Funded Grants

Metacommunity dynamics across scales and the design of marine reserve networks

Marine fisheries are failing and species from invertebrates to charismatic megafauna are threatened by fishing pressures and other environmental changes. The remedies are not simple, but clearly marine reserves have a fundamental role to play. The design of reserve systems requires a sound theoretical foundation, which has led to the beginning of a science of reserve design, both in marine and terrestrial systems. Complexity in the design of marine reserves results from the large number of species involved and from the underlying physical and biological heterogeneity of the landscape. More precisely, coastal ecosystems consist in an ensemble of spatially subdivided communities, each composed of species that interact with each other as well as with the environment across temporal and spatial scales. This description of complex marine systems actually corresponds to the definition of a metacommunity. The goal of this project is to develop a comprehensive theory of coastal systems where few key abiotic and biotic factors drive the collective dynamics of large ensemble of interconnected communities. This effort will integrate the complexity of coastal ecosystems within a well-defined theoretical framework. It will also lead to predictions that can be validated using existing large ecological datasets and used as the basis for the development of optimal marine reserve networks in order to maintain biodiversity and stability of marine species.

Ecological communities inhabiting rocky shores have served as the hallmark of ecological complexity. For example, the diversity of intertidal species along the West coast of the United States is in part maintained by waves disturbances affecting mussels attached to the substratum and allowing other less competitive species to colonize and persist. This succession of species observed after a disturbance typically involves many species and a very complex set of positive and negative interactions between them. Complexity is also present at larger scales. Marine invertebrate species often have a pelagic larval stage that up to several weeks. During that time, nearshore currents transport larvae over tens to hundreds of kilometers for many species. This process thus creates a complex set of interactions between communities exchanging larvae. However, most fundamental and applied theories of large-scale coastal systems addressing the dynamics of large ensembles of such communities still ignore the combined effect of this spatial interconnection and of species interaction. In other words, coastal ecosystems still lack any theoretical framework recognizing their intrinsic complexity. Rather current theories posit that large-scale variability is controlled by oceanographic heterogeneity at corresponding scales. The lack of agreement between current model predictions and observed regional patterns of species abundance and community structure in natural communities suggest that macroscopic properties of coastal systems are not simply obtained from accumulating our knowledge of local communities. It rather becomes important to explicitly understand complex networks of interactions, both between species, and across space if we expect to reach significant understanding and sound management of coastal ecosystems.

Our approach thus consists in studying the emergence of complexity within and among communities from simple ecological processes that are known to regulate rocky intertidal communities. More precisely, the self-organization of species assemblages featuring positive interactions will be studied in a metacommunity where nearby populations can exchange larvae. These localized interactions have the potential to explain the formation and maintenance of heterogeneity in the distribution of species at scale much larger than those of underlying ecological processes. Because natural and managed coastal ecosystems are characterized by strong environmental heterogeneity (shoreline configurations, ocean currents, reserves), we will then determine how locallygenerated self-organized variability interact with environmental heterogeneity imposed at multiple scales to govern regional dynamics and community assembly. Marine ecology theories lack such level of integration and complex-system theories mostly consider selforganized (intrinsic) and environmental (extrinsic) causes of patterns as alternative hypotheses, thus rejecting their potential synergy. General and specific predictions will then be built to assess the relative importance of intrinsic and extrinsic causes alluded to above, and tested using data gathered over 6 year (ongoing program) from 29 intertidal communities along the West coast of the United States (PISCO). The robustness of these validated hypotheses will further be tested using the data obtained from 1975 to 1986 at more than 150 sites in the gulf of St. Lawrence (Quebec, Canada).

The newly attained knowledge regarding the interplay between intrinsic and extrinsic sources of variability in marine community dynamics will be applied to the selection of optimal marine reserve networks. Marine reserve networks (no-catch zones) have been shown to increase community stability and promote biodiversity. However, the models currently used to create marine reserve networks typically simplify the complex dynamics of coastal systems by adopting static approaches where only the local ecological and economic value of sites is considered. Recent efforts integrating more dynamic processes such as larval dispersal largely ignore environmental heterogeneity and other important ecological processes such as species interactions. What is the potential implication of self-organized dynamics on the optimal selection of protected areas? How long would it likely take to detect the adverse consequences of failing to integrate intrinsic (self-organized) causes of large-scale heterogeneity into reserve design protocols? We will develop optimal marine reserve networks using optimization algorithms (i.e. simulated annealing) by minimizing cost (i.e. the number and size of reserves) and maximizing biodiversity, persistence and stability of populations and communities. This optimization scheme will be applied to model results and allow us to determine the location, number, size and distance between reserves in our networks. Once the optimal networks are determined, we will compare their performance to that of reserve design algorithms found in the literature.

By treating natural communities as complex systems and explicitly modeling the local interactions of their component species with the environment, we will further the theory of community ecology and marine biology by ascertaining the nonlinear interplay between abiotic and biotic factors and its role for regional patterns and community assembly. Our prediction is that coastal marine systems can be approximated as metacommunities in which larvae are exchanged among components, and in which the persistence of one species depends on that of others. The implication of our research for marine conservation is important: if the focus of research and planning is restricted to the local scale, or to static measures of ecosystem health, ill-conceived management schemes can result. Only through an integrated, dynamic global perspective can scientists and managers achieve the goals of marine conservation.