三棘鲎(Tachypleus tridentatus) (Leach, 1819)稚鲎在台湾澎湖青螺湿地复育关键因子探讨

Discussion on Key Factors of Restoration of Juvenile Tachypleus tridentatus (Leach, 1819) in Chingluo Wetland of Penghu, Taiwan

本研究主要探讨三棘鲎的稚鲎Tachypleus tridentatus (Leach, 1819)与环境因子有关的觅食活动。2018年12月至2019年2月在台湾澎湖青螺湿地实施6次净滩活动之后进行调查,结果表明:分布于青螺湿地的三棘鲎稚鲎夏季活动频度明显活跃,在2019年7月下旬与8月分别记录到25只(壳宽30.0~132.0 mm,平均约61.3 mm)及42只(壳宽28.0~147.0 mm,平均约57.8 mm)的稚鲎;其中8月所记录稚鲎个体偏小体型且数量明显多于7月(Mann-Whitney U test, Z = 1.783, p = 0.036)。数据也显示三棘稚鲎生长达第7期稚龄(壳宽25.1~31.0 mm)的个体才开始于退潮后进行广布式的地表觅食活动,且明显群集于排水系支流,流速缓慢,水深不及体高( 10 cm)之处。另外轨迹数据表明,第7~10期稚鲎在觅食活动前进时的方位是均匀的(Rayleigh Z test, r = 0.1422, Z = 0.4653, n = 23, p > 0.05),但总体爬行轨迹是体现偏向正趋流性行为(positive rheotaxis) (Nonparametric Binomial Test: test value = 45˚, test proportion = 0.5, n = 23, p = 0.011)。结论:台湾澎湖青螺湿地的三棘鲎保育,近来备受关注。例行调查中,特别是实施人为适宜干预之后(如净滩活动),纪录到三棘鲎稚鲎量随而增多;我们认为是脆弱的觅食微栖地已得到改善的结果。推测缓慢的水流有助于三棘鲎稚鲎觅食,支持趋化觅食策略假说;提出水流因素的管控是稚鲎栖地建设与管理之一优先项目。

The purpose of the present study was to examine the foraging patterns related to environmental factors of the wild juvenile horseshoe crabs, Tachypleus tridentatus (Leach, 1819). After six times beach clean-up activities, which were from December 2018 to February 2019 at Chingluo wetland of Penghu, Taiwan. We recorded that the T. tridentatus juveniles, had obviously seasonal activities in late July and August 2019, of which the average of prosomal width (abbr.: pw) (mm) (range, numbers) 61.3 (30.0~132.0, 25) and 57.8 (28.0~147.0, 42), respectively;and the sizes among months had a statistically significant difference (Mann-Whitney U test, Z = 1.783, p = 0.036). The data also demonstrated when ebbing, the juveniles of the 7th instar stage (pw of 25.1~31.0 mm) began emerging from the sediment of the nearshore habitat for surface feeding around tributary (water depth 10 cm). In the area of activities of the 7th~10th instar stage juveniles, where water flows weakly, crawling data showed the azimuths of advancing were uniform distri-bution (Rayleigh Z test, r = 0.1422, Z = 0.4653, n = 23, p > 0.05), but the final crawling trajectory positive rheotaxis (Nonparametric Binomial Test: test value = 45˚, test proportion = 0.5, n = 23, p = 0.011), i.e., supported the hypothesis: feeding likely rely primarily on chemical cues, which also lead to clumped-type of internal distribution pattern. Conclusions: The conservation of T. tridentatus in Chingluo wetland of Penghu in Taiwan attracts more attention, recently. During a routine survey, especially, after the artificial reasonable restoration policy (i.e. beach clean-up ac-tivities in this study) on the Chingluo wetland, where the population of juvenile T. tridentatus was recovered subsequently. Of which, we surmise that the weaker water current is one more important factor inducing arheo-chemotaxis strategy adopted by the juvenile T. tridentatus for foraging action, and the factor wants to be managed as the top priority in restoration policy.