Plant Cuttings

Invasive aliens, not always doom-and-gloom?

Another kind of experiment that takes place out in the real world is when non-native species are introduced into new areas. Usually, and understandably, this causes a knee-jerk response that assumes this must be a bad thing and the invaders must be removed at all costs. However, is such an ‘invasion’ always bad? Might there actually be some positives to come out of this situation? Well, work of Aaron Ramus et al. gives cause for pause for thought on this question – at least as far as plants or plant-like organisms are concerned.

Red lionfish (Pterois volitans) near Gilli Banta Island (near Komodo, Indonesia). Photo: Alexander Vasenin / Wikipedia.

They investigated coastal intertidal ecosystems in southeastern USA and the effects of introducing Gracilaria vermiculophylla, a non-native Japanese red seaweed that affects lagoons and estuaries throughout coastlines of the North Atlantic. To determine the impact of this invader on the local ecology, they measured changes in seven functions for which coastal ecosystems are highly valued *. What did they find? That the Gracilaria actually helped improve upon many of these measures. I.e., a habitat-forming, invasive species can provide vital ecosystem services, such as storm protection and food production, on which nearly half the human population depends. So, is this all good? Are non-natives always a positive influence? Not necessarily.

It is important to note that these positive effects were found in an area where otherwise barren mudflats were colonized by the non-native seaweed. I.e. such benefits only occurred in the absence of other mudflat-colonising native species, and may therefore be unique to habitat-forming invasives. [What might have caused loss of native species is a subject for another time.] In other situations where non-native species are definitely not welcomed, the smart move seems to be to eat them. This most visceral of reactions not only removes the invasive aliens, it also helps feed hungry humans: Win-Win?

* These functions include: soil stabilization and erosion control; storm surge and flood protection; biodiversity; food production; and the provision of nursery habitat for economically-important seafood species, including shrimp, crab and fish.

[Ed. – Contrastingly, Johann Martínez-Lüscher and Marianne Holmer found a deleterious impact of Gracilaria vermiculophylla on metabolism and survival of Zostera marina in a sub-marine investigation on the island of Fyn. Confirmationally, but confoundingly, when Mads Thomsen et al. investigated the impact of G. vermiculophylla on Z. marina at a depth of 2m in the northern part of Odense Fjord, they not only found a negative effect on ‘above-ground’ eelgrass biomass, but also positive effects on densities of most invertebrate taxa…]

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