Tomato soup on the waterfront

||| FROM RUSSEL BARSH for KWIAHT |||

An exceptionally large, dense orange algal bloom developed in Crescent Beach and Fishing Bay beginning Monday May 9 following several weeks of sporadic rainfall and a few days of warmer sunshine over the island.

The culprit, as usual, is Noctiluca scintillans (“scintillating night light”), a nontoxic but extremely fast-growing dinoflagellate native to our region that takes advantage of the surplus nitrates that wash off lawns and streets in winter when it is still too dark and cold for marine plants or algae.

Dinoflagellates are mobile, single-celled organisms. Most of them photosynthesize by day, and hunt and consume other plankton at night. Dinoflagellates usually have armor plating made of a polysaccharide like cellulose, but Noctiluca are just soft transparent bags. This enables them to grow faster (and larger).

Photosynthetic pigments lend Noctiluca its reddish color in daylight, while its nightly revels are usually accompanied by bright flashes of light – “sea sparkle”. Noctiluca do not produce any toxins. Large blooms, when they die and settle as dense brown muck, and begin to decay bacterially, can cause temporary anoxic conditions that mainly affect burrowing and sessile animals in beaches and mud flats.

There is also some evidence that fish swimming through dense blooms can be suffocated by dinoflagellates packing up in their gills. Fish can swim fast enough to avoid or escape blooms as they form, but fish eggs and tiny larval fish may be more vulnerable.

It will be interesting to see whether this dense bloom affects the herring spawned in Fishing Bay at the end of March. Eggs should have hatched by mid-April, and at least one larval herring was picked up by a Kwiaht beach seine at Indian Island on April 21. If the young herring remained in Fishing Bay to rear before heading south to deeper waters, they may have been affected by this week’s “tomato-soup” bloom.

Smaller Noctiluca blooms appear most years along the Eastsound waterfront, some developing as early as February or March, but this year’s May bloom is the largest we have observed.

FEATURE PHOTO COURTESY OF ANITA HOLLIDAY