Harbors and coastal embayments serve as focal points of invasion by sessile epibenthic invertebrates. Despite considerable information on the geographic distribution of such taxa, information on the patterns of their small-scale spatial variability and the importance of local environmental factors that influence these patterns is needed to better manage the spread of invasive species. Here I (1) quantify spatial patterns in recruitment of sessile epibenthic invertebrates of non-native, native and cryptogenic origins within Santa Barbara Harbor (SBH), (2) assess the extent to which spatial patterns in recruitment could be explained by variations in local environmental factors, and (3) evaluate the extent to which spatial patterns in recruitment could account for observed patterns of spatial variation in natural assemblages within the harbor.

The majority of invertebrate taxa found on SBH's floating docks (75%) and on recruitment plates (91%) were of non-native or cryptogenic origins. The non-native tunicates Ciona spp. (C. savygni and C. intestinalis) and Diplosoma listerianum, the bryozoan Watersipora subtorquata, the native bryozoan Celleporaria brunnea, and the taxonomically unresolved spirorbid polychaetes showed strong spatial patterns in recruitment within the harbor. Recruitment of Ciona spp. was negatively associated with water flow, whereas that of D. listerianum and W. subtorquata was positively associated with the presence of conspecifics on the floating docks. Spatial patterns in recruitment of two taxa ( Celleporaria brunnea and spirorbid polychaetes) were not associated with any measured environmental factor. However, spatial patterns in recruitment were positively associated with proportional cover of the epibenthic assemblage after 12 months of development for Ciona spp., C. brunnea and spirorbid polychaetes.

My results indicate that variation in water flow and the presence of conspecifics significantly influenced spatial patterns in recruitment within SBH for three of the five invertebrate taxa. Observational and experimental evidence suggests that water flow plays a significant role in the initial establishment of Ciona spp. However, other factors, such as competition for space, or mortality may also influence longer-term development of the epibenthic assemblage. Understanding the relationship between environmental factors and patterns in recruitment may improve our ability to predict the distribution of epibenthic invertebrate invasions. These results may be used to develop a predictive framework that considers location within a harbor, as well as harbor design, to optimize boat-hull cleaning strategies (e.g., frequency and timing) and target problem species.