Larvae of the spider crab (Maja squinado), the angular crab (Goneplax rhomboides) and the thumbnail crab(Thia scutellata). Each could sit comfortably on the head of a pin. 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."
www.oceandrifters.org
Larvae of the spider crab (Maja squinado), the angular crab (Goneplax rhomboides) and the thumbnail crab(Thia scutellata). Each could sit comfortably on the head of a pin. 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." www.oceandrifters.org
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Not Your Average Drifter – Plankton Part II

Categories: Guest Posters

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.

Diatoms. Photo courtesy of Wikimedia Commons.
Diatoms. Photo courtesy of Wikimedia Commons.
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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.

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.

bluesharkanddiver
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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.