Tiny copepod could have big impact on lobster industry

For the past few years, a mystery has been developing in the Gulf of Maine off the east coast of the United States: Where, exactly, are all the baby lobsters? 

Scientists first started sounding the alarm in 2016, when they noticed that the intermediary stage of lobster growth was missing for unknown reasons. The population of mature, egg-laying females was, and still is, relatively high. Surveys in the water column also showed that the crustacean’s youngest larval stage was present in great abundance. 

Yet the intermediate stage, when the lobsters first start to settle on the ocean floor, was practically nonexistent compared to the abundance of adult and larval lobsters.

“We’ve got ramping up of the abundance of the egg bearing females, we’ve got the ramping up of the abundance of the earliest larval stages, but then there’s this downturn in the abundance of the latest larval stages,” said Richard Wahle, of the University of Maine’s Darling Marine Center. “We’ve got this disconnect.”

That disconnect left scientists wondering: What’s happening to all the baby lobsters?

It’s a question that is incredibly important to the region’s economy, particularly the state of Maine. The lobster industry in the state landed 111 million pounds of lobster in 2017, which was down from 131 million pounds in 2016. All told, studies estimate that the industry adds USD 1 billion (EUR 807 million) to the Maine economy each year. A lack of baby lobsters means the fishery could be in trouble if the trend continues.

Since the worrying findings, biologists studying the gulf have been seeking the missing piece of the puzzle. One recently published paper indicates scientists think they may have found it  – Calanus finmarchicus. 

C. finmarchicus is a tiny copepod that’s of great importance to a lot of ocean life. Despite being smaller than a grain of rice, they exist in the ocean by the billions and provide nutrition to some of the largest creatures on the planet, including the endangered North Atlantic right whale. 

While the importance of C. finmarchicus to the ocean is well known, up until recently it wasn’t really linked to larval lobsters. Joshua Carloni, a biologist with the state of New Hampshire’s Fish and Game division, was one of the first to find a correlation between numbers of C. finmarchicus and larval lobster. 

“We know they can and do feed on them, but there’s no good literature out there of to what degree,” said Carloni. 

Carloni has been investigating the lack of baby lobsters, and managed to get access to one of the best data sets around to do so thanks to officials managing the Seabrook Nuclear Power Plant.

The power plant, located on the coast of Seabrook, New Hampshire, got its permits for construction back in 1976. One condition of that construction was extensive monitoring of the nearby sea life, both near the plant itself and at a distance, to ensure the plant didn’t have a negative effect. 

That monitoring started before the plant went online in 1990, and includes multiple tests in multiple parts of the water column, using a variety of net sizes, on a weekly basis from May through October. 

“When they went online, they continued that monitoring so they could do a comparison of before the plant went online and after the plant went online,” Carloni said. “They’ve been doing that for over 30 years.”

The tests have continued to indicate the plant has virtually no effect on the sea life. But for scientists, 30 years of consistent data covering a large breadth of sea life in the water column is almost unheard of. 

“There is a lot of data being collected, and we were lucky enough to look into it and use it,” Carloni said. 

Typically, lobster studies focus those that have already settled on the ocean floor. The Seabrook data, luckily, covers much more. 

“It’s a unique dataset to the extent that it’s really the only long-term monitoring of the larval stage of lobster,” Wahle said.  

What the data showed Carloni was fascinating. The Seabrook data indicates largely what scientists already knew: The youngest lobsters are still around in abundance, but the older larval stages are missing. But what it also showed was a surprising correlation between the numbers of older larval stages of lobsters, and that of C. finmarchicus. 

“They’re not just both going up or down at the same time, they seem to be going up and down together,” Carloni said. 

Of course, correlation is not causation, and the relationship still needs to be investigated further. But Carloni wrote and recently published a peer-reviewed paper on the relationship, and it’s starting to get more traction. 

Wahle helped co-author the paper, and said that so far, C. finmarchicus is starting to look like it might be a key food for larval lobsters. However, it’s no smoking gun. 

“We have to be a bit cautious here. It could be that there’s some larger factor driving the abundance of both,” he said. “Something like a larger predator or currents playing a roll.”

Still, some preliminary work has shown that the relationship between larval lobsters and C. finmarchicus may be greater than anyone realized. 

“So far, nobody has really suspected that there could be that strong a link between this particular copepod and lobsters,” Wahle said. He mentioned that a colleague of his at Bigelow Laboratory for Ocean Scientists, a nonprofit research institute located in Boothbay, Maine, has already done a few “preliminary grazing experiments” involving larval lobster and the small copepod by simply placing them in the same tank to see what happens. 

“Lo’ and behold, they [lobsters] just chow on them,” Wahle said. “Calanus is large as copepods go but it’s still really about the fifth or the tenth of the size of a larval lobster, they can easily handle it. They’re devoured in the experiments.”

While the studies are all promising, the new findings raise still more questions. The diet of larval lobsters is still relatively unstudied, and the correlation could just be a coincidence that’s the symptom of a larger systemic change in the habitat. 

Still, it’s interesting enough that Carloni and Wahle are both planning to try and study the relationship between C. finmarchicus and larval lobsters further. 

“We’re certainly going to pursue this and see where it leads, because it opens up a whole new box of questions,” Carloni said. “There are some grants in the works.”

Photo by Jessica Waller/University of Maine Darling Marine Center