by Matt Ogburn and Tuck Hines

To some following the blue crab recovery, the news earlier this month may have come as a shock. In 2012, the Chesapeake-wide Winter Dredge Survey estimated a record 764 million blue crabs in the Bay—the highest seen since 1991. Juvenile crab densities jumped to their highest levels ever. Then the 2013 survey released April 19 saw both those numbers drop.

Managers greeted the dwindling juvenile population with some depression. But those numbers may not matter as much, according to biologists Tuck Hines and Matt Ogburn of the Smithsonian Environmental Research Center. Ecologists at SERC have been tracking blue crabs for more than 30 years, almost a decade before the winter dredge survey began. They’ve discovered the population that really needs watching is the spawning females. Here is what the numbers are telling us:

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by Monaca Noble and Paul Fofonoff

The title question was raised by one of the readers of last month’s feature story on green crabs (Carcinus maenas). The reader asked, “If the green crab was first seen here [the East Coast of the US] in 1817, is it still considered an invasive species 200 years later? How far back do you go to claim something is invasive vs. native?” Several groups of people have drawn their own lines in the sand, but we wanted to examine current thoughts and perceptions. The following article is based on views expressed in a recent listserve discussion.

The term invasive was used in the green crab article because the crab is on the list of the world’s 100 worst invasive species. But it is also commonly used as a synonym of introduced. Which brings us to the importance of terms and definitions.

As one respondent pointed out, there are different interpretations of the term “invasive.” Some people define invasive in terms of a species’ ecological impact or behavior, while others use it to refer to a species’ origin, and sometimes both are part of the definition. If a species’ characterization as invasive is based only on its ecological behavior, then it is possible for a species to be both native and invasive. But if the species’ origin is part of the definition, then only nonnative species can be invasive. Others add another dimension to the word by making the mode of introduction important. Species can be spread naturally through dispersal and/or through human-mediated transport. Some people use invasive in reference to human-mediated introductions of nonnative species. Unfortunately, when we hear the word “invasive” we rarely know the definition behind it.

But whether something is considered invasive appears to be largely a matter of perception rather than just definition, and there are many contributing factors that muddy the water. Most responses from the discussion fell into three perception categories represented by these questions:

1) Do we benefit from the species, or is it harmful?

2) Is the species part of what we consider the natural landscape?

3) Is the species native?

Maybe our problem is that we view nature in the time frame of a biologist’s career-span.”

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by Kristen Minogue

Most gardeners consider the sight of an earthworm writhing in the dirt a good omen. The slimy invertebrates chew up and churn up the soil, making it easier for vegetables and flowers to access nutrients.

But for wild orchids, they’re more of a menace. Earthworms could prevent roughly half a forest’s orchid seeds from even germinating, ecologists from Smithsonian Environmental Research Center and Johns Hopkins University discovered in a study published online this March in Annals of Botany Plants.

The small size of orchid seeds (they are barely the size of dust grains) makes them particularly vulnerable. As earthworms chew up forest litter, they ingest orchid seeds as well. When that happens, two things can keep the seeds from germinating: One, the process of passing through an earthworm’s gut can render them unviable. Or two, if the seeds survive ingestion, they can end up buried so deep that they can’t access the fungi they need to germinate and grow. As a general rule, deeper soils are much less likely to have those fungi.

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by Kristen Minogue

If the massive snowstorms that pummeled the northeast this winter—and at least one downpour in spring—seem out of place in a warming world, climate scientists have a message: Don’t fret, it’s just physics.

For several years, scientists have anticipated a future of “less snow, more blizzards” in the winters ahead. The message may sound like a paradox. But for the planet, it boils down to one simple truth: Warm air holds more moisture than cold air.

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by Monaca Noble and Linda McCann

European green crabs are eating and marching their way up the west coast.

One of nine marine invertebrates to make the list of the world’s 100 worst invasive species, they’ve had major economic impacts on shellfisheries in New England, including blue mussels, the Virginia oyster (Crassostrea virginica) and Bay scallops. Impacts are mounting on the west coast too, where losses to bivalve fisheries (Pacific littleneck, Japanese littleneck, softshell clams and blue mussels) are projected to reach $20,000-60,000 per year. Ecologically, their impact has been no less severe, as they prey on and compete with other crabs, bivalves, gastropods like snails and slugs, and many other invertebrates.

