台灣東北部卯澳灣海域之海膽生物多樣性研究

Biodiversity of Sea Urchins in the Maoaw Bay of the Northeastern Taiwan

本研究以二階段方式調查台灣東北部卯澳灣海域的海膽種類及數量。首先依據該海灣底質特性劃分為第I、II、III、IV及Ⅴ區五個小海區。第一階段，在第I、II、IV區三個小海區中分別隨機選取1個點，第Ⅴ區隨機選取2個點，以長100m，寬1m的穿越線，進行垂直海岸的抽樣調查；第二階段再依據第一階段的結果，分別選取水深3m、6m、9m三種深度，進行等深線的詳細抽樣調查。調查過程中，記錄海膽的種類、數量及深度，並輔以拍照。在第一階段垂直海岸的抽樣調查中，所有海膽種類密度隨著深度的不同呈現顯著差異。在第二階段27條等深線的調查中，共記錄了5科11種2,901隻海膽，其中以白尖紫叢海膽（Echinostrephusaciculatus）的密度最高，其密度為88.81隻／100m2，梅氏長海膽（Echinometra mathaei）次之，其密度為16.33隻／100m2，其餘種類密度均低於10隻／100m2，依序分別為紫海膽（Anthocidariscrassispina）、紫叢海膽（Echinostrephus molaris）、口鰓海膽（Stomopneustes variolaris）、環鋸棘頭帕海膽（Pionocidaris baculosa）、刺冠海膽（Diadema setosum）、冠棘真頭帕海膽（Ecuidaris metularia）、白棘三列海膽（Tripeustes gratilla）、環刺棘海膽（Echinothrix calamaris）及藍環冠海膽（Diademasevignyi）。在整個海域中，白尖紫叢海膽的密度與其他10種海膽的密度有顯著差異，其數量在第I、II、IV區，大多數集中在3m的深度，6m次之，9m非常少，而在第Ⅴ區則大多集中在9m的深度。歧異度指數值無論在小海區或深度均低，而整個海域歧異度指數值隨著優勢種白尖紫叢海膽密度增加呈現遞減趨勢，顯示本海域海膽種類隨著海區、深度及底質不同，呈現多樣性分布。 The community structure and abundance of sea urchins in the Maoaw Bay of the northeasternTaiwan was surveyed in July to September 2002. A total of 2,901 individuals in 11 species of fivefamilies were collected. Echinostrephus aciculatus was the most dominant species and had an averagedensity of 88.81 individuals/100m2, while Echinometra mathaei was the secondly abundant at 16.33individuals/100m2. They were followed by the remaining nine species in a decreasing order fromAnthocidaris crassispina to Echinostrephus molaris, Stomopneustes variolaris, Pionocidaris baculosa,Diadema setosum, Ecuidaris metularia, Tripeustes gratilla, Echinothrix calamaris, and then to Diademasevignyi. Average densities of these species were less than 10 individuals/100m2. There were low valuesin species richness indices (ranged between 1.51 and 2.84), Simpson's species diversity indices (0.12 and0.36), Shannon's species diversity indices (0.12 and 0.28), and Pielou's evenness indices (0.17 and 0.37).The low values were primarily due to the low number of the species and a skew distribution of theirabundance, resulted from the high dominancy of a single species E. aciculatus. Each of the indicesshowed a decreasing trend with the increase in the abundance of E. aciculatus. The abundance of seaurchins differed by species, depths and sampling areas, suggesting that local environmental andoceanographic conditions determine the sea urchin community structure and abundance in the MaoawBay of Taiwan.