Motivation
Research Questions
Approach
Research Findings
Motivation
Much of the modeling of marine population dynamics depends on assumptions about dispersal distances. Genetics can help to quantify dispersal distances. For example, if genetic structure exists in a marine population (meaning that subpopulations have been substantially isolated over long time periods) and if the same genetic structure is consistently apparent over successive sampling periods, this information can be of great ecological importance.
A long-term PISCO goal is to study genetic structure and infer dispersal distances in a series of species chosen for taxonomic breadth and differences in dispersal potential. As a practical matter, we also intend to develop genetic approaches to species identification. Species-specific probes will allow us to identify and determine relative abundances of different species of larvae in mixed samples. This tool will reduce the time and cost associated with identifying, sorting, and counting larval samples. Combined with PISCO research on geographic and long-term temporal patterns of recruitment and oceanography, we have an unparalleled opportunity to characterize marine populations in ways that are immediately applicable to conservation and management.
Research Question
- How are marine populations connected through the exchange of larvae?
Approach
Our design is to sample at two scales: 10 samples spaced 10 km apart in two discrete locations within the PISCO study area, and 10 samples every 200 km along the U.S. West Coast. At each sampling site, we collect 50-100 individuals. To achieve adequate spatial resolution, we estimate that for each species, we need genetic systems involving at least 10-15 loci, with each locus moderately polymorphic (2-4 alleles). We sample at an unprecedented scale--the entire West Coast--with temporal replicates. Fine- and coarse-scale sampling of a number of loci of differently aged individuals at different times will help us to interpret ecological patterns emerging from PISCO recruitment studies.
The PISCO genetics study is currently a coordinated effort among several geneticists, each dealing with species that form the focus of their expertise. The great advantage of this approach is that it combines existing knowledge, a similar sampling design, coordinated PISCO monitoring data. Each collaborator will develop an appropriate set of genetic markers for the species of interest, then PISCO will supply the geographically structured samples. Our initial list of target species, all of which are important members of the nearshore community, and the associated collaborators is as follows:
| Kelp rockfish (Sebastes atrovirens) | Giacomo Bernardi, UCSC |
| Purple sea urchin (Strongylocentrotus purpuratus) | Stephen Palumbi, Harvard |
| Acorn barnacle (Balanus glandula) | Stephen Palumbi, Harvard |
| Open coast mussel (Mytilus californianus) | Grant Pogson, UCSC |
| Surfgrass (Phyllospadix scouleri) | Scott Hodges, UCSB |
| Feather boa kelp (Egregia menziesii) | Scott Hodges, UCSB |
| Sea Palm (Postelsia palmaeformis) | Ali Whitmer, U. Washington |
Research Findings
Genetic Dispersal Distances
To assess the degree of ecological linkage between marine
populations, Dr. Palumbi (Harvard University) and his colleague
Francesco Patti adapted technology originally created for the
Human Genome Project. By accurately detecting subtle genetic
variations from site to site, they developed a new measure of
connectedness among marine populations. In 2001, Palumbi and
Patti successfully tested the approach with purple sea urchins,
Strongylocentrotus purpuratus, collected from sites throughout
Oregon. One of the great benefits of this new technique is thatit
is applicable to many existing genetic studies of marine
populations. PISCO scientists already have used the approach to
construct the first frequency distribution of average dispersal
distances of more than 100 marine species of algae, invertebrates
and fish, which will be extremely useful for designing networks
of marine protected areas.
Species identification using genetic techniques
We are funding research on the development of species-specific probes in the laboratories of several PISCO research fellows: Giacomo Bernardi and Grant Pogson (UCSC), and Joseph Neigel (University of Louisiana). We now have probes available for several species of mussels (Mytilus spp.), barnacles (Balanus, Chthamalus, and Tetraclita spp.), and rockfish (Sebastes spp.). Dr. Neigel's lab is continuing development of competitive PCR techniques to multiplex and quantify species abundances in field-caught samples. We already are using single-species probes to verify lab identification of species and expect to have full automation trials underway in the near future.
In 2001, our investments in new genetic approaches began to bear considerable fruit. To estimate accurately the number of larvae of target species in mixed plankton samples, Neigel developed a new molecular sampling protocol called CADRE (Competitive Amplification of a Diagnostic Repetitive Element). To date, Neigel has successfully tested CADRE on three species of invertebrates in artificially generated plankton samples. Tests with field collected plankton samples are currently underway. Bernardi has developed similar approaches to identify visually indistinguishable larvae of kelp, copper, gopher and black and yellow rockfish.
By Bob Warner, Principal Investigator, and Renee Davis-Born, and Lydia Bergen, Policy Coordinators