Tuesday night's Secret Science Club lecture, by icthyologist Dr. Melanie L. J. Stiassny, was top-notch- it was the sort of talk that could appeal to the extreme-sport fanatic, as well as the person whose eyes don't glaze over when they hear the term "micro-allopatric speciation". The talk concerned the mind-boggling variety of fish species (many endemic) in the lower Congo River, specifically the rapid-running stretch of the river near the Malebo Pool.
The Congo River forms a major biogeographic barrier, with two distinct faunal assemblages on either side of the river. Until relatively recent geological time, the Congo Basin was a vast lake, which was drained when the Congo River was formed. The lower reaches of the Congo are characterized by incredible stretches of rapids (Dr. Stiassny appears in this video). The violent hydrology of the lower stretches of the Congo River is the most likely explanation of the diversity of endemic species. Due to the strong currents, fish populations separated by mere hundreds of meters can be prevented from interbreeding (Dr. Stiassny likened this micro-allopatry to a lack of interbreeding between Manhattanites and Brooklynites- to which a wag, not the Bastard, replied that such was the case). Another analogy she used to describe the effect of the current was that the rapids serve as a "Roach Motel", in that downstream trips are decidedly one-way.
One of the fishes she touched on was an eyeless, pigment-lacking thing which had turned up dead (or, in one case, a moribund fish which died in her hand)- laid low by rapid decompression. A survey of the river in the vicinity in which these blind fish were found (using a high-tech catamaran-mounted device launched from a fifty-foot dugout pirogue) revealed that there are "pools" in the Congo River which exceed seven-hundred feet in depth.
All told, the lecture was fantastic- part adventure travelogue, part description of scientific process, part summation of research results, with a hint of pathos as Dr. Stiassny touched on the violent conflict that affects some regions of the Congo, and a strangely touching anecdote about a pallid, eyeless thing dying in her hand.
For a taste of the lecture's greatness, check out National Geographic's article and accompanying video footage.