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Blue crabs decline–but recovery still on track

Tuesday, April 30th, 2013

by Matt Ogburn and Tuck Hines

Photo: Smithsonian Environmental Research Center

Photo: Smithsonian Environmental Research Center

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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Once an invasive, always an invasive?

Thursday, April 4th, 2013

by Monaca Noble and Paul Fofonoff

The European green crab has been on the east coast of the U.S. since 1817. (SERC)

The European green crab has been on the east coast of the U.S. since 1817. (SERC)

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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From the Field: One Final Search

Tuesday, February 26th, 2013

by Katrina Lohan

Sunset from the dock at the Bocas del Toro Marine Station, Smithsonian. (Katrina Lohan)

Sunset from the dock at the Bocas del Toro Marine Station, Smithsonian. (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 >>

From the Field: A Day’s Work

Monday, February 25th, 2013

by Katrina Lohan

Kristina Hill investigates a mangrove root at Rio Alejandro, Panama, to determine what kinds of oysters are living on it. (Katrina Hill)

Kristina Hill investigates a mangrove root at Rio Alejandro, Panama, to determine what kinds of oysters are living on it. (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.

From the Field: The Language Barrier

Monday, February 25th, 2013

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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From the Field: An “Unglamorous” Sampling Site

Thursday, February 21st, 2013

by Katrina Lohan

Life underwater. Fire coral, anemones, sponges and a diverse group of oysters cling to a dock at the Smithsonian's Bocas del Toro Marine Station. (Kristina Hill)

Life underwater. Fire coral, anemones, sponges and a diverse group of oysters cling to a dock at the Smithsonian's Bocas del Toro Marine Station.
(Kristina Hill)

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…

From the Field: More Oysters, Please!

Wednesday, February 20th, 2013

by Katrina Lohan

Katrina Lohan attempts to scrape Striostrea oysters off rocks in a tidal pool at Bique, Panama. (Kristina Hill)

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!

From the Field: Punta Caracol

Wednesday, February 6th, 2013

by Katrina Lohan

Mark Torchin collects oysters off mangrove roots, while Greg Ruiz and Kristina Hill sort and count the different oyster species. (Katrina Lohan)

Our first sampling site was Punta Caracol. We were able to find three oyster species attached to the mangrove roots at this site, including Ostrea sp., Crassostrea sp. and Isognomon sp. The salinity was about 30 parts per thousand, so well within the acceptable range for the three protozoan parasites that we are hoping to find.

I spent some time on the boat, but I desperately wanted to get in the water. Thus, when we had trouble finding Ostrea sp., I eagerly offered to jump in and snorkel around in the mangrove roots to look for more individuals. While I wasn’t too successful finding that species in the areas I was looking, I greatly enjoyed getting into the mangrove trees to search for them! I saw xanthid crabs, sponges and lots and lots of barnacles! We did eventually find enough individuals from all three species, at which point we headed back to the lab to process all the oysters.

Being in the water was definitely the best part of the day!

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From the Field: Scouting in Bocas del Toro

Tuesday, February 5th, 2013

by Katrina Lohan

After spending less than a week at the Naos Laboratory, Kristy and I headed to Bocas del Toro with collaborator Mark Torchin from STRI and my advisor, Greg Ruiz from SERC. The flight from Panama City to Bocas del Toro is only about an hour, so we left on the first flight out in the morning and arrived at the station in plenty of time to put in a full day’s work. Though tired from getting up early to make the flight, there is nothing that wakes me up faster than a chance to get in the water!

Reconnaissance cruise in Bocas del Toro, on the Atlantic side of Panama. Since the canal opened almost 100 years ago, species as well as cargo have been able to cross the waterway between oceans. (Kristina Hill)

The majority of our first day was spent settling in. We had a safety orientation with Plinio Gondola, the Deputy Scientific Coordinator at the field station. We then unpacked the gear and quickly took over our assigned space in Laboratory 100. Next it was time to settle into onsite accommodations. The Bocas del Toro field station has dormitories as well as houses for visitors. We are staying in one of the houses, the Casa Hoch, which has two rooms, a dining room, lounge area and full kitchen. Excellent accommodations!

After settling in, we decided to do some reconnaissance in hopes of determining at least one potential sampling location. Kristy, Greg, Mark and I headed out on one of the marine station’s boats to find oysters. We spent most of the time searching mangrove roots attempting to determine what species were present in the different locations we were surveying. While driving around the mangroves is nice, I particularly enjoyed the reconnaissance that involved snorkeling. While snorkeling, I was able to check out potential pathogen reservoirs in addition to noting the bivalve species in the area. So many research options and so little time!

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From the Field: Disease Reservoirs

Friday, February 1st, 2013

by Katrina Lohan

Katrina Lohan scrapes mud and algae off a rock at Punta Culebra. Later, Lohan will use genetic tools to see what protozoan parasites are inside that sample.
(Kristina Hill)

During the seven months that I have been a post-doctoral fellow at the Smithsonian, I have been intellectually challenged over and over again and I’m loving it! One thing that I have had to think about is what direction I want my future research to go and how my current fellowship project is helping to lead me in that direction. Through multiple conversations with both of my advisors, Dr. Robert Fleischer at the National Zoo and Dr. Gregory Ruiz at the Smithsonian Environmental Research Center, I have been able to hone in on my particular research interests and figure out how to alter some aspects of my fellowship project to better incorporate them.

I have realized that I am particularly interested in disease reservoirs. Unfortunately, this term is difficult to define. But basically, a disease reservoir can be anything (living or nonliving) where a disease-causing organism can survive outside of its host. As part of my fellowship project, I had already intended to use genetic tools to look for protozoan parasites in oysters and water samples. After further consideration, I have decided to also use genetic tools to look for parasites in other environmental reservoirs. It’s hard to predict what environmental reservoirs would be best to collect, so I was advised to choose a site, collect a few samples and just see what parasites are present. Then, I can use those results to help me decide how I should conduct a more extensive sampling scheme in the future.

With that in mind, Kristy and I headed to Punta Culebra to collect some reservoir samples. I was really excited, even though I wasn’t entirely sure how or what I was going to collect. But I was confident that I would know when I saw it. I decided to take three samples from five different sites along the rocks, roughly matching the sites where we had previously collected oysters. At low tide there are small tide pools within the rocks. I decided to collect from within these pools. In the end, I took three samples from each site. One was a sediment sample, which ranged from fine muddy sediments to larger coarse sediments with lots of shell bits. The second sample was from the living material that blanketed the rocks, which was probably a combination of mud, bacteria and turf algae. The third sample I took was a sample of a distinct clump of turf algae. I am really excited to see what protozoans I find!

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