Do changes in riparian zones affect periphyton growth and invertebrate colonization on rocky substrates in Atlantic Forest streams?

ABSTRACT: We evaluated the growth of periphyton and colonization of sterilized cobbles by invertebrates in three coastal streams of the Atlantic Forest (Southeast Brazil) that differ in the conservation level of riparian zones. Because of differences in light availability and water temperature, we hypothesized the growth of periphytic algae would be higher in the most altered stream. Consequently, invertebrate assemblages would differ among streams. Cobbles with similar sizes were ashed and incubated for 7, 15, 30, 45 and 60 days in the studied streams. Despite periphyton growth was faster in the most altered stream, contents of chlorophyll-a did not differ among streams. A total of 954 individuals (98% insects) belonging to 36 taxa was found. Invertebrate density was higher and increased throughout the experiment in the preserved stream, while invertebrate biomass was higher on the initial sampling intervals (7 and 15 days). A stream effect on invertebrate assemblages was observed after the 15th day and 17 taxa were found only in the preserved stream. Leptophlebiidae (Ephemeroptera), Hydroptilidae, Helichopsychidae, Leptoceridae (Trichoptera) and Orthocladiinae (Diptera) showed specificities with the assemblages found in the preserved stream and no taxa proved to be an indicator of the assemblages found in the altered streams. These results showed that changes in the riparian zones of Atlantic Forest streams did not affect the content of chlorophyll-a on rocky substrates, but the growth of periphyton influenced the density and structural composition of invertebrate assemblages. Our findings partially support the proposed hypothesis and conform to the notion of the importance of periphyton community for the colonization of exposed substrates by invertebrates and for evaluating the consequences of anthropogenic changes in ecosystem functioning and aquatic communities.

摘要：本研究于巴西东南部大西洋森林的3条河岸带保护水平各异的沿海溪流中，评估了周丛生物（periphyton）的生长情况，以及无脊椎动物对灭菌砾石的定殖过程。鉴于各溪流间光照可获得性与水温存在差异，我们提出假说：周丛藻类（periphytic algae）在受干扰程度最高的溪流中生长量更高，且不同溪流间的无脊椎动物群落（invertebrate assemblages）结构会存在显著差异。我们选取规格一致的砾石，经灰化灭菌处理后，在各研究溪流中分别野外培养7、15、30、45与60天。实验结果显示：尽管周丛生物在受干扰程度最高的溪流中生长更快，但各溪流间的叶绿素a（chlorophyll-a）含量并无显著差异。本次实验共采集到954个无脊椎动物个体（其中98%为昆虫类），隶属于36个类群（taxa）。在保护完好的溪流中，无脊椎动物密度更高且随实验推进持续升高；而无脊椎动物生物量则在初始采样时段（7天与15天）达到峰值。实验开展15天后，可观察到溪流生境对无脊椎动物群落的显著影响；另有17个类群仅在保护完好的溪流中被发现。扁蜉科（Leptophlebiidae，蜉蝣目Ephemeroptera）、纹石蛾科（Hydroptilidae）、距石蛾科（Helichopsychidae）、长角石蛾科（Leptoceridae，毛翅目Trichoptera）以及直突摇蚊亚科（Orthocladiinae，双翅目Diptera）类群仅在保护溪流的无脊椎动物群落中呈现特异性分布，未发现任何类群可作为受干扰溪流无脊椎动物群落的指示类群。本研究结果表明，大西洋森林溪流的河岸带变化并未影响岩石基质上的叶绿素a含量，但周丛生物的生长会显著影响无脊椎动物的种群密度及其群落结构组成。本研究发现部分支持了最初提出的假说，同时印证了周丛生物群落对于无脊椎动物在裸露基质上的定殖过程，以及评估人为活动变化对生态系统功能与水生群落造成的影响均具有重要意义这一学术观点。