Portland State University. Department of Biology
Date of Award
Master of Science (M.S.) in Biology
1 online resource, (p92.)
Barnacles -- Ecology, Algae -- Ecology, Nature -- Effect of human beings on, Intertidal ecology
Marine intertidal ecosystems are vulnerable to human interference,
because trampling can be a significant problem. I studied the impacts of
trampling on community patterns and succession in a rocky intertidal
habitats. This study was divided into two phases: ( 1) a trampling phase and
(2) a recovery phase. Both phases are focused on two barnacles, Balanus
glandula and Chthamalus dalli, and on fucoid and red algae. The trampling
phase tested the effects of trampling on these organisms. The effects of
herbivores, primarily limpets (Collisella digitalis) were also tested to
determine whether anthropogenic (trampling) and natural (herbivory and
limpet bulldozing) disturbances had independent or additive effects. The
recovery phase monitored the recovery of these species after trampling was
A randomized block design was set up at two sites on the Oregon coast. Light and heavy trampling regimes and herbivore inclusion and exclusion treatments were applied, to permit comparisons with control plots. During the trampling phase, experimental plots were trampled monthly from November 1992 to July 1993. During the recovery phase, the experimental plots were not trampled and recovery was monitored from August 1993 to October 1994.
Trampling severely reduced the abundance of B. glandula, but the smaller C. dalli increased. This increased abundance was due both to resistance of C. dalli to trampling and to reduced competition from B. glandula. Herbivores reduced abundance of newly-settled B. glandula, but had no effect on C. dalli. Cover of algae declined rapidly under trampling.
This was due both to direct effects and to removal of B. glandula, the settlement substrate. Trampling had severe effects on overall community composition. Some species were eliminated, and succession was prevented. In this study, light and heavy trampling had equally detrimental effects. Trampling swamped potential herbivore effects.
Recovery/succession after trampling was slow as B. glandula, afacilitative species was in low abundance. Chthamalus dalli abundancewas high due to high recruitment and to release from competition.Chthamalus dalli individuals grew to unusually large sizes, which enabledthem to function as a facilitative species. This occurrence enabledsuccession to proceed despite the absence of B. glandula. Because it hasalready established, C. dalli in this large form has a short term competitive dominance over B. glandula. With increased recruitment of B. glandula,over time, the pre-emptive competition will fail and B. glandula regaindominance
Grubba, Timothy Lawrence, "Human Trampling in the Upper Rocky Intertidal: Trampling and Recovery in Barnacle Mediated Succession" (1997). Dissertations and Theses. Paper 5373.