Noelle Swan

Archive for the ‘Marine Ecology’ Category

Horseshoe crab spawning: Take the kids on an after-bedtime adventure

In Marine Ecology, Science Education, Wildlife and Ecology on May 20, 2013 at 10:43 am

This article first was published as a guest post on The Christian Science Monitor blog Modern Parenthood on May 20, 2013.

Photo credit: Wikimedia commons author Hayden

Photo credit: Wikimedia commons author Hayden

Every year, ancient sea creatures resembling miniature armored tanks invade East Coast beaches with one mission — lay and fertilize as many eggs as possible before disappearing back into the sea.

For three nights, curious onlookers will have the opportunity to witness one of the oldest mating rituals in the world as scores of horseshoe crabs scuttle up onto the shores of Delaware BayCape Cod, and the coastal beaches along the East Coast.

The horseshoe crab, officially known by its scientific name, Limulus polyphemus, has been making annual pilgrimages out of the sea for hundreds of millions of years. Most wait for the full and new moons of late May and June to perform their mating dance.

This year marine biologists expect that the biggest horseshoe crowds will emerge on May 24, June 9, and June 23.

While some horseshoe crabs come ashore during the day, the majority will wait for the cover of night. Then, scores of them will emerge from the sea to begin their moonlit dance on the beach. The females will come first, many with males already in tow in search of a bit of sand to lay their eggs. The females are considerably bigger than males to accommodate the thousands of eggs beneath each helmet-like shell. The females dig nests in the sand before they drop off their young and return to the water. The males pace back and forth over the nests, fertilizing as many eggs as they can before they too return to the cool shallows of the water.

For families interested in gaining a front row seat to the show, Delaware Bay is the world’s largest spawning ground, but they have been spotted up and down the east coast. Citizen scientists can report sightings online to the Ecological Research and Development Group. InDelaware and New Jersey, volunteers can help count the horseshoe crabs as part of a survey during the several weekends this spring and summer. Some horseshoe crabs have already been tagged as part of monitoring projects conducted by the US Fish and Wildlife Service. If you come across a horseshoe crab with a circular or square white tag attached to the corner of the shell, make note of the number on the tag and report it to the US Fish and Wildlife Services online or by calling 1-888-LIMULUS.

Not really a crab at all, Limulus polyphemus is actually an arthropod and is more closely related to scorpions and spiders than any crab.

Limulus is a favorite species for marine biologists and teachers to share with children. The helmet-shaped shells, or carapaces, that protect them from predatory birds in the wild also make them hardy enough to thrive in aquarium touch tanks. While their blade-like tails may look menacing, they serve solely as a rudder for steering in the sand and helping the horseshoe crabs to right themselves should they become overturned by the tide.

Observant beachgoers may come across the discarded shells of horseshoe crabs that have outgrown their carapace and molted. These ghostlike shells can be great fun for kids to explore.

For families that cannot get to the shore, there are many non-fiction books for children describing these prehistoric creatures. Children’s book author Ruth Horowitz offers some moonlit magic in “Crab Moon”, a picture book illustrated by Kate Keisler and recognized by the National Science Teachers Association as an outstanding science trade book.


Digging Deep into the Chesapeake: UD Researchers Seek Clues to Curing Annual Dead Zone

In Marine Ecology, Wildlife and Ecology on June 4, 2012 at 5:50 pm

This article was first published by DFM News on June 4, 2012 under the title UD researcher seeks clues to curing annual Chesapeake Bay dead zone.

Dr. Deb Jaisi, Plant & Soil Science does work on sediment at the bottom of the Chesapeake Bay with the help of graduate students Sunendra Joshi (male) and Kiran Upreti (female). Photo courtesy: University of Delaware/Kathy F. Atkinson

Each summer in Chesapeake Bay, huge algal blooms, fueled by nutrient pollutants, blossom and die. Their remains sink to the bottom and are quickly devoured by bacteria that monopolize the Bay’s stores of dissolved oxygen, stressing or suffocating entire communities of marine life, such as clams, oysters and sponges.

“Restoration efforts in recent decades have helped improved water quality and ecological conditions in the Chesapeake Bay. However, the extent and severity of [the dead zone] has not improved as expected,” said Deb Jaisi associate professor of plant and soil science at the University of Delaware.

This past summer, in 2011, the Chesapeake received its worst report card yet from EcoCheck, a partnership between NOAA and the University of Maryland Center for Environmental Science, despite concerted efforts to reduce the amount of nutrients released into the bay through human activities.

The U.S. Environmental Protection Agency has named phosphorous as one of two major nutrient pollutants (along with nitrogen) contributing to the annual “dead zone.” Phosphorous is an essential element for life. It is found in every cell in the human body and nearly every food we eat. Humans, plants, and animals consume and excrete it. However, as with many things, too much phosphorous can be deadly.

Jaisi believes that a hidden record of phosphorous concentrations lies buried in the Bay floor. By decoding that record, he hopes to learn how concentrations have changed over time, and potentially pinpoint when and how a nutrient found in the bay for centuries became a pollutant capable of threatening the health of the entire bay.

