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Development of marine benthic algal communities on Juan de Fuca Strait, British Columbia Lee, Robert Kui Sung

Abstract

Developmental studies were made on certain intertidal algal communities at three sites on Juan de Fuca Strait, B.C. The object was to describe the form and structure of these communities and to provide an interpretation that would account for the manner in which they occur. Periodic observations were made on communities developing on denuded rock surfaces and on in situ communities. By using the denuded-quadrat method, a method familiar to terrestrial plant ecologists, species-distribution indices of frequency and abundance were taken to quantitatively describe the stages of recolonization. Data relative to the developmental process, such as life span and period of reproduction of the species involved, were also gathered. The experimental data reveal a pattern of development that is consistent and predictable. Despite the presence of an orderly sequence of events, there is no evidence to indicate that this is an expression of ecological succession. The partial or even total elimination of a population is concluded not to be due to any changes in habitat originated by that population. Instead its elimination, partial or otherwise, is considered to be a consequence of the degree of establishment of the proceeding population. The successional phenomenon, which can be altered by seasonal populants, is related to the morphological nature of the colonizing species. Unicellular forms appear before filamentous ones, and filamentous forms appear before parenchymatous ones. Such a succession is interpreted as being indicative of the relative growth rates and life spans of the growth forms. The length of time in which a population occupies an area is determined by these factors. The presence or absence of growth space can he a main cause for local distributional patterns, especially for ephemeral species. The dynamic structure of the communities studied is attributed to species interaction involving three interrelated factors: (1) the morphology of the organisms; (2) the phenological nature of germination, growth, reproduction, and of spore or gamete release; and (3) the competition for space.

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