The malacologicalsocietymalacological society of Japan VENUS Jour. Malac.)n# (Jup, - VoL 57, No. 2C]99R): 115 120 Distribution of Two Intertidal Gastropods, Batielaria 7n2LltofoTmis at a Co-oceurring Area and B. c2emingi (Batillariidae) Naoko ADAcHI and Keiji WADA (Department of Biological Science, fucutty of Science. IVitra Plk)men's University. Kitauaya-nishimachi, IVbra 630-8506, Jtapan) Abstract: Distributions of two intertidal gastropods, Batillaria multijbrmis (Lischke) and B. cumingi (Crosse), were studied in relation to intertidal height and vegetation on a tidal in the intertidalhigher flat where they co-occuTred. B. multijbrmis occurred abundantly lower tevel around tide shore line. In areas with level, while B, cumingi did in the low two species tended to segregate to each other with regard to plant halophilous plants, the in water to species. Laboratery experiment indicated that B. cumingi preferred to stay in interti- more extent than B. muttijbrmis, corresponding with the distributional difference dal height between the two species. Keywords: Distributien, Batillaria multijbrmis, BatiUaria cumingi, tidal flat Introduction to the family Batil- Batiltaria multijbrmis and B. cumingi are intertidal snails belonging lariidae. Their shel! morphology and anatomica! features are similar to each other, which has caused taxonomical confusion (Kurozumi, 1995). But phyletic analysis using mitochon- drial DNA has confirmed that they are distinct species (Ozawa, 1996). The form of egg capsule and the developmental mede has been also known to differ between them (Furota, personal communication). Whilst the two species occur in intertidal zone of various substrata such as rock, boulder and sand or mud in wave-protected bays and estuaries (Abe, 1934; Wells 1983; Adachi & Wada, 1997>, there has been no published work analyzing the distributional difference quantitatively between the two species. This study was under- taken to elucidate distributional diffeTence between B. muttijbrmis and B, cumingi at a co-occurring area. In addition, laboratory experiment was made to compare the preference for air-exposed/submerged condition between thern. Materials and Methods m2) 135055'E), Field study was conducted at a tidal flat(1750 in Yukashigata (33e36'N, middle Japan, located on O.5 km up the mouth of Yukawa Bay in Wakayama Prefecture, half of the during the daytime low tide of spring on 8 and 9 April, 1997. More than tetragonum, Artemisia flat area had halophilous plants such as Zqysia sinica, Limonium the surface water jukudo, and Phragmites communis (Fig. 1). Salinity and temperature of salinometer Toa measured at 3 points around the study area by portable (CM-14P: NII-Electronic Library Service The malacologicalsocietymalacological society of Japan 116 VENUS: Vol, 57, No.2(1998) Electronics Ltd.) at low tide of the study period, ranged from 11.6 to 29.0CVbo and from 16.0 to 34.90C, respectively. Distributions of B. multijbrmis and B. eumingi were investigat- ed by establishing 7 transects crossing the flat. Along each transeet, sampling points were selected at intervals of 2m. Additional 4 sampling points were established under water depth) below the