Recruitment success in infauna: geochemical cues This study will address two questions about recruitment, an important determinant of community dynamics: 1) what are the qualities of the sediment surface to which recruits are responding? and 2) what processes (physical, biological and chemical) control availability and acceptability of sites? Recent experiments and models suggest that some new recruits respond to substances common to a variety of habitats, namely porewater solutes such as ammonium and oxygen. These solutes appear to be indicative of habitat quality and disturbance history -- both of which may strongly influence survivorship of recruits. Most biologically active sedimentary systems are characterized by steep solute gradients within the top sediment layers, driven by organic matter decomposition (diagenesis) and transport processes (Bemer 1980). Most disturbances result in changes in chemistry that render the surficial sediments more suboxic or anoxic in character. The steep gradients in chemical properties in sediments and the changes in surficial chemistry that accompany disturbance provide a broadly available and potentially significant chemical signal for new recruits. This study will examine the hypothesis that organisms use this diagenetic information in the site selection process. This study will examine the significance of surficial sediment chemistry to the decision making phase for primary and secondary recruitment from an experimental and mathematical point of view. The research will address the following: (1) separate the signal provided by solutes from that provided by other, more commonly evaluated factors such as grain size and organic matter content; (2) evaluate the generality of the responses of new recruits to solute signals both experimentally and mathematically, for example, do organisms which as adults inhabit different sedimentary environments respond similarly to solute signals as new recruits; and (3) evaluate the implications of the disturbance-surficial chemistry link, for example how do the severity of the disturbance and the steepness of the solute gradients interact, and are the circumstances under which new recruits will accept a given location predictable on the basis of the solute profile and disturbance history? The study is expected to develop coupled experiments and models with an evaluative and predictive capacity; an understanding of the degree to which new recruits of species with significantly different adult distributions use solutes that are broadly distributed, but environmentally informative, as chemical cues to habitat suitability; and an appreciation for the influence of disturbance on surficial solute distributions and the adaptive significance of the responses of new recruits to disturbance signals. Overall, the integrated modeling and experimental approach will provide a predictive tool for evaluating recruitment patterns and choices in a variety of nearshore habitats.
