Long-term Research in the Rocky Subtidal Zone (Massachusetts 1977-1997).

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Long-term Research in the Rocky Subtidal Zone (Massachusetts 1977-1997).

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Title: Long-term Research in the Rocky Subtidal Zone (Massachusetts 1977-1997).
Author: Sebens, KP; Maney, EJ Jr; Gordon, A
Abstract: Rocky subtidal communities at three sites in Northern Massachusetts have been under intensive and continuous study for the past 20 years. Methods include photography of marked quadrants, transects of predator abundance, and measurement of selected aspects of the physical environment (Sebens 1985,1986,1990, Allmon and Sebens 1988, Graham and Sebens 1996). During those two decades there has been a dramatic increase in sea urchin (Strongylocentrotus droebachiensis) population density, and we have recorded the appearance and effects of several nonindigenous species. The predatory nudibranch Tritoniapkbeia and the colonial ascidian Botrylloides sp. have been the most successful nonindigenous species, and have had measurable effects on indigenous assemblages. Tritunia was responsible for decimating populations of the octocoral Alcyonium sidertum, which still have not recovered by 1997 (Allmon & Sebens, 1988, Sebens &Aiello, ms). Other ascidians (Botryllus schhsseri, Styela clava, Diplosoma sp.) have appeared only rarely in our samples and have not developed stable local populations at these sites. The combined effect of Akyonium removal by Tritonia and a doubling of sea urchin population density (both during 1984-1986) caused the loss of most other invertebrates from vertical rock surfaces, and a local increase in rock surfaces dominated by coralline algae. Horizontal surfaces that had been dominated by kelp and foliose red algae during 1978-1988 were reduced to coral line dominated urchin barrens when the urchins expanded into new habitats in 1989. Botrylloides sp. has been able to establish colonies on rock walls and horizontal surf aces where urchin grazing is intense, and most likely has chemical defenses that deter urchin feeding. The synergistic effects of urchin population increase and the arrival of several nonindigenous species within one decade has caused a major shift in invertebrate and algal assemblages at these sites. We hypothesize that continued high densities of urchins will preferentially select for urchin-resistant spatial dominants, which currently include indigenous coralline algae, sea anemones (Metridium senile) and sponges (Isodidya spp.), and nonindigenous species such as Botrylloides sp.
Description: American Academy of Underwater Sciences (http://www.aaus.org/)
URI: http://archive.rubicon-foundation.org/4649
Date: 1997

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