From Riverhead to East Hampton, a toxic “rust tide” has spread through the Peconic Estuary as reported by the lab of Christopher Gobler, a professor in the School of Marine and Atmospheric Sciences at Stony Brook University. Gobler is a marine biologist and leading researcher on the harmful algal blooms that have become increasingly common in Long Island’s coastal waters.
In Gobler’s research lab on Stony Brook’s Southampton campus, he and his colleagues have measured densities of the rust tide algae, known as Cochlodinium, exceeding 3,000 cells per milliliter. Densities above 500 cells per milliliter can be lethal to marine life. While large kills have not yet been reported, prior rust tides have brought kills to populations of fish and shellfish on eastern Long Island.
“We have identified climate change and specifically warm summer temperatures as a trigger for these large, widespread rust tides,” said Gobler. “In the 20th century, summer water temperatures were significantly cooler than they are today. When we have extended summer heat as we have seen this summer, a heavy rust tide often follows.”
Professor Gobler noted that the rust tide was muted in 2013 and 2014, as water temperatures were lower.
Beyond temperature, a 2012 paper from the Gobler lab identified excessive nitrogen as a second, equally important driving factor. The study, published in the journal Harmful Algae, demonstrated that high nitrogen levels make rust tides more intense and more toxic. As nitrogen loading has increased into eastern Suffolk County waters, these events have intensified. The study also noted the flexibility of the rust tide organism with regard to nitrogen, being able to feed off of high levels in near-shore regions but also being able to persist at lower levels in more open water sites.
“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.”
Experiments conducted in the Gobler Lab have demonstrated that this alga can kill fish in hours and shellfish in days. In recent years, bay scallop levels in the Peconic Estuary have trended with rust tide intensity. The last major rust tide in 2012 was accompanied by a large die-off of scallops in some regions during the rust tide. The impacts of this year’s rust tide will depend on its duration, coverage and intensity of the event.
“We anticipate the rust tide will intensify in the Peconics and spread to Shinnecock Bay in the coming weeks. Blooms typically persist into the fall or until water temperatures drop below 60 degrees,” said Gobler.
Professor Gobler rarely, if ever, mentions lawn chemicals as factors in nitrogen pollution, although his lab could certainly assure that fertilizer use washes harmful nitrogen compounds into our waters.