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Master Naturalists: Oil spill damages invertebrate animals on Matagorda Island

By By Paul and Mary Meredith
May 29, 2014 at 12:29 a.m.

A Caspian tern stands on washed up sargassum weed.  Its pale-yellowish brown color indicates freshness.  It's full of crabs, clams and tiny fish, which provides food for terns and shorebirds. The dark berm (foreground) is decaying sargassum. It's the primary food source for invertebrates like ghost crabs, numerous worm species and clams living in the moist sand.  Sargassum weed also feeds a tiny invertebrate community, small enough to swim between sand grains browsing on tiny plankton.  Both the large and tiny invertebrates were killed when they came in contact the oil, which fouled Matagorda Island beaches recently.

Most of the residual fuel oil spilled in the Texas City Y Barge collision was washed into the Gulf and drifted along the coast, coming ashore on 12 miles of Matagorda Island beaches. In a monthlong cleanup, the National Oceanic Atmospheric Administration, U.S. Coast Guard, General Land Office, Kirby Marine, U.S. Fish and Wildlife Service and Texas Parks and Wildlife Department and 470 contract companies removed 219,025 pounds of oiled material.

Residual fuel oil - petroleum refining dregs - contains dangerous concentrations of heavy metals and polycyclic aromatic hydrocarbons. Using it as fuel has been banned in Canadian and the U.S. territorial waters (200-mile limit) since 2012. Residual fuel oil clumps together as floating, viscous, tar like sheets. Residual fuel oil doesn't sink well into most beach sands. It doesn't evaporate, dissolve or quickly break down microbally in water.

Is everything back to normal?

Are things back to normal? Not really. Beach ecosystems - areas of sand and gravel occurring below mean high tide and above mean low tide - are not sterile or hostile to life, even if they look that way. They actually teem with life. Sandy beach residents' meals are derived almost entirely from external nutrients supplied by beach wrack brought in by wave action. Beach wrack - piles of dislodged offshore seaweed, Atlantic Ocean sargassum weed, terrestrial plants and animal remains - that washes ashore provides food for beach invertebrates. Sargassum is important. It provides shelter and food for colonies of crabs, fish and mollusks.

How much this open system food chain was interrupted by the removal of oiled sand and wrack is not known. Cleanup personnel reported that little or no sargassum washed in until week three of cleanup.

Uncontaminated wrack was not disturbed.

Benthic animals - small animals in the shallowest surf zone and wet beach sands such as sand worms, tube worms, clam worms, mollusks and tiny crabs - were killed, smothered or poisoned by contact with residual fuel oil's toxic components. Fouled areas will contain less food for foraging shore birds.

Get out your microscope

A microscopic community has been disrupted by the spill and cleanup. Spaces between surf zone and wet beach sand grains are home to a vast community of microscopic critters forming a closed food system.

Phytoplankton, such as diatoms, feed microbial food chains in surf waters and sediments. Those, in turn, feed what marine biologists call meiofauna - tiny, multi-celled invertebrates and single-celled protozoa that swim between sand grains foraging for prey. Meiofauna are in turn prey for zooplankton, fishes and seabirds.

How badly was this meiofauna community damaged? If it is damaged, how long will it take to recover to pre-spill levels? Previous oil spill research show disruption depends on several factors, such as oil characteristics, how much it has degraded, beach characteristics, how long oil contacted the bottom and wave-disturbed sediments (the benthic zone).

Each reported case showed damage - some more, some less - to residents. That leaves a lot more questions than answers.

A program to assess the damage would have to be undertaken. Sand cores samples would be taken and evaluated using scientific analysis before firm conclusions could be drawn about the extent and persistence of damage to these communities.

In discussions with Chip Wood, with U.S. Fish and Wildlife Service ecological services in the Corpus Christi Field Office, we found that a Natural Resources Damage Assessment will be prepared on how much damage was done by the spill.

It is in the Preliminary Assessment Phase at this time, and that phase will take several months and is only the first of Natural Resources Damage Assessment's three phases authorized under the Federal Oil Pollution Act. It will be a while before we know anything of substance or any restoration activity (if any) is started.

Sources: University of California Museum of Paleontology; animaldiversity.ummz.umich.edu; marbef.org; oceanspaces.org; audubonmagazine.org; response.restoration.noaa.gov

Paul and Mary Meredith are master naturalists. Contact them at paulmary0211@sbcglobal.net.

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