Oak Ridge Associated Universities, a consortium of PhD-granting institutions, and the University of Delaware have awarded matching grants to support this research.

Something of a molecular detective, Jaisi plans to examine sediment cores provided by oceanography professor and eminent scholar David Burdige of Old Dominion University for traces of excess phosphorous that have settled on the bay floor year after year. Each source of phosphorous, from various fertilizers, to sewage treatment discharges, has its own atomic structure, similar to a fingerprint.

This summer, Jaisi will be installing a thermo-chemical element analyzer to help identify these fingerprints. Assuming he can get his lab up and running by mid-summer, he hopes to have some answers by the end of the year.


The first signs of trouble — depleted dissolved oxygen in the depths of the bay — began to show in the 1930s. By the 1950’s the dead zone started making annual appearances and has grown larger with each passing summer.

Because the Chesapeake Bay watershed is 64,000 square miles — nearly the size of the country of Cambodia — the problems and solutions likely originate far beyond the bay shores.

While half of the phosphorous in the bay comes from terrestrial sources, the U.S. Geological Survey estimates that nearly 10,000 metric tons of phosphorous enters the Bay through the watershed each year. Sources can include excess fertilizers applied to farmland, discharges from sewage treatment plants, and leaching from septic systems. One third of Delaware lies in the Bay’s watershed, so its farms, sewage treatment plants and septic systems contribute to the problem.

While Pennsylvania, Maryland, Virginia, and the District of Columbia have been attempting to improve the health of the Bay for thirty years, the EPA widened the approach in 2010. It required other states in the Chesapeake Bay watershed to submit plans to curb nutrient pollution. Delaware, New York, and West Virginia each completed the second phase of planning this spring and are preparing to implement new anti-pollution measures.

For Delaware, “it’s not just about trying to improve the bay 100 miles away. It’s about trying to improve waterways in our own state.” said Delaware Department of Natural Resources and Environmental Control Secretary Collin O’Mara.

Because nutrients enter the bay from so many sources, O’Mara says that DNREC has had to enlist the help of local municipalities and industrial partners. “To achieve a healthy Chesapeake Bay is going to take the efforts of everyone from the local government to the county government, to the businesses and the farmers. We are going to have to work together so the bay can heal itself.”

O’Mara says the efforts will include upgrading wastewater treatment plants, improving storm water practices, and examining industrial sources of nutrient pollution.

However, 70 percent of Delaware’s nutrient runoff comes from agricultural activities, so individual farmers play a key role, says O’Mara. A cost-sharing program will encourage farmers to plant “cover crops” — ones that grow alongside desired crops and take up excess nutrients.

Doing more to reduce pollution in Chesapeake Bay will require significant financial investments, at a time when states are struggling to balance their budgets.

“The economic climate is tough, but efforts to clean up the Chesapeake Bay have been taking place for 20 to 30 years. We can’t delay implementation of additional pollution control measures because of costs,” said Nicholas DiPasquale, director of the Chesapeake Bay Program at the Environmental Protection Agency. “We must also consider the economic and non-economic benefits that will result from these efforts.”

Both DiPasquale and O’Mara point out that Delaware can expect some returns from these investments.

Improving storm water controls, using low-impact development techniques, and installing rain gardens will reduce flooding and the costs of responding to flood damage, says DiPasquale.

“If we’re able to improve the waterways to the point where more fish survive, it’s better for everyone,” said O’Mara.

Much of the seafood caught off the coasts of Delaware, Maryland, New Jersey, and the Carolinas started life in the waters of the Chesapeake. The success of Atlantic coastal fisheries—and the many livelihoods they support—depends directly on the health of the bay.

DiPasquale says he has started to see some success stories.

Numbers of striped bass, or rockfish, an important commercial and recreational sp that lives in the Chesapeake Bay and its tributaries dwindled in the 1980s, but since then the fish has recovered.

“We think we are starting to see the resilience of the bay restored,” said DiPasquale. “When you look at long term trends, you can see improvements in the health of the watershed, but we’re not there yet.”

Plastics in the Ocean May Be Grossly Underestimated

In Marine Ecology, Wildlife and Ecology on May 2, 2012 at 4:44 pm

This article first was published online by DFM News on May 2, 2012.

Photo Credit: Sea Education Association, Marilou Maglione

Surface trawling has long been used to estimate the level of plastic pollution in the ocean, from plastic soda bottles to disposable bags, but it turns out this method of measurement only scratches the surface of the problem… quite literally.

High winds cause plastic debris to mix well below the surface where more than half of the ocean’s plastic pollution has swirled about, uncounted, according to Tobias Kukulka, a University of Delaware assistant professor of physical ocean science and engineering.

In still water, plastic is buoyant, inevitably rising to the ocean surface, Kukulka explained in an email interview. “However, in a wind-driven turbulent ocean, this buoyant upward transport is balanced by a downward transport because plastic particles “catch a ride” with the turbulent motion,” he said.

Kukulka and co-lead author Giora Proskurowski, oceanography scientist at the University of Washington, published the results of a study of plastic pollution of the world’s oceans in the latest issue of Geophysical Research Letters.

Click here to read the article in full.