BLOOMING PLANKTON OF LAKE MERRITT, OAKLAND CA

Phytoplankton form the basis of marine food webs and through photosynthesis release oxygen to the atmosphere and into aquatic ecosystems where it fuels cellular respiration that most life forms depend on. In Oakland California, a phytoplankton species, Heterosigma akashiwo, entered the estuarine “lake” in August 2022 via the Lake Merritt Channel as part of a spreading East San Francisco Bay bloom. Within days, the explosive phytoplankton bloom (HAB) expired. However, ensuing bacterial decay caused dissolved oxygen in the lake to plummet to near zero. This resulted in an unprecedented highly publicized massive fish kill in the heart of a major city. The microscopic life of Lake Merritt has been studied scientifically for well over a century; however, the public paid little attention until now. A local nonprofit, Rotary Nature Center Friends at Lake Merritt, collected and archived microscope images of plankton in the field since 2021. We participated in two governmental plankton monitoring programs which provided professional assessments of the species present in the samples we collected: a SFRWQB EPA grant funded program and the CDPH Redtide program. Our examination of fresh plankton added to the picture of changing plankton populations in the lake. Young people participated in carrying out the protocols for collection and sending samples to professional labs. They also helped to view and collect images of fresh plankton.

Our results indicate that plankton populations change often in the lake. In addition to the August 2022 HAB, in the first quarter of 2023, at least three “blooms” were dominated by one type of phytoplankton. By providing young people with authentic experiences using microscopy and participating in real scientific monitoring we inspire the next generation of environmental researchers and stewardship professionals.