Competitive interactions among juvenile and adult life stages of northern Gulf of Mexico red snapper Lutjanus campechanus and a tropical range-expanding congener

摘要

Associated with regional warming, poleward species range expansions may have important consequences for biological communities. Within northern Gulf of Mexico (nGOM) offshore habitats, higher abundance of tropically associated lane snapper Lutjanus synagris is correlated with rising temperatures. Increased presence of juvenile and adult lane snapper could result in important competitive interactions with nGOM reef fishes, such as economically important red snapper L. campechanus, at multiple life stages and cause shifts in resource utilization and species composition of offshore fish assemblages. We investigated interactions between adult and juvenile lane and red snapper within experimental mesocosms. Although no significant effects on prey consumption were observed, interspecific competition between adults and juveniles was strongest, as adult lane snapper utilized habitats at higher rates than single juvenile red snapper in interaction trials. Additionally, adult red snapper most strongly displaced single juvenile lane snapper and increased their swimming activities in the presence of heterospecific juveniles. Adult red snapper also aggressively chased juvenile lane snapper and displaced them from habitats. However, less pronounced effects were observed for grouped juveniles in the presence of adults, especially juvenile red snapper, while adult lane snapper swam less in the presence of grouped juvenile lane and red snapper. Additionally, single juvenile red snapper swimming activities and prey consumption in the presence of adult snappers did not significantly differ from control values. Therefore, at small scales adult lane snapper may partially displace single juvenile red snapper, but clusters of red and lane snapper juveniles may be resilient to competitive effects of adult lane snapper and exert partial competitive pressures on them. As expected, we found that elevated aggressiveness by larger individuals resulted in dominance in space occupancy in one-on-one interactions. These findings suggest that prior occupation of preferred hard bottom habitat may be a determining factor for grouped juvenile red snapper competing against similar sized or larger individuals. Overall, our results indicate varying competitive vulnerabilities of red snapper to climate-related range expansions of tropical congeners.