Glowing Sea Surfaces Grace San Diego Shorelines Due to Red Tide Phenomenon

In the waters offshore San Diego, a unique phenomenon is currently unfolding. A red tide, caused by the presence of the dinoflagellate Ceratium falcatiforme, has been observed, marking the first time this species has been known to bloom along the US west coast.

This red tide is not associated with the bioluminescent Lingulodinium polyedra, another common dinoflagellate found in these waters. Unlike C. falcatiforme, each cell of L. polyedra contains a bit of sunscreen that gives it colour, a characteristic that is absent in the current red tide organisms.

On May 7, bright bioluminescence was observed from La Jolla to Encinitas, indicating the presence of these glowing marine organisms. However, it's important to note that not all red tides produce bioluminescence, and red tides are unpredictable in nature.

While the dinoflagellates comprising this red tide do not produce compounds known to be toxic, some people may exhibit symptoms due to sensitivity to the red tide. There is ongoing monitoring for the presence of harmful algal toxins, with the Southern California Coastal Ocean Observing System at Scripps Oceanography performing weekly sampling.

Several Scripps scientists are currently sampling the current red tide to learn more about the genetic and metabolic characteristics of the organisms. The full spatial range of the bloom is not yet known, and the duration of the current red tide is unknown, although previous red tides have lasted anywhere from a week to a month or longer.

Despite the lack of a red tide monitoring program, there is monitoring for harmful algal toxins. Bioluminescent displays are best viewed from a dark beach at least two hours after sunset.

Local red tides of L. polyedra have been known since the early 1900s, and this species is well known for its bioluminescent displays. However, it appears that the current red tide is dominated by C. falcatiforme, making this a particularly interesting event for marine scientists.

It's worth noting that a combination of physical, chemical, and biological factors are thought to be important in allowing a red tide to form, but the exact mechanisms are not fully understood.

As the current red tide off San Diego continues, it offers a unique opportunity for scientists to learn more about these fascinating marine organisms and the conditions that lead to red tides.