European green crab from Bailey Island, Maine. Photo by David Reed (dreed41) via Flickr.
European green crab from Bailey Island, Maine. Photo by David Reed (dreed41) via Flickr.
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Mean, Green Eating Machines: The European green crab is “one of the world’s worst invasives”!

Categories: Creature Features

The European green crab may look small, but it has an appetite of epic proportions. These tiny 2-4 inch marine invaders can consume up to 40 small clams a day- that’s more than you’d get on your average plate of fried clams!

Why are we so concerned about these crabs? Warming ocean temperatures have allowed green crabs to persist farther and farther north along the North American coastlines. Where cold winter chills used to keep its numbers in check, populations of green crabs are now booming places like the Gulf of Maine, and they are eating their way through our precious local seafood.

The European green crab, Carcinus maenas, is not exactly new to the northeast. In fact, it first arrived in the waters off Cape Cod during the 1800s, from its native range along the European coast and Northern Africa. Green crabs have since expanded their range northward through New Brunswick, and have even made their way over to the west coast, likely hitching a ride in ships’ ballast water tanks, or with commercial shipments of live seafood.

Green crabs dwell in many types of marine habitat, from rocky tidal zones to sandy beach flats, and are extremely good competitors. In a recent study, green crabs were found to be much more successful in introduced regions- including the east and west coasts of the US- as compared to their native regions. Crabs in the non-native study areas were also found to be larger and less affected by parasites, whose numbers were greater in the native region.

The green crab is a professional clammer- able to dig up and crack open young clams and oysters with ninja-like skill. A single crab can consume nearly three-dozen small mussels per day, and will basically try to eat anything around its size or smaller. Other crabs, fish, and even young lobster are all fair game for these tiny eating machines. In fact, green crabs may be the primary culprit in shutting down commercial clam harvesting in parts of Maine. Even worse, some fishermen in Maine are certain that predation from green crabs is responsible for shrinking numbers of other commercially-important mollusk populations – namely, mussels and oysters.

Fishermen worry that once the crabs work their way through shellfish populations, their next target may be lobsters. Green crabs are known to prey upon other species of crab and some fish, and have been shown to prey upon juvenile lobsters in a laboratory setting. The Washington Department of Fish and Wildlife also reports that green crabs are capable of learning and honing their predation techniques- a scary thought for our Maine lobsters!


Crachen cranc - Sacculina carcini

A “parasitic castrator” of the green crab – the barnacle Sacculina carcini. Photo by Gwylan via Flickr.

What can we do to defend our coastal seafood communities? Several management strategies have already been put into practice, including trapping and removal programs, chemical controls, and even protective netting for juvenile clams. However, the most interesting, and possibly most controversial, proposed method of control is to introduce a natural enemy. Sacculina carcini is a parasitic barnacle of European green crabs, which impairs its host’s reproductive organs, rendering them unable to reproduce. Parasites that do this are collectively known as ‘parasitic castrators.’ Some sources have suggested utilizing this species to curb crab populations, but recent studies have revealed that the parasite is capable of infecting other species of crabs in addition to the green crab, which may put native species at high risk. This, along with many unknown factors associated with introducing another non-native organism, make this type of biological control an unlikely solution to our green crab dilemma.

CBC News recently deemed green crabs to be “one of the world’s worst invasive species”, reporting problems associated with spikes in green crab populations as far north as New Brunswick. With ocean temperatures rapidly rising, the green crab is likely to continue its territory and population expansions. It is fast becoming one of the biggest threats to New England shellfish populations, and will need continued monitoring and novel control strategies in order to preserve local fisheries and prevent further destruction to our marine life.

A stack of 6 Crepidula fornicata individuals with alga growing off of oldest shell in the stack (and a little black high spired snail living on the alga). Photo credit: Paul J. Morris via Wikimedia Commons.
A stack of 6 Crepidula fornicata individuals with alga growing off of oldest shell in the stack (and a little black high spired snail living on the alga). Photo credit: Paul J. Morris via Wikimedia Commons.
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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.

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Shark diving – taking a bite out of Jaws

Just a few years ago only adrenaline junkies or daring visionaries would have thought of jumping in the water to dive near sharks. Today, it is a whole different story. Many divers and snorkelers hope to see sharks of all sizes, some of which were once considered man-eaters. These often greatly misunderstood creatures are now attracting divers who simply want to observe them and get a glimpse of their universe. As with any wildlife encounter it’s important to be responsible when diving near sharks. Use only well known dive operators that will teach you how to safely and respectfully interact with sharks and other ocean life.

While sharks have long been perceived by many as voracious killers, for me they have become a fascination. I have traveled around the globe for the pleasure of diving with them. I have been in places like Cocos Island in Costa Rica and the remote islands of Wolfe and Darwin in the Galapagos.

