水生植物品質對於福壽螺Pomacea canaliculata (Ampullariidae)成長與繁殖的影響：生物操控外來種的啟示

Abstract

Free water surface constructed wetlands (FWSs) are one of the most commonly built constructed wetlands as ex-situ mitigation to compensate the lost and degraded natural wetlands due to human developments and urbanization. Macrophytes are one of the most important biological components in FWSs since they can increase the pollutant removal efficiency and provide habitat for biodiversity. However, the exotic Apple snails Pomacea spp. (Gastropoda: Ampullariidae) have invaded most constructed wetlands causing numerous ecological impacts to local biodiversity and ecosystem functions. In this study, we conducted laboratory experiments using five common macrophyte species in FWSs of Taiwan including Ipomoea aquatica (Convolvulaceae), Acorus calamus (Acoraceae), Phragmites australis (Poaceae), Nymphoides hydrophylla (Menyanthaceae), and Commelina diffusa (Commelinaceae) for P. canaliculata as food source, and measured their corresponding developmental responses. The influences of the physical and chemical properties of the study macrophytes species on the snail developmental responses were also evaluated. Our results showed that P. canaliculata demonstrated different food preferences upon feeding on different plants and their developmental responses varied greatly. The highest consumption rate was found for I. aquatica. The snail fed on I. aquatica showed highest growth rates in terms of SL (0.104 ± 0.029 mm d-1), SFDM (3.202 ± 0.547 mg d-1), and AFDM (2.736 ± 0.547 mg d-1). In contrast, snails fed on P. australis demonstrated the lowest growth rates and fecundity performance. According to the plant quality analyses, I. aquatica, N. hydrophylla, and C. diffusa contained high nutrient contents, whilst P. australis and A. calamus showed strong defensive properties. Simple linear regression showed that the mass of macrophytes consumed by snails (g d-1) was negatively related to toughness (r2 = 0.52) and C/N ratio (r2 = 0.48) but positively related to nitrogen (r2 = 0.53) and chlorophyll b concentration (r2 = 0.59) of plant tissues. We concluded that the nutritive I. aquatica were largely consumed by P. canaliculata and highly supported the developmental responses. This species did not show significantly high pollutant removal efficiency as compared to other macrophytes in FWSs. Thus, planting of I. aquatica in FWSs was arguable. Since planting macrophyte species with low defensive property and high nutrient content in FWSs could facilitate the population growth of invasive, macrophytophagus P. canaliculata, alternative species with high pollutant removal efficiency and no beneficial effects to the common invader P. canaliculata could be considered for future FWS development.