臺灣旱招潮族群消長、分布變遷及棲息環境特徵分析

Succession, distribution, and habitat characteristics of Xeruca formosensis in Taiwan

臺灣旱招潮是招潮蟹的特有屬中的特有種。由於它主要分布在高潮位以上的泥灘海岸帶，數十年前曾經因人為開發，導致族群嚴重萎縮，有滅絕之憂。本研究自2019年至2021年，盤點臺灣6處臺灣旱招潮族群，將其棲地依河口和地理位置，劃分為香山濕地、高美濕地、大肚溪口、濁水溪口、八掌溪口、曾文溪口等，共規劃23個採樣站、185個4 m^2的樣區、124個土壤質地樣區及測量79個水質樣點。此外，本研究並回溯1992-2018年之調查資料，分析臺灣旱招潮的族群消長及棲地特性。臺灣旱招潮主要分布在壤質砂土、砂質壤土、砂質黏壤土的高潮線位置，沿著河岸上溯遠達3-6公里地區，而香山及高美濕地沿著海岸分布的族群，因周邊長年有淡水排入。香農多樣性指數相對較高的為出現在高美濕地和大肚溪口的樣區內，濁水溪口的族群呈現大面積單一優勢；降趨對應分析14種蟹類在185個樣區之分布序列，顯示濁水溪口的蟹種組成與其他地理位置分區不同。各種人為開發以及栽植紅樹林或海岸侵蝕，皆會導致棲地流失，進而威脅族群。臺灣旱招潮蟹最大的危機是其族群主要分布區大多僅列入重要濕地，卻不在野生動物保護區的範圍，雲林濁水溪口兩岸及臺西海園是目前完全沒有任何法規保護，棲地隨時會被開發利用。

Xeruca formosensis is an endemic genus and species in Taiwan. Distributed mainly in the supratidal zone of the mudflat coast, Xeruca formosensis has suffered from habitat destruction for decades, heading towards serious population decline and almost a threatened extinction. This study focuses on six stable populations of Xeruca formosensis in the tidal zones of Taiwan from 2019 to 2021. Our study was conducted in Siang-shan Wetland, Gaomei Wetland, Dadu estuary, Choshui estuary, Pachang estuary, and Tsengwen estuary. A total of 14 crab species from 185 sampling plots (4 m^2 per plot) were recorded. In addition, we have included 124 sampling plots for soil texture, and 79 sampling points for hydrology and water quality. Previous data collected from 1992 to 2018 were analyzed to understand the growth and decline of Xeruca formosensis, and to explore habitat characteristics and changes in different habitats in Taiwan. Xeruca formosensis was mainly distributed in loamy sand, sandy loam, and sandy clay loam in the high tide area along the riverbank, reaching upstream to as far as 3-6 kilometers from the sea shore in the Dadu estuary, Choshui estuary, Pachang estuary, and Tsengwen estuary. By contrast, distribution of Xeruca formosensis along the coasts in Siangshan Wetland and Gaomei Wetland was probably due to the long-term fresh water discharge from the surrounding area. Analysis show that the Shannon's index was higher in both Gaomei Wetland and Dadu estuary than in the other four sites, and the largest population occurred in the Choshui esturary among all sites. In the detrended correspondence analysis of 14 crab species in 185 sampling plots, we found that the composition of crab species in the Choshui estuary was different from those in other geographic regions. Artificial developments, artificial planting of mangroves or coastal erosion are a threat to the habitats of Xeruca formosensis in Taiwan. Currently, the most populated areas of Xeruca formosensis are only listed in Taiwan's Wetlands of Importance, but not included in the wildlife sanctuary. The Choshui estuary and Taixi Sea Park are currently not protected by any laws, and these habitats can be developed and used at any time.