Over the last several decades, human alterations have greatly changed the face of the California coastal zone, including the widespread loss of estuaries. The California halibut, Paralichthys californicus, is an ecologically and economically important finfish, and is known to depend upon inshore waters for nursery grounds. However, it remains poorly understood as to which specific habitat types (open coast, enclosed bays and estuaries, small lagoons) are most important as productive nursery grounds. In light of continued coastal change, information is needed on the relative importance of nursery habitat types for the proper implementation of marine reserves designed to protect the halibut.

The contribution of nursery habitat types will be determined using trace element analysis of California halibut otoliths (ear bones). These elements can be viewed as signatures that serve as a record of the environmental conditions experienced by fish over time and which differ across habitat types. Also, statistical analysis of long term CalCOFI data will be analyzed to examine how changes of coastal habitat types over time have affected the larval abundance's and distributions of the halibut. To determine the level of connectivity between halibut populations, stable isotope analysis of otolith material (which varies with temperature and indicates latitudinal position over time) will be employed as well as molecular tools. A matrix model, that includes life-history information on halibut from specific habitats, will be created. With sensitivity analysis, this model will describe how halibut standing stocks are affected by coastal habitat alteration. Additionally, a patch isolation model will be employed to examine the effects of disturbance on halibut metapopulations (why connectivity data is needed).

This study will identify key nursery habitat for juvenile California halibut and reveal the sensitivity of halibut standing stocks to perturbations of coastal habitat types. Also, this study will be one of few to incorporate microconstituent analysis, molecular tools, and modeling in order to more fully understand population structure and dynamics within a species.

Elements incorporated into developing hard parts of planktonic larvae record the environmental conditions experienced during growth. These chemical signatures, termed elemental fingerprints, potentially allow for reconstruction of locations of larvae. Here, we have demonstrated for the first time the feasibility of this approach for bivalve shells. We have determined the spatial scale over which we are able to discriminate chemical signatures in mussels in southern California and characterized the temporal stability of these signals. Early settlers of Mytilus californianus and Mytilus galloprovincialis were collected from eight sites in southern California. Shells were analyzed for nine isotopes using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). We discriminated among mussels collected in two bays and the open coast using Mn, Pb, and Ba shell concentrations. Shell concentrations of Pb and Sr were sufficiently different to discriminate between mussels from the northern and southern regions of the open coast, each representing approximately 20 km of coastline. These signals were relatively stable on monthly and weekly time scales. These results indicate that trace elemental fingerprinting of shell material is a promising technique to track bivalve larvae moving between bays and the open coast or over along-shore scales on the order of 20 km. Identification of spatial variation in elemental fingerprints that is stable over time represents a crucial step in enhancing our ability to understand larval transport and population connectivity in invertebrates.