Microchemistry

Aerial view of the Channel Islands where much of PISCO microchemistry research is based.

Establishing how marine populations replenish their numbers is a key question for managers. One way to achieve this is to determine where the larvae from a population have come from and the paths they travel before recruitment. By understanding these paths and sources we can determine the extent of connections between local marine populations and identify the proper scale for oceanographic studies. These studies represent a vital step in designing effective management practices such as the design and function of marine reserves.

One technique PISCO use is to study the microchemistry of structures contained within the bodies of pelagic larvae (otoliths in fish, statoliths and protoconchs in invertebrates) that grow as the larva grows. As these structures grow they incorporate trace elements from the surrounding ocean environment. By determining these environmental signatures and matching them to ocean zones, it is possible to identify the routes that larvae have traveled from source population to settlement. To do this we run ocean circulation models “backwards” from heavy recruitment events, to generate predictions of source populations that can be validated with microchemistry.

related Research

Natural Tags Indicate Fish Birthplaces

PISCO/UCSB scientists have discovered that water chemistry along the open coast varies enough to leave identifiable chemical signatures in the otoliths, or ear bones, of newborn kelp rockfishes (Sebastes atrovirens). These signatures may prove to be useful as natural “tags” that identify the birthplaces of rockfishes caught as adults.

The scientists collected larval rockfish from three areas along the mainland and islands near Santa Barbara. The scientists removed otoliths from the tiny fish and analyzed the chemical composition using mass spectrometry. They found detectable levels of several trace elements in the otoliths, and the chemical signatures varied in a way that was distinctive among the study sites.

Results suggest that otoliths could be used to identify the birthplace of adult rockfishes, after geographic and temporal patterns in otolith signatures along the coast are understood. Ultimately this method could reveal the connections among fish populations, enabling better fisheries management.

Researchers are Jennifer Caselle, Georges Paradis, Michael Sheehy, and Robert Warner (PISCO/UCSB); and Stephen Swearer (University of Melbourne, Australia).

Publication: Natal trace-elemental signatures in the otoliths of an open-coast fish. Limnology and Oceanography 50(2005): 1529–1542.

PISCO microchemistry research focuses on collecting juvenile rockfish and kelp bass in nearshore waters surrounding the Channel Islands and within Monterey Bay, during the recruitment season. PISCO UCSB is taking the organizational role in attacking these connectivity questions. In addition to microchemistry, our efforts also focus on population genetics. PISCO research consists of four interrelated efforts, each of which builds on the others:

Rockfish CAPTION NEEDS EDITING

We use isolated island systems as testing grounds, because both the sources and destinations of young are much more discrete and identifiable here than along mainland coasts.
We have proceeded from island systems to a study of U.S. West Coast island-mainland connections, focusing on the northern Channel Islands.
At the same time, we have developed larger-scale projects along the West Coast from Baja California to Monterey Bay, with the aim of describing the degree of population connectivity of several commercially important species.
We have conducted a lab-based validation program intended to specify the correspondence between environmental conditions (trace elements in seawater and food, temperature, and salinity) and the signature laid down in the larval structure.

Using this work, PISCO is building an atlas of larval source signatures for commercially and ecologically important fish species (taken from the otolith core) corresponding to larval recruitment events under different oceanographic regimes on the west coast. The atlas will enable scientists to find out where the adult fish and invertebrates living at a given site originated as larvae. Were they spawned locally, or did they drift some distance from elsewhere?