Get Glowing.

Scientists at the Tohoku Institute of Technology in Japan recently made an amazing discovery - we glow. That’s right. Humans actually GLOW as we emit photons of light energy. And while our photon auras are far too dim to be seen by the human eye (but certainly sensed in other ways), super-sensitive cameras at the Tohoku Institute have captured the human glow which actually changes over the course of the day. We glow the most from our faces, with peak glow occurring in the late afternoon. You can read more about the discovery of your inner light on Ed Yong’s blog, Not Exactly Rocket Science.

I must have been glowing a little bit brighter as I read this exciting news. Bioluminescence, the emission of light by a living organism, is a phenomenon that is actually quite common among creatures in the ocean, but it continues to mystify us dull humans. Shared by some of the Earth’s strangest creatures – jellies, nudibranchs, squid, and the grotesque anglerfish to name a few – bioluminescence is a trait that adds to their mysterious appeal. Bioluminescence is fascinating to many of us, but its varied mechanisms and evolutionary purpose are not well understood. Some organisms manage their shine through a series of chemical reactions, while others rely on the glimmer of symbiotic bacteria. This ability to glow can be used for communication, attraction, and camouflage. It was only recently that the flashes of fireflies, one of the few terrestrial biolumineers, were translated, earning major coverage in the New York Times (see “Blink Twice if You Like Me” by Carl Zimmer, 6/29/09). Now scientists from NOAA are taking their search for biological shine to the bottom of the ocean.

From July 20 – 30 Doctors Tamara Frank (HBOI@FAU), Sönke Johnsen (Duke), Edith Widder (Ocean Recon), Charles Messing (Nova Southeastern) and Steve Haddock (MBARI) will be studying bioluminescence on the deep-sea floor off the Bahamas. While bioluminescence in pelagic (open water) organisms is well-studied, information on benthic (living near the ocean floor) organisms in deep-sea areas is still limited due to the difficulty of collecting live specimens. To get a better look, these researchers will be deploying the Johnson Sea-Link Submersible to sit among the glimmering animals of the ocean floor. They are also baiting the deep-sea ORCA Eye-in-the-Sea camera to get up close and personal images of some voracious predators. You can follow the expedition of Bioluminescence Team 2009 on NOAA’s Ocean Explorer through daily video logs, podcasts, and amazing photographs of never before seen ocean activity. The attack by Cuban Dogfish and the shimmering Sea Pens are not to be missed!

Learn more about the organisms that really shine on NOAA's Ocean Explorer!

(Photo: Luminescing Bamboo Coral, Bioluminescence Team 2009 NOAA-OER)

The Green Sturgeon's Dangerous Diet

The enigmatic Green Sturgeon (Acipenser medirostris) patrols the benthos of the San Francisco Bay and near shore oceanic waters as a living relic of ancient seas. This large, long-lived fish species, which has persisted for millennia in evolving oceans, may have finally met its match in the environmental impacts of Bay Area development. The Southern Distinct Population Segment (DPS) of the Green Sturgeon, which is listed as threatened under the federal Endangered Species Act, swims through the San Francisco Bay to reach its only remaining spawning ground in the Sacramento River. As these animals swim through the Bay and Delta, they face deteriorating water quality, reduction of freshwater flows, potential poaching for caviar or bycatch in other fisheries, entrainment in water intake structures, and impassable upstream barriers. The principle threat to the Southern DPS is the disappearance of its spawning ground. Now restricted to a very narrow stretch of the Sacramento River, the elimination of the remaining spawning ground would mean the extinction of this genetically distinct Green Sturgeon population. The National Marine Fisheries Services (NMFS) is strengthening protective measures of the Southern DPS by proposing the same take prohibitions that are applied to species listed as endangered. Take prohibitions will make it illegal to hunt, harass, or otherwise harm the fish, including any action that degrades its critical habitat.

