Physical and Chemical Properties of the Nest-site Beach of the Horseshoe Crab Rehabilitated by Sand Placement

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1 J. Jpn. Soc. Soil Phys. No. 33, p.//0-,**/ ******* * Physical and Chemical Properties of the Nest-site Beach of the Horseshoe Crab Rehabilitated by Sand Placement Masami OHTSUBO*, Hidekazu ISHIDA**, Hisakatsu MINEI*, Shinya YAMAOKA*** and Takahiro HIGASHI* * Faculty of Agriculture, Kyushu University, Hakozaki 0+*+, Higashi-ku, Fukuoka-shi, Japan ** Faculty of Agriculture, Kyushu University (Fukuoka Prefecture at present) *** Graduate School of Bioresource and Environmetal Sciences Abstract Tidal flats in Imazu and Kafuri Bay in Fukuoka Prefecture, Japan, were well known as the nest-sites of horseshoe crabs, but their nesting has declined because of water and sediment pollution of the bay. To rehabilitate the polluted beach in the tidal flat, placement of fresh sand on the beach was performed by Fukuoka City, resulting in an increase of nesting of the horseshoe crab. We compared the factors that potentially a#ect nesting at Imazu and Kafuri beach : morphology, exposed time, grain-size distribution, water content, oxygen concentration, and redox potential. The elevation of the beach was higher at Imazu than at Kafuri, leading to a longer exposed time at Imazu than Kafuri. This induced low water content, and high oxygen concentration and redox potential at Imazu compared with Kafuri though the grain-size distribution and organic matter were almost the same at both beaches. We suggest that sand placement is an e#ective procedure to rehabilitate nesting sites of the horseshoe crab in terms of exposed time of the sites, water content, oxygen concentration, and temperature. Key words : horseshoe crab, nesting, rehabilitation, tidal flat, elevation, dissolved oxygen, redox potential + Tachypleus tridenatatus Leach, +31/ ; ; a, +332 b,,*** a,,*** b,,**, ;,*** * 2+,2/2+ 0+*+ ** *** 2+,2/2+ 0+*+ :

2 56 33,**/ ,*** +333, + +, 1 mm 0+0 m,,- m *.+*.2 m, *..* m -,/-/ cm , Fig. + Location of Imazu and Kafuri Bay. Picture + + General view of the investigation site.

3 : 57 Fig.,, Contour in the investigation site and sampling points. Fig... Tidal curve during high tide and elevation of beach. - Fig. - - Ground and tidal level of the investigation site. / *,* cm 31

4 58 33,**/ * +, + / a +32* / +32* /., +32* * 1 +33/ **m - +** m, / m, *., m - / Fig. / Habitat of the horseshoe crab Table + Nesting of the horseshoe crab at Imazu and Kafuri +32* * / +, +, +, +, +, +, 2-a /-c /-d /-e *4/ +,4* +4, * * * /4,,4. +4,,4+ * + : ; / -, : ;

5 : 59 *.*1/, mm +2, mm 2,,*** 0, ,*** 3 +, +* +- +, +.,**+ + 2, ph, +* cm +/,* cm ph cm HORIBA ph METER D-+-,* cm / /+ / 1,* +* +*,*,,*** Table, Change in the number of nesting horseshoecrab s pair with time , ,.+, 0, *4-/ *41, +4*3 *41+ Fig. 0 0 Nesting of the horseshoe crab before and after sand placement in Imazu.

6 60 33,**/ 3 Fig. 3 Fequency of water content at beach. Fig. 1 1 Grain size distribution at beach and mud ground. 2 Fig. 2 Frequency of organic matter content at sandy ground. +* Fig. +* Change in water content with depth * +* Table - - Saturation degree of beach and mud ground +, ** 3/ 33 +* ++ +, +- +., , +, +- 2, /,

7 : 61 Fig Void ratio versus coe$cient of permeability., - /, ,. mg L + +1*,0* mv +, mg L + +/*,** mv , Fig. +, Redox potential versus dissolved oxygen concentration in beach and mud ground. -.

8 62 33,**/ - + mg L + +/* mv cm +** - +, / +* - cm s + /- ph,*** +3 psu ;gkg + 0 mg L + +32/ -* +* psu +/ psu,*-/ psu. ph, ph 1 2 * / gl + psu,.,3 gl +,*** +3 psu , /,/,/-/ 3 -. mg L +, mg L + Table.. ph Soil ph and salt concentration in pore water +, , +- ds m +.*4/* -14-*.-4-*./40*.-4** gl +,/43,,-421,141*,34+2,14/, gl + Na 24+, , 240* 0423 K *4-3 *4-/ *4., *4.* *4-1 Ca +4+, +4*/ *2 +4*. Mg *4.+ *4-1 *4.- *4-2 *4-1 gl + Cl,* ,,4* *420 SO., ,4,3,4-1,4,3 Br *4+2 *4*3 *4+, *4+3 *4+/ F *4*, *4*, *4*- *4*, *4*+

9 : 63 +, Penn and Brockmann ** +,+1 /,/./ mg L +,,**-** mv +32/ : Acta Arachnology, -. : a :./ : +*3++*3/ b :./ : +*30++** : p. 0*.,*** a : - + : 13.,*** b :.1 : +,+0 +,,*.,**, :.3 : ++/0++0* : +31+ : :.//, : +31/ : ++,***.,*** : Tachypleus + tridentatus Leach // : +/, : - :,/, : : ++/ :. :.,*. Penn, D. and Brockmann, H. J. (+33.) : Nest-site selection in the horseshoe-crab, Limulus-polyphemus, Biological Bulletin, +21 (-) : :,** :,**. +, 2

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