Saturday, December 26, 1998 – Isla del Coco

I'll begin by confessing that if every young biologist were able to ask Santa for a special present, mine would have been to ask ol' Claus for a trip to the islands of Galapagos and Cocos. I must have been pretty good this year, because my wishes have come true. I spent June and July at the Galapagos Islands, studying the fishes and other marine life while making an IMAX film with scientists from the Smithsonian, and now I'm spending Christmas at Cocos Island. But seriously, the real Santa Claus was Michael Poliza, who invited me last year to join his crew of seagoing elves, so that I might continue my research on the evolution, relationships and adaptations of fishes. When I'm home, it's in San Francisco, where I am a research scientist at the California Academy of Sciences in Golden Gate Park. My specialty is ichthyology (the study of fishes), and there's still lots to learn -- there are more kinds of fishes (perhaps 25,000-30,000 living species) than all the rest of the vertebrates combined, and over the last 400,000,000 years they have adapted to planet Earth and have lots of useful stories to tell us.

Dr. John E. McCosker dissects a bigeye thresher shark (Alopias superciliosus) embryo he was given by a young boy at the Puntarenas pier.

The islands of the eastern tropical Pacific Ocean are a goldmine for studies of evolutionary biology. Charles Darwin redirected the course of history and our understanding of it after his voyage aboard the Beagle and his visit to the Galapagos Islands in 1835. Although his impressions and nascent theories of evolution by natural selection were influenced primarily by the birds, plants and tortoises that were marooned at those desolate rocks, he was also able to capture 15 fish specimens, and all were new species. Had Darwin a face mask, or better yet a scuba tank, available to him on his voyage he might well have recognized that evolution occurs below water, as well as above, and the result is species of fishes and invertebrates that, by their isolation, have become endemic (unique) to those offshore islands.

DJ and Dr. McCosker examine a white-striped angelfish (Holacanthus passer) collected at a depth of 45' (14 m) using anaesthetics.

During the last 25 years, my colleagues and I have studied the shorefishes and the island fishes of the eastern tropical Pacific, and a fascinating pattern has surfaced. Approximately 14 - 16% of Galapagos shorefishes, and many that inhabit Cocos Island, are endemic. And surprisingly, many of the shorefishes from not-too-distant Malpelo Island, a 1.5 km rock located 435 km west of Colombia, are endemic to that island. (Starship may ultimately visit Malpelo, and I hope that I will be aboard when she does!)

Squirrelfish (Myripristis murdjan) are shallow water nocturnal species, as evidenced by their large eyes.  This species is common at Cocos Island, but rare along the mainland of Central America.

Ichthyologists question if islands such as Malpelo and Cocos act as "stepping stones" to allow larvae of continental species to cross the 1000 km deepwater barrier that separates the Galapagos from Ecuador. And as such, do these stepping stones act as a filter or possibly as a link to the evolution of the more distant island forms? And, considering the youthfulness of such islands, how rapidly does evolution occur? As well, we may have an opportunity next week to explore for the first time a midocean seamount that comes within 3 m of the surface . It's about 140 miles (220 km) SSE of Cocos Island, and as far as we can tell, no one has ever made a scuba dive there, much less an ichthyologist! What species might inhabit that pinpoint in the middle of nowhere? And finally, I mentioned that I am particularly interested in the effect of the most recent El Nino/Southern Oscillation event upon these islands. The devastation that I observed underwater at Galapagos during June and July of 1998 was the greatest that I or any of my colleagues have ever experienced there. So far, it appears that its effects on the plants and animals at Cocos were minor by comparison, but we've only been here for two days.

Yours truly,

John E. McCosker