Climatide

Heather Goldstone

Nauset Marsh has been reopened to shellfishing after almost two months of red tide closures.

Massachusetts state officials announced today that shellfish in the Nauset Marsh system are once again safe to harvest. Levels of the algal toxin that causes Paralytic Shellfish Poisoning have dropped below levels of concern.

The Nauset Marsh area has seen outbreaks of harmful algal blooms (commonly known as red tides) 18 of the past 19 years – something that has local researchers asking why and exploring what can be done about it. This year, closures began in April and the entire Nauset Marsh system was closed by May 6th. Shellfish closures have also impacted areas around and north of Boston Harbor, but the rest of Cape Cod has remained unaffected by red tide this year.

Earlier this spring, Woods Hole Oceanographic Institution researchers forecast a “moderate” red tide bloom in New England. They cited “a modest amount” of cysts (algal seeds) lurking in coastal mud, but also changes in ocean conditions.

For example, in 2010 near-surface coastal waters were warmer, fresher, and lower in nutrients than usual.  The GOMTOX team believes this suppressed what otherwise would have been a major regional bloom, which had in fact been forecast for that year.  Recent observations … indicate that similar water characteristics may occur in 2011, suggesting the bloom could be suppressed this year as it was in 2010.

So is this climate change at work? The ocean is absorbing the vast majority of excess heat trapped by accumulating greenhouse gases, and ocean temperatures are rising accordingly. Snowier winters (leading to more melt-water runoff in spring) and heavier spring rains could contribute to fresher water along the coast; both are expected results of climate change, and both were in evidence in 2011.

But the idea that ocean changes related to global warming could be suppressing red tides is a little surprising. In contrast, Stephanie Moore of NOAA’s West Coast Center for Oceans and Human Health has said that spring blooms of harmful red tide algae are starting earlier and lasting longer in the Pacific Northwest and in the tropics. She warns that the consequence will be rising economic and public health costs.

Let’s not get ahead of ourselves, though. Don Anderson, a senior scientist at Woods Hole Oceanographic Institution and a leading expert on red tides, told me at the start of this year’s outbreak that he hasn’t yet noticed any major changes in the timing or severity of red tides in New England that could be pinned on climate change.

[UPDATED 9:54am] I emailed Don Anderson to get his thoughts on this red tide season: Is it over? Did it live up to expectations? Here’s his reply:

We expect that it is over for Nauset, and much the same for the western Gulf of Maine, though eastern Maine often kicks in in mid to late summer. Nauset behaved much like it has for years – the same pattern of outbreaks through time, with Mill Pond closing first, then the other ponds, and with cells found predominantly within the salt ponds and not in the central marsh. This year, like last year, we also saw a late season pulse of cells into the central marsh that we believe came in through the inlet from the widespread coastal Alexandrium bloom in the gulf of Maine. So once again, the system had its first phase of toxicity driven by internal cysts and blooms, and then as that winds done, there can be a second pulse of cells, usually very small and short-lived, that can add a second threat.

The forecast was quite accurate this year – we predicted a moderate outbreak, and that is what we got – closures down to about Plymouth in Mass Bay. I’m very happy with it. In more severe years, those closures reach the canal and beyond, and often hit the outer Cape as well as the islands. We have posted some of this on our NortheastPSP web site, though I believe we need to update that a bit.