Thursday, July 13, 2017

Tropical Travelers: What gulf stream orphans tell us about a Narragansett Bay of the future

By Adam Kovarsky, aquarium manager

Narragansett Bay is rich with hundreds of species of flora and fauna. The native species have existed here naturally for millions of years, perfectly intertwined in a symbiotic ecosystem suited to the Bay’s natural habitat and water conditions. Invasive species have been brought to Narragansett Bay from various parts of the world strictly by way of human intervention and have thrown off the delicate balance nature has honed for millions of years. At Save The Bay, we work to restore native populations and educate communities about the potential negative impacts of the invasives. We are also particularly interested in a third, lesser-known category of life in the waters of Narragansett Bay, because they may paint a picture of the marine life in a Narragansett Bay of the not-so-distant future.

I’m talking about species we call tropical strays, or Gulf Stream orphans, which natively occur in warmer tropical waters along the North American Eastern coast, usually between the Carolinas south to the Bahamas. These tropical travelers—typically either recently hatched juvenile fish or unhatched eggs—get displaced by the Gulf Stream current and washed 25-75 miles per day northward along the coast, becoming stranded in Narragansett Bay. They exist in our waters for the remainder of the warm summer months, only to perish in our cold New England waters in winter, save the few lucky larger adults that make it back to their native ranges— or those that make it to our Exploration Center & Aquarium. We have a strong partnership with many local fishermen who bring us spotfin butterfly fish, triggerfish, striped burrfish, crevalle jack, and others caught in their nets and traps, knowing they won’t survive our winters. At the aquarium, we use them to teach our guests about warming water temperatures and how they can help slow the process of climate change.

Figure 1: Global ocean conveyor belt.
Image by Thomas Splettstoesser via Wikimedia Commons. 
Tropical travelers are nothing new. The warm Gulf Stream current has been displacing marine life on earth for as long as it has existed, circulating as part of the constantly moving global ocean conveyor belt (Figure 1) controlled by temperatures and salinities in our planet’s oceans. These currents control the planet’s climate and weather patterns and give Earth the amazing ability to support life as we know it. The ocean is like the brain of our planet, regulating climate and weather. But today’s Gulf Stream orphans are telling us things are changing.
As our water temperatures have warmed by 4ยบ F in the past 50 years, these tropical fish are arriving earlier each summer and surviving later into the fall and winter seasons each year. This poses the question to local scientists: What will the Narragansett Bay of the future look like? Will cool water species such as lobster, winter flounder, tautaug and dogfish still reside in Rhode Island years from now? Or will our year-round Bay community consist of such critters as crusty blue crab, spikey striped burrfish, toxic trunkfish and aggressive permit, all now found far south of here? Only time will tell as changing climate conditions continue to warm the waters of our Bay. The question I ask myself is how these Gulf

As waters continue to warm, will we see more
Gulf Stream orphans like the permit and smooth trunkfish 

Stream orphan species will affect our Bay and its native inhabitants as newcomers arrive. When species’ native ranges shift along the coast, a myriad of interactions are created that are relatively untested, unobserved and unpredictable. 

“Blue crabs have always populated Narragansett Bay, but in recent years we have seen a noticeable increase in their density when trawling and surveying intertidal areas,” said Save The Bay Captain Eric Pfirrmann. As these blue crabs find the warming waters of the Bay desirable, they migrate northward.

Likewise, the American lobster, which prefers waters cooler than 60 degrees, has begun to migrate north as well, to places such as Maine coastal waters. “This has been the best several years for lobster fishing in Maine in a long time. We think that because so many lobsters are moving their range northerly, they are congregating in Maine in large numbers,” said a lobster fisherman from Maine who asked to remain anonymous.

While these sound like positives for lobster commerce in Maine and the potential for a stronger local blue crab fishery, we must consider broader impacts of spatial and temporal issues. As species migrate north, they can travel only so far until there are no more northern portions of our planet with the temperatures they require. Species that live at the poles are already feeling these effects. The most charismatic of mega-fauna that we all know and love are the plighted polar bears, which no longer have territory further north toward which to migrate and may soon be extinct due to lack of frozen ice cap habitat. Will lobsters one day arrive at the poles with no suitable habitat remaining?

Another potential negative impact of species range shifts is how the animals will interact with one another. Many Gulf Stream orphans have survival adaptations, or “novel weapons,” to which Narragansett Bay native species have never been exposed, posing the potential for outcompeting our native species. An example is invasive plants that produce a toxic chemical that acts as an herbicide against native plant species. When looking at the collection of novel weapons possessed by all potential Gulf Stream orphans, Narragansett Bay will have a lot to deal with as its population shifts.

The mission of Save The Bay is to protect and improve Narragansett Bay; we need to take action to educate the public, inform lawmakers and adapt our Bay to an uncertain future. It will be the civic responsibility of all Rhode Islanders to find innovative ways to reduce the effects of climate change to protect the native life in Narragansett Bay in the years to come.