Although California’s wetlands are known to be vulnerable to exotic invasions, few studies have sought to evaluate, in detail, the ecological consequences of non-native species.The purpose of this study was to examine closely the effects of the mat-forming Asian mussel (Musculista senhousia) and the burrowing Australian isopod (Sphaeroma quoyanum) on natural and re-created marshlands and tidal flats in Mission Bay in San Diego, San Diego Bay, and San Francisco Bay.

The roles of life history and behavior in the dynamics of dispersal, recruitment and population maintenance were investigated for a dense infaunal polychaete assemblage on the Kendall-Frost mudflat in Mission Bay, California. Polychaete life history features provided the framework for investigations of (1) the relevant scales and mechanisms of dispersal, (2) response to disturbance, and (3) the spatial and temporal predictability of species abundances in the plankton, during recruitment, and in the benthos. Field and laboratory studies of the Kendall-Frost polychaete species Pseudopolydora paucibranchiata Okuda, Polydora ligni Webster, Rhynchospio arenicola Hartman, Streblospio benedicti Webster, Exogone lourei Hartman, Fabricia limnicola Hartman and Capitella capitata Fabricius, revealed many shared life history traits which limit the spatial extent of dispersal. These include annual life cycles, small size, brood protection, small brood size and reduced or facultative planktonic larval stages.

Hydrographic studies and larval plankton distributions support the contention that dispersal is limited. Salinity and temperature gra­dients, and dye, drogue and drift tube trajectories demonstrated slug­gish back-bay circulation. Most larvae released on the Kendall-Frost mudflat remain in the back of Mission Bay, where dispersal is con­strained to small-scale oscillations in back waters or movements over the mudflat itself. Long distance transport between bays is minimal; drift tube releases and spionid larval distributions indicate a 3% pro­bability of transport out to sea for planktotrophic larvae originating on the mudflat. However, larvae which do leave the bay may experience longshore transport 100 km or more to the north or south, particularly during winter storms.

Small-scale dispersal was examined by studying patterns of lar­valavailability, recruitment into settling cartons and colonization of defaunated sediments. Polychaete distributions in the plankton and lar­val recruitment exhibited strong spatial and temporal variation includ­ing seasonal, lunar and diel cycles. Small-scale disturbance, commonly generated on the mudflat by ray foraging and human activities, was stu­died by artificially defaunating small (< 1 m2) sediment patches; a severe storm and consequent raw sewage spill created an episodic large-scale perturbation. Analyses of species' responses revealed colonization ability to be distinct from dispersal ability. Rates and mechanisms of colonization were governed by larval development, settlement and mobility patterns and varied with the scale of perturbation. For Streblospio, Exogone and Fabricia, factors such as brood protection, reduced or flex­ible pelagic larval phases, and post-larval movements, particularly by brooding adults, confer small-scale dispersal abilities which permit rapid colonization of disturbed patches and result in maintenance of high infaunal densities (over 200,000/m2). Pseudopolydora and Polydora possess planktotrophic, long-lived larvae whose planktonic abundances are highly seasonal and variable from year to year. The timing of disturbance must coincide with successful colonization by these species. In general, the annual life cycles and flexible small-scale mobilities of most species confer substantial community resilience.

Within the dense assemblage, intra- and interspecific behavioral interactions appear to mediate spatial pattern and influence the relative success of surface feeding species. The presence of dense Pseudopolydora or Fabricia tubes inhibits recruitment of Pseudopolydora lar­vae. Intraspecific territoriality in Pseudopolydora, manifested as uni­form tube spacing and aggressive palp contact, is initiated during settlement and enhanced during subsequent interaction. Interspecific interference by Pseudopolydora causes withdrawal and loss of foraging time in Streblospio and Fabricia.

These findings demonstrate that interference competition, life histories and dispersal influence population and community structure in Mission Bay and are probably of general ecological and evolutionary significance in most infaunal communities.

Given the increasingly widespread wetland restoration activities in California(Zedler 1996), it is imperative that reasonable measures of success be adopted. In thepast, monitoring of restored wetlands has focused on superficial indicators of structure, such as density or species number. Functional measurements have been more elusive(Zedler 2000). In this study we compared the trophic structure and function of a 6-7 yearold created salt marsh and adjacent natural marsh in Mission Bay, San Diego, Californiain an effort to develop means to assess recovery of trophic function. The majorobjectives of the study were to (1) evaluate of benthic community structure (density,composition and diversity), (2) track seasonal and interannual changes in trophicstructure based on natural abundance stable isotopic analyses, (3) conduct isotopicenrichment experiments to identify consumers of specific food sources (microalgae,cyanobacteria, Spartina and other bacteria), (4) perform of plant cover manipulations toevaluate the mechanisms by which Spartina influences benthic processes, and (5)improve conceptual understanding of trophic successional processes associated withrestoration. In combination these research results allow us to assess the extent to whichthe Crown Point Mitigation Site (CPMS) in Mission Bay California has come to resemblethe natural wetland (Northern Wildlife Preserve [NWP] and Kendall Frost Marsh) and themechanisms underlying this recovery.

