Macroalgae niche modelling: a two-step approach using remote sensing and in situ observations of a native and an invasive Asparagopsis

Abstract

We are facing a global loss of biodiversity due to climate change. This will lead to unpredictable changes in ecosystems, affecting the goods and services they provide and facilitating the introduction of non-indigenous marine species. This represents one of the major threats to marine biodiversity and therefore, there is a strong need to assess, map and monitor these alien species. The appearance of non-indigenous species is especially dangerous in fragile ecosystems, and it is of great importance to better understand the invasion mechanisms of these invasive species. This is the case for invasive alga Asparagopsis armata, present in the Azores Archipelago. In this study, we propose a methodology to define the realized ecological niche of this invasive alga, alongside the native Asparagopsis taxiformis, to understand better its distribution and potential impact on native communities and ecosystem services. These objectives comply with the EU Biodiversity strategy for 2020 goals and the need to map and assess ecosystems and their services. The lack of reliable high-resolution data makes this a challenging task. Within this scope, we propose a combination of Remote Sensing, Unmanned Aerial Vehicle based imagery together with in-situ field data to build ecological niche modelling approaches as a cost-effective methodology to identify and characterize vulnerable marine ecosystems. Our results show that this combination can help achieve monitoring, leading to a better understanding of ecological niches and the consequences of non-indigenous species invasion in fragile ecosystems, like small islands, when faced with limited data.

Systematic review and best practices for drone remote sensing of invasive plants

“…The most common overlap was 80% for both forward and sidelap (Casas et al, 2021;Lam et al, 2021;Weisberg et al, 2021), which adheres to recommendations for at least 70% forward and 40% sidelaps (Singh & Frazier, 2018;Su et al, 2016; Figure S2). About 5% of articles reported trigger cadence, which is the time interval between consecutively captured images (Kedia et al, 2021) and partially dictates overlap.…”

“…Image overlap was reported in 52% of studies, but there was high variability in the amount of overlap, ranging from 20% to 90% (Bolch et al., 2021; Lopatin et al., 2019; Wang et al., 2021). The most common overlap was 80% for both forward and sidelap (Casas et al., 2021; Lam et al., 2021; Weisberg et al., 2021), which adheres to recommendations for at least 70% forward and 40% sidelaps (Singh & Frazier, 2018; Su et al., 2016; Figure S2). About 5% of articles reported trigger cadence, which is the time interval between consecutively captured images (Kedia et al., 2021) and partially dictates overlap.…”

“…Reporting flight compliance adds credibility and legitimacy to a study and also helps future users address location‐specific regulatory concerns. Weather and site conditions including wind, precipitation, temperature and atmospheric haze can affect image quality and therefore the ability to discriminate invasive species but were only reported in about 30% of studies (Figure 6a; Gao et al., 2021; Kellaris et al., 2019), with studies most reporting that flights were performed on cloud‐free days with low winds, which are ideal conditions (Casas et al., 2021; Tian et al., 2022; Weisberg et al., 2021). Several studies mentioned capturing images under overcast conditions but did not specify the rationale (Chabot et al., 2017; Perroy et al., 2017; Qian et al., 2020).…”

“…However, we found no reference to these effects in the reviewed studies, suggesting they may be overlooked by users. Other important site factors can include tidal cycles, which can obscure or occlude invasive aquatic vegetation in coastal environments (Casas et al., 2021; Tian et al., 2022). About 73% of articles reported the flight altitude, which ranged from 10 to 1700 m (Figure 6b).…”

Quantification of the invasiveness risk of non‐native macroalgae in the Azores to support conservation measures

“…A. armata , a species introduced in Europe in the 1920s (Casas et al, 2021), is the only species ranked as high risk that is present in all Azorean islands. From the six species categorized as high risk and restricted to a single island, information regarding their population expansion is available only for C. webbiana .…”