Encyclopedia
Please note this is an old version of this entry, which may differ significantly from the current revision.
Subjects:
Ecology
Biological invasions in fresh waters cause biodiversity loss and impairment of ecosystem functioning. Many freshwater invasive species are fish, including the largemouth bass Micropterus salmoides, which is considered one of the 100 worst invasive species in the world. Fast individual growth rates, high dispersal ability, ecological tolerance, and trophic plasticity are among the characteristics contributing to its success. The negative impact of M. salmoides on littoral fish communities is believed to be mitigated by habitat structural complexity resulting from aquatic vegetation and coarse woody debris, while the main limits on its spread seem to be strong water flows and high turbidity, which impairs visual predation. Together with the human overexploitation of its potential fish antagonists, habitat alteration could result in M. salmoides having seriously detrimental effects on native biodiversity.
- invasive species
- fish
- M. salmoides
- environments
1. Habitat Structural Complexity: The Effect of Vegetation and Coarse Woody Habitats
The interactions of the largemouth bass with other organisms are influenced by habitat structural complexity. Coarse woody habitats (CWH) and aquatic vegetation play an important role by providing shelter to prey species, thus favoring their abundance and diversity [65,138], and by influencing M. salmoides’s behavior. Indeed, bass are able to opportunistically change their predation strategy in response to habitat complexity [52,61,63]: beyond a certain level of vegetation density or CWH debris abundance, the bass switch their strategy from cruising to ambushing.
Differences in bass diets have been found in environments with different types of aquatic vegetation cover [19,48]. In the presence of both vegetation and open waters, largemouth bass forage almost exclusively on open-water fish species [49]. Dense vegetation reduces (a) predator–prey visual contact, (b) attacks per prey via active search, and (c) captures per attack [52], thus increasing the handling time (for chasing and catching prey) and reducing predator–prey encounter rates. This decreases the maximum number of prey a predator can catch per unit of time [53,54,55].
In experimental systems, vegetation was found to be effective at reducing predation by the largemouth bass on centrarchids (Lepomis spp. and juveniles of the largemouth bass itself), the cyprinid Squalius alburnoides [35,49,52], and the guppy Poecilia reticulata [53,54]. Furthermore, using artificial vegetation, Gotceitas and Colgan [56] found a density threshold above which the success of bass foraging on juvenile L. macrochirus was reduced and suggested a non-linear relationship between habitat complexity and prey habitat choice.
The largemouth bass can have greater attack rates in a diverse macrophyte assemblage than in a monotypic canopy, since the former leaves more gaps that allow the bass to access prey than the latter [55]. This suggests that the optimal habitat for bass is a mix of open or semi-open areas and areas with moderately dense vegetation, which results in both high prey abundance and successful predation ([55,57], and references therein]), as well as higher individual growth and fecundity [50]. In enclosures with Myriophyllum spicatum, the largemouth bass consumed mainly fish, while in enclosures with Potamogeton nodosus, it fed mainly on invertebrates, despite similar macrophyte densities and prey items [58]. It has also been observed that in areas characterized by dense macrophytes, hypoxic conditions might enhance the refuge effect for prey species that are more tolerant of low oxygen concentrations than bass [51], further reducing M. salmoides’s predation success and population growth [59].
The detrimental effect of vegetation does not appear to be a feature of the relationship between M. salmoides juveniles and invertebrate/insect prey [47,60]. Younger individuals were observed in densely vegetated areas, and their diet mostly consisted of macroinvertebrates. By providing habitat and food resources for invertebrates, aquatic vegetation boosts their abundance and diversity, making them alternative prey for adult bass, which may adopt a more generalist diet, reducing predatory pressure on fish [19].
2. Effect of Turbidity on Predation by Sight
Bass occurrence and foraging ability can be limited not only by vegetation in shallow waters and low light intensity in deep waters, but also by loss of transparency due to suspended particles, which reduce visibility. Turbidity has been suggested as an explanation for the largemouth bass’s failure to establish itself in some ecosystems in South Africa [94]. Using bentonite clay, it has been experimentally demonstrated that turbidity lowers the encounter rate between prey and predator by reducing visibility [186], thus lowering the feeding rate [49] and affecting prey selection as the bass switch to slower prey or to prey that use clear-water habitats. High turbidity levels might not allow M. salmoides to catch its daily food ration [115,121].
However, although sight plays a key role in the success of largemouth bass predation, laboratory studies have shown high success, albeit with greater catch effort, when M. salmoides attacked prey blindly [142,187]. Indeed, the prey movements in the water could be also detected by the lateral line organ [142], which ensures the success of M. salmoides attacks even in dark conditions. In these cases, the largemouth bass usually changes its predation strategy by swimming more slowly and opening its mouth more quickly and widely near prey [142,187].
