next message in archive
next message in thread
previous message in archive
previous message in thread
Index of Subjects
Index of Subjects The horseshoe crab is a living fossil, virtually unchanged since the Jurassic Period (in the middle of the Age of Reptiles). Tracks of spawning horseshoe crabs have been found in Devonian rocks of Pennsylvania, which are far, far older. Fossil relatives are found in Manitoba from the Ordovician Period, about 445 MY old. There are only a few species of horseshoe crabs in the world (the American one, the subject of the program, and three minor Asian species). The American horseshoe crab is the largest and the most numerous, and the most spectacular to watch. New Jersey is the center for their abundance and average size, or at least it used to be. It is not the medical use that threatens the population, but the wasteful and (IMHO) lunatic use of horseshoe crabs as bait, or even fertilizer. I have not checked recently, but when last I looked an annual license to take unlimited numbers of horseshoe crabs (seized from the beaches while they are trying to spawn) was a mere $25. Horseshoe crabs have a long lifespan, and do not recover quickly from the depredation of being hauled away in truckloads. Actually, the Red Knot probably can increase its numbers faster with environmental change than can the horseshoe crab, because the generation time is shorter for the Knots. On 14 Feb 2008, at 2:04 AM, Stephen Shaw wrote: > Unfortunately missed the program, but I had a mild comment on the > species-ist > emphasis here (sent it earlier but it didn't do through). > > Nothing against the Red Knot and of course I hope it survives, but > the received > vertebratocentric perspective on this is interesting. As the blurb > below > states, > there are lots of other similar peep species around, but the > horseshoe "crab" > Limulus polyphemus is a unique species here and has been > practically wiped out > in many of its former habitats on the US East coast, according to > Bob Barlow, a > former student of Hartline (see below) who still works on it, > latterly on its > visual behaviour under water. Apparently the market for its blood > is the main > reason for the punitive "harvesting". > > Besides having a far more interesting, ancient lineage, Limulus has > contributed to several outstanding scientific discoveries in vision > science, > notably that of "lateral inhibition" by which the nervous system > sharpens up > percepts, enhancing edge-detection in images. This has emerged as a > common enhancing operation elsewhere in nervous systems, but > originally came > mainly out of work on the compound eyes of Limulus in the 40s-60s > -- netting a > Nobel prize for H.K. Hartline, of the then Rockefeller Inst (now > Univ). In the > 60s, S. Yeandle made the first recordings of single photon captures > in the same > eye (since then recorded in vertebrates, though not in Red Knots), > while in the > 70's, the first detailed analyses of how photoreceptor currents work > (semi-universal) came out of measurements on huge photoreceptor > cells in the > ventral nerve that had been thought before this to be an olfactory > structure > (analysed since in vertebrates, though not in Red Knots). > Circadian rhythm > mechanisms are big news at present (molecular mechanisms), and one > of the best > analyses of the circadian control of an eye by the brain came from > Barlow and > colleague's work on the Limulus lateral eyes. There are at least > two other > sets of eyes in horseshoe crabs, one UV sensitive and one in the > telson... > > None of these conceptual advances were minor cul-de-sacs and all > have become > incorporated into the neuroscience base, ever expanding. Limulus > deserves great > respect as a unique and unusual pioneer invertebrate animal that > ought to > survive. What has the Red Knot done to gain comparable respect? > > So, if I had to curry up votes for one of the two endangered > species, it would > be for the unique and illustrious horseshoe crab, first. "Why save > the Red > Knot?" indeed -- do it second. > Steve > ****************************************** > > > Quoting Elizabeth Doull <edoull@ns.sympatico.ca>: >> Why save the Red Knot? >> PBS >> flocks of shorebirds, the red knot is fairly average looking. In >> fact, only the most practiced bird watchers may be able to >> distinguish this medium-sized, plump peep from the thousands of >> other shorebirds playing tag with the waves. Yet, somehow the red >> knot has caught the attention of people around the world. >> >> The knot's dependence on the eggs of the heavily harvested >> horseshoe crab has placed it at odds with another species -- >> humans. Conservation groups, lawmakers, fishermen, scientists, and >> ordinary citizens have all entered the debate. But even as our >> actions have imperiled the red knot, we can also preserve the >> species, by regulating the fishing industry and keeping clear of >> the beaches that the knots rely on during migration. Where nature >> ranks in our system of values will dictate how far we are willing >> to go to protect the red knot. >> >> There are millions of shorebirds in the world. Why all the clamor >> over the red knot? How could this small bird stir up so much >> controversy and inspire such extraordinary efforts on its behalf? >> To begin to answer these difficult questions we must first become >> familiar with the red knot. >> >> The red knot may blend in with the other small shorebirds, but it >> makes a journey that certainly sets it apart. A master of long- >> distance aviation, the red knot makes one of the longest migratory >> trips of any bird -- 9,300 miles along the Atlantic flyway from >> its wintering grounds in southern South America to its high Arctic >> breeding grounds. The journey is so exhausting, it requires two to >> three stopovers for refueling. The horseshoe crab egg feast they >> will consume at Delaware Bay, is not just an indulgence -- it's >> absolutely crucial for the birds' survival. When the knots arrive >> at Delaware Bay, their bodies are half their starting weight, >> devoid of fat and even some muscle. Here, the red knot will take >> about two weeks to double its weight so it can continue its >> migration. >> >> The migratory trip is far from the only risk the peeps take in >> their lives. The life of the red knot is fraught with challenges. >> In their wintering grounds of Tierra del Fuego, blinding gales >> blow up without warning, and tides surge 25 and 35 feet every 12 >> hours. The challenges facing t