Green crabs are exceptional world travelers, making it from their native region along the European Coast to six major regions of the world, including the Northwest Atlantic (Maryland to Newfoundland), the Northeast Pacific (California to British Columbia), Patagonia, South Africa, Japan and Australia. Their mode of transport may vary, but evidence suggests they’ve been transported with the live-bait trade and in ships’ ballast water.

Green crabs have been on the East Coast of the US for about 200 years, according the NEMESIS database. They made their first appearance near New Jersey in 1817. From there they moved north, reaching the Bay of Fundy, Nova Scotia in 1953, the Gulf of St. Lawrence by 1994, and finally, Placentia Bay, Newfoundland in 2007. Their southward expansion stopped at the Chesapeake Bay; possibly they couldn’t compete with the blue crab (Callinectes sapidus).

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by Katrina Lohan

We had very little trouble finding two of the oyster species we needed at three different places. But with only three days left in our trip, we had yet to find Ostrea sp. at more than one location. With our hopes high, we headed toward Portobelo to see if we could find a saline river-like environment that had Ostrea sp. in high enough abundance for us to sample. The drive was gorgeous! We drove along the Atlantic Coast of Panama and stopped at five separate “rivers”, though most of them were pretty small and should probably be called streams instead. We also briefly drove into Portobelo so that we could drive past the old Spanish forts in the city.

We only found Ostrea sp. at one of the rivers, and we didn’t find enough to sample there. Our final stop on our way back to Naos was the French Canal. We had borrowed an inflatable canoe from Mark Torchin, which took us about 20 minutes to pump up. Once we did, we were able to get the canoe into the water and used it to more closely investigate what oysters were growing on the bridge pilings. We had our fingers crossed that it would be Ostrea sp. but, alas, it was Crassostrea sp. instead. Well, I can’t be too upset. While we didn’t get the ideal sampling we were hoping for, it was still a very successful trip!

Next month we head to Merida, Mexico to continue our sampling adventures. Stay tuned!

Complete parasite-hunting stories from Panama >>

by Katrina Lohan

The day after arriving in Panama City, we went out into the field to continue collecting. During our trip in December, we had sampled two locations on the Atlantic side of the Canal. Now we had to complete our sampling for the three genera we had been sampling in Bocas. So we headed out to an area near Colon, Panama, and rented a boat for a few hours to go find oysters in the mangroves. We were successful at finding all three species at one location and two of the three species at another location. Not bad for a single morning.

by Katrina Lohan

We were able to find a final location for Ostrea sp. in Bocas del Toro, which wrapped up our sampling there. So it was time to return to Panama City to complete our sampling on the Atlantic side of the Panama Canal.

Now I have been trying to learn and remember some Spanish phrases. There were times when my lack of fluency was awkward, and other times when it is more problematic. Our return trip to Panama City was one of the problematic occasions!

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by Katrina Lohan

To satisfy our sampling scheme, we needed one more location with all three genera present. The dock at Bocas del Toro wasn’t the most glamorous location to sample, but it was an amazing place to snorkel around. There were many bivalve species and an abundance of individuals for each species located on the pilings. There were lots of different fish, coral, hydroids and sponges. It was beautiful! We decided to make this our third sampling location as it was easily accessible and had all three species–or so we thought.

We know oysters are tricky to morphologically identify, as they have such a wide range of growth patterns. It wasn’t until we were back in the lab and had shucked a few of the oysters open that we realized what we thought was Ostrea sp. in the field was actually a different species, Dendostrea frons. Oops…

by Katrina Lohan

For the second oyster sampling excursion, we headed out to Bastimentos and Solarte to try to find another site where the same three oyster species co-occur. Unfortunately, Kristy was out of commission at the time due to illness (though I’m happy to report that she has made a full recovery).

Mark, Greg and I had scouted out a few potential locations the night before. While we had no trouble finding Isognomon sp. and Crassostrea sp. on the mangroves in multiple locations, we struggled to find a location where Ostrea sp. occurred with them. So, when we ventured out to collect in the morning, we decided to scout out a few more locations that might have all three species. At Solarte, we found just the right spot! Collecting all the oysters we needed didn’t take long at all, so I suggested that perhaps we do a little snorkeling while on our way back to the field station. Mark knew just where to go. We ended up snorkeling at a place called Hospital Point, where I saw a spiny lobster (Panulirus argus). Then we stopped at another snorkeling spot with huge sea stars, cute sandy gobies, sea cucumbers and beautiful coral!

The extra time spent in the water was just what I needed to motivate myself to get into the lab and process some oysters, as I knew that any data I helped generate would add to the ever-growing body of knowledge about the world beneath the waves!