Jellies in Narragansett Bay

By BRETT WARNKE

NARRAGANSETT—They do not pulse and they do not sting.  But they do glow.  From Narragansett's waters to Argentina comb jellies shimmer with refracted light from their ever-moving bodies and can be spotted through the dark night waters as a result of bioluminescence.  Comb jellies are a type of ctenophore (ten-o-for) and natural to Rhode Island’s waters and not dangerous to humans.  But their early reproduction cycles, which new studies show are a result of climate change, have encouraged researchers to learn more about this invertebrate’s life cycle in Narragansett Bay. 

For years Professor John Costello and a squad of scientists have been studying the versatile and plankton-hungry comb jelly (Mnemiopsis leidyl), tracking its velocity and learning about the mechanical signals it uses to avoid predators.  These brainless bulbs go with the flow, allowing currents to transport them around.  Yet, how they avoid strong mixing waves and wind is still unknown.  In their habitat comb jellies are effective predators.  They eagerly feed on zooplankton, crustaceans, and eggs as well as the larvae of other fish (though this has not been observed in Narragansett Bay.) The jellies move from currents generated by cilia, siren-like arms which also gently guide fish into their voracious mouths.  Once the luckless prey are trapped inside, sticky cells called colloblasts pop like a bag of glue and force the prey to adhere to the jelly’s body.       

A warning to the curious:  If you’re ever near an expert on invertebrates, be careful not to use the blanket term “jellyfish.”  They don’t like that.  “Jellyfish” includes both Medusae (poisonous pulsers) and Cnidarians (glowing and harmless swimmers without stingers or nematocysts) and the difference is narrow but deep.  The two share gelatinous bodies but are classified in different phyla. 

 What Costello and colleagues like Barbara Sullivan Watts (a former professor in URI’s Oceanography program) have discovered is both fascinating and unsettling.  “Mnemiopsis leidyl’s seasonality seems to be shifting—Dr. Sullivan Watts has suggested there was a link between this and climate change.  Our goal was to discover what was causing the early ballooning in the jelly’s population.”  The comb jellies are summer animals.  Yet, recently, they have been appearing early in the springtime.  Costello and the other researchers were supported by the National Science Foundation in order to determine what the conditions were that gave rise to the changes in comb jelly distribution. 

Temperature was a main component.  The jellies can reproduce in 50 degrees farenheit at which time food and survival become important.  But they cannot reproduce before 10 degrees centigrade.  Even now in December it is too cold for them to thrive.  During the winter, they become absent throughout the Bay, but where do they go? 

“Previous research done in the center of the Bay yielded no life during winter months,” Costello said.  Every 30-45 days Narragansett Bay flushes out like a dirty sink.  If currents sweep them away there is nothing that allows the jelly population to replace themselves.  But the jellies were there the whole time, hiding in cove-like embayments—like Greenwhich Bay where Costello later discovered them. 

The embayments have a water retention rate four times greater than the central bay and they warm up faster in the spring.  These spots were a haven which allowed the animals to linger during winter. 

But once the scientists discovered where the jellies went during the winter, the question remained:  Why are they reproducing ever earlier?  The scientists studied two winters in detail by sampling a number of sites in 2002-3 once a week for a year.  The jellies were always observable.

  “Here’s the way climate change works,” Costello said.  “It’s not that it changes everything evenly, it makes for milder winters and a more rapid increase in the embayments temperature in the spring.  In warm years reproduction is occurring earlier.  The time in the central bay when water reaches 50 degrees is about the same as it was 100 years ago.  But embayments can warm up really quickly.  This is why climate change affects these jellies.  They’re revving up earlier.  They are wintering in these embayments, and when they warm up faster, the population pumps out of these areas.”   

This is a problem.  The jellies eat. 

Because of amplified spring warming, jellies are showing up early to eat zooplanktons which are resting their eggs at the same time they always have.  “This alters the pathways of material flow within the system,” Costello said.  If the jellies take out their food sources before they can grow, then those copepods and zooplankton are not present to eat algae or be fed on by other fish.  The ecological dominoes could fall. 

The history of a notorious ecosystem collapse in the Black Sea weighs like an alp upon those watching further developments.  Once comb jellies arrived, the sea’s fish disappeared.  But, the Baltic, Mediterranean, and Caspian Seas survived such dramatic effects. 

“These changes shuffle the deck as to who the players are,” Costello said.  Dr. Sullivan’s research has recently shown that algae levels are rising in the Bay.  New scientists will be needed to discover the effects on the fish population.  And while Costello is not interested in fish, he admits that he and other scientists like Sean Colin at Roger Williams and John Deberry at Cal Tech (who are specialists) often must wander into new territory and expand the types of questions they ask. 

“You’re never without challenges that don’t have any idea how to resolve.  But you will find some way to resolve them.  You have to wait for that lighting to strike to help you get there.  At least collaboration gets us out in the water and in the bay,” he said.

Recently, Costello has worked with funding from Naval Research and the National Science Foundation to build a vehicle—a robot jellyfish.  Its stealthy movements, made possible by material engineers, are based on the principles of Medusae propulsion.  “One of the cool things about working with engineers is that their ideas can’t just stay on paper,” Costello said.