acquired December 2013 - December, 2016

Oyster Prospecting With Landsat 8



The cold waters of coastal Maine are well known for their bounty of lobsters. But in recent years, the aquaculture industry has put Maine on the culinary map for a beloved bivalve, too. Nearly 3 million oysters are now harvested annually from Maine’s waters. Between 2003 and 2015, the oyster market in the state boomed from less than $1 million per year to $4.8 million.

The demand for Maine oysters is leading aquaculturists to seek new places to expand their operations. Finding promising aquaculture sites can be a challenge, though; fish and shellfish farms may be successful in one place, but not another.

Now seafood farmers may be getting some help from above. In the first study of its kind, researchers from the University of Maine have demonstrated that Landsat 8 satellite data can be used to find locations where oysters farms should thrive.

Traditionally, finding new farm locations has been a mix of trial and error; mostly experimentation with new sites within proximity to existing farms. A team of researchers led by Jordan Snyder and Emmanuel Boss of the University of Maine set out to take the costly guesswork out of finding productive sites by creating a Landsat-based map with an “oyster suitability index.”

To create their map, the researchers went back to the basics of oyster physiology. The chief oyster grown in Maine’s waters is the American (or Eastern) oyster, Crassostrea virginica. This filter feeder is different from other oysters because its filtration rate—that is, its feeding ability—is strongly influenced by water temperature. The colder the water, the slower the oyster’s filtration speed and the slower it gets the nutrients it needs. For this reason, the researchers knew they had to find areas with temperate waters along Maine’s chilly coast.

They also considered the amount of food available for the oysters and the amount of non-organic matter floating in the water. Oysters feast on phytoplankton, so the team looked at chlorophyll a concentrations; when chlorophyll is abundant in the water, phytoplankton are too. At the same time, high levels of inorganic sediments are not good because the oysters have to filter a lot of non-food, which slows their feeding down. By measuring turbidity (suspended sediments) in the water, Snyder and Boss could help farmers avoid areas where oysters are more likely to get a mouthful of mud than food.

The team used visible, near-infrared, shortwave infrared, and thermal infrared measurements from Landsat 8 to derive sea surface temperature, chlorophyll a, and turbidity. They then created a formula that could rank the suitability of Maine’s coastal waters for oyster farming. The winning waters—where oysters can grow rapidly—are relatively warm, have high levels of chlorophyll a, and low turbidity.

Oyster suitability maps (like the one shown above) indicate that existing farms (marked by white circles) are sited in favorable areas. The data also indicate that there are many places along the coast where conditions look favorable for new farms.

Several oyster farmers are already using the maps. “One farmer is using the chlorophyll imagery to look for places with high food content downeast,” Snyder said. “And [oyster farmer and study co-author] Carter Newell is using the index in a flow model to look at new places for farming in the Damariscotta River.”

Landsat 8 is uniquely suited for this investigation because, unlike satellite ocean color instruments, it has fine enough spatial resolution (pixel size) to make measurements in the nooks and crannies of Maine’s coast. Maine has about 3,500 miles of tidal shoreline, and its jagged coast is a series of fjards—the shallow, broad cousins of fjords. It is in the upper reaches of those fjards that oyster farming is most promising.

The researchers validated their index in the Damariscotta River Estuary, site of about three quarters of Maine’s oyster operations. They found that temperature and turbidity measurements derived from Landsat data matched well with monitoring buoys in the water. The chlorophyll a measurements, while within expectations, were not as good as the team had hoped, but Snyder and Boss have some ideas about how those measurements could be refined. They also think the index could be further developed for other bivalve species and for marine environments outside of Maine.

NASA Earth Observatory map by Jesse Allen, using data provided by Jordan Snyder (University of Maine). Story by Laura Rocchio.