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=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.