June 4, 2018 — Leaning over the side of a small skiff in Salt Pond, Woods Hole Oceanographic Institution researcher David Kulis shook the excess water out of a plankton net, then emptied the contents into a water bottle.
The gold tint to the water, he said, was likely Alexandrium, single-cell algae that produce a powerful neurotoxin. When concentrated in shellfish meat that feed on algae, the toxin can paralyze respiratory muscles in humans, a condition known as paralytic shellfish poisoning, which can be fatal.
Kulis and Northeastern University intern Taylor Mannes were using the tools plankton researchers had relied on for decades: a windsock-shaped net, with fine mesh to capture the single-celled organisms, and a Niskin bottle, originally developed in 1894 for polar research to retrieve samples at discrete depths. Lowered by hand to marks on a line corresponding to various depths, its opening is closed by sliding a lead weight down the line.
But with human health and a burgeoning shellfish and aquaculture industry in the balance, red tide research has gone decidedly high-tech. Sophisticated instruments are now deployed offshore in the Gulf of Maine and at inshore sites like Salt Pond in North Eastham.
Salt Pond is a natural laboratory, said Michael Brosnahan, a red tide researcher at WHOI. It already has a native population of red tide cells that survive the harsh New England winter as hardened cysts on the bottom of the pond. The incoming tide also pushes additional cysts from the larger marsh down a narrow creek and deposits them in deeper water in the pond, beyond the reach of the outgoing tide.
Red tide algae produce food through photosynthesis, and when the cysts hatch in the spring, they swim up into sunlit waters between five feet and eight feet deep. They remain at depths below the outlet creek channel, and relatively few of the free swimming cells are swept back out into the marsh by the tide.