Inundated shore vegetation as habitat for cichlids breeding in a lake subjected to extreme water level fluctuations

Abstract

Climate change and human overexploitation of freshwaters jointly lead to extreme fluctuations in lake water levels. The latter induces changes in the structure and availability of littoral habitats, thereby affecting fish that reproduce in the littoral zone. Recent increased water level fluctuations in Lake Kinneret, Israel, provided an opportunity to evaluate the impacts of those fluctuations on reproduction of fishes that spawn in the littoral zone. We assessed the use of inundated shore vegetation for reproduction by the common native cichlids, Sarotherodon galilaeus and Oreochromis aureus, in a series of field surveys of reproduction activity in littoral areas with and without inundated vegetation. The cichlids spawned in spring and early summer, when water levels are at their annual maximum and part of the shore vegetation is inundated. Spawning was always in water <2 m depth. Lagoon habitats constituted nesting “hotspots,” with nest densities 3-fold higher than open-shore sites. At open-shore sites, significantly higher nest densities were found in areas with inundated vegetation than in plant-free areas. Juvenile cichlids were significantly more abundant in littoral zone habitats with inundated vegetation. These findings highlight the important role of inundated vegetation, particularly at low lake levels when lagoon habitats are dry. We recommend maintaining water levels that support the existence of lagoons and vegetated littoral habitats. When development of lakeshore vegetation is massive, we recommend selectively removing part of the vegetation to form narrow vegetation-free corridors. In addition, wherever possible the vegetation should be removed to form lagoon-type habitats. Our insights and recommendations are probably applicable to similar situations of seasonal destabilization of lake water levels elsewhere.