PARENT SESSION
Oral Session # 63: Marine Ecology II: Communities, Barnacles, and Clams.
Presiding: RA Feagin
Thursday, August 7. 8:00 AM to 11:30 AM, SITCC Meeting Room 101.

Shifts in species dominance on rocky shores under human and natural disturbance regimes.

Kappel, Carrie^*,1, Micheli, Fiorenza¹, Heiman, Kimberly¹, Osio, Giacomo¹, Sagarin, Rafael¹, Sethi, Suresh¹, Shelton, Andrew¹, ¹ Stanford University, Palo Alto, CA

ABSTRACT- Through intensive biodiversity surveys of rocky intertidal habitats of Monterey Bay, CA, we assessed how human and natural disturbances interact to affect these coastal communities. Specifically we examined whether differences in human disturbance and wave exposure lead to differences in dominance patterns within these communities and whether disturbances differ in their effects on common and rare species. The eight survey Areas span a gradient in human disturbance, taking advantage of existing marine reserves and other areas representing different levels of access and legal restriction of human activities. Areas fell into 4 Categories: (1) open access, no restrictions; (2) open access, reserve, no enforcement; (3) closed access, no restrictions ('de facto reserve'); (4) closed access, reserve, restrictions enforced. Each Area was divided into a wave-exposed and a protected Site and Transects were stratified by tidal elevation within each. Relative rank abundance patterns were compared among Areas, Sites, and Categories of human disturbance. Results suggest that human disturbance through trampling, collecting, and other impacts leads to shifts in species dominance. Sites with no restriction on access or harvest exhibited decreased dominance of common species and increased abundance of rare species relative to reserves with restricted access and effective enforcement. This was most apparent among sessile invertebrates and algae, i.e. those species that compete for primary space, suggesting that patchily distributed human disturbances open up primary space and decrease competitive dominance on rocky shores. Differences between exposed and protected sites were less striking than those for human disturbance, but sessile species did exhibit decreased dominance and increased equitability in wave-exposed sites. Relative abundances of common species were most sensitive to differences in disturbance. Rank abundance patterns among rare species were generally similar among Areas and Sites, though identities of these species varied. Mobile invertebrates exhibited similar patterns across human and physical disturbance gradients.

Key words: Rank abundance, Marine reserves, Human disturbance, Biodiversity