Tracking Larval, Newly Settled, and Juvenile Red Abalone (Haliotis rufescens) Recruitment in Northern California

Recruitment is a central question in both ecology and fisheries biology. Little is known however about early life history stages, such as the larval and newly settled stages of marine invertebrates. No one has captured wild larval or newly settled red abalone (Haliotis rufescens) in California even though this species supports a recreational fishery. A sampling program has been developed to capture larval (290 mu m), newly settled (290-2,000 mu m), and juvenile (2-20 mm) red abalone in northern California from 2007 to 2015. Plankton nets were used to capture larval abalone using depth integrated tows in nearshore rocky habitats. Newly settled abalone were collected on cobbles covered in crustose coralline algae. Larval and newly settled abalone were identified to species using shell morphology confirmed with genetic techniques using polymerase chain reaction restriction fragment length polymorphism with two restriction enzymes. Artificial reefs were constructed of cinder blocks and sampled each year for the presence of juvenile red abalone. Settlement and recruitment were found to vary with year and site from 2007 to 2015. In some years such as 2010 and 2013, there were many larvae and newly settled abalone, whereas in other years there were none. The two exceptionally poor years for larval and newly settled abalone were 2012 and 2015 (warm El Nino years). In 2013, there was spatial concordance between two sites 18 km apart with respect to the sizes of the newly settled individuals suggesting they were spawned and settled on the same day. The methods developed here, quantifying early life history stages, may shed light on the "black box" of recruitment and help address what are the drivers of good and bad recruitment years for red abalone in northern California.