken a close look at plankton recently, both the plant and the animal variety. These sea-drifters are responsible for at least half of the oxygen we breathe, and they lie at the base of a food chain that produces hundreds of millions of tons of food for us. Their importance cannot be overstated.

But how do you study a group of organisms that are so small in size and so large in number? Well, it’s not easy, especially when you’re trying to determine the amount of phytoplankton on a global scale. Some have tried, and a widely publicized report from Nature found that phytoplankton numbers have been declining over the past century, an alarming finding given their importance. But the study has been hotly contested, and the only certain fact coming from the debate is that we need more information.

And that’s where you come in. Dr. Kirby figures the best way to get more information is to enlist the help of the roughly 7 billion amateur-scientists that may already be out at sea, whether it be working, sport fishing, or just pleasure cruising. He has developed a free mobile phone app that allows you to easily record a measure of plankton abundance from anywhere in the ocean.


The system is based around a simple little device that marine scientists have been using since 1865: the Secchi disk. Named after its inventor, Father Pietro Angelo Secchi, a Secchi disk is basically just a weighted white disk attached to a tape measure (instructions on how to make one can be found here). You lower the disk into the water and record the depth at which it disappears from sight. That is called the Secchi depth and it gives scientists a measure of how much plankton is in the water. If the water has a lot of plankton, it’ll be tougher to see the disk, and it will disappear from sight at a shallower depth.

After you determine a Secchi depth you enter it into the free Secchi App, which records your location along with the measurements that you made. All of this information is stored on your phone and passed along to Dr. Kirby once you get an internet connection. Voilà! You’re part of a major study to help figure out the changes that our world’s oceans are going through. You can even check out the data coming in from all over the world!

Our technological advances and changing climate have intersected to make this the perfect time for such an ambitious study. Dr. Kirby notes “This app enables seafarers around the world to take part in a science project and if we can just get a small percentage of the global population of sailors involved, we can generate a database that will help us understand how life in the oceans is changing. It would help us learn much more about these important organisms at a crucial time when their habitat is altering due to climate change.”

So next time you’re heading out to sea, make sure to bring your Secchi disk and your phone, and help us to understand what’s happening to our global ocean. While you’re at it, put a picture of you doing your citizen science on our Facebook page so everyone knows how awesome you are!

Casey Diederich is a 5th year PhD candidate in Tuft’s University’s Biology Department, and is conducting his research on slipper-shell snails. We are thrilled to have Casey guest blogging for us about some of the more fascinating plants and animals in our ocean. – Ed.

Photo via Dr. Richard Kirby

Not Your Average Drifter – Plankton Part II

Last week we met some of our most important New England residents – the phytoplankton. Now, we are happy to introduce their animal counterparts – the zooplankton. These animals drift around in the sea in truly astonishing number and form . If you missed our post on their plant partners – the phytoplankton – you can find it here. Go ahead and read it, I’ll wait.

Okay? Well, those phytoplankton are extremely productive, and they’re eaten by many animals, most of which fall into the category of “zooplankton.”

Microscopic or massive, if you’re an animal that can’t swim against the current you’re part of the zooplankton. Some of these animals drift in the water their entire lives. These are what we scientists (who enjoy inventing and using large words) call the holoplankton (holo = entire, plankton = wanderer). The copepods are a perfect example of this.

Copepods may be the most abundant animal group on the planet, and although they contain considerable diversity, most of them are holoplanktonic. They are also usually gonorchoristic (I know, again with the huge words), which means they come in both the male and female variety. When two of them get together, so to speak, the fertilized egg will develop through many larval stages, until they finally metamorphose into the adult form. But all the way through this life cycle – egg to adult – the copepod will remain drifting along in the water.

The same is true for countless other animals, from the familiar jelly to the bizarre Phronima. All of them spending a life adrift, in a world that seems more like science fiction than reality.

Contrast this to members of the meroplankton (meros = partial), who spend only a portion of their lives in the water column. These animals may not be so foreign to you, as most of the meroplankton are the larval forms of animals that we know and love (and love to eat!). These animals drift around as larvae until they metamorphose and become large enough to swim against the current (at which point they are said to be “nektonic” – like a fast-swimming fish), or until they settle to a life on the sea floor (these animals are “benthic” – like a snail or mussel).