These are expensive destinations but I and many other divers think it’s worth it. The reason is simple: they remain two of the best places in the world to dive with scalloped hammerhead sharks who congregate there by the thousands. There are so many other examples of how shark diving is making a positive contribution to our tourist economies:

  • On a shark diving trip to the Maldives, a small island nation located in the middle of the Indian Ocean, I was thrilled to see a billboard advertising shark ecotourism, but not in the usual way. The ad showed various parts of a shark that can be sold – each with a price tag. But there was another price tag showing that this same shark could generate far more in shark tourism if left alive than the shark parts would ever bring in.


  • In New England, in places like Maine and Rhode Island, operators offer day trips to snorkel or dive with blue and mako sharks. Anyone can participate – if you’re not a certified diver, you can still snorkel. Blue sharks used to be one of the most abundant species on the planet. Sadly, they have dramatically suffered from finning, overfishing and bycatch.



  • Going north of Maine, in Quebec (Canada), you can dive with a prehistoric looking animal: the Greenland shark (below). I have dived with this animal on several occasions and it is always a very unique experience. This shark moves slowly to conserve its energy and if you are lucky enough, it will let you swim by while it remains nearly motionless. Blue sharks and porbeagle sharks can be seen in Quebec as well.

Greenland shark

Interacting with sharks is an incredible experience, and it makes you realize that they are very different from how they are portrayed in the movies. It is so humbling to look at the graceful movement of a shark passing by. Shark conservationists and scientists have played an important role in changing the way we look at sharks and the Jaws aura surrounding sharks is slowly fading. Fear of sharks is being transformed into respect and curiosity, and an increasing number of people are coming down with what ails me: shark fever!

Today’s guest post is by our friend Michel Labrecque. Michel is a published underwater photographer and contributor for various underwater medias. He is also a PADI Master Instructor, IANTD Trimix Instructor, a DAN and EFR Instructor Trainer and an HSA Instructor. He co-owns Plongée XL, a PADI 5 Star IDC Dive Center located in Victoriaville, Canada with Julie Ouimet who signs most of their articles.

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Frilled Sharks – A good reason to stay in the shallow water

Photo by Getty Images

What if sea monsters really existed? Well, here’s one shark that proves that they actually kind of do. Frilled sharks are one of the most prehistoric species of shark, and could very well have been the inspiration to sea monster stories around the world. Resembling the offspring of a Chinese dragon and an eel, frilled sharks are not only truly bizarre looking, but a great example of how much we don’t know about our largely unexplored ocean.

One of the oldest extant (or still-living) sharks, the frilled shark, or Chlyamydoselachus anguineus, is believed to date back to somewhere between 95 and 150 million years ago! This places them in a distinct group of plants, animals and bacteria that we call ‘living fossils’, because their closest relatives are extinct and known only through fossil records. Some well-known animals that fall into the category of living fossils are alligators and crocodiles, horseshoe crabs, coelacanths, and opossums.

Living fossil or not- personally I would feel nothing but terror if I ever came across one of these things in the ocean. Lucky for me, the frilled shark is generally found only in really deep places humans cannot go- part of what makes it so mysterious and, well, creepy.

Though the existence of frilled sharks has been known for over a century- since Samuel Garman first described them in 1884- surprisingly little is known about their behavior. Frilled sharks inhabit the deep ocean, anywhere from around 600m (~2,000ft) to 1,500m down. It is for this reason that so little is known about the species, we’re mostly unable to observe it in its natural habitat.

Though most commonly seen near Australia, New Zealand, and Southeast Asia, frilled sharks span a nearly global range, and have even been reported off the coast of New England. In size, the shark is known to grow up to 2m in length. They have extremely long reproductive rates, with a gestation time of at least 78 months- that’s around three and a half years- the longest gestation of any known vertebrate!

Frilled sharks sport a mouth full of 25 rows of needle-like, trident-shaped teeth, perfect for trapping unsuspecting prey. Because they move slowly and are thought to be pretty weak swimmers, their 300 teeth are their best weapons to capture their prey, which generally consists of squid and smaller species of shark and fish.

Even though it is not a commercially-targeted species, the IUCN’s Red List of Threatened Species has listed the frilled shark as “Near Threatened” because of its slow reproduction rates and rarity. Frilled shark populations are particularly sensitive to accidental capture or by-catch, an unfortunate but common cause of death for this species.

One rare occasion brought one of these mysterious sharks to surface waters near Japan’s Awashima Marine Park, giving marine biologists and YouTube viewers alike the chance to see a frilled shark swimming. Unfortunately, the park’s marine biologists believe that this individual came to the surface because it was dying. Regardless, this deepwater species cannot survive in shallow surface waters, so the shark only lived for a couple of hours after it was found.

A new species sharing the frilled shark’s family was recently discovered in 2009 along the southeastern coast of Africa. This discovery of the Southern African frilled shark marks the second and only other extant member of its family, Chlamydoselachidae.

Animals like the frilled shark- and discoveries like that of the Southern African frilled shark- remind us how strange and unknown the ocean really is to us. Continued exploration of the deep-sea is the key to unlocking more of the ocean’s mysteries like the frilled shark!


