Competitive Interactions between Invasive Nile Tilapia and Native Fish: The Potential for Altered Trophic Exchange and Modification of Food Webs

Recent studies have highlighted both the positive and negative impacts of species invasions. Most of these studies have been conducted on either immobile invasive plants or sessile fauna found at the base of food webs. Fewer studies have examined the impacts of vagile invasive consumers on native competitors. This is an issue of some importance given the controlling influence that consumers have on lower order plants and animals. Here, we present results of laboratory experiments designed to assess the impacts of unintended aquaculture releases of the Nile tilapia (Oreochromis niloticus), in estuaries of the Gulf of Mexico, on the functionally similar redspotted sunfish (Lepomis miniatus). Laboratory choice tests showed that tilapia prefer the same structured habitat that native sunfish prefer. In subsequent interspecific competition experiments, agonistic tilapia displaced sunfish from their preferred structured habitats. When a piscivore (largemouth bass) was present in the tank with both species, the survival of sunfish decreased. Based on these findings, if left unchecked, we predict that the proliferation of tilapia (and perhaps other aggressive aquaculture fishes) will have important detrimental effects on the structure of native food webs in shallow, structured coastal habitats. While it is likely that the impacts of higher trophic level invasive competitors will vary among species, these results show that consequences of unintended releases of invasive higher order consumers can be important

Seagrasses, fish and fisheries

Seagrass meadows have extremely high primary and secondary productivity and support a great abundance and diversity of fish and invertebrates. A number of commercially and recreationally important species (including both fish and invertebrates) have been linked to seagrass at some stage of their life cycle, although few such species use seagrass throughout their life. Non-commercial species within seagrass may be an important food source for commercial species (forming trophic linkages). In addition, some species that do not inhabit seagrass may derive benefit from seagrass by way of exported seagrass detritus or resident/transient species that move out of seagrass (some of these topics are dealt with elsewhere in this volume: e.g. Heck and Orth, Chapter 22, Kenworthy et al., Chapter 25 and Bell et al., Chapter 26). © 2006/2007 Springer. All Rights Reserved.http://trove.nla.gov.au/work/1348907