Using DNA to map out the food that keep fish alive

San Francisco Examiner –

In April, a visitor to our research center’s open house watched a child dunk a net into a swimming pool, mimicking the act of how we trawl for tiny critters in the nearby estuary. Then that person asked me a question: “How bad is the health of the estuary, really?” As a new mother who has had to be careful to avoid eating local striped bass because of mercury levels in the fish, this question is one that hits me close to home.

Let’s look at the facts. San Francisco’s estuary, which includes waters from the Golden Gate all the way up through connected rivers like the Sacramento River and all the wetlands in between, has had more than 95 percent of its historic marshes leveed and filled. Our estuary is also the most invaded in the world, hosting more than 200 non-native species. These changes have led to such a dramatic shift in the structure of local food webs that the estuary can never return to a pre-invaded state. Partly due to the declining food resources that resulted from invasive species, scientists have also observed major declines in native and other established fish populations over the past few decades. But that doesn’t spell doom for the estuary — it just means we have to work harder to support native species and to keep a close eye on the use of freshwater resources that the area’s fish rely on.

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