Salinity tolerance of diapausing eggs of freshwater zooplankton

Abstract

Summary 1. Many freshwater zooplankton produce diapausing eggs capable of withstanding periods of adverse environmental conditions, such as anoxia, drought and extreme temperature. These eggs may also allow oligostenohaline species to survive increased salinity during periods of tidal flux or evaporation, and here we test the ability of diapause eggs to withstand such conditions. 2. Salinity tolerance may also enable organisms to invade new environments. The increased rate of introduction of non‐indigenous species to the Laurentian Great Lakes since 1989, when ballast water exchange regulations (to replace fresh/brackish water at sea with full seawater) were first implemented for transoceanic vessels, has stimulated studies that explore mechanisms of introduction, other than of active animals, in ballast water. One hypothesis proposes that freshwater organisms transported in ballast tanks as diapausing eggs may be partially responsible for the increased rate of species introduction, as these eggs may tolerate a wide array of adverse environmental conditions, including exposure to saline water. 3. We collected ballast sediments from transoceanic vessels entering the Great Lakes, isolated diapausing eggs of three species (Bosmina liederi, Daphnia longiremis and Brachionus calyciflorus), and measured the effect of salinity on hatching rate. In general, exposure to salinity significantly reduced the hatching rate of diapausing eggs. However, as non‐indigenous species can establish from a small founding population, it is unclear whether salinity exposure will be effective as a management tool.

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

“…This work has proved how the increase of NaCl affects significantly survival and life history traits, which can cause changes in the zooplankton community structure. Other authors (e. g. Nielsen et al 2003, Bailey et al 2004) state that, if salinity changes occur very rapidly, organisms can not adapt and freshwater taxa can become locally extinct, transferring dominance to salt tolerant taxa. According to our results, changes in reproduction and growth occur at a range of sodium chloride concentrations very close to lethal levels.…”

“…As a consequence of this, we hypothesize that salinity will produce a drastic "all-or-nothing" effect in cladoceran assemblages, leading to their extinction, as they are unable to survive or reproduce as soon as their tolerance level is reached. A small increase in salinity seems to be clearly deleterious for indigenous daphnids (D. longispina) and it is not surprising that, under saline stress, freshwater systems quickly shift to a more halotolerant assemblage (Nielsen et al 2003, Bailey et al 2004). However, Bailey et al (2004) demonstrated that resistance eggs of Daphnia sp.…”

“…A small increase in salinity seems to be clearly deleterious for indigenous daphnids (D. longispina) and it is not surprising that, under saline stress, freshwater systems quickly shift to a more halotolerant assemblage (Nielsen et al 2003, Bailey et al 2004). However, Bailey et al (2004) demonstrated that resistance eggs of Daphnia sp. hatched when returned from high levels of salt to freshwater conditions, suggesting that rapid re-colonization is possible from local ephippial egg banks.…”

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

“…The studied shallow ponds used to be agricultural land and were excavated and started fully operating as fish ponds in year 2006. We suspect that the zooplankton dormant egg bank formed during the three previous years (2006, 2007 and 2008) contributed much less in 2009 to the zooplankton community of ponds due to increased salinity (Bailey et al, 2004). There are different scenarios that can happen to the dormant eggs bank due to unfavourable habitat conditions, from degradation and loss of viability of eggs over time (Gyllstro¨m and Hansson, 2004) to low survivorship of hatchlings (Nielsen et al, 2003).…”

Efficacy of NaCl brine for treatment of ballast water against freshwater invasions

“…I also did not examine efficacy against resistant taxa associated with ballast sediments, such as invertebrate dormant stages (Bailey et al, 2004(Bailey et al, , 2005Briski et al, 2010). Previous studies have demonstrated that dormant stages of freshwater zooplankton can withstand exposure to high salinity levels and other chemical treatments (Bailey et al, 2004;Gray et al, 2006;Raikow et al, 2007a, b).…”