The federally endangered black abalone (Haliotis cracherodii), a large broadcast spawning gastropod found in the rocky intertidal and nearshore shallow waters ranges from northern California to southern Baja California. In 2014, Multi-Agency Rocky Intertidal Network (MARINe) black abalone monitoring plots were established at multiple sites on San Nicolas Island (SNI), California, the outer most of eight Channel Islands. Large-scale population declines at SNI have been linked to mortalities associated with a Withering Syndrome (WS) disease that increases during warm water events, such as the 2015 southern California El Niño. After this event, 2016 population data showed a decline at two sites Cosign (SNCO) (34%) and Marker Poles (SNMP) (42%). Given the density dependent nature of black abalone, understanding the juvenile life history stage is a critical component for species recovery. New monitoring methods were developed to specifically identify microhabitats utilized by juveniles (<35 mm) within SNI black abalone plots.
Results/Conclusions
Between two sampling events (November 2016 and February 2017), 779 juveniles were found at Cosign and Marker Poles. During survey efforts, 48.5% of juvenile abalone were found behind/near/adjacent to seven non-motile invertebrates. Mean proportion species associations were comprised of solitary anemones (Anthopleura spp.) (SNCO: 37.0% +/- 0.23; SNMP: 36.7% +/- 0.08) and sea urchins (Strongylocentrotus purpuratus) found within divets (SNCO: 40.0% +/- 0.22; SNMP: 38.3% +/- 0.17) were the most common species associations. Juveniles demonstrated strong substrate preferences for rock overhangs (SNCO: 45.4% +/- 0.10; SNMP: 19.3% +/- 0.10) and crevices (SNCO: 11.6% +/- 0.08; SNMP: 43.0% +/- 0.24). Within these substrates, 87.7% of the juveniles were found on crustose coralline algae, which may suggest grazing behavior. Sites were similar in juvenile species association preferences and are likely gaining protection and food resources by associating with non-motile invertebrates. In contrast, substrate preferences differed between sites, which suggests juveniles are opportunistic in their attachment preferences and utilize substrates based on unique geological formations specific to a site. Proximity to crustose coralline suggests this may be an alternate food source during this life history stage with a likely transition to largely consuming drift kelp as they mature.