Spatial variation of invertebrate survival in Central California kelp forests
Field surveys and empirical predation assays (i.e., tethering experiments) were conducted inside and outside of three no-take marine reserves, one established in 2007, and two 30+ years old in central California kelp forests. Densities of micro-invertivours fishes were 1.5x higher and biomass of pooled invertivorous fishes was 2.8x greater inside reserves compared to fished areas. The increased abundance of predators inside reserves translated to a significant reduction in survivorship of two species of decapod crustaceans, the dock shrimp, Pandalus danae, and the cryptic kelp crab, Pugettia richii. Shrimp mortality rates were 4.6x greater, while crab mortality rates were 7x greater inside reserves. Video analyses indicated that micro-invertivorous fishes arrived 2x faster (W) to tethering assays at reserve sites. Major shrimp predators inside reserves were Hexagrammos decagrammus (31%), Embiotoca lateralis (16%), Scorpaenichthys marmoratus (10%), and small sculpins in the family Cottidae (9%). Strike rates per hour were similar across sites, except strike rates by small sculpins, which were 14x greater inside reserves than outside. Based on the condition of the remaining crab carcass after predation events, the majority (72%) of predation events on crabs were attributed to Octopus rubescens.