Implications of multiple climate drivers for sea urchins were investigated across a spectrum of biological organization ranging from the urchin guild scale, to individual life history traits, to the geochemistry, material properties and porosity of sea urchin calcium carbonate skeletal tests. Using pink fragile sea urchins (Strongylocentrotus fragilis) on the southern California upwelling margin as a model species, links between biological traits and environmental parameters in nature across multiple spatial and temporal scales revealed correlations with dissolved oxygen (DO), pH, and temperature. Temporal trends in sea urchin populations assessed from trawl surveys conducted in southern California over the last 20 years (1994-2013) revealed changes in deep-sea urchin densities and depth distributions that coincide with trends in DO and pH on multidecadal and interdecadal (El Niño Southern Oscillation) time scales. The shallower urchin species (Lytechinus pictus) decreased in density in the upper 200 m by 80%, and the deeper S. fragilis increased in density by ~300%, providing the first evidence of habitat compression and expansion in sea urchin populations associated with secular and interdecadal variability in DO and pH. In this context, marketable food quality properties of the roe were compared between S. fragilis and the currently fished California red urchin, Mesocentrotus franciscanus, to assess the feasibility of developing a climate change-tolerant future S. fragilis trap fishery. Although roe color, texture, and resilience were similar between the two species, smaller and softer S. fragilis roe suggest it may only supplement, but not replace M. franciscanus in future fisheries. In comparisons across natural margin depth and climate gradients from 100-1100 m, S. fragilis exhibited reduced gonad production, smaller, weaker and more porous calcified tests in the Oxygen Minimum Zone (DO < 22 µmol kg-1) and pH Minimum Zone (in situ pHTotal <7.57) than those collected from less acidic and more oxygenated shelf and oxygen limiting zones above and the lower OMZ below. Thus S. fragilis may be more vulnerable to crushing predators if low oxygen, low pH OMZs continue to shoal and intensify in the future. This research highlights the utility of quantifying natural variability in species’ traits along natural gradients on upwelling margins to improve understanding about potential impacts of changing climate drivers.

Methane seepage often generates precipitation of carbonate rocks, which host microbes and a diverse fauna. These rocks may also promote an interaction between seep and background communities that may last for centuries, providing hard substrate even after seepage ceases. I analyzed composition, density, and trophic structure of macrofaunal invertebrates on carbonate rocks at and surrounding Mound 12, a methane seep site off the coast of Costa Rica, to examine how species and trophic diversities respond to changes in seepage activity at different spatial and temporal scales. By sampling in situ carbonate rocks at active and transition sites, I observed declining density and a community shift from a gastropod dominance to more annelids and peracarid crustaceans under less seepage, while carbonates promoted an interaction between such communities functioning as hard substrate for attachment. Defaunated carbonates deployed for 7 years at active and transition sites indicated that grazers are amongst the most successful colonizers, although the community and its trophic structure were not able to fully recover. However, both seep and transition communities showed rapid response, persistence and recovery when carbonates were transplanted to sites with lesser/more seepage activity for 17 months. Finally, wood and bone deployed for 7 years at active and transition sites showed shared species indicating potential interaction between whale, wood, and seep ecosystems when in close proximity. This multi-experimental study offers insight on the resilience of macrofaunal communities and helps us predict community responses to disturbances in seepage activity that may result from growing anthropogenic interference on margins.

The San Pedro Basin (SPB) contains thousands of DDT-production waste barrels dumped on the seafloor from 1947 to 1961. DDT, a harmful pesticide now banned, still impacts California marine life. This study evaluates the relationship between these waste barrels, DDX concentrations (DDT + related metabolites), and benthic macrofaunal assemblages. It analyzed sediment samples from around six waste-barrels and three background sites to address (1) the DDX concentration and depth in relation to the barrels, (2) barrel-proximity effects on macrofaunal (> 300 µm) community structure, vertical distribution, or diversity of the macrofauna, (3) the potential relationship between DDX and macrofauna density, and (4) the potential role of the macrofauna to mix or mobilize DDX. DDX concentration was highest in the 2-6 cm fraction but showed no correlation with macrofaunal density. Macrofauna densities, relatively low (1553-11802 ind/m2) compared to other low-oxygen areas of similar depth. Dominant among the macrofauna were Entoprocta (Barentsiidae), but nematodes were by far the most numerically abundant group. Paraonid, dorvilleid, and cirratulid polychaetes were present. Diversity was lowest within the bacterial halos surrounding the barrels and highest adjacent to the barrels. There is potential for the macrofauna to remobilize DDX into the water column and ultimately the SPB food web, but macrofaunal densities are low. Overall, the study suggests waste barrels have minimal impact on macrofauna communities. However, a broader regional survey, including megafauna and pelagic biota, is necessary for a more comprehensive understanding of how DDX is mobilized in the Southern California Borderland.