lowest level (1-32cm of low tide. Total number of sampling points was 99 (-40 cm to +58.5 cm relative to mean tide level). At each point, snails were collected by hands to the depth of 2cm, using two 25 x 25 cm quadrats. For quadrats where vegetation occurred, the species plant were recorded. Substratum of all the quadrats was muddy sand with pebbles. The following diagnostic characters were used to identify BatiUaria snails, based on their shell morphology, except small snails for the (<10 mm in shell length) lacking charac- teristic features of respective species. B. multijbrmis; 1) varix turned to siphonal canal well developed, 2) outer lip and shell shape smoothly projecting curved from shell apex to siphonal canal, 3) callus between outer lip and inner white and well developed, B. lip cumingi; 1) no varix turned to siphonal canal, no 2) projecting outer lip,and shell shape not smoothly curved from shell apex siphonal canal, callus to 3) between outer lip and inner lip translucent and not developed. Snail species was identified in case when the speci- men had all the three or the two characters of each species, When the specimen showed beth characters of B. muUijbrmis B. and cumingi or intermediate character between B. muttijbrmis and B. cumingi, its species was not determined. Among 2362 BatiUaria snails collected through the survey, specimens identified as B. multijbrmis accounted for 18.80glb and those as B. cumingi for 64.44{7b. Data of species-undetermined specimens were omitted from analysis. Laboratory experiment was carried out to compare preference for air-exposed!submerged condition between B. muttijbrmis and B. cumingi, using two plastic tanks (19 x 12 x 12 cm high) under constant temperature (250C). Each tank, with seawater (2 cm deep), was tilted in order to make one fourth area of the bottom exposed to air and the remaining area submerged. Ten snails of each species, after being kept under seawater for 12 hours, were placed at the center of each tank, where submerged. The numbers of snails staying under water and those above water were counted at 10 minute intervals during an hour. The experiment was carried out sirnultaneousty between the two tanks (two species) and triplicat- ed, using different individuals. Results Densities of Batillaria multijbrmis and B. cttmingi at sampling points are shown in Fig. 1. B. muttijbrmis was found above low-tide shore-line of the southern half of the study area, whereas B. c"mingi occurred in high density around low-tide shore-line of the northern half of the study area. B. multijbrmis occurred from -16.5 cm to +48.5 cm relative to mean tide level (MTL), while B. cumingi did widely from - 40 cm to + 51.5 cm relative to MTL. The mean (± SD) density per O,125 m2 were 4.67 ± 13.03 in B. mutti- formis and 15.25 ± 26.02 in B. cumingi. The highest density was recorded at 39.5 cm above MTL (73 snails per O,125 m2) in B. miltijbrmis and at 25.5 cm below MTL (133 snails per O.125 m2) in B. cumingi. NII-Electronic Library Service The malaoologloalmalacological societysoolety of Japan Adach1 ＆ Wada Distnbution of Bati〃arla ll7 Seaward B ．