Tiny Copepod Causes Quivers in Gulf of Maine Food Web

It’s hard to imagine but the well-being of animals as diverse as the giant North Atlantic right whale and the diminutive herring are dependent on a creature the size of a grain of rice: Calanus finmarchicus, a cold-water copepod.
C. finmarchicus is the dominant species of copepod found throughout the Gulf of Maine, the southern-most extent of its range. It’s the preferred food of just about every creature in the Gulf because it is like a floating French fry — C. finmarchicus is packed with fat.
Before it hits sexual maturity, C. finmarchicus remains dormant deep in the water column, drawing on its reserves of fat, which can reach 60% of its body mass. Sometime in the early spring it will rise toward the surface, molt and grow into a mature adult. When this copepod appears and in what density matters a great deal, not only to right whales and herring but also, it appears, to juvenile lobsters.

It may be the size of a rice of grain, but C. finmarchicus is a giant in the Gulf of Maine food web. It’s presence in dense schools provides critical food for the endangered right whale. NOAA fisheries.

Right whales have been turning up in unusual numbers in the late winter and early spring in Cape Cod Bay, presumably to feast on the copepods. Researchers from the Center of Coastal Studies in Provincetown reported this year that much of the known population of North Atlantic right whales (453) could be found in the bay until mid-May. But the whales did not look like their normal plump selves. Observers reported seeing notably thin whales. Furthermore, no calves have been spotted accompanying their mothers anywhere along the East Coast this year.
Right whales often converged in the eastern Gulf of Maine in areas like Jordan Basin to socialize and mate during the summer months. Warmer-than-average water has influenced the presence of C. finmarchicus in the region in recent years, according to several researchers. Nick Record of the Bigelow Laboratory for Ocean Sciences in East Boothbay said the deep-water population of C. finmarchicus in the eastern half of the Gulf has been in decline.
“I’ve been seeing really warm temperatures especially in the deep basins where Calanus is, and at the time when right whales are in the eastern Gulf,” Record said. “That’s the habitat the whales have abandoned in the last few years, so it may be connected to the changes in the deep water coming into the Gulf.”
Jeffrey Runge, a a biological oceanographer at the Gulf of Maine Research Institute, thinks that C. finmarchicus is continuing to enter into the Gulf carried by the cold-water current that runs from the Gulf of St. Lawrence along Nova Scotia and into the Gulf of Maine. C. finmarchicus can continue to exist in that thread of cold water, even if the Gulf itself is warmer. Runge has been sampling two sites in the Gulf of Maine — Wilkinson Basin and the mouth of the Damariscotta River — for 15 years. Since 2010, Runge has seen a 30% decline in the volume of the copepod at both sites during the summer.
The cause of the decline in C. finmarchicus is unclear. “It’s hard to say whether it is due to a long-term climate change or if it is a local event,” he said. The springtime abundance of C. finmarchicus, on the other hand, is off the charts, five times what it was in 2010. However, by rising to the surface earlier in the year due to warmer surface waters, C. finmarchicus reproduces earlier as well, making them less fat at the time that right whales arrive.
The presence of C. finmarchicus also appears to influence the survival of juvenile lobsters as well. A recent study by Joshua Carloni, a research scientist in New Hampshire’s Fish and Game Division, tackled a question that has troubled lobster scientists: why are there so few juvenile lobsters settling in the Gulf of Maine when the population is at record abundance? Given the huge increase in commercial landings in the last decade, there should be a corresponding increase in the number of baby lobsters turning up in the yearly American Lobster Settlement Index, a survey of young-of-the-year conducted since 1989. But settlement figures have been going down for four years, according to Rick Wahle, senior research scientist at the University of Maine, who has overseen the survey since its inception.
Carloni examined data accumulated by the Seabrook Station nuclear power plant operators since the 1980s. As part of its original permit, the company agreed to conduct extensive surveys of the waters around its New Hampshire plant. Carloni pored through the data to see if juvenile lobster abundance could be linked to food sources.
“The data revealed significant increasing trends in lobster stage I larvae, consistent with the mounting levels of egg production in the Gulf of Maine. The planktonic post-larvae from the same survey have been in decline in recent years, and this decline correlates well with estimates of young-of-year lobster,” Carloni said. “We found that both post-larval and young-of-year lobster are significantly correlated with the abundance of C. finmarchicus, but not other potential zooplankton prey available during the summer lobster larval season.”
Wahle said it’s not completely certain that baby lobsters are dying off due to a lack of C. finmarchicus. They might be settling in new places, or lobsters and C. finmarchicus might be under pressure from bigger predators, like jellyfish.
C. finmarchicus is not the only copepod in the sea. There are dozens of other species that can be found in the Gulf of Maine, and some that may migrate from southern areas as the Gulf continues to warm.
But C. finmarchicus is the dietary prize for so many marine species because it is so rich in fat; the cost to a young lobster or right whale in terms of energy to catch and devour a gallon of C. finmarchicus is offset by the calories the copepods contain. The same amount of effort to gulp down an equivalent volume of another species of copepod, such as C. glacialis, does not return the same amount of calories. The long-term effect of this likely shift in copepod species remains unclear.

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