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 latus, 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 macroinvertebrates 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 macroinvertebrates, regional oceanographic processes (i.e. upwelling and productivity) may be more influential in determining the overall abundance and productivity of these diverse animal communities.

Evidence for regional‐scale controls on eelgrass (Zostera marina) and mesograzer community structure in upwelling‐influenced estuaries

“…Here, we extend those findings by showing that epiphytic microalgae, mesograzers, and mesopredator fish follow a similar pattern that is likely predominately controlled by regional oceanography and, to some extent, local trophic interactions and physical factors. Other recent studies support the contribution of regional variability in organizing eelgrass community structure (Duffy et al ; Schmidt et al ) and rocky intertidal community structure (e.g., Moulton and Hacker ; Vinueza et al ; Menge et al ) and illustrate why it is important to consider multiple scales when characterizing the structure, function, and ecosystem services in marine ecosystems.…”

Bottom-up and top-down interactions in coastal interface systems

“…In rocky intertidal systems, recycling of nutrients is very limited relative to physically mediated inputs, but ammonium excreted by mussels can be important in isolated tidepools and for macrophytes in close association with mussel beds (Bracken and Nielsen, 2004;Aquilino et al, 2009;Pather et al, 2014). Excretion by small macroinvertebrates may also affect surfgrass growth (Moulton and Hacker, 2011). Interestingly, despite the very high nutrient uptake capacity of macrophytes, local nutrient depletion is rare (in contrast to soil nutrient pools in terrestrial ecosystems), with the exception of isolated tidepools or environments with low water flow (Hurd, 2000;Nielsen, 2003).…”

“…Figures based on data presented in Menge et al, (in press). desiccation and thermal stress is high (e.g., Bertness et al, 1999;Burnaford, 2004;Moulton and Hacker, 2011). Urchins, chitons, limpets, and other gastropods, as well as a suite of meso-grazers (e.g., isopods, gammarid amphipods, small gastropods) feed directly on benthic macroalgae, the smaller epiphytic algae that colonize them, and the microalgae, algal spores, and cyanobacteria that form thin films on otherwise unoccupied rock surfaces.…”

“…only occur in the North Pacific (Short et al, 2007). Phyllospadix scouleri is a dominant, late-succession species (Turner, 1983;Moulton and Hacker, 2011). It is relatively invulnerable to direct herbivory due to a combination of chemical and structural traits, but some specialized limpets feed on the leaves (Fishlyn and Phillips, 1980).…”

“…Surfgrasses are vulnerable, however, to seed predation by small crustaceans (Holbrook et al, 2000). Low intertidal zone meadows of surfgrass are an important, and sometimes dominant, seascape element that provides habitat for dozens of species of macroinvertebrates (Moulton and Hacker, 2011) and nearshore fishes (Galst and Anderson, 2008).…”