Impact of habitat structure on fish populations in kelp forests at a seascape scale

Habitat use by a species is a vital component in explaining the dynamics of natural populations. For mobile marine species such as fishes, describing habitat heterogeneity at a seascape scale is essential because it quantifies the spatial extent to which fishes are interacting with their environment. Here, we explored the relationships between habitat metrics and the density and size of kelp forest fishes across a seascape that is naturally fragmented. Multibeam sonar and GIS analysis were employed to create a seascape map that explicitly defined bathymetry and spatial configuration of rocky reefs in southern California (USA). Georeferenced subtidal transects were conducted across this seascape to describe habitat attributes, including the density of macroalgae, and record the number and size of fishes. Multiple regression analyses were conducted to identify which variables of habitat structure were most important in describing numerical density, biomass density, average size, and maximum size for fishes. Responses to different habitat components were dependent on particular species, choice of spatial scale, and the inherent characteristics of the seascape itself. Notably, the relative influence of seascape components was dependent on the configuration of the seascape, where fishes in a more isolated and less connected seascape were more influenced by spatial configuration than fishes in a seascape with greater habitat connectedness. This study demonstrates that explicit habitat maps allow for a more comprehensive understanding of population structure when describing fishes across large spatial scales

Duration and severity of Medieval drought in the Lake Tahoe Basin

This paper is not subject to U.S. copyright. The definitive version was published in Quaternary Science Reviews 30 (2011): 3269-3279, doi:10.1016/j.quascirev.2011.08.015.Droughts in the western U.S. in the past 200 years are small compared to several megadroughts that occurred during Medieval times. We reconstruct duration and magnitude of extreme droughts in the northern Sierra Nevada from hydroclimatic conditions in Fallen Leaf Lake, California. Stands of submerged trees rooted in situ below the lake surface were imaged with sidescan sonar and radiocarbon analysis yields an age estimate of ∼1250 AD. Tree-ring records and submerged paleoshoreline geomorphology suggest a Medieval low-stand of Fallen Leaf Lake lasted more than 220 years. Over eighty more trees were found lying on the lake floor at various elevations above the paleoshoreline. Water-balance calculations suggest annual precipitation was less than 60% normal from late 10th century to early 13th century AD. Hence, the lake’s shoreline dropped 40–60 m below its modern elevation. Stands of pre-Medieval trees in this lake and in Lake Tahoe suggest the region experienced severe drought at least every 650–1150 years during the mid- and late-Holocene. These observations quantify paleo-precipitation and recurrence of prolonged drought in the northern Sierra Nevada.Support for this work was provided by US Geological Survey/ Desert Research Institute under Project ID# 2003NV39B, a Geological Society of America graduate research grant and the IRIS undergraduate internship program. F. Biondiwas supported, in part by NSF Cooperative Agreement EPS-0814372 to the Nevada System of Higher Education. N. Driscoll was supported in part by a grant from CA DWR