Masters Thesis

Community succession in macroalgal wrack implications for prey resources of breeding Western Snowy Plovers (Charadrius alexandrinus nivosus) on northern California beaches.

This study examined wrack-associated macrofaunal communities in northern California, providing base line data and documenting potential prey for federally threatened Western Snowy Plovers. I investigated three hypotheses regarding beach wrack macrofaunal ecology: (1) Sandy beach macrofauna exhibit habitat selection based on wrack availability, preferring macroalgal wrack deposits to bare sand. (2) Experimental wrack patches in the moist intertidal zone are more hospitable then in the drier, supratidal zone therefore macrofauna would exhibit preferences for intertidal wrack patches. (3) On northern California beaches, macrofauna abundance varies across taxa, as it does in central California and Spain and predicted the density of talitrid amphipods would be greater than other wrack associated taxa. Macrofauna exhibited a significant preference for wrack deposits over bare sand habitat. Although not significant, abundance differed among intertidal and supratidal wrack deposits and between years. Some inter-annual variation was partially explained by variation in weather conditions. When data from both years were combined, mean taxonomic richness peaked on day nine and declined significantly by day twenty one. Community composition varied significantly between wrack and sand and between years. Dipteran flies, primarily larvae, were the most numerous taxonomic group comprising 50% of all macrofauna collected. In 2007, talitrid amphipods were proportionally the second most abundant taxa; in 2008, they were the least numerous. Off Highway Vehicle impacts may have reduced talitrid amphipod populations in 2008. Trophic level implications include possible reduced prey for Western Snowy Plovers and other shorebirds.