Bonnie J. Becker

Complex larval connectivity patterns among marine invertebrate populations

Based on the belief that marine larvae, which can spend days to months in the planktonic stage, could be transported considerable distances by ocean currents, it has long been assumed that populations of coastal species with a planktonic larval stage are demographically open and highly “connected.” Such assumptions about the connectivity of coastal populations govern approaches to managing marine resources and shape our fundamental understanding of population dynamics and evolution, yet are rarely tested directly due to the small size and high mortality of marine larvae in a physically complex environment. Here, we document a successful application of elemental fingerprinting as a tracking tool to determine sources of settled invertebrates and show that coastal mussel larvae, previously thought to be highly dispersed, can be retained within 20–30 km of their natal origin. We compare two closely related and co-occurring species, Mytilus californianus and Mytilus galloprovincialis, and determine that, despite expected similarities, they exhibit substantially different connectivity patterns. Our use of an in situ larval culturing technique overcomes the previous challenge of applying microchemical tracking methods to species with completely planktonic development. The exchange of larvae and resulting connectivities among marine populations have fundamental consequences for the evolution and ecology of species and for the management of coastal resources.

What Controls Connectivity? An Empirical, Multi-Species Approach

The exchange of individuals among habitat patches (connectivity) has broad relevance for the conservation and management of marine metapopulations. Elemental fingerprinting-based research conducted over the past 12 years along the open coastline and bays of San Diego County in southern California evaluated connectivity patterns for seven species: one native and two invasive mussels, an oyster, a brachyuran crab, and two fishes. The studies spanned different years and seasons but overlapped considerably in space, allowing comparisons of dispersal patterns across species, and assessment of the relative importance of location, circulation, and intra-annual and inter-annual variability. We asked whether the species exhibited commonalities in directional transport, transport distances, sources and sinks, self-recruitment, and bay-ocean exchange. Linked connectivity-demographic analyses conducted for two species of mytilid mussels and two fishes allowed evaluation of the contributions of realized connectivity to metapopulation dynamics relative to other life-history attributes. Common trends across species include average along-shore dispersal distances of 15-35 km and seasonal changes in direction of dispersal that mirrored patterns of along-shore circulation. We observed greater isolation of back-bay populations, significant exchange from front bay to ocean, and high self-recruitment in locations on the northern, open coast, and in the southern bays. Connectivity was rarely the most influential driver of growth and persistence of metapopulations, but influenced the importance of other vital rates. Several locations served consistently as sources of larvae or as nurseries for multiple species, but there were few sites in common that were sinks. For the mussels, reproductive timing guided directional transport. These results imply that local management (e.g., habitat protection, opening of the mouths of lagoons, location of aquaculture farms) may be effective along this coastline. Regional, multi-species assessments of exchange of larvae should move us closer to ecosystem-based management.

Evaluating the skeletal chemistry of Mytilus Californianus as a temperature proxy: effects of microenvironment and ontogeny

Thesis (M.S.) Department of Geological Sciences. Base map: coordinates provided by the author on page 3.

A Nonlethal Anesthesia Protocol for Accessing the Mantle Cavity of Olympia Oysters in the Laboratory or Field

ABSTRACT An effective method of anesthesia for Olympia oysters (Ostrea lurida) would allow for nonlethal sampling of tissues for genetic analysis, biopsy for diseases, assessing reproductive status, and collection of brooding larvae. The use of magnesium sulfate (MgSO4) as an anesthetization method for Olympia oysters was assessed in laboratory trials and field use. Three replicate groups of 10 oysters were exposed to MgSO4 at three concentrations (0, 75, 85, and 100 g/L) in the laboratory to investigate the optimal concentration for anesthetization. Laboratory trials determined that 45 min of treatment with 100 g/L MgSO4 was the most effective. In the field, more than 14,000 oysters were exposed to MgSO4 as an anesthetic to assess reproductive status and validate the procedure. In field trials, the anesthetization method of 45 min air exposure followed by 45 min submersion in 100 g/L MgSO4 was found to have a success rate >80%. No influence of sampling date, location, or reproductive status on anesthetization was detected. Shell height was negatively correlated with anaesthetization success rate, with small oysters more likely to open their shell in response to MgSO4.

DETERMINING DISTRIBUTION AND SIZE OF LARVAL PACIFIC GEODUCK CLAMS (PANOPEA GENEROSA GOULD 1850) IN QUARTERMASTER HARBOR (WASHINGTON, USA) USING A NOVEL SAMPLING APPROACH

ABSTRACT Realistic species-specific information about larval life history is necessary for effective management of shellfish and parameterization of larval connectivity models. The patchiness of dispersing larvae, and the resources needed for sorting and identifying them, has limited many studies of larval distribution in the field, especially for species that are less common. In particular, little is known about in situ larval distribution of Pacific geoduck clams (Panopea generosa Gould 1850), a commercially important species found in Puget Sound, WA. A novel approach—time-integrating larval tube traps paired with molecular identification and sorting (FISH-CS)—was used to determine the distribution of geoduck larvae over 4 mo at 3 stations in Quartermaster Harbor. Larvae were found consistently at the surface and thermocline rather than at the bottom. More and larger larvae were captured in the inside and middle of the harbor than the outer harbor, indicating at least some larval retention. Two pulses of larvae were captured, in March and late May to early June. Size—frequency distributions of larvae indicate that these were 2 separate cohorts of larvae, with the possibility of a pulse of larvae from elsewhere toward the end of the season. The only physical parameter associated with relative larval abundance was degree of stratification, although the association was weak. These data represent the first reported study of geoduck larval distribution in the field and the first use of the FISH-CS technique for field collections. In the future, this approach can be used to answer many relevant management questions locally and more broadly, including quantifying larval export from shellfish farms, placement of restoration sites and marine protected areas, and spread of invasive species.