Invasive Plant Species Hydrocharis morsus-ranae L. Breaking Bio-Geographical Barriers- Juniper Publishers

 

Juniper Publishers- Journal of Oceanography

Abstract

Recent report of Hydrocharis morsus-ranae from Kasmir Himalaya-India should serve as an early warning to the whole South Asia that this invasive species might be already in the phase of breaking down of the historical biogeographic barrier (Himalayas) and may be introduced in the adjoining areas of South-East Asia in the near future. Therefore, it is high time to initiate early detection and rapid response, the most cost- effective strategy with maximum chances of success in the management of plant invasions.

Keywords: Early warning; South Asia; Invasion; Biogeographic barrier

Introduction

The genus Hydrocharis L. is widely distributed in tropical and temperate regions of the old world (Cook and Luond, 1982), and comprises of 3 species namely: H. dubia (Blume) Backer, H. morsus- ranae L. and H. chevalieri (De Wildeman) Dandy. Biogeographically, these 3 species are allopatric with H. dubia distributed in South and East Asia, H. morsus-ranae in West and North Eurasia and H. chevalieri in Central Africa [1] (Figure 1). As reported in other regions of South Asia, H. dubia also occurs in the Kashmir Himalaya [2,3]. Recently Hydrocharis morsus-ranae L. has also been reported form Kashmir Himalaya-India [4].

Biogeographical Significance

Hydrocharis morsus-ranae is widely distributed in west and central Europe, extending from Portugal, the British Isles and W France northwards to S. Sweden and S. Finland and southwards to northern Italy [1]. In the Eastern Europe, it is represented by scattered records reaching to 40 °E. In the neighboring parts of Asia, it is sparingly represented in Turkey, the Caucasus and the southern shore of the Caspian Sea [5]. The species has been also recorded from isolated places of Central Siberia [1]. The species has been introduced to North America where it has naturalized and spread fast as invasive [6-13].

The record of H. morsus-ranae in Kashmir Himalaya, India [4] was in fact a first record of this species from the entire South- and East Asia. This report represents a typical case of breaking down of historical biogeographic barrier i.e. Himalaya between two allopatric species of H. dubia and H. morsus-ranae (Figure 1). The species most likely has been introduced by migrating waterfowl particularly from Siberia which usually visits the Kashmir Himalayan water bodies [14,15].

Risk of Plant Invasion

By reporting the occurrence of H. morsus-ranae in Kashmir Himalaya [4], clearly depicts the presence of sympatric populations of two species of the genus Hydrocharis. The presence of two species of the genus in Kashmir Himalaya i.e. earlier H. dubia and now H. morsus-ranae may facilitate hybridization and formation of hybrids. The role of hybridization in promoting invasiveness is evidenced by Ellstrand & Schierenbeck [16] who provided 28 examples where invasiveness was preceded by hybridization and attributed in many cases to hybrid vigor. Furthermore, in aquatic plants, most notable vegetative propagule is the turion, a specialized structure with few functional counterparts in the terrestrial flora. The species produces turions, and the latter are produced at the end of growing season in the month of October in the Kashmir Himalaya. The turions are ellipsoidal, 5-10mm long, dark green in colour. Active vegetative propagation also greatly contributes to stabilize the hybrids derived from hybridization [17,18]. At present, such aquatic invasive plants have caused devastation to the natural biotic communities worldwide [19].

The invasive species are known to alter the aquatic ecosystem structure and functions [20-23]. Rapid spread of H. morsus-ranae is well-documented in the North America, and it has been reported that the species spread with an overall rate of 15.6km/year [10]. In the H. morsus-ranae, extensive stoloniferous growth in the summer months enables an individual turion to produce more than ten ramets and each ramet in turn may produce as many as ten turions by autumn [24]. The production of as many as ten overwintering turions per ramet ensures the species of a large overwintering biomass that promotes dispersal and growth potential of the species [24]. The turions also help in the dispersal of the species, the dispersal of plants, stolon buds, and turions is achieved by winds and currents [25] and the relatively small size of turions (ca. 1cm long) facilitates such transport [26]. Whole plants or portions with turions may be transported to new localities, in the feet or bills of ducks and other waterfowl [26]. The high reproductive potential of the species is reported to form dense, impenetrable mats of floating vegetation that prevent sunlight from reaching the submersed aquatic plants; and thus the poor growth conditions created by H. morsus-ranae can affect the survival of native plants [8]. Zhu et al. [27] reported that mild gradual global warming would likely facilitate invasion of H. morsus-ranae in either oligotrophic or mesotrophic lakes.

Management Implications

On a global scale, the spread of invasive alien species, such as H. morsus-ranae, has become a major environmental concern, which requires control and monitoring of such alien species that threaten ecosystems, habitats and other species [28]. The cost of managing these invasive plants is enormous and for example estimated in the United States alone around 35 billion dollars each year [29]. Predicting future invasion success of these species is important for allocation of resources to prevent invasions. The recent report of Hydrocharis morsus-ranae from Kasmir Himalaya [4] should serve as an early warning to the whole South Asia that this notorious weed might be already in the phase of breaking down of the historical biogeographic barrier and may be introduced in the adjoining areas of South-East Asia in the near future. Therefore, it is high time to initiate early detection and rapid response, the most cost-effective strategy with maximum chances of success in the management of plant invasions.

For more about Juniper Publishers please click on: https://twitter.com/Juniper_publish

For more about Oceanography & Fisheries please click on: https://juniperpublishers.com/ofoaj/index.php