Assessing the relationships between marine protected areas and invasive species – PAVIS

WP 2: Literature review
We conducted a comprehensive survey of the peer-reviewed literature to compile a database of studies that investigated the effects of MPAs on alien species. We used the research engine Web of Science (https://www.webofknowledge.com). Eligibility criteria included any paper or review published between 1950 and the cut-off date 10 June 2016 with the terms: «marine protected area*«, «marine reserve*«, «no-take area*«, «no-take zone*«, «marine park*« in the title, keywords and/or abstract. Each of these searches where refined using the terms: «exotic«, «alien«, «invasive«, «non-indigenous«, «NIS«, «non-native«, «introduced species«, «foreign species«.

WP 3 & 4: Visual census
We sampled rocky habitats at 6-10 m depth, at 2-4 replicate stations within each MPA according to their size, and at another 2-4 replicate stations in control (unprotected) areas. At each site, we conducted SCUBA surveys of the abundance and size of fishes along visual transects. The same observer (SG) conducted 6 replicate 25 m-long and 5 m-wide transects at each station. The diver swam at constant speed, identifying, counting and estimating the size of all individuals within 2.5 m on either side of the transect line. We also estimated the density and biomass of key herbivore invertebrates. Algal cover was estimated for the following groups: turf, encrusting algae, erect algae, and canopy, by analyzing 24 images (0.250 m2 sampling area) for each sampling station (total n=1248).

WP5: Fish tethering experiments
Fish tethering experiments were conducted to quantify the role of predation within and outside the selected MPAs. The tethering experiments experiments were designed to account for the putative effects of the factor «protection« (fixed factor, 2 treatment levels: MPA versus external location) as well as the spatial variability (3 sites per treatment at each location, with «site« as a random factor orthogonal to «protection«).

WP2: We found only 17 studies that were suitable for the qualitative and quantitative synthesis. We included studies that provided data on alien species from both inside and outside MPAs. The largest proportion of the available literature provided data on alien molluscs (40%), followed by algae (28%). Information on the effects of protection on alien/invasive species is available for only 11% of the marine biogeographic provinces; principally, for the Mediterranean and Caribbean Seas. Only four studies provided adequate quantitative data to estimate the effect of protection on the density and biomass of 12 alien species. We found that protection had a significant negative effect on half the species, whereas 33% of the species were positively affected. Our review demonstrates the scarcity of data on this crucial topic. More evidence on various species and taxonomic groups across marine regions is necessary to draw robust conclusions.

WP 3&4: In the South and Eastern Mediterranean MPAs, the biomass of alien and native range expanding fishes often exceeded 50% of the total fish biomass. Conversely, in the North and Western Mediterranean, alien fishes were absent. Average and minimum sea surface temperature (SST) over six consecutive years were positively correlated with the total biomass of alien species; no alien fishes were recorded below 20.5 °C average SST and 13.8° C minimum SST. The biomass of alien and native range expanding fishes was found to be higher in the South and Eastern Mediterranean MPAs than in adjacent unprotected areas. The association of barrens (rocky reefs deprived of vegetation) and invasive herbivores was observed at all eastern sites, regardless of protection status. Currently, the level of fishing pressure exerted on alien and native range expanding fishes seems to be the most influential factor determining the lower biomass of invasive fishes at unprotected sites compared to MPAs.

The project is still in progress and its findings so far show that much more work should be done in order to be able to assess what are the relationships between marine protected areas and invasive species. The data obtained by our experiment may shed light on this important topic. Moreover, WP 6 will provide important guidelines to decision makers on what actions can better mitigate the impacts of invasive species depending on their characteristics. The work conducted during this project is novel and it opens many perpectives for future research.

The results of our review which are reported in detail in the chapter 1 of the submitted report were published in the peer-reviewed journal «Frontiers in Marine Sciences« : Giakoumi, S., and Pey, A. 2017. Assessing the Effects of Marine Protected Areas on Biological Invasions: A Global Review. Frontiers in Marine Science 4: 49.

Preliminary results were presented in the International Conference «Sfécology« organized by the French Ecological Society in Marseille (24-27 October 2016). The PDF of the presentation is provided in Appendix 1 of the submitted report as it is the first deliverable of WP4.

Moreover, the results of WP 3 & 4, described in detail in chapter 2 of the submitted report, were submitted to the peer-reviewed journal «Ecological Applications«. The paper is currently under its second review.

Humans depend on marine ecosystems for valuable services, such as food provision and climate regulation, but at the same time ecosystems are threatened by multiple human stressors. Marine protected areas (MPAs), areas of the ocean designated to enhance conservation of marine resources, have emerged as a prominent management tool for threat mitigation and recovery of marine communities. Under the European Union Marine Strategy Framework Directive, member states are committed to developing strategies, including the establishment of new MPAs, to achieve ‘‘Good Environmental Status (GES)’’ by 2020. One descriptor determining GES dictates that alien species introduced by human activities should be at levels that do not adversely alter ecosystems. Through competition, predation, and habitat alteration, invasive aliens can radically change the biodiversity, functioning of native ecosystems, and consequently services provided to humans. At the same time, global warming of the oceans has triggered the range expansion of thermophilic native species (called range-expanding), some of which may severely impact the recipient ecosystem, in a similar way to invasive alien species. Currently, the role of MPAs in controlling invasive species populations is generally unknown. At the same time, assessments of impacts of invasive species on marine ecosystems within and outside MPAs are scanty.

This project will aim to investigate the following hypotheses: 1) whether MPAs influence the expansion of alien/range-expanding species and mitigate their effects on native assemblages, 2) whether the ecological effects of such species could alter, reduce, or nullify ecosystem responses to protection in MPAs (e.g., ecosystem-wide recovery), and 3) whether local economic activities, such as artisanal fisheries and recreational diving, performed within MPAs and in adjacent areas, have been impacted by the presence of alien/range-expanding species (e.g., impoverishment or enhancement of fisheries catch). The study will focus on alien/range-expanding fish species that have been characterized as invasive species or are considered to impact ecosystems in a similar way (regardless of their origin) in the Mediterranean Sea. During the first year of the project, a broad-scale observation of species distribution patterns will be conducted. Non-destructive observation methods will be used in 8 MPAs and fished adjacent sites, following a replicated sampling design over multiple spatial scales. Data on fish and benthic assemblages will be collected along biogeographic gradients, and along a gradient of impact by alien/range-expanding species, contrasting MPAs and adjacent fished areas to assess potential effects of MPAs on alien/range-expanding species distribution and estimate impacts of such species on native communities. At the same time data on fishing catches will be collected through questionnaires administered to key actors (e.g., fishers). During the second year we will investigate the specific processes which explain the patterns observed by conducting a series of experiments in a subset of sites within the study region. Fish tethering experiments will be performed in 3 MPAs and adjacent sites to examine the effects of alien/range-expanding large predators on native fishes, as well as the effects of large native predators on alien/range-expanding fish species. During the third year of the project the results of the first two years will be synthesized with the aim to: 1) provide a better understanding of the relationships between invasive species and MPAs, and 2) inform spatial planning by forming site-specific guidelines on additional actions and strategies to be implemented to mitigate the impacts of invasive species. The output of the project will assist decision-makers in France and the EU to achieve the desired “Good Environmental Status” and develop marine spatial plans in a changing world.