The osmoregulatory ability and salinity tolerance of four species of decapod crustaceans (Decapoda: Natantia) were evaluated to test the degree of physiological adaptation to variations in salinity (2 d exposure to 10, 20, 25 and 32. The ecophysiological salinity tolerance of two penaeids (Metapenaeus joyneri and Penaeus semisulcatus) and two palaemonid species (Palaemon pacificus and Exopalaemon orientalis), representative of natant crustacean species inhabiting coastal shallow-water environments were evaluated. Our results show that both E. orientalis and P. pacificus are tolerant of all salinities tested here due to displaying both hyper-/hypo-osmoregulatory ability (in low and high saline waters, respectively), consistent with osmoregulatory patterns displayed by other species in the family (Palaemonidae). The two penaeid species evaluated here displayed efficient hyporegulatory ability in full-strength seawater; however, high mortality was observed in both species at low salinity exposure (10) (73% and 87% mortality for M. joyneri and P. semisulcatus, respectively). In terms of salinity tolerance and thus osmoregulatory ability (which is the mechanism of euryhalinity) of the four species, the following relative order could be assumed: Palaemon pacificu > Exopalaemon orientalis > Metapenaeus joyneri > Penaeus semisulcatus.

抄録全体を表示

Planktonic ciliates below sea ice in Franklin Bay, Canada were studied in terms of their taxonomic composition and species descriptions. They occurred at an abundance of 2,400 cells L⁻¹ and a biovolume of 4.24×10⁶ μm³ L⁻¹. Loricate ciliates (Tintinnida, Spirotrichea) occupied a very small percentage of the total both in terms of abundance (1.7%) and biovolume (1.9%). On the other hand, aloricate ciliates were predominant; in particular Myrionecta rubra (Cyclotrichida, Litostomatea) in terms of abundance (50%) and Lohmaniella oviformis (Choreotrichida, Spirotrichea) in terms of biomass (19.2%). Diagnoses and descriptions are given for ten aloricate species; eight of these species (Leegaardiella ovalis, Lohmaniella oviformis, Tontonia gracillima, Strombidium acutum, S. constrictum, S. dalum, S. epidemum, Myrionecta rubra) were identifiable in the present material. Compared with previous descriptions, six of these species (not S. constrictum or M. rubra) have more or less distinct characters incompatible with reported intraspecific variations.

抄録全体を表示

Seasonal and year-on-year variations in physicochemical properties (i.e. temperature, salinity, dissolved inorganic nutrient concentration), chlorophyll a (Chl-a) concentration, Chl-a size composition and abundance of microphytoplankton (>63 μm) assemblages were investigated at a neritic survey station in Sagami Bay, Kanagawa, Japan, from January 2001 to December 2009. These abiotic/biotic variables varied seasonally in an essentially similar way during the 9 year period. During spring blooms (February–May), the micro-size fraction (>20 µm) comprised a greater proportion of the total Chl-a, whereas during other periods the pico- and nano-size fraction (<20 µm) comprised a large portion. Larger diatoms (e.g. Eucampia zodiacus, Coscinodiscus spp.), which dominated the microphytoplankton during the initial–mid stage of spring blooms, were substituted by smaller ones (e.g. Chaetoceros spp., Pseudo-nitzchia pungens, Skeletonema spp.) during the final stage of spring blooms, and then these smaller diatoms continued to be dominant in summer. Dinoflagellates (e.g. Ceratium fusus, C. furca) increased their population densities after the decline of spring diatom blooms, maintained their abundance in spring–summer and became sporadically dominant in the microphytoplankton in summer. The deficiencies in concentration and molar ratio of Si, P and Si-P together in seawater in spring, especially in the photic zone, induce the final stage of spring blooms and lead to the variations in Chl-a concentration, Chl-a size composition and microphytoplankton abundance and species (size) composition. The year-on-year variations in Chl-a and abundance of microphytoplankton assemblages are correlated weakly with the temporal variations in physicochemical properties in relation to water conditions.

抄録全体を表示

Polyps of Chrysaora pacifica were found on sediments sampled from the sea bottom in Sagami Bay near the mouth of the Sagami River on 26 June 2009; they were identified from released ephyrae in the laboratory. This is the first record of wild polyps of C. pacifica. Polyps and/or podocysts were found from five among the six stations. They were found on 25 shells (2.5–9.2 cm in width, 1.6–5.3 cm in height) and on 22 stones (1.5–8.0 cm in width, 1.3–5.0 cm in height). The shells with polyps were mostly from the dead clam Meretrix lamarckii. Polyps and podocysts were mostly found on the concave surface of bivalve shells, or in hollows of the stones. The number of polyps and podocysts per shell ranged between 0–52 (median = 9) and 0–328 (median = 28); and those per stone were 1–12 (median = 2) and 0–26 (median = 1.5). The number, especially of podocysts, was much greater on shells than on stones. On a convex substrate they can easily be removed by being hit with other substrates during dredging and washing, and such a process may also occur in natural conditions. They were induced to strobilate and release ephyrae by decreasing the temperature from 22–23°C to 5–10°C.

抄録全体を表示