SEA 



SCIENCE 



E 



EELGRASS: 



. Binge Eaters 

 in the Estuary 



By Pant Smith 



Photos courtesy of the North Carolina State University 

 Center for Applied Aquatic Ecology 



lelgrass is a nitrogen junkie. 

 That's no laughing matter, says Brant 

 Touchette, since the ecologically important 

 seagrass quite literally can eat itself to death 

 in nutrient-enriched estuarine waters. 



Findings from Touchette' s eelgrass 

 research provide new insights into the 

 metabolism of seagrasses — perhaps a key to 

 solving the disappearing eelgrass mystery. 



Eelgrass, a submersed aquatic plant, 

 plays an important role in the estuarine 

 nursery. It provides habitat for aquatic life, 

 and it helps increase water clarity and lessens 

 erosion by reducing wave energy and 

 trapping loose sediments, says Touchette. 



In recent decades, there has been a 

 widespread decline in eelgrass. 



"Where we see declines in eelgrass 

 habitat, we usually see declines in commer- 

 cially valuable finfish and shellfish popula- 

 tions," explains Touchette, an assistant 

 professor of biology at Elon University. 



Touchette conducted his eelgrass work 

 while completing doctoral and postdoctoral 

 studies at North Carolina State University's 

 Center for Applied Aquatic Ecology. Articles 

 based on his North Carolina Sea Grant- 

 funded research have been published in 

 several scientific journals. 



Building on the previous work by center 

 researchers, including director JoAnn 

 Burkholder, Touchette conducted his field 

 work in the estuarine waters surrounding the 

 National Oceanic and Atmospheric 

 Administration's Beaufort Laboratory. 

 Submerged eelgrass beds there provide 

 abundant samples for both field observations 

 and controlled lab experiments. 



Touchette' s study shows that eelgrass 

 leaves will take up nitrate at all costs. 



"Seagrass is nitrogen limited, so it is 

 geared to recognize nitrogen going through 

 the water column," Touchette explains. 



"A little nitrogen is a good thing. But, 

 eelgrass is a nitrate junkie. It will deplete its 



growth effort to go after nitrate." 



Unlike other plants that have control 

 mechanisms, eelgrass has no turn-off switch. 

 It therefore uses all its energy to go after 

 nitrate from the water — energy that should 

 go towards its growth, development and 

 sugar production. 



Eelgrass can't stop taking up nitrate 

 until it runs out of soluble carbohydrates. 



In a controlled lab setting, Touchette 

 could manipulate the amount of nitrogen in 

 the water column to observe its affects on the 

 eelgrass. 



"It's amazing to see what occurs with 

 increased nitrate levels," he says. "The leaves 

 break off, the main growing area crumbles, 

 and the plant begins to deteriorate. Its growth 

 is stunted." 



Another surprise finding is that eelgrass 

 takes up nitrate from the water column day 

 and night. In laboratory experiments, 

 Touchette found that the activity of the key 

 enzyme in nitrate assimilation — nitrate 

 reductase — was induced during dark 

 periods, as long as nitrate was available in the 

 water column. 



Most other plants shut down at night, 

 since the sun produces the energy needed for 

 photosynthesis, he notes. 



Continued 



ABOVE: Brant Touchette is ankle-deep in estuarine waters surrounding the NOAA Beaufort Laboratory — a prize spot for eelgrass. 

 RIGHT: Sea Grant researchers are making important discoveries about submersed seagrasses, critical links in the estuarine foodchain. 

 Specimens shown here are growing at the North Carolina State University Center for Applied Aquatic Ecology. 



22 HOLIDAY 2002 



