Brent Hughes

EFFECTS OF EGREGIA MENZIESII ON A ROCKY INTERTIDAL ALGAL ASSEMBLAGE

Kelp is common along all temperate rocky coasts of the world (Lüning 1990). The effects of kelp on intertidal communities are well known in Chile, South America, and New Zealand (see Velimirov and Griffiths 1979, Kennelly 1987, Santelices 1990). However, the effects of kelp on the surrounding communities due to variability in kelp morphology is not very well known, especially in the rocky intertidal on temperate west coast North America. Egregia provides an opportunity to investigate such effects rocky intertidal algal assemblages on the west coast of North America, since Egregia is robust (Fig. 1), abundant and has a wide distribution along the west coast of North America. The effects of disturbance on the population dynamics of intertidal kelp have also not been thoroughly investigated (but see Dayton 1975). The purpose of my thesis is to (a) investigate the effects of Egregia on intertidal algal assemblages, (b) explore the consequences of variable duration and severity in disturbance to Egregia on intraspecific persistence and community dynamics, and (c) determine whether those effects are general across a broad spatial scale.

To examine the effects of Egregia on the intertidal algal assemblage (a), experimental plots were established in July 2004 at Soberanes Pt in south Monterey County. A randomized block experimental design was used to compare treatments (complete Egregia removal) to control plots. Algal composition and percentage coverage were estimated repeatedly in plots for one year using random point contacts. Treatment plots were maintained monthly by removing creeping Egregia fronds and recruits. Differences in percentage cover of algal assemblages between treatment and control plots varied greatly during the experiment. Differences were highest during summer months, due to desiccation stress in treatments, and lowest during winter months, due to waves decreasing coverage in both control and treatment plots. After one year, significant differences were detected in algal composition, coverage and species richness between treatment and control plots, but not to the extent observed during the previous summer. These data suggest that Egregia does impact the intertidal algal assemblages, likely positively through stress amelioration and negatively through physical scouring, but that the effect may be short lived as algae acclimate to the change in environmental conditions.

Literature Cited
Black, R. 1974. Some biological interactions affecting intertidal populations of the kelp Egregia laevigata. Marine Biology 28:189-198.

Dayton, P. K. 1975. Experimental evaluation of ecological dominance in a rocky intertidal algal community. Ecological Monographs 45:137-159.

Friedland, M. T. and M. W. Denny.1995. Surviving hydrodynamic forces in a wave-swept environment: Consequences of morphology in the feather boa kelp, Egregia menziesii (Turner). Journal of Experimental Marine Biology and Ecology 190:109-133.

Kennelly, S. J. 1987. Physical disturbances in an Australian kelp community. II. Effects on understory species due to differences in kelp cover. Marine Ecology Progress Series 40:155-165.

Lüning, K. 1990. Seaweeds Their Environment, Biogeography, and Ecophysiology. John Wiley & Sons, Inc., New York, U. S. A.

Santelices, B. 1990. Patterns of organizations of intertidal and shallow subtidal vegetation in wave exposed habitats of central Chile. Hydrobiologia 192:33-57.

Velimirov, B., and C.L. Griffiths. 1979. Wave-induced kelp movement and its importance for community structure. Botanica Marina 22:169-172.

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Acknowledgements
This project was funded by: PADI Foundation, Packard Foundation, Meyers Grant, and the Phycology Lab at Moss Landing Marine Laboratories

Thanks to: Mike Graham, Pete Raimondi, Christopher Kitting, Mike Foster, Diana Kohtio, Laurie McConnico, Amber Phillips, Max Overstrom-Coleman, Jenn Jorve, Diana Steller, Aurora Alifano, Selena McMillan, Nicole Hughes, Lee Murai, Bernat Hereu, Alta Anzalone, Vince Christian, Thew Suskiewicz, Rosemary Romero, Elizabeth Keddy, Tom Wadsworth, and the BEERPIGS.