The abundance, distribution and diversity of invasive and indigenous freshwater snails in a section of the Ogunpa River, southwest Nigeria

This study investigated the abundance, distribution and diversity of freshwater snails at four sites in the Ogunpa River, Nigeria from May 2018 to December 2018. A total of 2067 freshwater snails was collected, belonging to two sub-classes, four families, and seven species: <i>Physella acuta, Amerianna carinata</i>, <i>Melanoides tuberculata</i>, <i>Physa waterloti</i>, <i>Bulinus globosus</i>, <i>Bulinus senegalensis</i>, and <i>Lymnaea natalensis</i>. Invasive freshwater snails (82.15%) were more abundant than indigenous species (17.85%). <i>Physella acuta</i> (30.05%) and <i>P. waterloti</i> (20.61%) were the most abundant species, while <i>B. globosus</i> (4.35%) and <i>B. senegalensis</i> (3.92%) were the least abundant. The presence of <i>P. acuta</i>, <i>B. globosus</i>, <i>B. senegalensis</i>, and <i>M. tuberculata</i> constitute potential economic and health risks to animals and humans in contact with this waterbody. Freshwater snail numbers showed variation among sites, seasons, and site-season interactions. Water depth, turbidity, and pH correlated significantly with the numbers of freshwater snails, except that pH did not correlate with <i>P. waterloti.</i> There were strong positive correlations between the numbers of molluscs and the abundance of <i>Commelina diffusa</i>, <i>Amaranthus spinosus</i>, <i>Murdannia nudiflora</i>, and <i>Ipomoea aquatica</i>. Stepwise multiple regression showed that water depth, <i>C. diffusa</i>, and <i>Sacciolepis africana</i> were the primary variables affecting snail distribution and abundance in the Ogunpa River.

本研究于2018年5月至2018年12月期间，针对尼日利亚奥贡帕河（Ogunpa River）的4个采样位点，开展了淡水螺类的丰度、分布及多样性调查。本次调查共采集到淡水螺类2067只，隶属于2个亚纲、4个科，共计7个物种：尖膀胱螺（Physella acuta）、隆起截口螺（Amerianna carinata）、瘤拟黑螺（Melanoides tuberculata）、沃特洛膀胱螺（Physa waterloti）、球形萝卜螺（Bulinus globosus）、塞内加尔萝卜螺（Bulinus senegalensis）以及纳塔尔椎实螺（Lymnaea natalensis）。其中入侵性淡水螺类占比达82.15%，显著高于土著螺类的17.85%。尖膀胱螺（30.05%）与沃特洛膀胱螺（20.61%）为丰度最高的两个物种，而球形萝卜螺（4.35%）与塞内加尔萝卜螺（3.92%）的丰度最低。尖膀胱螺、球形萝卜螺、塞内加尔萝卜螺及瘤拟黑螺的存在，对接触该水体的动物与人类均构成潜在的经济与健康风险。淡水螺类的种群数量在不同采样位点、季节以及采样位点-季节交互作用下均存在显著差异。水深、浊度与pH值均与淡水螺类的种群数量呈显著相关，唯pH值与沃特洛膀胱螺的种群数量无显著关联。软体动物的种群数量与鸭跖草（Commelina diffusa）、刺苋（Amaranthus spinosus）、裸花水竹叶（Murdannia nudiflora）及蕹菜（Ipomoea aquatica）的丰度呈显著正相关。逐步多元回归分析结果显示，水深、鸭跖草（C. diffusa）以及非洲镰序草（Sacciolepis africana）是影响奥贡帕河淡水螺类分布与丰度的核心影响变量。