Abstract
This study aims, first, to examine the limit for tolerance to lower salinity by an oceanic sea skater, Halobates micans, and , second, to make it clear whether exclusively fresh water Halobatinae species, Metrocoris histrio has salinity tolerance. Adults of H. micans were collected using Neuston Net from the starboard side of R/V MIRAI on a fixed station at 8°S, 80°E, whereas those of M. histrio were collected from a small pond filled with a spring fresh water in Kochi (33°N, 133°E), Japan. Time in survival was measured in starved condition under several salinity conditions: 0‰, 2‰, 4‰, 6‰, 8‰, 9‰ and 10‰ for H. micans; 0‰, 5‰, 10‰, 12.5‰, 15‰ for M. histrio. Half of adults were in coma due to lower salinity under 10‰ and time in survival was less than 10 hours under less than 4‰ for H. micans. Time in survival was half at 5‰ of 80 hours on average at 0‰ as a control and less than 10 hours at 10‰ or higher salinity for M. histrio. Relatively flexible osmo-regulation ability by H. micans would be related to wide variety of salinity condition of surface oceanic water, whereas very limited tolerance even to lower salinity of 5‰ may be permitted by the no chances to be exposed to brackish water in natural habitats of M. histrio. This study showed that salinity tolerance of Halobatinae species would reflect, directly, the salinity condition of their habitats.
Highlights
Salinity tolerance has been studied on a wide variety of organisms living in the coast: plant [1], mollusks [2], macro-invertebrates [3], fishes [3]-[7], crabs [8]-[11] and shrimps [12]-[17], spiders [18] and even in insects [19] [20]
How great is the variation of the salinity tolerance for the organisms? In a specialist salt marsh species of a wolf spider, Arctosa fulvolineata, an increase in the hyper salinity (70‰) exposure for 12 days increased the salinity tolerance showing “hypo-osmoregulator” [18]
This study aims, first, to examine whether salinity tolerance of Halobatinae species would reflect, directly, the salinity condition of their habitats, using an oceanic sea skater, Halobates micans, and a fresh water Halobatinae species, Metrocoris histrio
Summary
Salinity tolerance has been studied on a wide variety of organisms living in the coast: plant [1], mollusks [2], macro-invertebrates [3], fishes [3]-[7], crabs [8]-[11] and shrimps [12]-[17], spiders [18] and even in insects [19] [20].1.1. In a specialist salt marsh species of a wolf spider, Arctosa fulvolineata, an increase in the hyper salinity (70‰) exposure for 12 days increased the salinity tolerance showing “hypo-osmoregulator” [18]. As another hypo-osmoregulator, a population of the ground beetle, Merizodus soledadinus, which has been introduced at the Kerguelen Islands a century ago, survived for 15.9 or 19.5 days on average even under 70‰ in comparison with 21.4 or 27.0 days under 35‰ [20]. The euryhaline white shrimp, Litopenaeus vannamei, inhabits both coastal and oceanic areas through ontogeny Both larvae and adults of this species have high function of hyper- and hypo osmo-regulation. For example direct exposure from sea water to several salinities of 5‰, 10‰, 20‰, 32‰, 45‰ and 60‰ permitted all 17 stages larvae survive even 5 hours after the exposure to 20‰, 32‰ and 45‰ [17]
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