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

人工濕地的設計為模擬自然濕地，旨為補償因人類利益開發而消失或惡化的自然濕地並提供多項生態系統功能如淨化水質、防洪蓄水、調節氣候、提供野生生物棲地及人類休憩場所等。水生植物在人工濕地佔有重要的一席，因其本身能吸收水中的營養和汙染物，增加水中懸浮物的沉降效率，而水生植物的植株表面亦能提供微生物的附著空間以增加其對水質淨化的時間。然而，外來種福壽螺(Ampullariidae: Pomacea canaliculata) 普遍入侵人工濕地，攝食大量的水生植物降低人工濕地去污效率，並在河域大量繁殖導致人工濕地的水質改變，更與當地的原生螺類競爭食物來源而造成原生螺類滅絕。 本研究選取5種人工濕地常見的水生植物，分別為空心菜(Convolvulaceae: Ipomoea aquatica)、菖蒲(Acoraceae: Acorus calamus)、蘆葦(Poaceae: Phragmites australis)、水蓮菜(Menyanthaceae: Nymphoides hydrophylla)、竹仔葉(Commelinaceae: Commelina diffsa)，依據福壽螺對不同水生植物的攝食量評估其攝食偏好，並分析攝食不同植物後的成長及繁殖參數，並進一步進行水生植物的物理及化學性質分析，探討其與福壽螺成長及繁殖參數的關係。 實驗結果顯示福壽螺對不同種類的水生植物具有不同的攝食偏好，並呈現不同的成長與繁殖反應。福壽螺對空心菜表現出最高的攝食率，且呈現最高的殼長成長率(0.104 ± 0.029 mm d-1)、乾重成長率(3.202 ± 0.547 mg d-1)及無灰乾重成長率(2.736 ± 0.547 mg d-1)；相反地，攝食蘆葦及菖蒲的福壽螺不僅攝食率偏低，其殼長、乾重及無灰乾重亦成長緩慢。在繁殖反應方面，福壽螺在攝食水蓮菜後產下的卵呈現最高孵化率(59.78 ± 30.84 %)及單顆卵重量(7.13 ± 5.18 mg)。母螺在攝食蘆葦後，皆呈現最低的繁殖反應包括卵塊尺寸、孵化率及單顆卵重量。 根據水生植物的物理、化學性質分析結果，空心菜、水蓮菜及竹仔葉呈現最高的營養成分包括氮和磷含量，而蘆葦和菖蒲則呈現最高的防禦特性包括韌度、酚、木質素及碳含量。簡單線性回歸結果顯示福壽螺攝食的水生植物量(g d-1)與水生植物的韌度和碳氮比成負相關而與氮含量和葉綠素b呈現正相關。 我們的結果發現空心菜因其含有較高的營養成分，使得攝食空心菜後的福壽螺呈現較高的成長及繁殖反應。此外，比較空心菜與其他人工濕地常見的水生植物會發現，空心菜並非為最高去污能力的水生植物。因此，本研究認為未來在設計人工濕地的水生植物群落時，應避免種植具低防禦性和高營養成分的水生植物(如空心菜)，以有效地抑制外來種福壽螺族群的擴散。為促進人工濕地的永續發展，我們建議可種植兼具高去污能力及對入侵種福壽螺無益的水生植物作生物控制策略。

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.