Density of Tripneustes gratilla in different seagrass meadows in Changuu Island (Unguja Island, Zanzibar Archipelago, Tanzania)

To assess the sea urchin distribution across the seagrass species, we measured the sea urchin density in three monospecific meadows (T. ciliatum, C. serrulata and H. uninervis) and two mixed meadows (dominated by T. hemprichii and by S. isoetifolium) in the study site. We selected three patches per meadow type. Each patch was 25 square meters, delimited with a transect tape. We counted the number of sea urchins at high tide, and divided this number by the surface of the patch to calculate sea urchin density per square meter of meadow (individuals per square meter).

为评估海胆在不同海草生境中的分布特征，本研究于研究区域内的3片单优海草床（涵盖T. ciliatum、C. serrulata与H. uninervis三个物种）及2片混合海草床（分别以T. hemprichii和S. isoetifolium为优势种）中开展海胆密度测定。每种海草床类型选取3个样斑，单个样斑面积为25平方米，以样带绳划定边界。于涨潮时段统计样斑内的海胆总数量，将总数量除以样斑面积，即可计算得到每平方米海草床内的海胆密度（单位：个/平方米）。