Noctiluca Observed in Southeast AK, Summer 2019

The Sitka Tribe of Alaska (STA) received a call on June 20th reporting red-colored water in Silver Bay. In response, STA’s team of Tribal Youth went out to collect samples. Citizens often call the Tribe when they notice a change in water color, wondering if the discoloration could indicate a negative impact on harvesting or marine life. Through their environmental monitoring programs, members of the SEATOR network are equipped to differentiate harmful algal blooms (HABs) and nontoxic red tides for the public. Water samples must be analyzed through microscopy to determine which species are blooming and what effect those species have on subsistence harvesting and the coastal ecosystem.

Left: Keet Lorrigan collects phytoplankton in Herring Cove; Right: Morgan Feldpausch collects phytoplankton at Whale Park. / Photos by Angela Hessenius.

Sampling Process

To collect water samples, the Tribal Youth interns conducted a plankton tow and collected one liter of water at each of three sites: Herring Cove, Sawmill Cove dock, and Whale Park. These sites were selected in order to try to encapsulate the geographic area where the bloom might be happening to better inform the boundaries of the bloom. The samplers also checked for visible evidence of discolored water; although they did not see a visible change in the overall color of the water from any of the sampling sites, at Herring Cove, after conducting the plankton tow, water in the sample bottle had a reddish tint.

Map of Sampling Locations. / Created with Google Maps and Canva.

What We Found

Back at the lab, the water samples were analyzed under the microscope. Overall, the abundance of plankton was not abnormally high; in fact, it was lower than an average sample taken during summer months. However, this could be at least partially explained by the fact that these were not regular sampling sites, which made conducting an effective plankton tow more difficult. The most abundant plankton genera that was observed was Noctiluca, with 13 cells observed in the Herring Cove sample, 6 cells observed in the Sawmill Cove Dock sample, and 2 cells observed in the Whale Park sample.

Noctiluca cells. Images accessed from BioWeb

This finding is consistent with our expectations, as Noctiluca is known to produce red or orange discoloration of water during blooms. Noctiluca is a dinoflagellate and is perhaps best known for its quality of bioluminescence (although in the Northeast Pacific region, Noctiluca are not bioluminescent). Noctiluca does not produce toxins. However, it can be considered a HAB species because during large blooms Noctiluca can produce ammonium, which may be toxic to fish, or lead to deoxygenation of the water.

There have been other sightings of red- or orange-colored water this summer in other places in Southeast Alaska as well. For example, in Haines, orange water discoloration was observed on July 12 by Luke Williams (Chilkoot Indian Association), and in Kasaan, orange-colored water suspected to be caused by a Noctiluca bloom was reported by Carol Fletcher (Organized Village of Kasaan) on July 13. Additionally, in Juneau, red and brown water patches were observed in Gastineau Channel on July 31.

View of plankton bloom in Haines. / Photo courtesy of Luke Williams, accessed via LEO Network.

What’s the deal with red tides, anyway?

“Red tide” is a commonly used term to describe a harmful algal bloom, or HAB, especially one that causes the water to turn orange, red or brown. The term can create some confusion, however, because not all algae blooms that turn the water red are harmful, and not all HABs or toxin-producing species change the color of the water. Visual observations can give great information that something is happening in our waters. However, blooms of toxic plankton such as Alexandrium, the type of algae that produces the neurotoxins responsible for Paralytic Shellfish Poisoning (PSP), and Pseudo-nitzschia, which produces the neurotoxin domoic acid responsible for Amnesiac Shellfish Poisoning (ASP), are not always visible. Therefore, they require consistent monitoring by taking a water sample and looking under the microscope to see what kinds of phytoplankton are in the water at that time. This is why SEATOR partners play such an important role, keeping consistent eyes on the water and looking out for the specific kinds of plankton that can disturb marine ecosystems and cause health risks for humans.

This is why SEATOR partners play such an important role, keeping consistent eyes on the water and looking out for the specific kinds of plankton that can disturb marine ecosystems and cause health risks for humans.


This post was written by AmeriCorps VISTA Angela Hessenius, with help from the Tribal Youth interns Muriel Reid, Morgan Feldpausch, and Keet Lorrigan.


Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s