Most fish have larvae, as do barnacles, urchins, lobsters, mollusks, and many others. Some have giant spikes coming out of their heads, others look like flying saucers. But the fact that free-living larval stages exist in most marine animals means that they are (or were) evolutionarily important. Perhaps they evolved for dispersal – to avoid competition or inbreeding. Or maybe larvae evolved as a means to temporarily avoid predation on the sea floor… in truth, we don’t know for sure why the larval form evolved.

What we do know is that they are extremely abundant, and together with the holoplankton they make up an undeniably important and enormous group of animals. If the phytoplankton are at the base of the food chain, then the zooplankton are at the first rung. They are so massive in number that they can sustain huge populations of larger animals, some as large as our own North Atlantic right whales, which filter copepods, krill, and other zooplankton out of the water. But some zooplankton are eaten by their tiny buddies (other carnivorous plankton, like some fish larvae), which can make the marine food web a bit complicated.

And though they can’t swim against the current, they’re on the move. Their ecological importance makes the news of a study showing that climate change has caused dramatic shifts in the distribution of many planktonic species troubling. In the study, the investigators found that phytoplankton and zooplankton were two of the groups whose distribution was changing the quickest. As the authors’ of the study state, “species’ interactions and marine ecosystem functions may be substantially reorganized at the regional scale, potentially triggering a range of cascading effects.”

Translation: As the great drifter Bob Dylan said, “The times they are a changin’.” But that doesn’t mean you have to sit idly by… “If your time to you is worth savin’” then find out how you can help.

Up next in our plankton series – we’ll talk about a really cool citizen science plankton project you can get involved in using little more than your smart phone. Stay tuned!

Casey Diederich is a 5th year PhD candidate in Tuft’s University’s Biology Department, and is conducting his research on slipper-shell snails. We are thrilled to have Casey guest blogging for us about some of the more fascinating plants and animals in our ocean. – Ed.

Images copyright of Dr Richard Kirby, Plymouth University. These and other images can be found in the book on plankton, “Ocean Drifters, a secret world beneath the waves.”

Not Your Average Drifters – Plankton, Part I

Have you ever accidentally swallowed a mouthful of seawater at the beach? You probably didn’t think much of it, other than “well that was pretty gross.” But you might be surprised to find out just how much you ate in that liquid refreshment! The broad term for the microscopic plants and animals that you’re chowing down on is “plankton,” a group of organisms that we’ve talked about here before, but they definitely deserve a closer look.

Calcareous phytoplankton, SEM

“Plankton” is a term that comes from the Greek meaning “wanderer” and was coined to describe any organism that doesn’t have the ability to swim against the water current. So, technically, even some very large animals like jellies are members of the plankton, but most planktonic organisms are very small, and as the title suggests, the best things come in small packages.

Unlike our favorite New England ice cream, plankton basically come in only two flavors: phytoplankton (plants – the subject of this blog) and zooplankton (animals – I’ll talk about these next time). Both the plant and animal type contain a dizzying array of form and function, and their beauty may be unrivaled in the sea.

Why should we care about phytoplankton? Well, we owe our lives to the horde of single-celled plants that float around in the ocean. Literally – they produce at least half of the oxygen on our planet, and perhaps as much as 80%! Just think about those numbers for a second; amazing production from something so small. It’s obvious, then, that the phytoplankton’s strength is in numbers, which is how they also form the base of the marine food chain.

Phytoplankton provide sustenance to a wide variety of herbivores (including most of the zooplankton), some of which are of great commercial importance, like mussels, oysters, and scallops. As these herbivores are eaten, the productivity of the phytoplankton is transferred up the food chain, ultimately to us.

Those are some pretty good reasons to love plankton, but I’m not done yet. You know all of that carbon that we’re pumping into our atmosphere? Well, phytoplankton take much of that carbon out of the atmosphere through photosynthesis. And when they sink to the bottom, phytoplankton sequester a massive amount of that carbon to the deep sea. Even when they’re long gone they’re important, because their hard bits are preserved in the fossil record, helping scientists to decipher everything from the age of rocks to past environmental changes.