Cynthia Wigren

An Interview with Cynthia Wigren, President and Co-founder Atlantic White Shark Conservancy

Atlantic White Shark Conservancy is an all-volunteer nonprofit organization committed to raising public awareness of white sharks. AWSC supports scientific research, improves public safety, and educates the community, to inspire conservation of white sharks in the Atlantic.

Keren: Thanks so much for taking the time to chat with me and NEOO readers about the Atlantic White Shark Conservancy! The last time you checked in with us was in January, can you tell me a little about what has happened with your work since then?

Cynthia: Atlantic White Shark Conservancy’s (AWSC) primary mission is to help fund state shark expert Dr. Greg Skomal’s research. His white shark work is entirely funded by grants and private donations.

We had three goals for this season when we started: Purchase ten acoustic tags for Dr. Skomal’s research, send five kids to summer camp, and send a tagging boat out on five trips. So far we have gotten ten acoustic tags and are sending 5 kids to nature camps – 3 to the Massachusetts Audubon in Chatham and 2 to the Cape Cod Museum of Natural History! We have also raised enough funds to send the tagging boat out on 3 trips – we’re still working on the last two.


Marianne Long Shark Education Coordinator at AWSC, teaching children about sharks in Scituate.

Marianne Long Shark Education Coordinator at AWSC, teaching children about sharks in Scituate.


We’ve had a few educational events for 1-8th graders, we want to teach the next generation about sharks’ important place in the marine environment, and nurture their fascination. We have also partnered with MassGeneral Hospital for Children.  Shark biologist John Chisholm visited the Hospital with us to talk to kids about sharks and we are working with the Hospital on a shark themed event in September during National Childhood Cancer Awareness Month.

Keren:  Do you find people becoming more receptive to the idea of white shark conservation?

Cynthia:  In 2004 when a white shark got stuck in a salt pond on Cape Cod, people worked quickly and effectively to get the shark out- and Dr. Skomal had his first opportunity to tag a great white- unfortunately the tag popped off as soon as the shark hit the open ocean! Something similar had happened fifty years before and the shark was killed within two hours- there’s definitely been a shift but there’s also still a lot of work to be done.

It will be interesting to see how this summer goes on the Cape regarding tourism and sharks being here- we’re seeing all kinds of businesses embracing sharks’ presence. In Chatham they had a ‘Sharks in the Park’ event. People seem to be realizing sharks are going to keep coming here and it’s a good thing for the ecosystem. People travel all over the world to see sharks- I traveled to South Africa to see white sharks!

Keren:  Can you talk more about various organizations that are important partners in your work?

Cynthia:  Sure, we actually hosted a round table discussion in June with a number of organizations. My philosophy is, “it takes a village.” OCEARCH is doing great shark research and education. The Cape Cod Museum of Natural History has a great shark exhibit through the rest of the year; they just decided to extend it for another year. The Massachusetts Audubon camp is incorporating shark curriculum into their summer camp. The Provincetown Center for Coastal Studies will be co-hosting and shark/seal research presentation with us on August 25th.

Keren:  A lot of our readers are interested in marine conservation and sharks in particular- what can people who are concerned about sharks do?

Cynthia:  It’s important to raise awareness about what’s taking place, for instance with shark finning, 20-70 million sharks a year have their fins cut off and are thrown back in the water- it’s just not sustainable, and we’ve seen a huge decline in many species of sharks. We’re starting to put out a newsletter, if they’re interested in sharks on the East Coast, they could follow our organization.

Facebook and Twitter are great for keeping people connected and raising awareness about shark conservation.

There are a number of great shark conservation organizations out there- just get involved!

Keren:  Do you have a favorite shark fact?

Cynthia:  White sharks are endothermic, warm blooded. They maintain a body temperature higher than the surrounding water temperatures! I think it’s a really cool and rare thing, especially given there are over 400 species of sharks and only a few are warm blooded.

Actually, one of the tagged OCEARCH sharks (Mary Lee) traveled up north to Georges Bank in February! That type of activity hadn’t been documented before. It was really interesting for everyone to see her in the winter in really cold water temperatures; being warm blooded is a really incredible function of these sharks.

Keren:  What do you hope for future shark research and conservancy?

Cynthia:  Our main goal is to have sustainable, comprehensive research for white sharks here; this is the first time that scientists have had predictable access to them and it’s really critical that research be funded long term.

It can be difficult to raise awareness about sharks, because there’s fear and a lot of stuff happening not in front of you, but in international waters. Shark finning for instance- when you see shark finned, and how vulnerable that animal is, it changes your perception.

I hope to see conservation measures start to work, and populations of sharks increase. It’s important to realize sharks are slow growing, late to mature and don’t produce many offspring. Populations are very vulnerable when reduced in size. Sharks play an important role in the marine environment, an environment that’s a lifeline for us in terms of food and oxygen. With climate change issues, we’re looking at a challenging future.  I’m looking to see sharks being appreciated for what they bring to the marine environment that we rely so heavily on.

I truly believe shark conservation is only going to be successful if many people actively participate in the effort.