Rough Around the Edges: Lessons Learned and Future Directions in Marine Edge Effects Studies
Purpose of Review
After several decades of research on edge effects in marine habitats, we still have little understanding of how organisms respond to marine ecotones, and methodological gaps appear to be limiting our progress. Using recent literature (2010–2018), we synthesized responses and processes of organisms across several marine habitats. Specifically, we examined the uniformity of studies across biogenic habitats, the scales selected for exploring edge effects, the experimental approaches used, and the confounding influences that muddle our interpretation of results.
The majority of edge effect studies are still conducted in seagrass systems and focused on response patterns. We found that the majority of studies were equally likely to report an increase, decrease, neutral, or equivocal effect depending on the context of the organism or habitat. Additionally, only a single measure, or a few related responses, is assessed and causal mechanisms are rarely tested. We note that most studies quantitatively defined an edge habitat as a linear distance from a habitat boundary (e.g., < 1 m, < 5 m), but the distances were not usually scaled to the size, trophic level, or mobility of focal organisms.
We provide a conceptual diagram as a roadmap for researchers for navigating the myriad influences that affect floral and faunal responses to marine habitat edges. Future efforts should seek to move beyond mensurative searches, explicitly incorporate potentially confounding variables, and more consistently test putative causal factors when known or hypothesized. Additionally, we advise expanding research on habitat types other than seagrasses (e.g., mangroves, shellfish, corals) and adjusting observational scales to more appropriately match mechanisms. Ultimately, we should move beyond pattern description, repeated in a limited subset of nearshore habitats, and toward a quantitative understanding of the processes acting in these unique and potentially impactful marine ecotones.
KeywordsEdge Biogenic habitat Ecosystem Habitat loss Spatial scale Ecotone
We would like to thank Dr. Kevin Hovel and Dr. Lenore Fahrig for inviting us to participate in this review. In addition, a number of people participated in initial ideas and discussions for this paper, including Dr. Bradley Peterson of Stony Brook University, Dr. Joel Fodrie at the University of North Carolina and Dr. Lauren Yeager at the University of Texas. Finally, we would like to thank Dr. Laura Treible from Georgia Southern University for providing feedback on this manuscript.
All authors were involved in determining the scope of this review. J.M.C. was responsible for overall literature searches, summarizing the shellfish literature and writing the initial draft. D.A.K. was responsible for summarizing the overall literature in terms of patterns and processes. Both B.T.F. and A.D.S. were involved in reviewing relevant literature in their study areas, and summarizing issues in scaling. All authors made significant contributions to the subsequent drafts and have given their final approval for publication.
Compliance with Ethical Standards
Conflict of Interest
John Carroll, Bradley Furman, Danielle Keller and Amber Stubler declare that they have no conflicts of interest.
Human and Animal Rights and Informed Consent
This article does not contain any studies with human or animal subjects performed by any of the authors.
Papers of particular interest, published recently, have been highlighted as: • Of importance •• Of major importance
- 1.• Kangeri AKW, Jansen JM, Joppe DJ, Dankers N. In situ investigation of the effects of current velocity on sedimentary mussel bed stability. J Exp Mar Biol Ecol. 2016;485:65–72. https://doi.org/10.1016/j.jembe.2016.08.011A combination ofin situmeasurements and manipulations to examine how flow speed and sediment characteristics affect mussel byssus production and likelihood of being dislodged across a mussel bed. They found higher byssal production and courser sediment associated with higher flow at bed edge, the combination of which increased adhesive strength of mussels in these locations. CrossRefGoogle Scholar
- 10.Didham RK, Lawton JH. Edge structure determines the magnitude of changes in microclimate and vegetation structure in tropical forest fragments. Biotropia. 1999;31:17–30.Google Scholar
- 15.•• Manderson JP. Seascapes are not landscapes: an analysis performed using Bernhard Reimann's rules. ICES J Mar Sci. 2016;73:1831–8 An important review paper because it describes the major differences in chemical and physical properties between air and water and why that might affect our ability to apply terrestrial landscape ecological principles to seascapes. CrossRefGoogle Scholar
