During the past week, a toxic ‘rust tide’ has grown to span across the entire Peconic Estuary. The Gobler Laboratory of Stony Brook University’s School of Marine and Atmospheric Sciences noted that while the problem started as isolated patches in locations like Sag Harbor and Three Mile Harbor in early August, it has expanded from Riverhead to East Hampton at densities beyond 3,000 cells per milliliter. This is an issue as when rust tide algae, known as Cochlodinium, reaches more than 500 cells per milliliter it can be deadly to marine life. Although large kills have not been documented yet these year, previous Cochlodinium has resulted in the demise of both natural and caged, aqua-cultured populations of fish and shellfish that live on eastern Long Island.
“We have identified climate change and specifically warm summer temperatures as a trigger for these large, widespread rust tides,” explained Professor Christopher Gobler. “In the twentieth century, summer water temperatures were significantly cooler than there are today. When we have extended summer heat as we have seen this summer, a heavy rust tide often follows.”
Water temperature is a key factor in the growth of Cochlodinium, and lower water temperatures in both 2013 and 2014 suppressed the rust tide. It also thrives when there is excessive nitrogen, according to a 2012 paper from the Gobler laboratory that was published in the international peer-reviewed journal, and a higher nitrogen level causes rust tides to become more powerful as well as more toxic. An increase of nitrogen loading into eastern Suffolk County waters has intensified the issue.
“The links between these toxic blooms and excessive nitrogen loading are now well-established and are playing out again this year,” said Gobler. “Near-shore regions on the East End experience intense nitrogen loadings from wastewater and farms and get these events first, after which they are transported to open water regions. It is likely that the recent, intense rainfall will intensify the rust tide in the coming week.”
As The Gobler Lab further studied the alga, they discovered that it can kill fish within mere hours and shellfish can last slightly longer, for a few days. 2012 saw the previous major rust tide, which led to a sizeable die-off of scallops in certain areas. The lower water temperatures in 2013 and 2014 resulted in a very mild bloom and a great boost to scallop harvests. The effects of this year’s rust tide have yet to be seen.
“We anticipate the rust tide will intensify in the Peconics and spread to Shinnecock Bay in the coming weeks,” added Gobler. “Blooms typically persist into the fall or until water temperatures drop below 60 degrees.”