The role of disturbance in the evolution of life history strategies in the intertidal mussels Mytilus edulis and Mytilus californianus

Abstract

The intertidal mussels Mytilus edulis and M. californianus compete for space on the west coast of North America. An analysis of differences in size, growth rate, age at first reproduction, life span, mode of reproduction, niche and habitats between these two species demonstrates that their life history strategies are different in several important ways. M. californianus is a larger, sturdier, slower growing mussel which has effective predator-deterring mechanisms and is an overall superior competitor for space in the intertidal. Its reproductive strategy is based on continually spawning at a very low level throughout a yearly cycle. M. edulis is a classic fugitive species which rarely attains a large size but matures early and is characterized by a single massive reproductive output each year. The differences noted in their life history strategies are very likely the result of either a) a "pre-adaptation" for coexistence, or b) a competitively-induced regional evolutionary divergence.In Washington a band of small M. edulis (removed from most predation and competition) exists in a high intertidal spatial refuge, and contributes relatively little to the gene pool. Larger individuals exist in disturbed areas lower in the intertidal zone. These lower zones represent a relatively high risk, and usually only temporary, habitat for M. edulis because of mortality due to competition and predation. Individuals, however, colonizing these two intertidal patches contribute 43 times as much as their high intertidal counterparts in terms of reproductive fitness (calculated on a populationwide basis).

Historical baselines and the future of shell calcification for a foundation species in a changing ocean

“…We combined the two sites in order to bracket the greatest range of relationships that we might see in the midden shells and make the most conservative comparison, but our conclusions are qualitatively the same when we use only the larger modern shells from Yellow Banks. For Tatoosh GL, we used the measurements reported by Paine [29], supplemented by those of Suchanek [37], because the shells were measured in the 1970s and no longer exist. In cases where the original data from the published studies were not available, we digitized the x and y coordinates of each point in the published figures using IMAGEJ.…”

Group living and the effects of spatial position in aggregations of Mytilus edulis

“…However, mussels at Point Richmond were, on average, small. Suchanek (1981) (Kitching etal. 1959;Ebling etal.…”

Invasion resistance on rocky shores: direct and indirect effects of three native predators on an exotic and a native prey species

“…The preference for M. galloprovincialis is likely due to its thinner shell (Landenberger 1968), which would require less handling time for a drilling predator (Hart & Palmer 1987). The whelk also preferred M. galloprovincialis to M. californianus in the laboratory, but it preferred M. trossulus to (Suchanek 1981), which explains why it was preferred to M. californianus. However, it cannot be ruled out that M. trossulus provides the greatest nutritional reward among the mussel species.…”