Facilitation research in marine systems: state of the art, emerging patterns and insights for future developments

Abstract

Summary1. Positive species interactions are increasingly recognized as important drivers of community structure and ecosystem functioning. Although the literature on facilitative interactions in terrestrial environments has been reviewed and emerging patterns have been synthesized, comparable attempts are lacking for the marine realm. 2. By means of a quantitative survey of the literature, I provide a critical summary of current knowledge on positive species interactions in marine environments. In particular, I (i) assess how marine facilitation research compares to that carried out in terrestrial environments in terms of focus and philosophical approach; (ii) illustrate the mechanisms by which facilitation takes place in different habitats; (iii) assess whether benefactor and beneficiary species are more likely to belong to the same or to a different trophic level; and (iv) provide examples of how including facilitation into ecological theory might advance our understanding of the mechanisms that regulate ecosystem functioning. 3. Except for some studies in intertidal habitats, few studies in marine environments have been framed within mainstream facilitation theory (e.g. the Stress Gradient Hypothesis) and research does not seem to be organized in a self-contained theme. Amelioration of physical conditions appears to be the most common mechanism of facilitation in intertidal habitats, whilst associational defence predominates in the subtidal. 4. In contrast to the terrestrial literature, dominated by plant-plant interactions, marine benefactors and beneficiary species often belong to different trophic levels. This might imply little overlapping of resource niches or a differential response to environmental conditions or consumer pressure, with implications for the persistence of facilitative effects at the extreme ends of stress gradients. 5. Recent research shows that facilitation can enhance temporal variability and invasibility of marine communities and emphasizes the central role of positive species interactions in regulating the functioning of natural ecosystems. 6. Synthesis. Studies encompassing a wide variety of life histories and environmental conditions are central to achieving a unified facilitation theory. Research in marine environments can provide new insights into the mechanisms underlying variations in the strength and direction of species interactions, but this will require greater awareness and consideration of facilitation.

Community assembly and drivers of phytoplankton functional structure

“…At the same time, positive interactions, for example the facilitation, have gained more attention among ecologists in the last two decades, also in marine realm (Bulleri ). In a series of invasibility experiments with freshwater green algae, Narwani et al .…”

Understanding the responses of ocean biota to a complex matrix of cumulative anthropogenic change

“…Such studies enhance our understanding of the extent and nature of the 'ecological surprises' that may result from a changing climate (Lindenmayer et al 2010). Other ecologically relevant topics which may influence or result from differential vulnerability across trophic levels, but which are beyond the scope of this Introduction, include: biodiversity and ecosystem dynamics (Vinebrooke et al 2004); altered species distributions through migration (Parmesan et al 1999) and invasion (Jaspers et al 2011); and the nature of competitive versus facilitative relationships between organisms (Bulleri 2009). …”

Facilitation in the conceptual melting pot

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