- 18.•• Hanke MH, Posey MH, Alphin TD. The influence of habitat characteristics on intertidal oyster Crassostrea virginica populations. Mar Ecol Prog Ser. 2017;571:121–38. https://doi.org/10.3354/meps12094One of just a few studies that investigated oyster reefs, this paper investigated within patch location and patch size effects on oyster demographic rates at both natural and constructed oyster reefs; they found mixed patterns. Oyster density increased with distance from the patch edge, although recruitment decreased over the same scale. Oyster condition was not affected.CrossRefGoogle Scholar
- 19.• Macreadie PI, Geraldi NR, Peterson CH. Preference for feeding at habitat edges declines among juvenile blue crabs as oyster reef patchiness increases and predation risk grows. Mar Ecol Prog Ser. 2012;466:145–53. https://doi.org/10.3354/meps09986This paper investigated the role of predator behavior and feeding at habitat edges in artificially created oyster habitats in mesocosms. Even at a small spatial scale of operation, the authors demonstrated that small predators altered their edge habitat use, and thus their predation on prey resources, when their predators were present. CrossRefGoogle Scholar
- 20.Sheaves M, Johnston R, Baker R. Use of mangroves by fish: new insights from in-forest videos. Mar Ecol Prog Ser. 2016;549:167–82. https://doi.org/10.3354/meps11690The authors investigated fish use of mangroves on incoming tides to determine whether and where they dispersed over time. CrossRefGoogle Scholar
- 24.• Stubler AD, Jackson LJ, Furman BT, Peterson BJ. Seed Production Patterns in Zostera marina: Effects of Patch Size and Landscape Configuration. Estuar Coasts. 2017;40(2):564–72. https://doi.org/10.1007/s12237-016-0165-2This paper investigated seed production inZostera marinabeds across multiple spatial scales, and found that within patch location did not have an effect on seed production, but rather, production was impacted by the total seagrass cover in the surrounding seascape. CrossRefGoogle Scholar
- 25.• Langston AK, Kaplan DA, Angelini C. Predation restricts black mangrove (Avicennia germinans) colonization at its northern range limit along Florida's Gulf Coast. Hydrobiologia. 2017;803(1):317–31. https://doi.org/10.1007/s10750-017-3197-0A field survey and manipulative approach to asses location and predation effects on mangrove propagule survival. More soil disturbance and burrowing activity at creek edges, but almost 100% mortality of uncaged propagules regardless of location. CrossRefGoogle Scholar
- 26.•• Mahoney RD, Kenworthy MD, Geyer JK, Hovel KA, Fodrie FJ. Distribution and relative predation risk of nekton reveal complex edge effects within temperate seagrass habitat. J Exp Mar Biol Ecol. 2018;503:52–9. https://doi.org/10.1016/j.jembe.2018.02.004A combination of mensurative and manipulative approaches were used to assess predation pressure on common mesopredators in seagrass landscapes. They found higher survival in seagrass edges, but no differences in their capture rates (i.e., spatial distribution) or the foraging patterns of an important higher order predator. Interactive effects of seagrass shoot density were also considered. CrossRefGoogle Scholar
- 29.Amortegui-Torres V, Taborda-Marin A, Blanco JF. Effect of Neritina virginea (Neritimorpha, Neritinidae) population in a black mangrove stand (Magnoliopsida, Avicenniaceae: Avicennia germinans) in southern Caribbean. Pan-Am J Aquat Sci. 2013;8:68–78.Google Scholar
- 30.•• Jurgens LJ, Gaylord B. Edge effects reverse facilitation by a widespread foundation species. Sci Rep. 2016;6. https://doi.org/10.1038/srep37573The authors were able to demonstrate an edge effect on mussels across a small (~12cm) spatial scale but also were able to link this effect directly to a temperature stress gradient.
- 32.• Hanke MH, Posey MH, Alphin TD. The effects of intertidal oyster reef habitat characteristics on faunal utilization. Mar Ecol Prog Ser. 2017;581:57–70. https://doi.org/10.3354/meps12261This paper investigated within patch location and patch size effects on oyster reef associated fauna on both natural and constructed reefs and found that spatial patterns varied across fauna, reef size and reef type. CrossRefGoogle Scholar
- 36.• Reis JA, Giarrizzo T, Barros F. Tidal migration and cross-habitat movements of fish assemblage within a mangrove ecotone. Mar Biol. 2016, 163(5). https://doi.org/10.1007/s00227-016-2885-zVideo analysis of fish use of mangroves. They found that the mangrove ecotone was used by the entire fish assemblage, but depending on tidal stage, fish migrated to a number of microhabitats.
