Efforts to understand population change in marine species by looking at their larvae are made challenging by the fact that larvae recruiting to a location may have little chance of originating from that site. How can you tell where a barnacle larva has come from? How do we know what species a microscopic fish larva will grow up to become? Questions such as these are fundamental when scientists try to understand population dynamics for marine organisms.
To answer these questions and others, PISCO scientists are turning to genetics. PISCO genetic studies are principally aimed at measuring larval dispersal of economically and ecologically significant species. When genetics data are combined with PISCO research on geographic and long-term temporal patterns of recruitment and oceanography it creates a powerful tool to characterize marine populations in ways that are immediately applicable to conservation and management. For instance, using genetic differentiation of west coast species can provide an effective way to understand the movement of water masses along shorelines that may deliver larvae to distant populations. Information such as this is especially important in light of climatic changes that could alter nearshore currents distribution and significantly affect marine populations.
Through genetics research PISCO are trying to answer this simple question.
PISCO genetics research takes place over the west coast of the USA, across a scale that transcends management boundaries between states and between management regions within states. Where are there invisible fences in the ocean that keep populations apart? Genetics is a powerful way to answer this kind of question.
Through PISCO genetic research we have determined that levels of connectivity – how much larval transport there is between localities - are highly variable among species, and that conventional explanations (that connectivity varies chiefly with pelagic larval development time) are not very accurate.
For example, among invertebrates, explanations of structure come from adult habitat and larval behavior. Species that inhabit the high intertidal or that have larvae that act as predators in the plankton have higher levels of structure. Data for fish show similar patterns.
But where do larvae actually come from? For species with genetic structure, PISCO genetic markers can help pinpoint larval arrival direction and distance, creating the first-ever maps of larval trajectories. For instance with the acorn barnacle Balanus glandula, we have been able to show that the genetic signature of larvae captured in the plankton or at settlement can be used to predict the original population from which these larvae derive. These data show that many more larvae than expected can move up the coast from south to north – seemingly against the offshore currents. How they do this, and what this means to other species that also disperse in the plankton, are major questions for the future.
Species-specific probes allow us to identify and determine relative abundances of different species of larvae in mixed samples. Reducing the time and costs associated with identifying, sorting, and counting larval samples. Another approach is to use Universal probes to copy the DNA of an entire water sample – then use massive DNA sequencing throughput to delineate all the species in the sample. One of the great benefits of this new technique is that it is applicable to many existing marine plankton – from eukaryote to prokaryote – and relies on automated technology to produce the data.