What are the effects of macroalgal blooms on the structure and functioning of marine ecosystems? A systematic review protocol

We will search a number of online databases to gather empirical evidence from the literature on the impacts of macroalgal blooms on: (1) species richness and other univariate measures of biodiversity; (2) productivity and abundance of algae, plants, and animals; and (3) biogeochemical cycling and other flows of energy and materials, including trophic interactions and cross-ecosystem subsidies. Data from relevant studies will be extracted and used in a random effects meta-analysis in order to estimate the average effect of macroalgal blooms on each response of interest. Where possible, sub-group analyses will be conducted in order to evaluate how the effects of macroalgal blooms vary according to: (1) which part of the ecosystem is being studied (e.g. which habitat type, taxonomic group, or trophic level); (2) the size of blooms; (3) the region in which blooms occurred; (4) background levels of ecosystem productivity; (5) physical and chemical conditions; (6) aspects of study design and quality (e.g. lab vs. field, experimental vs. observational, degree of replication); and (7) whether the blooms are believed to be anthropogenically induced or not.Coastal marine ecosystems are under increasing pressure from multiple drivers of human-induced environmental change, including resource extraction, habitat modification and destruction, species introductions, ocean acidification, and inputs of pollutants and nutrients [1]. One of the consequent changes experienced by these ecosystems is an increase in "species outbreaks", or large, rapid, and temporary increases in the abundance of a species. These outbreaks can, in turn, cause changes in the structure and function of the broader ecological community, modify the physical and chemical environment, and affect human health, ecosystem services, and the economy [2-5]. Large blooms of macroalgae provide a striking example of species outbreaks. These blooms are normally formed by opportunistic, ephemeral algae, which are a natural