Long‐term effects of salinity and disturbance regime on active and dormant crustacean communities

Abstract

In a large-scale and long-term outdoor mesocosm (400-liter) experiment, we studied the interacting effects of salinity and disturbance (hydrological) regime on the active and dormant crustacean communities of Mediterranean temporary wetlands (Camargue, southern France). Sixty-four mesocosms, inoculated with a regional species pool (mixed dormant egg banks), were exposed to a full factorial treatment combination of four salinity levels and four disturbance regimes during three consecutive years. Both in the active and dormant community component, considerable shifts in community composition occurred because of direct and probably also second-order effects of the treatments. All large branchiopod species had low long-term salinity tolerances and showed species-specific preferences for disturbance regimes according to their life cycle strategy. The highest salinity (5) was not limiting for cladocerans and ostracods, which thrived in the absence of the competitively stronger, predatory, and bioturbating large branchiopods. Copepods were negatively associated with salinity and coped better with the imposed biotic pressure. Zooplankton diversity and density peaked in intermediatedisturbance regimes, probably because only specialized species survived the high-disturbance regimes, whereas at low-disturbance frequencies high densities of predatory Triops controlled zooplankton communities. Although crustacean dormant egg banks can temporarily buffer against unfavorable conditions, persisting bad conditions may lead to their exhaustion within 4 to 10 yr. Predicted aridification (leading to more intense disturbance regimes) may result in the loss of late successional species (chydorids and ostracods), whereas salinization may wipe out sensitive freshwater species such as large branchiopods.

Salinization triggers a trophic cascade in experimental freshwater communities with varying food‐chain length

“…Copepod nauplii were the least tolerant to salt in our experiment. It is possible that a sublethal effect of salinity suppressed reproductive output but survival was unaffected (Waterkeyn et al 2011). We did not observe a direct impact of salt on overall cladoceran abundance in the absence of fish.…”

“…At the community level, Van Meter et al (2011a) concluded high chloride levels (645 mg/L) reduced competitive interactions for algal resources between tadpole and zooplankton grazers. In some cases, salinization can alter community succession and wipe out many sensitive zooplankton species (Waterkeyn et al 2010(Waterkeyn et al , 2011. Salinization can also act as an environmental filter by altering community structure toward salt-tolerant species in wetland (Petranka and Doyle 2010, Van Meter et al 2011b, Van Meter and Swan 2014, and lotic ecosystems (Cañedo-Argüelles et al 2016b, Kefford et al 2016, Wallace and Biastoch 2016.…”

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

“…, 2010), although at higher salinities there may be reduced viability of some eggs from freshwater species (Bailey et al. , 2003; Waterkeyn et al. , 2011).…”

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).…”

“…The most significant change occurred in assemblages of Cladocera, Rotifera and Bacillariophyta that were very abundant in 2008, but almost completely disappeared in 2009 (See List of taxa and their abundances in two investigation years after References). A lot of field and experimental studies have proved that the abundance and species richness of assemblages of Rotifera and Cladocera decreases with the increase of habitat salinization (Boronat et al, 2001;Nielsen et al, 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 ).…”