A Fish Eye View » atlantic coast

Mole crab molts litter the beaches

Mason Posner — Thu, 20 May 2010 02:03:25 +0000

What a difference a month makes. Back in April I brought my marine biology class to the Outer Banks of North Carolina for our end of semester field trip. We saw lots of surf clam shells on the beach then, and some arks, but not a lot of other diversity in shells. And the month before on a spring break trip the beaches were covered in purse crabs. But this week it’s clear that mole crabs are in season, as the beach is littered in little Emerita molts.

Mole crab molts on the beach in Southern Shores, North Carolina

Adult mole crabs start mating in early spring and go through to fall. Like other arthropods, males copulate with females and fertilize eggs internally. The females then hold the developing embryos under their abdomens for 2-3 weeks (see image below), after which the larvae leave the females and live on their own in near shore areas. The larvae then leave the water column to settle back into the surf zone in June/July and September/October, where the juveniles and adults feed on small plankton and detritus in the swash zone of the beach. The molts I have been finding on the beach this week are all about 2 cm in length, and may be from actively mating crabs. We did find some crabs in the swash zone back in April, but not this large number of molts. Are the females molting prior to mating, like in blue crabs?

Female mole crab with egg mass

A very interesting study examined whether female mole crabs time the release of their larvae. They found that the larvae do in fact leave the females in quick 5-15 minute bursts just after it becomes dark. What is really interesting is that the larvae themselves control this timing, as the rhythmicity is also seen in egg masses that have been removed from the females. And this rhythm continues in constant darkness, showing that it is due to some internal clock in the embryos, not simply a response to darkness.

These little ubiquitous beach crabs can pull off some impressive tricks.

A successful field trip to the Outer Banks

Mason Posner — Fri, 30 Apr 2010 01:01:53 +0000

I recently returned from my latest class field trip to the Outer Banks of North Carolina. I am fortunate to teach an upper level marine bio course at Ashland University in Ohio. Yes, Ohio. My students can see live marine specimens in our saltwater aquarium, and lots of collected organisms from the Atlantic and Pacific coasts, but the highlight of the course is definitely our trip to North Carolina, where we stay at the Oregon Inlet campsite and make day trips up and down the coast. This is the third time I have taken my class to the OBX, and as usual we lucked out on weather. We avoided rain, had great temperatures, but did get blown out of our campsite the last night by high winds (a late night escape to my Mother’s house in Southern Shores got us some sleep before the 13 hour drive back home).

Here is a taste of our trip (thanks to my colleague Patty Saunders for serving as trip photographer). Still to come, some video and food highlights:

Our welcome to the beach after 15 hours on the road

Breaking camp the first morning

Kayaking out of Manteo harbor with the Queen Elizabeth II in the background

Official portrait on the Manteo dock

Lots of beachcombing, and a mini-study on how Oregon Inlet affects shell deposition on the beach

Beach seining yielded some small blue crabs, croaker (or spot), silverside and shrimp. The water was cold, but it was worth it.

Juvenile dolphins playing off the beach just south of Oregon Inlet

. . . and a large group of royal terns. You can see Bodie Light wrapped up in the distance while it gets a refurbished Fresnel lens (right side of picture).

Birding on Pea Island

At the top of Hatteras Light, after a great history lesson in the failures of beach stabilization by a Lighthouse volunteer

One of many beautiful sunsets over the dunes

We made it to the beach

Mason Posner — Fri, 16 Apr 2010 03:10:24 +0000

It took us almost 15 hours in our two vans to get from Ashland, Ohio to Oregon Inlet, but we had some great BBQ (Currituck BBQ) on the way and a quick stop at walmart for the camping gear we left behind. But we are here, tents are up, my students had their first trip through the dunes to the beach, and it looks like we may have fantastic weather. And with an almost new moon the stars are amazing.
More tomorrow. Must get sleep after all the driving. But I must say it is pretty cool to be posting from my iPhone in my tent next to the beach.

Marine Biology in the Outer Banks

Mason Posner — Thu, 15 Apr 2010 08:21:18 +0000

End of the semester teaching and a slew of chair duties have kept me away from the blog for a few weeks. But it is now 4:18 am and I am off with a colleague and 10 students for my semi-annual field trip to Oregon Inlet, North Carolina in the Outer Banks for my Marine Biology class. Look for frequent posts about our trip over the next few days.

Trying out the new Flip video on breakers at the beach

Mason Posner — Sat, 13 Mar 2010 04:03:48 +0000

I recently purchased two Flip video cameras for my Senior Capstone biology majors to use when shooting 60 second science videos later this semester. During this past week of spring break I took it on myself to give one a shakedown cruise to see if the built in editing software would do the trick for our class.

So I present my first Flip video, edited on Flip software and annotated on YouTube. The topic is the three types of breakers found on sandy beaches – something we are talking about in my marine bio class this coming Monday. Just to entice you, there are dolphins, and my daughter says something funny at the end. Helpful comments always appreciated.

Collapsed bay fishery loses historic culture

Mason Posner — Tue, 30 Dec 2008 01:37:47 +0000

Chesapeake Bay watermen

Pollution, nutrient runoff and overfishing have destroyed the crab and oyster harvest of the Chesapeake Bay. Excessive algal growth from the overabundant nutrients produces low oxygen “dead zones” and prevents sunlight from reaching sea grasses on the bottom. But another casualty has been the local watermen culture. The uniqueness of the Chesapeake Bay has produced a one of a kind fishing way of life based on crab and oyster harvesting over hundreds of years. A new report from the Washington Post details how the people involved in the fishery are trying to adapt to the loss of their livelihood.

Efforts since 1983 to reduce nutrient levels in the bay have not met their goals. State officials and the EPA recently announced that their previously set long-term goals for bay cleanup will not be achieved and are now setting more short-term goals for reduction of pollution runoff from land. It does not seem that the crabs or oysters are coming back anytime soon. The Post profiles three Maryland communities and the ways they are changing with the Bay. Everywhere on the Eastern Shore of Maryland people are losing the knowledge that came from intimate lives with the Bay – how to predict when crabs will molt based on their shell color so that the more valuable soft shells can be brought to market – or the slang used to describe water conditions on the bay. Locals have sold off their skipjacks, the sailing vessels used to dredge oysters, and moved on to jobs outside of fishing when they can be found. One town on the Eastern Shore, St. Michaels, has turned itself into a tourist destination and is often haunted by the likes of Dick Cheney. Locals find it particularly humorous that the town funeral parlor is now an inn.

: Oyster dredging skipjacks

There is an excellent collection of maps, photos and videos at the Post site along with their continual coverage of this fascinating science, environmental and societal story.

Virginia to buy back crabbing licenses

Mason Posner — Sat, 27 Dec 2008 13:00:31 +0000

Crabbing in Virginia

When the Chesapeake Bay crab fishery was declared a federal disaster the Comonwealth of Virginia was promised $10 million in disaster aid. Virginia has decided to use some of that money to purchase back crab licenses to ease the financial burden on local watermen. The state had already planned to freeze 800 crabbing licenses for 2009 (these were licenses that had not been used for the past several years). And they will ban a type of crabbing called dredging, in which hibernating female crabs are scraped off the bottom of the bay. Some of the federal funds will also be used to pay crabbers to find and remove ghost pots – lost pots that continue to catch and kill crabs.

Virginia and Maryland hope to sustain crabbing as a sustainable fishery in the Bay.