Visual pigments and optical habitats of surfperch (Embiotocidae) in the California kelp forest

We studied the optical microhabitat use and visual pigment variation among a group of closely related teleosts (surfperch: Embiotocidae) living along the nearshore central California coast. We employed a diver-operated spectroradiometer to record the optical microhabitat use of eight surfperch species in Monterey Bay, and microspectrophotometry to measure visual pigment absorbance for nine surfperch species. Species were dichromatic with mixtures of A₁- and A₂-based visual pigments exhibiting extensive maximum absorbance (λ_max) variation across species: 455-482 nm for SWS cones and 527-546 nm for LWS cones. Interspecific variation in sidewelling irradiance measurements (mean λFmax_S) significantly accounted for 63% of the variation in surfperch LWS visual pigments and 83% of the interspecific variation in SWS visual pigments using a phylogenetically-corrected regression technique. Optimality models for maximizing relative photon capture of background radiance demonstrate that the LWS cone λ_max values are tuned for maximizing photon capture of the species-specific horizontal visual field, while the SWS cone λ_max, are well offset from the dominant background radiance. This study is one of the first to demonstrate species-specific differences in habitat usage at microhabitat scales accounting for differences in photoreceptor peak absorbance among closely related, sympatric species.