An Invisible World: What Monitoring Can Reveal Below the Surface
I prefer my oysters plain. Sure, a Thai inspired mignonette or even Hog Island Oyster Co.’s hogwash tastes great on an oyster. But for me, the oyster’s liquor is an exploration of the water source and environment it came from. Will it taste brackish, sweet, or algal? The oyster farmer in me comes out of my shell. Sometimes, when I close my eyes, I can hear the gentle lapping of water against the work skiff and the tumbling of oysters in their cages. The warm sun kissing my shoulders as I haul dozens out of the water, the cold bay water running down my wrists. I imagine what the harvest was like in places like Washington, Alaska, or Tomales Bay. Then the microalgae nerd in me comes out.
What’s living in the water and feeding these oysters?
Flavor isn’t just determined by salinity or geography; it’s also influenced by what’s happening on a microscopic level. Water quality and algal activity play a critical role in the health and safety of every harvest. That’s where things like harmful algal bloom (HAB) monitoring and cyst mapping come in. These might sound unfamiliar, so it’s helpful to understand what these tools can do for oyster farmers and consumers. But first, what is a HAB and what causes them?
Harmful algal blooms are rapid overgrowths of algae in water, often triggered by factors such as nutrient pollution, warm temperatures, sunlight, low water flow, and changes in water chemistry. These blooms can be harmful to both ecosystems and human health, leading to economic losses through shellfish harvesting closures, and in severe cases, even causing illness or death. Some algal blooms produce toxins that cause illnesses such as Amnesic Shellfish Poisoning (ASP) and Paralytic Shellfish Poisoning (PSP).
Remember how I said oysters are a reflection of their environment? Since oysters are filter feeders, these toxins can accumulate in them, and other shellfish, staying in their tissues long after the bloom is gone. That might sound scary, but the good news is we have effective monitoring systems in place to ensure these toxins don’t make their way to your plate.
So how do we actually keep an eye on these harmful blooms?
This is where HAB monitoring comes in. California has a well established statewide network called CalHABMAP (California Harmful Algal Bloom Monitoring and Alert Program) that utilizes satellite imagery to identify bloom intesity and location, models that predict the movement of water masses and ocean physics, and statistics to predict the likelihood of a bloom and its toxicity. The State of California Water Board also utilizes satellite imagery. Another method of monitoring that is common is field sampling via the collection of water samples and algal material. These samples are tested in a lab to confirm a bloom and its toxicity. All of these methods work together to provide early warnings, confirmation of blooms, and public alerts that let people know if a body of water is safe to swim in, fish in, or harvest from. HAB monitoring is not only important for the general public, but extremely important for oyster farmers who rely on the health of the water.
While monitoring efforts have come a long way, what else lies beneath the surface? Another monitoring effort that is popular in Alaska but has yet to make its way to California is algal cyst mapping. Many HAB forming algae have a dormant stage where they sink and accumulate in seafloor sediment. This is when they are called a cyst. They can remain there for decades waiting for perfect conditions to bloom. By collecting sediment samples, identifying and counting cysts, and modeling their abundance, a clear map can be made to show what’s going on.
Having information that can be interpreted as an image and be utilized in ways that farmers can implement themselves is a major benefit as well. It gives the farmers the opportunity to identify high risk areas, the choice to adjust harvest timing to minimize economic loss, increase testing, and overall move from reacting to HAB blooms to anticipating them. Sometimes the most useful science isn’t done by studying charts. Approaches to monitoring like cyst mapping can turn an invisible world into a story that farmers can understand. The knowledge isn’t kept in the lab; it moves beyond it and into the hands of the people most affected.
meet THE AUTHOR
Isidra Trejo
B.s. from California State Polytechnic University, Humboldt & 2025 MIA Summer intern
