Dr. Paul H. Barber is a Harvard biologist who studies the dispersal of stomatopods, marine crustaceans that are important to the food chain. Several species of these are interesting as a way to track the dispersal of marine organisms and the use of genetic markers in these observations. On January 7 Barber discussed his work in a lecture at the Smithsonian Tropical Research Institute's Tupper Auditorium. The subject of the talk was "Larval dispersal biogeography and evolution of Indo-West Pacific Mantis Shrimp."

Within the Indonesian Archipelago there is a rough boundary line between a mix of species associated with Australia, New Guinea and Oceania on the one hand, and Southeast Asia and the Indian Ocean on the other. This applies famously to terrestrial reptiles, amphibians, birds and mammals. If one wants to study linguistics, DNA types and other racial and cultural indicia, the dividing line also roughly applies to indigenous human populations. It also seems that a similar regional genetic divide works among the area's marine species.

"We're using genetics to look at bio-dispersal," Barber explained. He noted that bio-diversity is affected by both evolutionary and physical processes, sometimes working in tandem.

For example, mantis shrimp will vary according to the length of their larval stage, and given knowledge of the currents in which these larvae are spawned, the range of physical dispersal can be charted. Moreover, if the current doesn't carry the larvae to ecological niches where they can survive as adults, it won't in the long term disperse the species.

The confluences of ocean currents, creating eddies and changes of direction, often correspond to "biogeographic breaks," Barber explained. One of these is in Indonesia, where a strong current comes west out of the Pacific and turns southwest through the Makassar Strait between Sulawesi and Borneo, then turns by Java and flows on into an Indian Ocean current. The whole system, called the Indonesian Through Current, creates the Halmahera Eddy where it pivots northeast of the Makassar Strait. This current and eddy combine to isolate biological populations, whether you want to look at crabs, starfish, mantis shrimp or human beings.

Taking samples of three species of mantis shrimp at various points along and around the Indonesian Through Current, Barber and his colleagues were able to look at genetic markers, and then by comparison with geological records and with other knowledge, it's possible to get a better idea of the dynamics of species dispersal and diversity.

Traditionally, variations in the area's marine species had been thought to be largely the result of lower sea levels in the Pleistocene Epoch (1.8 million to 11,000 years ago), which isolated many creatures and set them on the path to evolving into distinct species from their ancestors. However, the results of the genetic studies that Barber and others have done suggest that not all of the diversity can be ascribed to Ice Age sea level changes, and moreover indicate that there are more biogeographic regions along the Indonesian Through Current than the conventional wisdom had recognized.

With one of the species that Barber studied, the sea bottom off the Halmahera Eddy is an effective barrier to migration. These mantis shrimp can only live on shallow coastal reefs, while relatives that Barber also looked at can live on deep ocean reefs. Though the former shallow dwellers can send their larvae a long way into the current, there is no place for them to survive as adults. The latter, however, can find viable habitats and so do not find the eddy a biological barrier.

Barber, along with Harvard colleague S. R. Palumbi and Indonesian scientist M. K. Moosa, also looked at two species of mantis shrimp around Krakatau. The island was the scene of a cataclysmic 1883 eruption which killed many people and, between superheated gas in the atmosphere and lava-heated boiling seawater sterilized the entire area within several miles. Thus, by looking at the genes of stomatopods found there today, one can get a good idea of from whence they came.

Krakatau's stomatopods are descended from populations in southern Indonesia, with none from the other side of the Makassar Strait and Halmahera Eddy. Barber thinks that this shows that the primary barrier to species dispersal from northern to southern Indonesia is physical.

Barber was here for a week to collect samples along the Atlantic side, part of a similar study of stomatopod species' dispersal within the Caribbean Sea, Gulf of Mexico and Atlantic Ocean. The known oceanography suggests that shrimp who get their larvae into the Gulf Stream will spread far and wide --- but we know that it's not that simple, and are likely to find how complicated it really is when scientists look at the phenomenon through the genetic markers in the specimens they capture.

So other than a better appreciation of Life, The Universe, And Everything, what use might Dr. Barber's work have? "This may provide a regional context for conservation programs," he noted. "Oceanic currents may be a good starting point" for understanding the habitats of fish or turtles that we want to save, but the biologist said that it can't be assumed that this is all we will need to know.