- 38.• Rietl AJ, Sorrentino MG, Roberts BJ. Spatial distribution and morphological responses to predation in the salt marsh periwinkle. Ecosphere. 2018;9(6). https://doi.org/10.1002/ecs2.2316A mensurative study of snail density and biomass along 50m transects from marsh edge to interior across multiple sites in Louisiana. They found that snail density tended to be highest around 10m from the edge, whereas biomass was highest 20-30m from the edge. CrossRefGoogle Scholar
- 42.Kallen J, Muller H, Franken ML, Crisp A, Stroh C, Pillay D, et al. Seagrass-epifauna relationships in a temperate south African estuary: interplay between patch-size, within-patch location and algal fouling. Estuar Coast Shelf Sci. 2012;113:213–20. https://doi.org/10.1016/j.ecss.2012.08.006.CrossRefGoogle Scholar
- 48.• Gross C, Donoghue C, Pruitt C, Trimble AC, Ruesink JL. Taxonomic and functional assessment of mesopredator diversity across an estuarine habitat mosaic. Ecosphere. 2017;8(4). https://doi.org/10.1002/ecs2.1792A seining survey that found edge habitats to be intermediate to sand and core habitats in terms of mesopredator community structure, with site effects generally exceeding edge effects.CrossRefGoogle Scholar
- 50.• Gross C, Donoghue C, Pruitt C, Ruesink JL. Habitat use patterns and edge effects across a seagrass-unvegetated ecotone depend on species-specific behaviors and sampling methods. Mar Ecol Prog Ser. 2018;598:21–33. https://doi.org/10.3354/meps12609Seine and video data were used to assess mesopredator abundance and diversity in eelgrass-dominated landscape. Edge effects, relative to core and unvegetated sites, varied by species and sampling method based on available species pools and species-specific behavioral characteristics. CrossRefGoogle Scholar
- 53.Barnes RSK. Are seaward pneumatophore fringes transitional between mangrove and lower-shore system compartments. Mar Environ Res. 2017;125:99–109. https://doi.org/10.1016/j.marenvres.2017.01.008This paper found various macrobenthic assemblages across habitat ecotones, which shows consideration should be given to examining transitions between complex focal and matrix habitats. CrossRefPubMedGoogle Scholar
- 59.• Beninger PG, Boldina I, Katsanevakis S. Stengthening statistical usage in marine ecology. J Exp Mar Biol Ecol. 2012;426–427:97–108 This review provides numerous examples of problems with using traditional statistics and assigning too much weight to P values. In particular, the authors point out the differences between statistical significance and biological relevance, and make suggestions for other methods of data analysis and interpretation. CrossRefGoogle Scholar
- 62.Espino F, Gonzalez JA, Haroun R, Tuya F. Abundance and biomass of the parrotfish Sparisoma cretense in seagrass meadows: temporal and spatial differences between seagrass interiors and seagrass adjacent to reefs. Environ Biol Fish. 2015;98(1):121–33. https://doi.org/10.1007/s10641-014-0241-z.CrossRefGoogle Scholar
- 63.• Carroll JM, Furman BT, Jackson LJ, Hunter EA, Peterson BJ. Propagule risk in a marine foundation species: seascape effects on Zostera marina seed predation. J Ecol. 2019. https://doi.org/10.1111/1365-2745.13154The authors investigated seagrass seed predation across multiple spatial scales, and using structural equation modelling, demonstrated that within patch locations explained a small proportion of the variation in seed predation, with predation being increased at patch centers. CrossRefGoogle Scholar
- 65.Arroyave-Rincon A, Amortegui-Torres V, Blanco-Booksellers JF, Taborda-Marin A. Border effect on ble crab population Cardisoma guanhumi (Decapoda:Gecarcinidae) in the mangrove swamp of El Uno Bay, Uraba gulf (Colombia): an approach to its artisanal capture. Biol News. 2014;36:47–57.Google Scholar
- 69.Caitano B, Dodonov P, Delabie JHC. Edge, area and anthropization effects on mangrove-dwelling ant communities. Acta Oecol. 2018;91:1–6. https://doi.org/10.1016/j.actao.2018.05.004A field survey approach for arboreal ant communities in fragmenting mangrove forests. They found no effect of distance to edge on ant abundance or community measures.CrossRefGoogle Scholar