Rilov et al. Environmental Evidence 2012, 1:10 http://www.environmentalevidencejournal.org/content/1/1/10 SYSTEMATIC REVIEW PROTOCOL Open Access How strong is the effect of invasive ecosystem engineers on the distribution patterns of local species, the local and regional biodiversity and ecosystem functions? Gil Rilov1*, Rebecca Mant2, Devin Lyons3, Fabio Bulleri4, Lisandro Benedetti-Cecchi4, Jonne Kotta5, Ana M Queirós6, Eva Chatzinikolaou7, Tasman Crowe3 and Tamar Guy-Haim1 Abstract Background: One of the most influential forms of biological invasions is that of invasive ecosystem engineers, species that affect other biota via alterations to the abiotic environment. Such species can have wide-reaching consequences because they alter ecosystems and essentially “change the rules of existence” for a broad suite of resident biota. They thus affect resources or stressors that affect other organisms.The objective of this systematic review will be to quantify the positive and negative impacts of invasive ecosystem engineers on ecosystem structure and functioning, and to identify factors that cause their effects to vary. Methods: We will search a number of online databases to gather empirical evidence from the literature on the impacts of invasive ecosystem engineers on: (1) species richness and other univariate and multivariate measures of biodiversity; (2) productivity and abundance of algae, and animals; and (3) biogeochemical cycling and other flows of energy and materials, including trophic interactions. Data from relevant studies will be extracted and used in a random effects meta-analysis in order to estimate the average effect size of invasive ecosystem engineers on each response of interest. Keywords: Biological invasions, Ecosystem engineers, Biodiversity, Ecosystem functioning Background ecosystem-level impacts by modifying their receptive en- Ecosystem engineers (also termed habitat modifiers or vironment, thus inhibiting or facilitating other species, bioconstructors) are defined as organisms that affect either invasive or indigenous [3]. other biota via alterations to the abiotic environment [1,2] either directly with their bodies (e.g., add structure) Ecosystem engineers or their activities (e.g., dig a hole) or indirectly through Jones et al (1994) identified two types of ecosystem engi- their biotic interactions (e.g., eat the canopy and let neers (that are not mutually exclusive, i.e., a species can more light in the forest). Such species create, destroy, or be both types) based on the way they alter the ecosystem: otherwise modify habitats, and thereby affect resources Autogenic engineers modify the environment with their or stressors (e.g., living space, sediment load, light avail- own bodies which act as part of the engineered habitat ability and temperature) that have an impact on other and this engineering is dynamic (when engineers grow organisms. Invasive species have the potential to play a they can modify the environment in different ways). For dominant role as ecosystem engineers and can have example, as mussels grow, their shells increase the avail- able habitat for other organisms (e.g., by providing settle- ment space and/or ameliorating environmental stress). * Correspondence: [email protected] Allogenic engineers are species that modify the envir- 1National Institute of Oceanography, Israel Oceanographic and Limnological Research, Haifa, Israel onment by mechanically changing living and non-living Full list of author information is available at the end of the article materials (or structures or landscapes) from one physical © 2012 Rilov et al.; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Rilov et al. Environmental Evidence 2012, 1:10 Page 2 of 8 http://www.environmentalevidencejournal.org/content/1/1/10 state to another. Different types and numbers of other Marine invaders as ecosystem engineers organisms will thrive in the area where an ecosystem There are quite a few studies, and several reviews among engineer modified the environment than would in a them, that treat marine invaders as habitat modifiers or non-modified area. The classical examples for such engi- ecosystem engineers [1,2,7], but to the best of our know- neers are beavers that alter the flow of rivers by building ledge a comprehensive systematic review of invasive dams. Mussels can also be considered to be allogenic ecosystem engineers that includes meta-analysis on the engineers. By extensively filtering the water in a lake or size and direction of the impacts has not yet been con- a bay they can clear it enough to increase light penetra- ducted. This is in contrast, for example, to two (though tion thus affecting benthic macroalgal communities by limited) such analyses on freshwater systems, one on facilitating growth. carp and crayfish impacts and one on the impacts of There are numerous examples of animals and plants dreissenid mussels [8,9]. Although some marine invasive that function as ecosystem engineers. Trees in the engineers have been intensely studied in the last decade, forest are an example of autogenic engineers on land, it is still unclear at this point if there is enough data whereas, coral reefs or kelp forests can be considered published to allow a comprehensive meta-analysis of as engineers in the sea. Allogenic engineers that shape their impacts on the marine environment. The purpose their environment on land are elephants and termites. of this systematic review is to investigate the current Burrowing worms and sea urchins play a similar role in state of knowledge on the topic and to scope for existing the sea. data thus aiming to perform a meta-analysis in order to achieve evidence-based generalizations on the pheno- menon and its impacts on marine ecosystems. In this Marine bioinvasions study, we consider all brackish and transitional waters Invasive species are species that have spread beyond (e.g., estuaries) as marine ecosystems. their natural biogeographical range to new regions, usu- ally with human assistance, and have the potential to Objective of the review affect the native ecosystem and its biodiversity [2]. Inva- This review is aimed to identify the type, direction and sions, in and of themselves, are rated high as a cause strength of effects of invasive species that are recognized of native biodiversity loss and economic damage [4,5]. as potential ecosystem engineers on the distribution pat- But invasions also interact with all other factors that terns of native species, biodiversity patterns and ecosys- compromise the integrity of marine ecosystems, such as tem functions in the marine environment. Wherever habitat destruction, pollution and climate change. Bio- possible, we will try to identify/separate the engineering logical invasions are also assumed to induce ecosystem- effect of the invasive species investigated from other scale impacts (i.e., significant effects on community effects (e.g., direct food web effects, such as cases when biodiversity and/or ecosystem functions), though this the invasive species are used as food source by local spe- has yet to be clearly demonstrated [6]. cies or when they affect local species directly as preda- Marine biological invasions are a fast growing environ- tors or grazers). This is a global review that includes all mental concern that is facilitated mostly through the regions and all species, and studies that will be consid- growth of trade as organisms traverse oceans attached to ered relevant based on the criteria stated below. the hulls of ships, carried within ballast water, via aqua- culture, as live marine seafood and bait, by the aquarium Primary question trade and through canals connecting different bodies of How strong is the effect of invasive ecosystem engineers water [2]. Although we have been much slower to realize on (a) the distribution patterns of local species, (b) the the extent and impacts of invasions in the sea compared local and/or regional biodiversity (α and γ diversity) and to those on land, our experiences with problematic (c) the ecosystem functions? aquatic invasions continue to mount. For example, the green alga Caulerpa taxifolia, a popular aquarium spe- Secondary question 1: are there any indigenous species cies, now carpets many square kilometers of seafloor in at risk of extirpation or extinction due to the invasion the Mediterranean suffocating other species; Caulerpa of these ecosystem engineers? racemosa increases sedimentation and creates an anoxic Secondary question 2: is there a difference in the sediment layer underneath its roots thus causing the strength of the impact between autogenic and allogenic degradation of seagrass (Posidinia oceanica) meadows; a invasive engineers? comb jelly native to the western Atlantic, caused the col- lapse of fisheries when introduced into the Black and The list of components that will help guide the search Caspian Seas; and invasive marsh grasses and mangroves and analysis of the data is shown in Table 1. With regard are transforming wetlands around the world. to the primary question, it is important to consider how Rilov et al. Environmental Evidence 2012, 1:10 Page 3 of 8 http://www.environmentalevidencejournal.org/content/1/1/10 Table 1 Is a list of components that will be investigated for the review questions Population