Impact of invasive species

Invasive alien species (IAS) have become an important driver of biodiversity change and can have severe impacts on marine ecosystems and food webs. The development of mechanistic modeling approaches to assess and predict their distributions and impacts, and evaluate management options, has increased substantially^[1] [2]. Multispecies and ecosystem models are the main tool used to develop applications around the impact of IAS, and in most cases, the models include an additional stressor: mainly fisheries, climate change or nutrient loading. However, the number of Ecospace AIS applications is low and represents a future research venue^[3].

One of the main limitations is data availability, accessibility and quality related to the plausible roles of IAS in new ecosystems. There is a need for predictive methodologies to forecast existing, emerging and potential IAS and their impacts. Models that allow capturing the arrival, establishment and spread of IAS and assess their impacts in an integrated way are still unavailable and highlight a critical gap in IAS modeling despite recent developments.

The development of spatial–temporal methodologies that integrate the arrival, establishment and spread of IAS and their impacts within an ecosystem context is needed to inform management advice and contribute to the analyses of future scenarios of global change. A recent example of novel approach to deal with IAS modeling was presented by Sadchatheeswaran et al.^[4], where an Ecospace model was developed to study the spatiotemporal impacts of structural complexity created by alien ecosystem engineers in a rocky shore community. In a previous temporal dynamic Ecosim model^[5], the authors modelled the successive arrivals by three alien ecosystem engineers on the rocky shore between 1980 and 2012 that led to substantial changes in species composition and diversity. The use of a non-spatial model concluded with the suggestion to add structural complexity and spatial zonation to add reality to the approach because the invasive species changed the physical environment between 1980 and 2015 substantially (Fig. 21).

Figure 1. Zonation of Marcus Island, Saldanha Bay as determined by dominant species in 1980 (pre-invasion), 2001 (post-invasion by Mytilus galloprovincialis in Zones 2– 6), 2012 (post-invasion by Balanus glandula in Zones 3a and 3b, as well as Semimytilus algosus in Zones 5–6), and 2014–2016 during quarterly biomonitoring. Zones are aligned with standard tidal terms: HWST (High Water Spring Tide), HWNT (High Water Neap Tide), MTL (Mid Tide Level), LWNT (Low Water Neap Tide), and LWST (Low Water Spring Tide). 

The Ecospace simulations included a control simulation that restricted drivers to depth and habitat preferences; two simulations to account for structural complexity as a function of the biomass of alien ecosystem engineers – the first indirectly via mediation, and the second via a new plug-in Ecoengineer (see User Guide); and a final simulation that included wave action to replicate its effects. Only the simulation that included the Ecoengineer routine matched empirical observations of species diversity and the exclusion of the native mussel by the arriving IAS. Results emphasized that when analyzing benthic ecosystems with structural habitat complexity, an explicit representation of that complexity over time and space can be a promising approach. The EcoEngineer routine has been released with EwE version 6.6.