Consequences of climate-induced salinity increases on zooplankton abundance and diversity in coastal lakes

Abstract

Intermittent saline intrusions are a common feature of many coastal lakes and wetlands. These ecosystems are often important sites of biodiversity, biological productivity, and ecosystem services such as the removal of sediment, nutrients, and contaminants from inflowing rivers. Predicted effects of global climate change, including sea level rise, are likely to intensify saline intrusions into such ecosystems. Analyses of taxonomic diversity and abundance of zooplankton at different salinities in Lake Waihola, South Island, New Zealand, are supported by results of laboratory studies of salinity tolerances of 3 crustacean taxa Gladioferens pectinatus, Boeckella hamata and Daphnia carinata obtained from the lake. The field and laboratory analyses show that severe perturbations of zooplankton community structure and abundance are caused by even minor saline intrusions into Lake Waihola that raise the salinity to >1.2 psu. Our analyses of Lake Waihola, and data from brackish ecosystems around the world, show that even relatively small increases in salinity levels can drive such systems to a state of depleted biodiversity and abundance, altering ecosystem functioning.KEY WORDS: Zooplankton diversity · Zooplankton abundance · Climate change · Community structure · Shallow lake · Salinity · Lake Waihola · Saline intrusion Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 251: [181][182][183][184][185][186][187][188][189] 2003 a medium sized (surface area = 5.4 km 2 ), shallow (mean depth = 1.15 m), tidal (mean tidal range ca. 0.40 m) lake, connected to the sea via a 10 km reach of the Taieri River, ca. 30 km southwest of the city of Dunedin. The lake has a diverse fish community and a high catch per unit effort (CPUE) relative to other New Zealand lakes, though not relative to shallow Danish lakes (Jeppesen et al. 2000). Lake Waihola has a hydraulic residence time of 153 d, based on non-tidal, freshwater inflows (Schallenberg & Burns 2003). During drought conditions, when water levels in the Taieri River are low and when other freshwater inputs are small, intrusions of saline water enter the lake, as occurred in the austral summers 1997/98 and 1998/99. Global climate change is expected to affect New Zealand in ways similar to the El Niño climatic pattern, in which westerly and southerly airflows dominate and the east coast of New Zealand experiences dry (drought) conditions more frequently (Mullan 1996, NZMfE 2001. During dry summers, Lake Waihola often experiences saline intrusions which create strong temporal and spatial salinity gradients within the lake. Results of a calibrated hydrological model of the Taieri catchment, which was run using meteorological inputs based on downscaled global circulation models and 2 global climate change scenarios (NZMfE 2001), indicated that runoff in the Taieri catchment will decrease during summer months under both scenarios (B. Fitzharris unpubl. data). In addition to decreased summer freshwater inputs, Lake Waihola will ...

Salinity effects on survival and life history of two freshwater cladocerans (Daphnia magna and Daphnia longispina)

“…of the estuary, in the study. Schallenberg et al (2003) stated that, at salinities above 2.7 p.s.u., the zooplankton community changes from one consisting of copepods, rotifers, cladocerans, amphipods and amoebae at low salinities, to one represented only by rotifers.…”

“…Other studies (Barron et al 2002) proved phytoplankton can adapt to salinity conditions, although this process becomes slower as NaCl concentration increases. Some algae (such as the ones belonging to the genus Dunaliella) are haloterant, growing at high saline media due to physiological adaptations, such as glycerol intracellular accumulation (Avron 1986) and a salt-induced protein (p60) present in the plasma membrane (Fisher (Teschner 1995, Schallenberg et al 2003, Rokneddine & Chentoufi 2004.…”

“…The ability of the organisms to survive and reproduce in such unstable environments is as high as their tolerance (Rokneddine & Chentoufi 2004). Studies have been carried out in freshwater ecosystems threatened by salinity, in order to evaluate how the raise in salinity affects zooplankton, altering ecosystem structure and function , Nielsen et al 2003, Schallenberg et al 2003, Rokneddine & Chentoufi 2004. Still, there is little information on how the increase of salinity affects ecosystem integrity in order to predict the impact and rehabilitate aquatic systems (Nielsen et al 2003).…”

“…These systems can suffer important alterations with the increase of salinity due to global climate change, such as the action of rainwater and wind, evaporation and sea level rise (Schallenberg et al 2003). This is particularly important in coastal freshwater systems or in estuaries, which occupy a large area in our country (Portugal).…”

“…This is particularly important in coastal freshwater systems or in estuaries, which occupy a large area in our country (Portugal). Several authors (e.g., , Schallenberg et al 2003 have reported a reduction in the diversity and abundance of zooplankton communities exposed to salinity increases. Freshwater species must either adapt or avoid the saline stress in order to survive and reproduce.…”