MEPS 532:123-136 (2015)  -  DOI: https://doi.org/10.3354/meps11335

ABSTRACT: Disturbance has both direct and indirect effects that may allow non-native species to proliferate outside of their native range. Disturbance facilitates invasions indirectly by mediating negative interactions with native species, but less is known about the role of direct effects, which are typically considered to be negative. However, the direct effects of disturbance may increase spread of the invader if the damage causes reallocation of resources to reproduction. To examine this possibility, we considered the direct effects of disturbance on reproductive allocation of the dwarf eelgrass Zostera japonica Aschers. & Graebn. across different sediment disturbance regimes in Yaquina Bay, Newport, Oregon, USA. We pair data from 2 yr of monitoring at 6 sites with a field experiment at 3 sites. Both the observational and experimental studies showed that there was a negative linear relationship between vegetative biomass of Z. japonica and sediment deposition among the sites; the experiments showed a 50% decline at sediment deposition of ~1 cm mo^-1 and nearly 100% decline at rates above ~3.5 cm mo^-1. The experiments also showed that flowering responded unimodally to increasing sediment deposition; it was greatest at sediment deposition rates of ~0.75 cm mo^-1 and declined at ~1.5 cm mo^-1, and for rates up to 1.0 cm mo^-1, flowering biomass was negatively correlated with vegetative biomass, suggesting a tradeoff was occurring. The results show that there are tradeoffs in resource allocation in response to disturbance, favoring sexual reproduction as a potential escape response to increasing severity.

KEY WORDS: Disturbance experiments · Direct effects · Resource allocation · Reproductive strategy · Biological invasion · Sedimentation · Seagrass · Tradeoff · Zostera japonica