Crab Love

By Linnea Huston
Volunteer naturalistcrabmating2

This week in the lab, we got to see two of our Atlantic rock crabs (Cancer irroratus) in the process of mating. To some, it looked like they were fighting, or like one was eating the other alive. In fact, they were in the “doubler” position, which looks as though the two are hugging each other.

In the pictures, the male crab is the larger of the two and the female is the smaller. Female crabs will molt right before or during mating, and this one did just thatan object came away from the pair that looked like a second crab. We realized that that was her shedded outer shell and that she
was now darker in color (Which you can see
in the second picture).

crabmatingThese two were in the doubler position only a few hours, but mating crabs can stay like this from five hours to three days. The female will store the male’s sperm under her abdomen, which will later attach to her eggs. She’ll then carry the fertilized eggs under her abdomen for about two weeks until they hatch.

Always something interesting to see in the Marine Lab!

So, what’s the difference between the Northern and Common seastar?

Not much, it turns out. The most common sea star in the North Atlantic (and the waters around Star Island) derives its name from being just that: the common sea star. Otherwise known as Asterias rubens for you scientists. You’ve likely seen them many times in the marine lab over the years.

The common sea star or Asterias rubens.

The common sea star or Asterias rubens.

So what, then, about the other ubiquitous species the Northern sea star or Asterias vulgaris? Turns out scientists have long ago concluded they are the same species. This two-named sea star eats bivalves (a favorite prey item is the blue mussel) and gastropods. They also eat crustaceans and worms. They act both as active predators and scavengers.

P.S. We stopped calling them star fish a long time ago since they actually aren’t much like fish. They do not have gills, scales, or fins like fish do and they move quite differently from fish. While fish propel themselves with their tails, sea stars have tiny tube feet to help them move along.

Another common species in the North Atlantic, around Star, is the Forbes seastar or Asterias forbesi.

The Forbes seastar or Asteria Forbesi

The Forbes seastar or Asteria Forbesi.

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Happy New Years! Plus a European surprise…

Oysters of the Northeast

Wondering what you are looking at in the pages above?

Well, I wanted to let you in on a discovery the naturalists at Star Island made last year. Several times in the harbor between Smuttynose and Malaga and on Star’s swimming beach we found mysterious loner oysters. Some of you stopped in the lab and saw them.

European or edible oyster (Photo courtesy of massoyster.org)

European or edible oyster (Photo courtesy of massoyster.org)

Others of you no doubt know, most oysters naturally grow in estuarine bodies of brackish water. Together a group of oysters is commonly called a bed or oyster reef which provides home for hundreds of animals such as sea anemones, barnacles and hooked mussels.

After researching the oysters in Life Between the Tides: Marine Plants and Animals of the Northeast, we realized they were the edible (or European) oyster. These oysters were brought to Maine to foster an aquaculture industry unlike the differently shaped Eastern oyster also found in the Gulf of Maine.

As the book says:

Although scientists thought the Maine water temperatures were too cool in the summer for this species to reproduce, they have found occasional individuals in unusual places, suggesting that reproduction and survival may have occurred…

The oysters have spread as far South as Rhode Island. Pretty cool right? What other well-known species in the Gulf of Maine are invasive? Leave us a comment or question if you know. And have a happy new year!

Watling, L., Fegley, J., & Moring J. (2003) Life Between the Tides: Marine Plants and Animals of the Northeast. Tilbury House, Gardner, ME.

Ever seen a coral polyp up close?

Coral and ocean acidification

A coral polyp and it’s skeleton (Photo by Liz Drenkard, Woods Hole Oceanographic Institution)

Today’s Woods Hole Oceanographic Institution picture of the day catches a coral polyp early in it’s life (three-weeks-old) at left and its delicate skeleton at right.

MIT-WHOI Joint Program student Liz Drenkard studies the way corals respond to increasing ocean acidification, which can impede their ability to build their calcium carbonate skeletons.

Drenkard recently reported that:

Under both normal and high carbon dioxide levels, baby corals that she fed well built larger skeletons and thus calcified more rapidly than unfed corals, which obtained nutrition primarily from their photosynthesizing symbiotic algae.

Drenkard’s results suggest that corals living where there is ample food may withstand the effects of ocean acidification better than corals living where food is scarce.

Ocean Acidification (Courtesy of NOAA’s Pacific Marine Environmental Laboratory Carbon Dioxide Program)

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