Thursday
February 27, 2003
4:30-5:30 pm
102 Fishery Sciences
(auditorium)
Social follows talk
Steve PalumbiProfessor of Biology, Stanford UniversityWhat Genetics Tells Us About Ocean Populations, Conservation, and Sustainable Fishing |
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Recent advances in molecular genetics provide a host of new tools to measure dispersal by examining the geography of genetic differences between populations of the same species. Sometimes genetic results are at odds with the conventional wisdom derived from oceanography or larval biology, and these results inform us about how dispersal really happens in the sea (Avise 1994, Barber et al. 2000, 2002). For example, populations of mantis shrimp on reefs near reserves in Indonesia show dramatic genetic differences over a few 100 km, despite strong ocean currents and the potential of larvae of these species to drift 500-1000 km in a single generation (Barber et al. 2000, 2001). These results show that there is very little movement of populations among potential reef reserve localities, and that management of these populations would have to take this invisible division into account.
Similarly, recent genetic evidence has turned up genetic differences in barnacle populations along the Oregon coast of the USA over as little distance as 50 km. Coastal populations of barnacles on the shores of the Heceta Bank, which directs south-flowing currents offshore, have genetic compositions different than populations north or south of the Bank. These differences are slight - on the order of the differences among humans on different continents - but they indicate that coastal populations along the edges of the Heceta Bank are not freely exchanging with populations of the same species off the bank (Sotka and Palumbi, unpubl.).
By carefully measuring the build-up of genetic differences over space, and comparing these patterns to simulations of genetic differentiation along virtual coastlines, we have been able to measure dispersal distances in new ways (Palumbi 2003). Results suggest that barnacle larvae may typically travel only 10's of km before settling, and that larvae from other sedentary invertebrates and fish that spend a month or so in the water may drift less than 50 kilometers or so before settling. These are surprising results, because conventional wisdom in marine biology is that species with high dispersal potential have high amounts of gene flow (e.g. Palumbi 1994, 1996). However, gene flow is usually measured over large distances and long time intervals (1000s of km and 1000s of generations), whereas the new genetic tools recently developed allow us to examine dispersal over small temporal and spatial scales.
These genetic data are closing in on the demographic scale that managers need to work with to make decisions about local fishing effort and sustainable resource use. With high resolution data, we can discern subtle signals of local retention, signals that have a strong message about dispersal, but that have been buried in the 'noise' of genetic data collected in the past. In many cases, ocean populations may be regulated on local scales far smaller than conventionally thought. If this is true, then local management action can have local benefits.
Barber et al. 2000 Nature
Palumbi 2002 Ecol. Applications in press
Palumbi 2002 Pew Ocean Commission report on Marine Reserves
Palumbi et al. 2003 Frontiers in Ecology and the Environment submitted