3. Anthropogenic Alteration of Freshwater Systems
The effects of largemouth bass introduction are often exacerbated by other anthropogenic alterations to freshwater ecosystems (e.g., flow regulation, pollution, water extraction, and introduction of other exotic species). All these drivers can threaten local species if they are endemic or have a restricted distribution range [148,160,188,189].
In South Korea and southern Africa, the introduction and spread of M. salmoides and other invasive species have been linked to anthropogenic alterations to rivers, including the construction of impoundments and large dams, where exotic species recovered better than the native fauna [94,156]. In many other ecosystems, M. salmoides occurrence was greater in (or restricted to) sites influenced by dams [13,37,190]. Indeed, largemouth bass do not tolerate high flow conditions [75], as they are easily flushed out, or the intermittent conditions that are typical of Mediterranean streams [45]. The regulation of river flow can, thus, facilitate invasion by this species. Reservoirs provide lentic and stable conditions [43,44,45] and are characterized by simple communities and “vacant niches” [117,191,192], especially shortly after an inundation. Reservoirs and impoundments favor the establishment and spread of exotic fish species and can provide propagules of invasive species to nearby water bodies, acting as stepping stones [193]. They might also serve as bases for the recolonization of parts of the river from which bass have been displaced [75] and as nursery sites, producing juveniles that are able to populate downstream sections [18].
4. The Influence of Climate Change
Climate change influences an ecosystem’s vulnerability to invasion by non-native fish species, as it can change the distribution ranges of many species, including M. salmoides, prompting them to spread northward and colonize new environments [105,106], thereby threatening native species [95,106] or changing their distribution [80]. Adults of M. salmoides do not seem to be particularly constrained by low winter temperatures, tolerating long periods in cold and ice-covered waters [78,79,194]. However, M. salmoides displays lower growth and feeding rates at temperatures lower than 10 °C [9,33], and severe temperatures can limit its recruitment. Indeed, under long-lasting cold conditions, 0-year-old largemouth bass often fail to gain sufficient size and energy reserves to survive until the next favorable season [9,109]. In addition, ice coverage of water bodies can reduce oxygen levels in waters and, thus, promote winterkill, further reducing bass survival [9,33]. A warmer climate in the northernmost areas of M. salmoides’s current range could remove these limitations. In addition, the global increase in annual mean temperature appears to be the main factor in predicting the spread of bass toward higher altitudes, with an average movement of about 9 m per decade [155].
Climate change might also influence the spawning periods, growth rates, diets, behavior, and distribution of invasive fish, including the largemouth bass [77,155,195], with negative consequences for native species [147,196].
The effects of temperature on M. salmoides‘s foraging rates [86,197] are highlighted by several bioenergetic models, which estimate the fish energy budget and its variation [108,198]. Using this approach, Rice et al. [82] showed that seasonal temperature variation has an indirect effect on bass body condition, as it influences prey density and, thus, feeding rates. Based on bioenergetics and field studies, the lower increase in M. salmoides’s per capita prey demand with temperature and its higher capacity to tolerate prey decline could explain its increasing densities with respect to the congeneric M. dolomieu [144].
Altered foraging activity and individual growth rates are likely to influence the interaction of the largemouth bass with other piscivores: in a simulation of climate change scenarios for 2040 and 2060, the bioenergetic model showed increased impact on prey species and potential changes to the fish assemblage [118]. A comparison of 359 lakes in Wisconsin suggested that the negative effect of climate warming on the recruitment of other piscivores (e.g., the walleye Sander vitreus) was amplified where bass densities were high [112].
Climate change is also expected to favor flow regime alterations due to changes in rainfall patterns, increased evaporation rates, and reduced runoff, which, combined with changing thermal regimes, water chemistry, and DO dynamics, will stress local communities, leading to changes in the interactions between bass and native biota. These effects can be exacerbated by human activities. Indeed, climate change, along with water extraction and the construction and use of dams, is expected to increase the frequency of severity of drought events and the intermittence of freshwater ecosystems [86,161]. Habitat fragmentation could favor the development of pools in which organisms undergo severe stress related to extreme temperature variation, low resource availability, and strong biotic interactions [161]. This could increase the spread of highly tolerant top-predator species such as Micropterus salmoides, further stressing and threatening the persistence of native communities [86,153,161]. In contrast, as a limnophylic species that needs protected nursery and wintering habitats, bass will struggle to colonize intermittent streams, as they are able to survive only in the dry-season pools of downstream reaches [35,161].
Climate change could also influence bass abundance in large and deep lakes, where rising temperatures will generate a larger total volume of thermally suitable habitat for this invasive species than small and shallow lakes [199]. Furthermore, climate change is expected to have negative effects on the vegetated littoral belt and its associated species richness, exacerbated by human activities [62,156]. All this can result in both direct and indirect benefits for warmer and opportunistic species such as M. salmoides, with strongly negative effects not only on native fauna, but also on the functioning of the entire ecosystem.
This entry is adapted from the peer-reviewed paper 10.3390/w15213796
This entry is offline, you can click here to edit this entry!