Their importance might be matched by their looks; even in a place renowned for its beauty, phytoplankton stand out. Take the diatoms, for example, which make breathtakingly beautiful skeletons made from silica (the compound used to make glass). Or the dinoflagellates, which are normally harmless but can occasionally bloom and release toxins that form the sinister red tides. There are cyanobacteria, better known as “blue-green algae” that are actually ancient photosynthesizing bacteria. But my personal favorite, and maybe the most curious, has to be the coccolithophores, which cover themselves in buttons made of calcium carbonate. Why would they do such a thing? Scientists aren’t really sure, and debate abounds, but what they are surer of is that more acidic seawater will not be good for the coccolithophores.

In fact, when we look at the big picture, global phytoplankton concentrations have been on the decline for the last century. This is a scary trend, given their importance, and some researchers have even proposed fertilizing large areas of the ocean to cause phytoplankton blooms. Sounds promising, but one of the challenges associated with such large-scale interventions is predicting the unintended consequences. For example, what effect would those blooms have on the zooplankton? Stay tuned, we’ll take a look at those little guys in Part II.

Casey Diederich is a 5th year PhD candidate in Tuft’s University’s Biology Department, and is conducting his research on slipper-shell snails. We are thrilled to have Casey guest blogging for us about some of the more fascinating animals in our ocean. Watch for his close-up look at plankton, Part II, coming soon. You might be surprised at how interesting and important these little guys are! – Ed.

Feature image via Wikimedia Commons

Stacks of Sex-Changing Sea Snails

This could be happening right in your back yard! The picture above shows the common but oft-ignored sea snails Crepidula fornicata (best scientific name around*), also called slipper-shell snails or just slippers. In New England, if you step out onto a rocky beach or wade into the ocean you may happen upon these humble creatures. And, while they may not be as charismatic as, say, sea angels or the Atlantic wolffish (Crepidula don’t even move for about 95% of their lives), there’s more to these critters than meets the eye.

For starters, the reason they live on top of each other in that weird looking stack (there are at least 6 individuals in the picture) is because they don’t move around as adults. So, once they find a mate in the vast ocean it’s worth hanging on for dear life.

But what if one of these snails finds a partner but they’re both males? Time for a sex change! One becomes a female, which causes the other to remain male. These snails are “protandrous sequential hermaphrodites,” which is a big sciency way to say that they get the best of both worlds – they all start their lives as males, and eventually they will all become females. How?

The large snails at the bottom of a stack are always female and the small snails at the top are always male. As the larger, older females die, the next largest member of the stack switches sex from male to female… and on it goes. Not so boring after all.

But it’s not just their life-style that’s interesting; they’re also an important member of our coastal ecosystems. Unlike most snails that eat seaweed or scrape algae off of rocks, Crepidula make their living by filtering food particles out of the water. So, they often compete for food with commercially important species like mussels and oysters. When not competing they’re getting eaten themselves, by important New England species like crabs and sea stars. Some parasitic sponges and snails use Crepidula as a host, and even when they die their old shells provide homes for a host of species, some of which you may have had as a kid.

And, while Crepidula may be a natural part of our marine ecosystem in New England, they’re a shockingly successful invasive species along some European coastlines. In a few areas you can find up to 9,000 of them in a square meter! And they’re starting to have an effect on some important fisheries there.

Susceptible to pollution and high temperatures (not to mention the potential threat of ocean acidification on their microscopic larvae) in New England, it’s difficult to predict the fate of this species in the years to come. But their ability to successfully colonize new environments all over the world offers hope that they’ll also be resilient to the effects of climate change.

So, although they may not look that much different from a rock, Crepidula are one of the many New England creatures that make our oceans special, and worth fighting for. Who knows, one day soon you may be introduced to them, perhaps with a little garlic butter.

* Though we think that this species has one of the best names around, it’s probably just a happy coincidence. It was most likely named fornicata due to its arched shape (fornicata = arched) that the longer stacks form.

Casey Diederich is a 5th year PhD candidate in Tuft’s University’s Biology Department, and is conducting his research on slipper-shell snails. We are thrilled to have Casey guest blogging for us about some of the more fascinating animals in our ocean. Watch for his close-up look at plankton, coming soon. You might be surprised at how interesting and important these little guys are! – Ed.

Photo credit: Paul J. Morris via Wikimedia Commons