Influence of Salinity Concentration on Aquatic Insect Community Structure: A Mesocosm Experiment in the Dead Sea Basin Region

Abstract

Salinity varies considerably among temporary pools in the Dead Sea Basin, Israel. We experimentally assessed the effects of four salinity levels (0, 10, 20 and 30 g NaCl per liter) on the aquatic insect community in this basin in an artificial pool experiment. Each salinity level was randomly assigned to six pools (total ¼ 24 pools). Salinity did not affect total insect abundance but strongly affected abundance and distributions of different species, and consequently, community structure. Of 13 taxa colonizing the pools, 12 were Diptera including 10 mosquito species. Five taxa were sufficiently common to assess abundance in relation to salinity. Polypedilum nubiferum Skuse (Diptera: Chironomidae) was largely salinity intolerant being abundant only in the freshwater. Ephydra flavipes Macquart (Diptera: Ephydridae) was most abundant at the highest salinity level and was rare in freshwater. Ochlerotatus caspius Pallas (Diptera: Culicidae) abundance tended to be highest at 10 g/l and lowest at 30 g/l although the differences were not statistically significant. Anopheles multicolor Cambouliu (Diptera: Culicidae) was relatively euryhaline although numbers dropped significantly at the highest salinity. Cleon dipterum Linnaeus (Baetidae: Ephemeroptera) was also euryhaline and showed no significant differences in abundance across salinities. For the mosquito species, we also estimated survival to pupation. Survival to pupation was significantly lower for O. caspius in freshwater, but was not statistically significantly different across salinities for A. multicolor. Species diversity was highest at the two lowest salinities tested and then dropped with increasing salinity. Evenness was not significantly different across salinities. Community similarity generally decreased with increasing salinity differences though dissimilarity was greatest when comparing freshwater to other salinities. Thus, regional diversity is likely increased when there is a range of salinities among pools.

Salinity as a driver of aquatic invertebrate colonisation behaviour and distribution in the wheatbelt of Western Australia

“…As such, our results suggest that C. alternans also preferentially oviposits in fresh water when available. In support of our results, Silberbush et al (2005) observed a similar oviposition preference by Polypedilum nubiferum Skuse (Diptera: Chironomidae). Paracymus sp.…”

“…Diptera remained numerically more abundant than Coleoptera in mesocosm and field samples, most likely because their colonisation occurred by oviposition. In a similar experiment, Silberbush et al (2005) also found Diptera to be the most abundant ([95%) colonisers of mesocosm. In particular, Culicidae can lay large numbers of eggs (approximately 20-200) per female (Liehne, 1991).…”

“…Behavioural selection of habitat is a determinant of animal distribution in terrestrial (Singleton, 1989;Terpstra & Wilson, 1989) and aquatic systems (Mokany & Shine, 2003;Blaustein et al, 2004;Silberbush et al, 2005). Numerous studies have documented biotic interactions, such as predation and competition, influencing oviposition decisions by mosquitoes (Diptera: Culicidae) (Stav et al 1999;Juliano & Gravel, 2002;Mokany & Shine, 2003;Blaustein et al, 2004;Hagman & Shine, 2006), and most likely colonisation by other insects with aquatic life phases.…”

“…Numerous studies have documented biotic interactions, such as predation and competition, influencing oviposition decisions by mosquitoes (Diptera: Culicidae) (Stav et al 1999;Juliano & Gravel, 2002;Mokany & Shine, 2003;Blaustein et al, 2004;Hagman & Shine, 2006), and most likely colonisation by other insects with aquatic life phases. Surprisingly, the influence of abiotic conditions, such as water chemistry, is rarely documented with reference to colonisation behaviour (whether by direct colonisation as an adult or oviposition) (Trimble & Wellington, 1979;Bailey et al, 1981;Pappas & Pappas, 1983;Roberts, 1996;Silberbush et al, 2005).…”

“…camptorhynchus, to be prevalent in saline areas (Pinder et al, 2005;Jardine et al, 2007;Lindsay et al, 2007). However, little attention has been given to the significance of colonisation behaviour in distribution (but see, Silberbush et al, 2005). Laboratory studies demonstrate salinity influences oviposition preferences of mosquitoes (Trimble & Wellington, 1979;Bailey et al, 1981;Pappas & Pappas, 1983;Roberts, 1996), but laboratory results do not always reflect field distributions.…”