No. 73: Jan-Feb 1991
We don't read much about "waterguns" in the modern scientific literature, but a century ago Nature published many ear-witness accounts of them. These muffled detonations heard near the coasts of almost all the continents are believed by some to be caused by eruptions of methane from the seafloor. The same eruptions probably also account for the myriads of "pockmarks" found in the sediments of shallow seas. Whether this outgassing of methane comes from shallow accumulations of organic matter or from deep within the crust is still debated.
Here, geophysics merges with biology. Recently, a group of researchers discovered a large (540 square meters) patch of chemosynthetic mussels in a brine-filled pockmark, at a depth of 650 meters, off the Louisiana coast. The mussels grew in a ring around the concentrated brine. The mussels harbor symbionts which consume the methane still seeping up through the brine from a salt diapir (a massive fingerlike intrusion 500 meters below the brine pool. The origin of some diapirs is not well-understood.) The mussels get the oxygen they require from the ordinary seawater covering the dense brine. Like the biological communities surrounding the "black smokers" and other ocean-floor seeps, the brine-filled pockmark community includes several species of shrimp, crabs, and tube worms. We have here another example of the astounding ability of lifeforms to take advantage of unusual, even bizarre niches. (MacDonald, I. Rosman, et al; "Chemosynthetic Mussels at a BrineFilled Pockmark in the Northern Gulf of Mexico," Science, 248:1096, 1990.)
Comment. Such examples of life's adaptability are so common one hesitates to label them as anomalous. Yet, one wonders how and why life acquired this property. Is the human urge to go to the planets a genetically derived extension of this urge to colonize new terri tories.