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Creatures from the black lagoon

Lake Merritt

Lake Merritt, Oakland, California.

Very little was known about wetland ecology back in 1869, when Samuel Merritt dammed a former tidal slough and began developing its surrounding wetland as his "Jewel of Oakland." By restricting the flow of waters in and out of the newly created tidal lagoon, a.k.a. Lake Merritt, silt and algae were allowed to accumulate and within a few years the lake had become a bit of an environmental disaster. Nevertheless, part of it was designated by Teddy Roosevelt as our nation's first wildlife refuge, protecting more than 90 species of migrating waterfowl. Lake Merritt serves as a drainage basin for the regional flood control system, receiving urban runoff from a 4,650-acre watershed through 60 storm drain outfalls. Four creeks drain into this 145-acre lagoon from the east, while tidegates regulate flow to the south through a narrow channel that connects it with Oakland Inner Harbor and San Francisco Bay. The lagoon is also polluted by illegal dumping of substances such as paints, solvents, and oil, which are highly toxic to marine life. In addition to mechanical harvesting of its widgeon grass, 1,000 to 7,000 pounds of trash are removed from the lagoon every month. Merritt’s short-lived dream as a spectacular swimming hole in downtown Oakland is, in reality, more accurately described as a very large recreational sewer.

Despite all of its tarnish, the Jewel of Oakland has been a haven for some organisms that thrive on an abundant supply of bacteria and algae and tolerate the tidal, seasonal, and anthropogenic changes of this stressed environment. Among them are a few species of microscopic foraminifera (think of sand-sized shelled amoebas) that are being monitored by Ken Finger, Jere Lipps, and Dawn Peterson. Recent studies have shown that foraminifera might be useful environmental indicators of pollution. Lake Merritt presents an opportunity to study how they will respond to the remediation measures planned by the City of Oakland. Currently, only the shoreline of the lake supports living populations of foraminifera, while the deeper lake bottom is a dead zone of black mud stinking of methane. Why is that, you ask? Well, all of the algae, widgeon grass, bird droppings, and other organic waste that escapes harvest sinks to the bottom, and the process of their bacterial decomposition depletes the dissolved oxygen in the stagnant water just above. In contrast, wind-driven circulation keeps the surface waters and shallow margins circulating and aerated, enabling fish, invertebrates, plants, and foraminifera to survive.

But the foraminifera have a higher coincidence of malformed shells in Lake Merritt than in San Francisco Bay, which could be related to their stressed environment, where temperature, salinity, and oxygen levels change regularly. Studies elsewhere suggest that these micro-mutants result from high levels of contaminants, heavy metals, industrial pollution, and domestic sewage. In 2002, Oakland passed a bond measure that will clean up and improve the health of the lake by increasing tidal flow and installing aeration units. With these changes, will the shell deformities become less severe or more infrequent? Will living foraminifera begin to colonize the deeper parts of the lake? We hope to answer these and other intriguing questions as we continue to collect and analyze these minute “creatures from the black lagoon.”

Lake Merritt Dawn Peterson Ammonia tepida - normal Ammonia tepida - deformed Ammonia tepida