First Advisor

Leonard Simpson

Term of Graduation

Spring 1997

Date of Publication

6-2-1997

Document Type

Thesis

Degree Name

Master of Science (M.S.) in Biology

Department

Biology

Language

English

Subjects

Barnacles -- Ecology, Algae -- Ecology, Nature -- Effect of human beings on, Intertidal ecology

DOI

10.15760/etd.7246

Physical Description

1 online resource (vii, 80 pages)

Abstract

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 stopped.

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, a facilitative species was in low abundance. Chthamalus dalli abundance was high due to high recruitment and to release from competition. Chthamalus dalli individuals grew to unusually large sizes, which enabled them to function as a facilitative species. This occurrence enabled succession to proceed despite the absence of B. glandula. Because it has already 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 regain dominance.

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Comments

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Persistent Identifier

https://archives.pdx.edu/ds/psu/30829

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