Modelling changes in trophic and structural impacts of alien ecosystem engineers on a rocky-shore island

Abstract

Between 1980 and 2012, successive arrivals by three alien ecosystem engineers on a rocky shore community at Marcus Island on the west coast of South Africa led to substantial changes in species composition and diversity. An ecosystem analysis of this open intertidal system was developed using Ecopath with Ecosim to determine the impacts of these aliens and the services they provide on the native community. A baseline Ecopath model of the community in 2015 was generated using values of biomass, production/biomass, consumption/biomass and the dietary composition of 30 functional groups. Ecosim, a time-dynamic modelling routine, was then used to simulate the changes in biomass of native species. A 1980 model (pre-invasion) was constructed and 22 simulations were run up to 2015 by systematically adding (1) biomass time series for non-native species; (2) relative biomass time series for native species; (3) mediation functions that mimicked biomass impacts due to changes in substrate, shelter and feeding grounds created by the alien ecosystem engineers; and (4) the effects of wave action as a source of mortality. Positive or negative influences of these ecological processes on diversity and the final biomasses of all groups in 2015 were assessed. Trophic impacts by the alien species affected diversity and biomass at the end of all simulations, but the addition of shelter or a combination of all three ecosystem services provided by ecosystem engineers (shelter, substrate and feeding grounds) resulted in 2015 model ecosystems that most closely matched the diversity and individual group biomasses empirically measured on Marcus Island in 2015. Wave action had only a minor impact. Marcus Island's rocky shore community was therefore driven mainly by the fixed input of alien species biomass and made more realistic by the incorporation of their ecosystem services. However, structural complexity and zonation, explored in a follow-up paper invoking spatial modelling, need to be represented for a more complete realisation of the ecosystem. the Pacific barnacle Balanus glandula (Harley, 2006;Harley and O'Riley, 2011). Besides changes to native biodiversity due to modulation of access to resources, ecosystem engineers may also alter (1) the amount of surface area or substrate (

Exploring multiple stressor effects with Ecopath, Ecosim, and Ecospace: Research designs, modeling techniques, and future directions

“…Alva-Basurto and Arias-González, 2014; Capitani et al, 2021a;Dahood et al, 2020Dahood et al, , 2019de Mutsert et al, 2021;Espinosa-Romero et al, 2011;Fretzer, 2015;Frisk et al, 2011;Goncalves et al, 2021;Gregr et al, 2020;Hoover et al, 2013a;Lewis et al, 2016;Pedersen et al, 2021;Pitcher et al, 2002;Plummer et al, 2013;Rogers and Allen, 2012;Sadchatheeswaran et al, 2021Sadchatheeswaran et al, , 2020Sayer et al, 2005; Steenbeek et al, 2020;Suprenand and Ainsworth, 2017;Zunino et al, 2021 Eutrophication and deoxygenation Bauer et al, 2019Bauer et al, , 2018Beecham et al, 2015;Costalago et al, 2019;Daskalov, 2002;de Mutsert et al, 2016;Ehrnsten et al, 2019;Hansson et al, 2007;Hyytiäinen et al, 2021;Kao et al, 2014;Libralato et al, 2015;Ma et al, 2010;Niiranen et al, 2013;Okey et al, 2004;Österblom et al, 2007;Piroddi et al, 2021;Sakamoto and Shirakihara, 2017;…”

“…In Ecosim, changes in biogenic habitat availability are typically represented by mediating functions affecting the vulnerabilities and search rates of species associated with the habitat. This approach has been used, e.g., to simulate the loss of shelter for some species when removing unwanted patches of floating vegetation (Rogers and Allen, 2012), changes in eelgrass meadows (Plummer et al, 2013), the loss of fish habitat provided by coral reefs (Alva-Basurto and Arias-González, 2014), the effects of invasive ecosystem engineers providing substrate and shelter (Sadchatheeswaran et al, 2020), the loss of biogenic habitat to acidification (Zunino et al, 2021), the removal of oyster aquaculture racks (Lin et al, 2009), and the expansion of kelp habitat after the reintroduction of sea otters (Gregr et al, 2020;Espinosa-Romero et al, 2011).…”

“…Arias- González et al, 2011;Chagaris et al, 2020;Corrales et al, 2018Corrales et al, , 2017aEspinosa-Romero et al, 2011;Gregr et al, 2020;Haak et al, 2017;Harvey and Kareiva, 2005;Kao et al, 2014;Kitchell et al, 2000;R Kumar et al, 2016;Langseth et al, 2012;Li et al, 2014;Libralato et al, 2015;Pine and Kwak, 2007;Pinnegar et al, 2014;Rogers et al, 2014;Sadchatheeswaran et al, 2021Sadchatheeswaran et al, , 2020Vilas et al, 2021b;Wang et al, 2021;Woodruff et al, See section "Habitat loss and restoration"…”

“…Fishing mortality is then removed at the time of introduction, allowing the new species' biomass to grow from its low level. For historical simulations, the biomass of the new species can be forced with time series (Rogers et al, 2014;Sadchatheeswaran et al, 2020). For species that are not yet established, growth can follow the EwE simulation, be forced to correspond to a theoretical model such as logistic growth (Corrales et al, 2018;Haak et al, 2017), or be forced to grow to biomass levels observed in similar systems where the new species is already established (Vilas et al, 2021b).…”

Exploring multiple stressor effects with Ecopath, Ecosim, and Ecospace: Research designs, modeling techniques, and future directions

“…In Ecosim, the effects of changes in biogenic habitat availability are typically represented by mediating functions affecting the vulnerabilities and search rates of species associated with the habitat. This approach has been used, for example, to simulate the removal (via a "fishery") of unwanted patches of floating vegetation in Florida (Rogers and Allen, 2012), changes in eelgrass meadows in Puget Sound (Plummer et al, 2013), the loss of fish habitat provided by coral reefs (Alva-Basurto and Arias-González, 2014), the effects of invasive ecosystem engineers providing substrate and shelter (Sadchatheeswaran et al, 2020), the loss of biogenic habitat to acidification (Zunino et al, 2021). And the removal of oyster aquaculture racks (Lin et al, 2009).…”