Unfortunately this step may not be enough to ensure the long-term survival of the population. A combination of human-influenced factors, now woven into the ecological fabric of the San Francisco Bay and Delta, has turned this estuary into a toxic environment where animals are actually poisoned by their food web. The Green Sturgeon feeds on invertebrates that it finds bottom of the Bay, including the invasive Overbite Clam (Potamocorbula amurensis). This prolific bivalve, which can be found in densities as great as 50,000 per square meter in some areas of San Francisco Bay, is likely to compose the better portion of the Green Sturgeon’s diet. The Overbite Clam itself has a voracious appetite, and it rapidly filters food particles out of the water column with amazing efficiency. Although it may be seeking tiny organisms and detritus, the clam inadvertently consumes the contaminants that pollute the water column including selenium, a bioaccumulative element that comes from oil refineries and Central Valley agriculture. The efficiency with which it incorporates selenium into its tissues makes the Overbite Clam a toxic meal for any predator it succumbs to.

The impact of selenium may not be immediately apparent in the individual adult fish, but it can cause massive reproductive failure. Selenium from a diet of contaminated Overbite Clams will bioaccumulate in fish tissues over the course of its lifetime. Although it may not harm the adult fish, selenium is transferred from a female fish to her eggs, which can cause embryonic death or fatal deformities upon hatching. These reproductive impacts can be severe enough to devastate a population. All fish species in the San Francisco Bay that feed on the Overbite Clam are at risk; however, the unique life history of the Green Sturgeon makes it more vulnerable to this poisonous prey.

In many ways the life of the Green Sturgeon is similar to that of a human. It has a remarkably long lifespan of up to 70 years, and it does not reach sexual maturity until it is at least 15 years old. As an adult it has an iteroparous reproductive strategy, meaning it allocates energy to multiple spawning efforts over the course of its lifetime as opposed to a “big bang” spawning effort once before death. The Southern DPS of the Green Sturgeon, which spends the majority of its adult life in the ocean, returns to the Sacramento River every 2 to 5 years to spawn. Even though it spends more time in the ocean than other sturgeon species, Southern DPS adults may live in the estuary for seven months of the year and juveniles can live here year-round, all the while exposed to dietary selenium.

Given its late age of sexual maturity, the Green Sturgeon will accumulate selenium in its body for at least fifteen years before it first spawns. The level of bioaccumulated selenium imparted to eggs will then increase for all subsequent reproductive efforts as the sturgeon ages. As a result the reproductive impacts of selenium are likely to be more severe for the Green Sturgeon than for a fish with a shorter lifespan and quicker maturation. This reproductive challenge can greatly reduce recruitment within the Southern DPS, meaning that fewer individuals are surviving to reproduce and maintain the size of the population. With this obstacle to the population’s survival so deeply rooted in the ecology of the San Francisco Bay and Delta, the actions that result in the take of an individual animal seem relatively easy to avoid. The proposed take prohibitions are a necessary step in slowing the decline of the Southern DPS, but they are by no means the solution. The elimination of selenium discharges to the San Francisco Bay and Delta may be the only way to ensure the population’s long-term survival.

(Photo credit: David Gotschall)

After 150 Years - Clarity and Consequences

Earlier this spring during a spate of unusually hot weather in the Bay Area, rays of sunlight stretched below the surface of Richardson Bay to trigger an intense algal bloom. Like all blooms, this rapid proliferation of algae was encouraged by the warm temperatures and an adequate supply of nutrients. About a month later another bloom occurred. Both events resulted in floating clumps of innocuous red algae and calls to the Baykeeper pollution incident hotline from concerned shoreline residents. My response: Don’t panic. If it doesn’t smell, it’s not a sewage spill.

According to an article by James Cloern, et al in the 2006 Pulse of the Estuary, Bay Area residents should become familiar with this sight. Algal blooms have been occurring with increasing frequency in the San Francisco Bay since the late 1990s, and the trend is likely to continue. The cause has been uncertain, however, because a host of factors promote the growth of algae. These include predators, nutrients supply, temperature, and metals. In every ecosystem one of these variables must be the limiting factor that controls algae growth and prevents bloom events. In many aquatic systems, such as the Chesapeake Bay, nutrients are the limiting factor. Given the excessive agricultural runoff in the Chesapeake Bay watershed, it is no surprise that algal blooms have been a serious problem. Despite the always reliable winter sewage spills, however, nutrient levels in the San Francisco Bay have been consistently low. So what is the variable that allows this unusual and unseasonable growth of algae? The upcoming 2009 issue of the Pulse of the Estuary will shed more light onto this question. The answer, in fact, is light.

