This research will investigate how an ecologically important intertidal fucoid alga (Fucus gardneri) allocates resources in response to variation in two key environmental variables, herbivory and desiccation stress (such as that experienced high in the intertidal zone). These variables are typically studied independently, yet it is their combined effect on seaweeds that must be important in nature. Algae must make "decisions" about how to allocate acquired energy to growth, reproduction, deterrency (e.g., anti-herbivore chemicals), and other key life-history functions, particularly when stress reduces resource acquisition capacity. While resource allocation patterns are being investigated intensively in terrestrial plants, almost no comparable work exists for algae, despite their ease of manipulation, abundance, interesting phylogenetic contrast to vascular plants, and important roles in nearshore marine ecosystems. In addition, virtually nothing is known about the consequences of allocation patterns to seaweed fitness. Fitness here is represented as the finite rate of population growth. Linking physiology to fitness is critical because changes in growth, or even reproduction, may not translate to effects on seaweed populations. In this project, a simple model that balances resource acquisition will be developed first (as Net Primary Production) against all known major resource allocation sinks for fucoids (growth, reproduction, phlorotannins, storage, exudation, loss to herbivores). This model will provide a tool to compare the physiological response of Fucus to gradients in stress and herbivory in the field and when manipulated in mesocosms. The research will involve: 1) observations of field populations of fucoids to quantify variation in their allocation patterns across natural gradients in herbivory and stress; 2) physiological measurements in the laboratory of Net Primary Production (emersed and immersed) and the other terms of the model for field-grown thalli; 3) manipulation both in the field and in laboratory mesocosms of the key variables of stress (emersion time, desiccation) and herbivory where thalli will be raised to reproductive size under these conditions, and then their allocation patterns will be assessed; and 4) development of demographic models to estimate population growth rates from life-history transitions measured in thalli across an intertidal gradient in stress and herbivory. Preliminary studies of the chemical composition and deterrency of extracts thought to contain anti-herbivore compounds will also be performed. The approach is designed to evaluate several specific issues involving resource allocation in, and its consequences for, intertidal seaweed populations that have broader implications than the response of seaweeds to stress and herbivory. Although virtually all previous studies of resource allocation in organisms assume that resource acquisition is constant, this project will test this assumption with measurements of Net Primary Production. Net Primary Production hypothetically varies across intertidal gradients in stressful conditions. If the assumption is false, allocation trade-off comparisons would not be valid without accounting for variation in resource acquisition. It is also hypothesized that there is a critical stress level above which reallocation among resource sinks is not possible. A physiological limit to the capacity to reallocate resources has rarely been addressed. Finally, allocation patterns demonstrated in adult organisms often are assumed to represent an important aspect of fitness or adaptedness. Yet, the adult phase might not be the most important life history stage in contributing to the population growth rate, and thus persistence of the populations. Sensitivity/elasticity analyses of the demographic models will determine which life history transitions (e.g., adult survival and reproduction versus recruitment) are most critical to the population growth rate, and thus, if allocation patterns within adults are important to seaweed population growth. . - This research will provide the first integrated approach to questions of resource allocation in seaweeds, and will demonstrate to what extent environmental harshness (biotic or abiotic) is reflected in algal performance. In this way, it will provide a link between physical changes (such as might occur during global warming) and the ability of algal individuals to grow and reproduce and seaweed populations to persist.
