Patterns of abundance and size of dictyoceratid sponges among neighbouring islands in central Torres Strait (CRC-TS Project: Task Number T1.6a) 2005

Spatial variability in community structure of dictyoceratid sponges (Class Demospongiae; Order Dictyoceratida) was examined on coral reefs in Torres Strait, an archipelago of islands and reefs between northern Queensland, Australia, and Papua New Guinea. Dictyoceratid sponge abundances and environmental parameters were recorded at 4 locations, separated by 50-220 km. Each location was subdivided into 5-7 sites, each ≥2 km apart. At each site four 50x2 m belt transects were quantitatively surveyed, recording dictyoceratid numbers, substrate type (rock, rubble and sand), water clarity, degree of reef slope and depth. Dictyoceratid abundance was similar among locations, averaging 15.5 individuals per 100 m2, but varied significantly among sites. Twenty three dictyoceratid species were recorded in Torres Strait, with approximately half (12/23) found in only one location. Canonical Correspondence Analysis determined that the measured environmental factors explained only 26% of the spatial variation. Cluster analysis revealed a complex dictyoceratid community structure with consistent patterns among neighbouring sites and among sites separated by hundreds of kilometres. Conversely the dictyoceratid community could vary greatly between neighbouring sites 2 km apart and on the same reef complex. The results of this study suggest that spatial variability of dictyoceratid sponges in Torres Strait is influenced by a combination of environmental, biological and stochastic processes.

本研究针对托雷斯海峡（Torres Strait）珊瑚礁生境中网角海绵（隶属于寻常海绵纲Demospongiae、网角海绵目Dictyoceratida）的群落结构空间变异性开展调查。托雷斯海峡为介于澳大利亚昆士兰州北部与巴布亚新几内亚之间的群岛与珊瑚礁海域。研究人员在4个间距50~220千米的大区域内记录了网角海绵丰度与环境参数；每个大区域进一步划分为5~7个样点，样点间间距不小于2千米。在每个样点中，研究人员采用4条50×2米的带状样带开展定量调查，记录网角海绵个体数量、底质类型（岩石、碎石与沙质）、水体透明度、珊瑚礁坡度与水深。不同大区域的网角海绵丰度整体相近，平均密度为15.5个/100平方米，但不同样点间的丰度存在显著差异。本次调查在托雷斯海峡共记录到23种网角海绵，其中约半数（12/23）仅在单个大区域中被发现。典范对应分析（Canonical Correspondence Analysis）结果显示，本次测定的环境因子仅能解释26%的空间变异。聚类分析（Cluster analysis）结果表明，网角海绵群落结构呈现复杂特征：相邻样点间以及间距数百千米的样点间，群落结构均存在一致的分布模式；与之相反，间距仅2千米且位于同一珊瑚礁复合体中的相邻样点间，网角海绵群落结构却可能存在显著差异。本研究结果表明，托雷斯海峡中网角海绵的空间变异性受到环境、生物与随机过程的共同调控。