Molecular identification of pelagic fish eggs and interannual variability in the abundance and distribution of spawning in the southern California bight

The distribution and abundance of fish eggs in the plankton provides a valuable measure of local spawning activity. Combined with a time series of samples, identification of eggs permits a dynamic picture of how spawning changes in space and time. To investigate the extent to which spawning in the Southern California Bight varies interannually, this study examined changes in distribution and abundance of pelagic fish eggs obtained from four winter cruises of the California Cooperative Oceanic Fisheries Investigations (CalCOFI) for 2002 (mild La Nina), 2003 (moderate El Nino), 2004 (neutral) and 2005 (mild El Nino). Because many species of eggs are morphologically indistinguishable, this study employed a DNA barcoding approach, sequencing the COI gene of individual eggs and identifying the sequences by comparison to a validated DNA sequence database. Results showed that the relationship between environmental factors (such as sea surface temperature and chlorophyll a concentration) and the structure and distribution of fish assemblages was complex. Some patterns were evident. Consistent with previous studies based on larvae, the egg distribution of the highly migratory species, Merluccius productus (Pacific hake) shifts northward during El Nino years. Abundances of two coastal species, Citharichthys sordidus (Pacific sanddab) and C. stigmaeus (speckled sanddab) were negatively correlated, showing opposite responses to environmental changes. To better resolve relationships between climate and spawning activity, future studies would benefit from sampling a larger geographic region and extending the time series to include years with more extreme climate regimes.