Potential and realized interactions between two aquatic invasive species: Eurasian watermilfoil (Myriophyllum spicatum) and rusty crayfish (Orconectes rusticus)

Abstract

With multiple invasions, the potential arises for interactions between invasives inhibiting or promoting spread. Our goal was to investigate the interaction between two invasives, Eurasian watermilfoil (Myriophyllum spicatum) and rusty crayfish (Orconectes rusticus), which co-occur in several lakes in western Quebec, Canada, and to determine their overlap with littoral fish communities. Crayfish potentially aid milfoil dispersal by fragmentation or, alternatively, inhibit its proliferation through destruction and direct consumption. With a mesocosm experiment, we quantified milfoil fragment production versus biomass reduction by crayfish. More fragments were produced at medium to high crayfish densities, with a significant reduction of milfoil only at the highest densities, demonstrating the potential for both positive and negative interactions. Second, we determined the habitat preferences of each species by conducting a survey in the same lake. There was little overlap in the species' distributions, with each preferring different habitat features, indicating either a low probability of interaction or that interaction occurred historically, resulting in a contemporary exclusion pattern. While our experiment showed a potential for significant interaction, the low natural co-occurrence of these species suggests that they do not currently influence each other or that they previously excluded each other.Résumé : L'interaction entre de multiples espèces envahissantes peut inhiber ou favoriser leur dispersion. L'objectif de notre étude était de déterminer l'interaction entre deux espèces envahissantes, le myriophylle à épis (Myriophyllum spicatum) et l'écrevisse à taches rouges (Orconectes rusticus), introduites dans plusieurs lacs de l'ouest du Québec, Canada, et de déterminer leur chevauchement avec les poissons littoraux. Les écrevisses peuvent favoriser la dispersion du myriophylle par fragmentation, mais aussi diminuer sa prolifération par leur consommation et leur destruction. Une expérience en mésocosmes fut réalisée pour quantifier la production de fragments et la réduction de la biomasse des myriophylles par les écrevisses. Plus de fragments furent produits à des densités d'écrevisses moyennes et élevées alors que seules des densités élevées réduisirent significativement la biomasse, démontrant un potentiel d'interactions positives comme négatives. Ensuite, leurs habitats préférentiels furent déterminés par un échantillonnage dans le même lac. Il y avait peu de chevauchement dans leurs répartitions, chacune préférant différentes caractéristiques de l'habitat, ce qui indique une faible probabilité d'interaction ou alors une interaction historique ayant mené à l'exclusion actuelle. Alors que les expériences indiquent la possibilité d'une interaction significative entre ces deux espèces envahissantes, le faible chevauchement et les densités dans le milieu naturel suggèrent qu'elles ne s'influencent pas pour l'instant ou qu'elles se sont exclues l'une l'autre dans le passé.

Ecological mechanisms of invasion success in aquatic macrophytes

“…In a potential example of invasional meltdown, Maezo et al (2010) studied interactions between invasive M. spicatum and invasive crayfish Orconectes rusticus. They found positive and negative interactions between the species but noted that microhabitat partitioning would likely result in very little realized interaction.…”

Experimental test of the Invasional Meltdown Hypothesis: an exotic herbivore facilitates an exotic plant, but the plant does not reciprocally facilitate the herbivore

“…Exotic herbivores may also directly facilitate exotic plants via non-consumptive mechanisms. For instance, plant fragmentation may increase the dispersal of exotic plants (Maezo et al, 2010). A greenhouse study showed that mechanically generated A. philoxeroides' single-node fragments survived and grew in a moist soil mix, so fragmentation may increase the rate of spread of this clonal species (Dong et al, 2012).…”

“…For instance, exotic red deer (Cervus elaphus) and fallow deer (Dama dama) indirectly facilitated exotic Douglas fir (Pseudotsuga menziesii) by preferentially consuming the native evergreen conifer Austrocedrus chilensis (Relva, Nuñez & Simberloff, 2009). In addition, crayfish (Orconectes rusticus) may facilitate the invasion of exotic Eurasian watermilfoil (Myriophyllum spicatum) by increasing plant fragmentation (non-consumptive) (Maezo, Fournier & Beisner, 2010). Likewise, exotic plants may facilitate exotic herbivores by providing a higher quality food source (Engelkes & Mills, 2013) or by supplying higher quality substrata for reproduction (Burks, Kyle & Trawick, 2010) or shelter (Sessions & Kelly, 2002).…”

Predicting aquatic invasion in Adirondack lakes: a spatial analysis of lake and landscape characteristics

“…); factors that influence water quality, number of game fish, number and type of boat ramps, bedrock type, littoral area, water source, number of residences, and proximity to roads (Buchan and Padilla ); distance to nearest invaded waterway, lake size, alkalinity, Secchi depth, and lake depth (Roley and Newman ); riparian use, interaction with other IS, substrate material, and debris (Maezo et al. ); wave action, water‐level drawdown, photic zone depth, aquatic vegetation shading, and native species present (Olson et al. ).…”