COS 152-6 - Characteristics of rocky reefs with high fish biomass across the Southern California Bight

Thursday, August 10, 2017: 3:20 PM
B112, Oregon Convention Center
Susan E. Piacenza1, Jeremy T. Claisse2, Daniel J. Pondella1, Jennifer E. Caselle3, Amanda J. Zellmer1, Jonathan P. Williams1 and Chelsea M. Williams1, (1)Biology, Occidental College, Los Angeles, CA, (2)Biological Sciences, California State Polytechnic University - Pomona, Pomona, CA, (3)Marine Science Institute, University of California, Santa Barbara, Santa Barbara, CA

Understanding the relative influence of habitat characteristics and anthropogenic impacts on species biomass underpins ecosystem based management (EBM). One major tenet of EBM is to restore ecological communities. For temperate rocky reefs, it is unclear what oceanographic, habitat, biotic, and anthropogenic factors best explain high biomass communities, and subsequently what characteristics may best support restoration. Thus, we asked what are the characteristics of rocky reefs with high fish biomass? Using a data set that spans the Southern California Bight (SCB), we analyzed rocky reef fish communities using generalized linear modelling within the information-theoretic approach. Fish abundance and length were visually sampled, via SCUBA, within a random stratified sampling design using line transects across depth strata in <20m depth. Fish abundance was converted to biomass using published length-weight relationships. Our spatially resolved explanatory variables included sea surface Chlorophyll a, maximum wave height, kelp biomass, urchin density, habitat relief and substrate indices, social factors, such as minimum distance to port and fishery harvest intensity index, among others. We also ran similar models to relate the biomass of the six most abundant species to the correlates.


Based on preliminary model runs, the confidence model set (<2 ΔAICc) for total fish biomass included the variables distance to the shelf break, sea surface chlorophyll a, sea surface temperature, and slope. The explanatory variables had different relationships with fish biomass, for example, distance to the shelf break was positively correlated with high fish biomass, but chlorophyll A was negatively correlated with high fish biomass. Different suites of the environmental variables were correlated with biomass of the most abundant fish species. Not all rocky reefs in the SCB equally support high densities of fish biomass, and our results suggest that an optimal combination of environmental and habitat conditions may support increased reef fish biomass, and could also inform the design of manmade reefs and interpretation of spatial management action effectiveness, including marine protected areas.