Taxonomic and functional diversity of mollusk assemblages in a tropical rocky intertidal zone

ABSTRACT We investigated the spatial variation of molluscan assemblages with different habitat-forming species and bare rock habitat in a rocky intertidal zone in northeastern Brazil. The high intertidal zone substrate was covered predominantly of barnacles [Chthamalus bisinuatus (Pilsbry, 1916)], the mid-intertidal of mussels [Brachidontes exustus (Linnaeus, 1758)] and the low intertidal of macroalgae chlorophytes [Gayralia oxysperma (Kützing) K. L. Vinogradova ex Scagel et al., 1989 and Ulva lactuca Linnaeus, 1753], phaeophytes [Sargassum vulgare C. Agardh] and rhodophytes [Palisada flagellifera (J.Agardh) K. W. Nam, 2007]. A total of 3,861 mollusks were recorded, belonging to the classes Gastropoda (9 species; 3,800 individuals), Bivalvia (3 spp.; 54 ind.), and Polyplacophora (1 sp.; 7 ind.). Functional diversity was accessed through the trophic structure, in which we identified food guilds: suspension feeders, grazers, herbivores, and carnivores. The analysis revealed significant differences in mollusk abundance, species richness, diversity indices, and trophic diversity among barnacle belts, mussel beds, algae habitat, and bare rock habitats. The highest species richness and trophic diversity were detected in algae habitat and mussel beds, which showed low abundance. In contrast, barnacle belts registered low species richness and trophic diversity and a high number of individuals. Bare rock recorded low values in all surveyed indices. This result points to the effect of environmental modification caused by habitat-forming species in this system. These species increase environmental complexity and enable the establishment of organisms through facilitation processes. The various food guilds found in this study reaffirm the role of habitat-forming species in providing niches that support different occupation patterns.

摘要 本研究针对巴西东北部岩相潮间带中，不同造栖物种（habitat-forming species）生境与裸岩生境下的软体动物群落空间分布差异展开调查。该区域高潮间带基质主要被藤壶[Chthamalus bisinuatus (Pilsbry, 1916)]覆盖，中潮间带以贻贝[Brachidontes exustus (Linnaeus, 1758)]为优势类群，低潮间带则分布有绿藻门大型藻类[Gayralia oxysperma (Kützing) K. L. Vinogradova ex Scagel et al., 1989、Ulva lactuca Linnaeus, 1753]、褐藻门物种[Sargassum vulgare C. Agardh]以及红藻门物种[Palisada flagellifera (J.Agardh) K. W. Nam, 2007]。本次调查共记录到软体动物3861只，涵盖腹足纲（9种，3800只）、双壳纲（3种，54只）及多板纲（1种，7只）。本研究通过营养结构分析评估软体动物的功能多样性，共识别出4类取食功能群：滤食者、刮食者、植食者与肉食者。分析结果显示，藤壶带、贻贝床、藻类生境与裸岩生境的软体动物丰度、物种丰富度、多样性指数及营养多样性均存在显著差异。其中藻类生境与贻贝床的物种丰富度及营养多样性最高，但软体动物丰度较低；与之相反，藤壶带的物种丰富度与营养多样性偏低，但个体数量极高；裸岩生境的各项调查指数均处于较低水平。上述结果表明，造栖物种可通过生境改造对该系统产生生态调控作用：这类物种能够提升环境复杂度，并通过促进定植过程助力其他生物的建立。本研究中发现的各类取食功能群，进一步证实了造栖物种可通过提供生态位来支撑不同的生存栖息模式。