Congeneric variation in surfgrasses and ocean conditions influence macroinvertebrate community structure

Abstract

Foundation species are important components of ecosystems because they provide habitat and ameliorate stressful conditions for residents. Comparisons of congeneric foundation species have mostly been limited to comparisons of native and invasive species, with less attention paid to multiple native species. Surfgrasses (Phyllospadix spp.) are ubiquitous foundation species on the coast of Oregon, USA, protecting resident invertebrates from waves and providing them with access to sandy substrate in an otherwise rocky habitat. Two native surfgrass species, P. scouleri and P. serru la - tus, have superficially similar morphological characteristics and co-occur within the same rocky intertidal zones. We investigated whether these native congeneric species function similarly as foundation species by comparing the 2 species' morphology, sediment accretion and associated resident macro - invertebrates at 3 capes that vary in oceanographic conditions. The results show that although the macroinvertebrate abundance was the same between surfgrass species, macroinvertebrate species richness, composition and functional groups varied considerably, with more infauna and deposit feeders found within P. serru la tus. P. serrulatus also had fewer tillers and rhizomes, and lower biomass per given area, but greater sediment accretion than its congener P. scouleri. One notably strong result was the difference in macroinvertebrate abundance among capes, with Cape Perpetua having 2.5-3 times more animals per given area than Capes Foulweather or Blanco. Overall, we conclude that although the 2 co-occurring surfgrass congeners provided functionally different habitat for resident macro - invertebrates, regional oceanographic processes (i.e. upwelling and productivity) may be more influential in determining the overall abundance and productivity of these diverse animal communities. © 2011 Inter-Research.