RUI: Analyzing demographic variability of the intertidal sea urchin Strongylocentrotus purpuratus in the context of oceanographic changes using a unique time series data set

Villanova University, Villanova PA

Investigators

Abstract

Many marine species, from plankton to sea birds, show a response to changing physical conditions in the ocean. Some responses may be due to redistribution of individuals but others appear to be due to changes in productivity and the subsequent cascade to secondary production. Intertidal species should show demographic responses to changing oceanographic conditions but this prediction has not been tested, primarily because of a general lack of long-term data sets for most intertidal species. This project uses historical demographic data for the purple sea urchin, Strongylocentrotus purpuratus, from Vancouver Island, Canada, to Punta Baja, Mexico. Some data are from previous work of the investigators in the 1960s and 1980s and some were compiled from the literature and contributions from colleagues. The focus of this study is to build on and extend this unique time-series of demographic data and analyze it in the context of oceanographic changes. The researchers will revisit sites (and specific tidepools) along the coast where sea urchins were sampled in the 1980s and earlier to test the hypothesis that intertidal species respond to large-scale changes in ocean conditions. Local variability could obscure or swamp any oceanographically-driven changes, and particular tidepools characteristics could determine site-specific processes. The focus is to assess the effects of large-scale oceanographic processes on five aspects of demography: growth, reproduction, recruitment, density, and survival. Robust growth estimates are central to separate age-0 from older individuals in estimating recruitment. In addition, growth combined with size structure is the basis of estimating survival and secondary production. Four specific growth questions will be addressed: 1) Do growth rates respond to changing ocean conditions? To assess oceanographic effects on growth requires accounting for growth variability due to changes in conditions between the time of marking urchins and subsequent collection after one year. In addition, growth allometry of jaw size relative to body diameter changes in response to available food. This change will be assessed for the present study period. Accordingly, the second question is: 2) Does year-to-year variation in growth affect methods used to quantify growth and can growth allometry be correlated with oceanographic metrics? Previous work demonstrates the potential significance of local physical conditions so the third growth question is: 3) Does exposure of a tidepool or position within it affect growth and do allometric differences reflect microsite resource variability within a pool? Interpretation of the growth data in these questions is model dependent, so: 4) Which growth model is most appropriate? To assess changes in reproduction, monthly gonad sizes will be measured at eight sites. At some sites, historical data from the 1950s and 1960s as well as the 1980s are available. We will assess changes in recruitment based on size structure of populations sampled from the 1960s through '80s and for the few available sites in the 1990s. Shifts in shapes of size distributions and in particular the fraction of the population represented by age-class-0 address the question: How does the center of maximum recruitment along the coast from Canada to Mexico shift in response to changing ocean conditions? There exist density estimates from the 1950s, 1960s and 1980s and so it will possible to assess whether size-specific density has changed and whether any changes are associated with physical-oceanographic changes or other environmental changes (such as changes in sea otter populations)? Changes in survival rates over the past two decades will be quantified. Recognizable geographic patterns that can be associated with temperature, disease, or predation will be explored. Broader Impacts & Education: This project will enhance opportunities for student participation in research at a primarily undergraduate institution (Villanova). Students will be involved in all aspects of the project: field and lab work, data analysis, authorship on publications, and presentations at conferences. Villanova offers an undergraduate course, Field Ecology and Evolution, that includes an extended field-based component. This course will be offered in 2008 and concentrate on the Pacific intertidal biome of North America and highlight field sites in this study. In addition, the information produced from this project will be shared with a wider audience through the Science NOW program at the California Academy of Science.