BAR HARBOR — As Maine’s waters are growing warmer and more acidic, lobster researchers are looking at how that’s affecting both the mothers and offspring of the state’s most prized crustacean.
One thing is known for sure: Mature female lobsters have been shrinking.
Over the past three years, Jesica Waller, a lobster scientist at the state’s Department of Marine Resources, has collected and analyzed more than 1,200 female lobsters along the coast. She has found that since the 1990s, mature females are getting smaller.
“DMR research shows that the carapace/shell length at which most females reach maturity has decreased coastwide over the last 25-30 years,” she wrote in an email. “We sampled and analyzed females along Maine’s coast, and we found that the length at which most females reach maturity has decreased between 5.6 mm and 6.7 mm over this period (mid-1990s to today).”
Waller also found that, while there’s a decrease across the entire coast over the last three decades, there is a latitudinal gradient to the decrease as well, with females reaching maturity at smaller sizes than females farther Downeast.
This research has quantified anecdotes from lobstermen who have seen smaller egg-bearing females show up in their traps and it also lines up with the average size of egg-bearing females in other sea sampling programs conducted by DMR.
A suite of factors is likely behind the shrinking of mature female lobsters, but many researchers have identified temperature as an important driver of the changes.
“There is a body of research to show that the temperature has a significant impact on the growth pattern of lobsters, and the development of reproductive tissues (like ovaries), with higher temperatures yielding faster development,” Waller wrote. “In addition, it’s been well documented that lobsters that experience areas with relatively warm temperatures reach maturity and produce eggs at a smaller size than females in cooler areas.”
Historically, lobsters go for quantity when they produce eggs, laying tens of thousands of eggs at a time. With smaller females laying fewer eggs, researchers are trying to find out if the quality changes in the eggs that are produced.
Studies from Atlantic Canada have shown that smaller females may produce eggs that are smaller and have less of the proteins and fats that sustain larvae while they are developing when compared to eggs produced by larger females, Waller said.
There’s also evidence to suggest that small females in some Canadian regions are more likely to carry abnormally small egg clutches/batches of eggs on their tail.
In Maine, research is underway to figure out what happens when egg-bearing females are smaller.
“We have a student in the lab who did a whole bunch of experiments, looking at the size of the eggs, the number of the eggs, and differences along latitudinal gradient with temperature and then looking at once they hatch, if their performance becomes less,” said David Fields, a senior research scientist at the Bigelow Laboratory for Ocean Sciences in East Boothbay.
The data from those experiments is currently being analyzed and the researchers are looking at the lipid content in the yolks of the eggs. But at least one initial test indicated that the quality did not improve.
To measure the caloric output of an egg, researchers at Bigelow put them in an oven at 700 degrees Celsius and turned all the matter into carbon dioxide.
“It looks like the females that come from warmer climates, their eggs have less caloric value,” Fields said. “So that’s kind of an early sign that there is less investment.”
While we know mother lobsters are getting smaller, Bigelow has also done work to see how the species offspring in the larval stages handle rising temperatures and ocean acidification.
The larvae seemed to be able to handle ocean acidification. Previous research showed it had little effect on their growth and metabolism, but a study published earlier this year by Maura Niemisto, a research associate at Bigelow, found that it is changing them at a molecular level.
Through genes, all living organisms can regulate a range of biological processes that can be influenced by changes in the environment.
Niemisto’s study focused on the post-larval stage of lobsters that live in the upper water column where ocean acidification and temperature are changing quickly. At this stage, the lobsters are planktonic, meaning they have limited control on their movement and can’t simply move on to more favorable environments.
The scientists exposed the post-larval lobsters to the temperature and acidity levels projected for the end of the century and found that the lobsters’ cells adjusted gene regulation to support shell structure and immune functions.
The response was stronger in relation to increased acidity than increased temperature, but when the environment was both warm and acidic, the lobsters showed significantly more genetic response than when exposed to either one alone.
“Stressors on an organism have the ability to compound into something that makes it really hard to grow through all the developmental stages to get to a full-grown lobster,” Niemisto said in a statement earlier this year.
Lobsters may be able to adapt to a changing environment, but it takes a significant amount of energy that comes from a limited budget.
“So, if they’re spending a lot of energy on building proteins to respond to stressors, something else has to give,” Niemisto said.
As iconic as the species is in Maine, not much is known about the larval stages of lobster. Bigelow is also studying what they eat at that point in life to figure out if that’s another pressure point on the species.
While this all sounds potentially ominous for the future of the species, the current conditions have been a boon to lobstermen, who have enjoyed banner years as of late.
“The populations of larval lobsters surviving as temperatures increased got better,” said Fields. “We’ve been having boom years of lobster recruitments.”
But what giveth also taketh away, he said.
In theory, because of climate change and other factors, smaller females could be producing fewer and lower-quality eggs that are then hatched into environments that are increasingly tougher for larvae to survive in — basically, weaker baby lobsters are being born into a harsher environment.
If that turns out to be true, the research going on now could point to better ways to manage the fishery to keep it sustainable.
“It’s an ecological conundrum,” Fields said, “But I think we’re starting to get the variables right and we’re studying them in ways that will help us understand how they work.”