cumln I ● 一 ● 、 ● ’／ 紅 孝 数 ’一一，，一● P ● 、 、 ● ， ■ ； ● 、 ノμ 響 、 ’， ■ ， 」 鮮 ● 、、 ， ● 、 ’ 緊 、、一 ！” o 雲 修 二 ● 、、、 ● 嫡 穿 丶 ’／ ● 丶 ● 窺 莚 圭 ・ ： 、 （、 喝4 霊 靠 、、噛眇噛 6 ≒ ； ． ｝ 9 、 ● ・ 1 ’ で 豊 ： ＼ ＿一 ・ ノ 。 、、■ ： 《 o ’ 、 、 一 ’ 丶 ・ 0＜ ＜ 20 丶ご ！ 、臓 二 毒 ● ！ 、、 ノ r 、 書 ’ ● 20 ≦ ＜ 50 、、 ● ， 一 ， ＼ ● 50 ≦ 丶 ↓ 一．．− r （denslty per O 125m2 ） ： F 且91Densttie 、 of Bantlana mutttformls and B cutntngt at each sampling pomt Sohd hne， broken】lne dnd 、hddcd area lndlcaIe nverbank （at low tide｝， low t置de shore lme of tidal fldt dnd 、 dlt marsh arca respectively 各採集 地 声 て の ウ ミ ニ ナ と ホ ソ ウ ミ ニ ナ の 密 度 実線 は 川 岸 （十 潮 時 〕 を ， uH 線 及 ひ そ の 内 側 は 人 潮 低 潮線 と i 出域 を，灰 色 の 部 分 は 植 生 σ）範 囲 を 示 す Table l shows the denslty of the two specles ln re 且anon to vegetatlon In areas wlthout vegetatlon the mean of multtformts was at the mld −nde whlle ， denslty B hlghest level， of β cu 〃 llngl was at the −tlde areas wlth vegetatlon that hlghest low level In ， the hlghest denslty of both specles was observed ln hlgh−tlde level η 〃 ， and the denslty of B ． 7〃 妙 br lts was hlgher ln sampllng domlnated by Zoysla slnlca and Limonium ごetragonum whlle polnts ， the denslty of 、B cumlngl was hlgher m sampllng polnts domlnated by Phragmites communIS − Laboratory experlment showed that the number of snalls found above water was slgnlfl cantly ln muttOformls larger B than ln 8 cumln81 ln one of trlpllcates，and the mean va 匡ue was hlgher ln B 〃 zulhfor 〃 lls than ln B ．α 〃 ltngl ln an the trlpllcates（Table 2） 一 NII-ElectronicN 工 工 Eleotronlo LibraryLlbrary Service ・The malaoologioalmalacological societysooiety of Japan ll8 VENUS ： Vol ．57 ， No ．2 （1998 ） Tabie 1Mean and range of densities（per O ．0625 m2 ）of βα ∫1〃aria mutt ヴformis（1eft values ）and B ． − cumingi （right values ）at sampling points with vegctutkon und without vegetation （bare）， sepa − and rately for three tide leve且s of high（35−60 cm above MTL ）。 mid （0 35 cm above MTL ） low （40−O cm below MTI ．）， 植 生 の あ る 調 査 点 と 植 生 の な い 調 査 点 に お け る ウ ミ ニ ナ （左 側 の 値 ） と ホ ソ ウ ミ ニ ナ （右 ・ 側 の 値） の ，密 度 の 乎均 値 と 最 大 最 小 値 ．調 査 点 を 潮 位 に よ り，高潮 位 （平均 海 水 面 に − − 対 す る 高 さ ： 35−60cm ），中 潮 位 （O 35 cm ），低 潮位 ← 40 O・cm ＞ に 分 け て 示 し た ． Vegetation dominated by Level Bare ZoysiasinicaLimonium ノ 4厂 ’emis ’c〜 厂σ 8〃1’1θ∫ 1・’〃lonium tet厂agonu 〃 1 fukudoPh comm 初 n ’5 ＆ 14 厂ごe 〃 2 ’∫’α HighMeanRangeN 0／0 ．80 3．5／30 9 ．2／1．5 0 ．3／00 0／18 0．4／0．5 ／O−711 −46 ／0 −42 0−42 ／0− 10 −1／0 0〆14−22 0−3／0−4 39 12 4 2 8 MidMeanRangeN 4 ．9／10．3 0 ．5f1 ．50 1／00 0／0 ．50 − 0−34／0 −56 − 1／0−3 ＿2／0 ／O 1 68 2 2 2 LowMeanRangcN 0 ．5／12レ9 0−8／0− 104 48 Tab 且e 2 The number of snails recorded as staying above water at 6 counts during l hour in each of replicate ： 10 and itsstatistical comparison three replicates （number of snails used in each ） between Batillaria muttiformis and B ． cumingi ， n ．s ．： not significant ． ウ ミ ニ ナ と ホ ソ ウ ミ ニ ナ の 水 に 対 す る 選 好性 の 室 内実 験 の 結果 ．水 槽 内 に お い て ，水 中 に 放 逐 後 ，水 の な い 場 所 に い た 個体 数 を ，10分 お き に 1 時 間 ま で 記録 し，そ の 平均 値 と 標 準 偏 差 お よ び そ れ の 2 種 間 で の 違 い の 検 定 結 果 を 示 し た ． Replicate B ． mutttformis B ． cumingi Wilcoxon signed −ranks test No ． Mean ± SDRange Mean ± SDRange 1 1．50 ± 1．12 0 −30 0 00 n ．s ． （p ＝0．0679 ） 自う 1．33 ± 1．ll −31 00 n ，s ． （p ＝0．0679 ） 3 l．33 ± 0 ．75 −3 ，17 ± 0．37 〇一1 p く 0．05 （p ＝0 ．043D Discussion