Resting egg banks can facilitate recovery of zooplankton communities after extended exposure to saline conditions

Abstract

Summary 1. Salinisation has had a major effect on the diversity of biota associated with freshwater wetlands. However, there is no information available about whether elements of the biotic communities would be able to recover if the concentration of salts within secondarily salinised wetlands was lowered to levels more typical of freshwater wetlands. 2. We tested the hypothesis that dormant eggs of zooplankton are able to persist in wetlands with elevated salinities for extended periods of time by using zooplankton communities that had developed in mesocosms exposed to either salt concentrations of 13 500 mg L−1 or freshwater (<300 mg L−1) for a period of 22 months. We measured the response of the zooplankton community as concentration was reduced along a gradient of decreasing salinity from 13 500 mg L−1 to freshwater. 3. In the freshwater mesocosms, the zooplankton community was abundant and taxon rich. In comparison at the start of the experiment in the high salinity mesocosms, the zooplankton community had low abundances and very few taxa. Numbers remained low in these mesocosms until salinity was reduced to <2500 mg L−1. Below this, there was a rapid increase in the abundance, and richness of zooplankton and communities became similar to the communities in the freshwater mesocosms. 4. These results indicate that dormant eggs of zooplankton are able to persist in wetlands exposed to high salinity levels for up to 22 months and provide a means for zooplankton communities to rapidly respond once a wetland returns to freshwater. 5. It is likely that if the underlying causes of secondary salinisation in wetlands are addressed, it will be possible to undertake restoration activities that allow the rapid return of some components of their biotic communities.

Road Salts as Environmental Constraints in Urban Pond Food Webs

“…While this increase in density was primarily due to proliferation of calanoid copepods under more freshwater conditions, cyclopoid copepods and cladoceran densities also increased. In two interrelated mesocosms studies, Nielson et al [57] – [58] reported that with salinity increases (up to 15,000 mg L −1 sea salt), the developing zooplankton communities diverged greatly from the original freshwater species pool and ultimately resulted in domination by a small number of salt-tolerant species. As salinity levels in these artificial ponds were subsequently decreased (<2500 mg L −1 sea salt), zooplankton communities became increasingly similar with more taxa representative of freshwater systems.…”

The response of phytoplankton, zooplankton and macrozoobenthos communities to change in the water supply from surface to groundwater in aquaculture ponds

“…Some authors suggest that in brackish and other transitional waters species richness is lower than in freshwater and marine habitats (Remane, 1934). Previously published data show that freshwater zooplankton species, mostly rotifers and cladocerans, show low tolerance to increasing salinity (Hart et al, 1991; Boronat et al, 2001;Nielsen et al, 2003Nielsen et al, , 2012North and Houde, 2003;Waterkeyn et al, 2011).…”

“…Hart et al (1991) showed that freshwater Cladocera are less tolerant to salinities above 1000 mg.L x1 (2000 mS.cm x1 ). Furthermore, Nielsen et al (2012) reported that average densities of the zooplankton community increased at salinities below 2500 mg.L x1 (4000 mS.cm x1 ), otherwise were < 1 ind.L x1 . The common taxa at salinities above 2500 mg.L x1 were Cyclopoida and copepod nauplii, Lecane spp.…”

“…The common taxa at salinities above 2500 mg.L x1 were Cyclopoida and copepod nauplii, Lecane spp. and Lepadella spp., whereas no Cladocera were reported (Nielsen et al, 2012). Boronat et al (2001) investigated Cladocera in a salinity gradient and reported a negative relationship between species richness and salinity.…”

Full life-cycle toxicity assessment on triclosan using rotifer Brachionus calyciflorus

“…For monogonont rotifers, resting eggs is the end-product of sexual reproduction and can survive at extreme environmental conditions such as low temperature or aridity (Pourriot and Snell, 1983;Nielsen et al, 2012;Ricci, 2001). Its production process encompasses the full-life cycle of rotifer, which can thus avoid the limitations of partial life-cycle toxicity tests if resting eggs are chosen as testing endpoint (Preston and Snell, 2001).…”