Archive for August, 2010

Learning to Love Jellyfish?

Wednesday, August 11th, 2010

We love to hate jellyfish.  Growing up, my cousin and I used to list jellyfish along with mosquitoes as critters that appeared to have no clear reason for being.

Sea nettle

Streaming stinging tentacles, sea nettles are a nuisance, but they are also part of the Bay's ecology.

The jellyfish in question are the stinging sea nettles, Chrysaora quinquecirrha.  With their long streaming tentacles, they pulse like ghostly white umbrellas, beat like white hearts in the Bay’s chest.  For hours on lazy summer days I’ve watched them.

I saw my first jellyfish from my grandmother’s pier on the York River, but it wasn’t until I was twelve that I saw mats of them.  That was in Sturgeon Creek, off the Rappahannock River, when I started summer camp.  We used to joke that you could walk across the creek on that mat of jellyfish.

What a place to learn to water ski.  As the skis sprayed through the water, white blobs streamed by.  The motivation for not falling down was powerful.  I can’t count the number of times I’ve been stung by jellyfish over the years.  As some people say, if you haven’t been stung, you haven’t been swimming in the Bay.

Are there more jellyfish now than in the past?

Probably not.  According to Denise Breitburg at the Smithsonian Environmental Research Center, there actually appear to have been more jellyfish in the 1960s than now.  Breitburg’s been delving into past records, including those kept for some thirty years by David Cargo at the Chesapeake Biological Laboratory pier.  He started his regular recordkeeping in 1960.

The observation that there were a lot of nettles back then squares with my experiences on the York and Rappahannock rivers.  I was twelve in 1959, so my eyewitness account on Sturgeon Creek (though entirely unscientific) began about the same time as Cargo’s more rigorous monitoring.

And there’s more to the story.  According to Breitburg’s analysis, declines in sea nettle populations track closely with declines in the Bay’s oyster population.  There’s a logic in this, since in their polyp stage sea nettles attach to hard surfaces on the bottom.  In an earlier Bay, where oyster shell abounded, there would have been many more hard surfaces to attach to.

Breitburg suggests that there may be a synergy between oyster reefs and jellyfish.  The oysters give the jellyfish a place to settle.  The jellyfish consume (and out-compete) their fellow jellyfish, the comb jellies, which are predators of oyster larvae.  It could be that there’s a natural symbiosis here.

Breitburg says that the joint decline of jellyfish and oyster bars seems pretty clear, but that our observations have occurred since World War II, in a Bay that had already seen increases in nutrients.  We can’t be sure how many jellyfish there were in a less-nutrified Bay.  “What the sea nettle population looked like in the 1920s is anyone’s guess,” she says.

What we can be sure about is that while we may curse the stinging jellyfish, the truth is that they were just as abundant — and perhaps more so — fifty years ago, when underwater grasses flourished, when the waters were clearer, when the Bay was in better shape.

And if Breitburg’s hypothesis linking jellyfish and oyster reefs turns out to be right, I guess we’ll have to learn to love them.

I’m not sure if I can.

For good descriptions of Denise Breitburg’s research linking jellyfish and oyster bars, see Scientist Looks to Data from the Past and Recovering Resilience.