The San Francisco Bay is becoming clearer! The concentration of suspended sediment in the Bay has been steadily decreasing since 1999, allowing sunlight to reach further below the surface of the water, stimulating algae growth and causing blooms. Incredibly, the reason for our water clarity today stems from human activities during the Gold Rush Era. In the late 1800s hydraulic gold mining sent tons of sediment, waste from the search for gold in the Sierra foothills and the Coast Range, down the Sacramento River and other Central Valley rivers. At the same time, development in the Bay Area caused the erosion of stream banks. Shoreline tidal marshes that were diked off to increase buildable and farmable land area could no longer capture this eroded sediment at the shore before reaching open water. As a result, the sediment settled on the floor of the Bay – so much sediment in fact, that the Bay became shallower. Bay Area residents are very familiar with the dredging platforms that regularly remove sediment, carving navigation channels into the floor of the Bay. In addition to dredging, natural wave patterns and burrowing wildlife can stir up sediment and re-suspend it in the water column. High concentrations of suspended sediment reduce the depth to which sunlight can penetrate the water, thus controlling algae growth and preventing most blooms.

Recent USGS data suggest that the Bay experienced a dramatic increase in clarity when this erodible supply of sediment was depleted in the late 1990s. In this year’s Pulse of the Estuary, David Schoellhammer of USGS offers an explanation as to how this may have happened. As long as the San Francisco Bay received sediment from upstream sources and held suspended sediment at capacity, erosion from the floor of the Bay was minimal. Although the Sacramento River delivered sediment, it also gently flushes the Bay and gradually pushed sediment through the Golden Gate. River banks in the Central Valley were protected during the 1900s to prevent erosion, and other sources of sediment are trapped behind dams. The remainder of the hydraulic mining supply slowly moved downstream until it reached the Bay. As a result the Sacramento River delivered clear water, which increased the erosion of sediment on the Bay floor. In 1998, a wet year during which the strong, clear flows from the Sacramento River persisted well into the summer, most of the remaining sediment supply was likely eroded pushed out of the Bay. The following year saw the suspended sediment concentration of the Bay waters decrease by 50%.

This great sweep of sediment through the Golden Gate did not unearth an ecological time capsule to the Bay’s pre-Gold Rush condition. The subsequent increase in clarity in the Bay is a major shift in water quality, which is causing a cascade of ecological and economic consequences in light of modern environmental stressors. As Bay Area residents have recently witnessed, the low concentration of suspended sediment in the Bay makes more light available to stimulate the growth of photosynthetic organisms – aquatic plants, algae, and other phytoplankton. As these organisms thrive they feed higher trophic levels, and the Bay food web becomes more robust. As Schoellhamer points out, the San Francisco Bay has crossed a threshold and become an estuary with a level of primary production that is more typical of temperate latitudes. This increased productivity has implications of its own. With a greater availability of light, nutrient inputs have a greater impact in the growth of algae. While the San Francisco Bay regularly receives nutrients from agricultural runoff or sewage spills, the low light has always prevented excessive growth of phytoplankton. Under current conditions, however, these inputs may trigger more intense bloom events and their associated problems.

The loss of sediments may also hinder coastal wetland restoration efforts. Wetland restoration usually involves opening up a previously diked area to the tides, so that suspended sediments in the water will naturally settle out along the shore, gradually building up until the land is high enough for plants to colonize. The lower the concentration of suspended sediments in the water, the longer it will take for the wetland to develop. Now with rising sea levels threatening to inundate our shorelines, the growth of new wetlands will likely be outpaced. To speed up the process, wetlands restoration projects may also utilize dredge spoils. With the loss of sediment from the Bay bottom, however, there is less of a need for dredging and a limit to sediment available for these restoration projects. Incredibly, the natural expulsion of sediments from the Bay, which caused supplies to shrink while demand has recently grown, has changed hidden Gold Rush waste into a valuable natural resource.

Learn more about Bay sediment in the 2009 Pulse of the Estuary, from the San Francisco Estuary Institute. The Pulse is the annual report for water quality in San Francisco Bay. You can find it at www.sfei.org

(Photo Credit: Michael Slater 2006)