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Ecology and conservation of seagrass and seaweed beds.Seagrasses are protected under the US Clean Water Act and the loss of seagrass from deliberate causes must be mitigated. I found that the transplanting eelgrass (Zostera marina) to mitigate its loss has eroded the genetic diversity so important for its long term adaptation to the rapid changes (ocean warming, sea level rise, eutrophication) occurring in its estuarine and nearshore habitats. More importantly, transplanted eelgrass populations with low levels of genetic diversity grow slower than populations with higher genetic diversity, even over the short time period mandated for evaluation of mitigation success. These and my previous results on eelgrass genetic diversity provided the basis for the National Marine Fisheries Service to modify eelgrass mitigation policy in southern California.
Ecology and management of marine invasive species.Marine invasive species are one of the top environmental concerns for the ocean. Research in my lab has focused on the ecological effects of the non-native Asian mussel (Musculista senhousia), the stinging anemone (Bunodeopsis sp.), and the ‘killer’ seaweed (Caulerpa taxifolia) on seagrasses in southern California. We have identified the double threat that the Asian mussel and eutrophication pose for eelgrass. Nearshore marine ecosystem function.Seaweed Biodiversity and Ecosystem Function- Dr. Matt Bracken and I have been funded by the National Science Foundation to evaluate the consequences of nonrandom biodiversity changes in intertidal seaweed assemblages on primary production and nutrient acquisition. Most studies to date have addressed the influence of random changes in biodiversity on community structure and function, yet we know that diversity changes in predictable, nonrandom ways in response to eutrophication, physical stress, and herbivory. Moorea Coral Reef LTER- I am a collaborator in the Moorea Coral Reef project supported by the National Science Foundation. I am addressing the environmental controls on nitrogen fixation by coral reef algal turfs. This research complements my long-standing interest in how herbivory and nutrients interact to influence the primary production and nitrogen cycling by seagrasses and seaweeds.
Interactive Effects of Herbivory and Stress on Seaweed Resource Acquisition, Allocation, and Fitness.This study is a collaborative NSF-sponsored project with Dr. Megan Dethier (Friday Harbor Laboratories, U. Washington). Using the high intertidal rockweed, Fucus gardneri, as a model, we are investigating how herbivory and stress interact to influence how seaweeds gain resources (carbon) through photosynthesis, how they allocate resources to key processes of growth, reproduction, herbivore-deterrent compounds (polyphenolics), and storage. Ecological theory predicts that organisms should make trade-offs among such processes when challenged by the environment. While the effects of herbivory on seaweed metabolism and populations are well-described, and there is considerable literature on temperature and desiccation effects, the interaction between herbivory and stress has not been investigated. Fucus is stressed over a sharp gradient in physical factors across its intertidal distribution over a tidal cycle and among seasons. (See Fucus Research.) We have measured photosynthesis of Fucus from 14 sites on San Juan Island, Washington, in both water and air to determine its carbon balance (resource capital), accompanied by measurements of mannitol and laminaran (brown seaweed storage products analogous to starch in green plants), polyphenolics, growth, and reproduction to evaluate resource allocation patterns. We have manipulated herbivory and stress in the field and in controlled outdoor mesocosms, making similar measurements. Our preliminary results indicate that, at our sites, stress is more important than herbivory in influencing growth, polyphenolic concentration, and perhaps reproduction. Resource acquisition through photosynthesis is limited more by the amount of time Fucus spends exposed to air than how desiccated it is at low tide, although desiccation does reduce photosynthetic rates. Fucus is remarkably tolerant to large increases in temperature. If these effects are important beyond the level of an individual, the population growth rates of Fucus living in different environments should reflect the differences. To test this, in collaboration with Dr. Jeff Wright, we are constructing a demographic model to estimate population growth rates across the intertidal distribution of the seaweed. |