Foundation species provide physical structure that enhances the diversity and abundance of associated organisms. Canopy‐forming seaweeds are known to act as foundation species on rocky shores by lowering temperature and desiccation stress. Direct solar radiation, including ultraviolet (UV) light, can also reduce photosynthetic rates in algae, cause oxidative stress and DNA damage. The reduction in UV exposure provided by an algal canopy could therefore be important for understory organisms, including the red alga Chondrus crispus on New England’s (USA) rocky shores, and this relationship may be more important at higher tidal elevations with increased low‐tide exposure time. In field experiments, we investigated the relationship between tidal elevation and an index of C. crispus UV exposure, the concentration of UV‐absorbing pigments. Low on the shore, C. crispus grew without a canopy. Higher on the shore, in the mid‐intertidal zone, C. crispus was found under the canopy‐forming rockweed, Fucus distichus subsp. evanescens. At this elevation, C. crispus was shaded (>50%; >1 m above MLLW). We performed a canopy removal experiment that spanned the mid‐zone where C. crispus and F. distichus subsp. evanescens co‐occur and the low‐zone (no canopy). Following canopy removal in the mid‐zone, UV pigment concentrations increased with tidal elevation. After accounting for the effect of elevation, removal of the algal canopy resulted in UV‐protective pigment concentrations 2‐fold higher than in un‐manipulated control plots. These results suggest that amelioration of solar UV exposure might be another mechanism by which canopy seaweeds, acting as foundation species, facilitate understory seaweeds on rocky shores.

中文翻译：

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潮间带冠层形成海藻调节林下海藻光保护化合物


基础物种提供了增强相关生物多样性和丰富度的物理结构。众所周知，形成树冠的海藻可以通过降低温度和干燥压力来充当岩石海岸的基础物种。直接太阳辐射，包括紫外线 (UV) 光，也会降低藻类的光合作用速率，导致氧化应激和 DNA 损伤。因此，藻冠提供的紫外线暴露减少对于林下生物来说可能很重要，包括新英格兰（美国）岩石海岸上的红藻卷曲角叉菜，并且这种关系在潮汐海拔较高且低潮暴露增加的情况下可能更为重要时间。在现场实验中，我们研究了潮汐高度与苋菜紫外线暴露指数（紫外线吸收色素浓度）之间的关系。在海岸低处，苋菜生长时没有树冠。在海岸较高处的潮间带，在形成树冠的岩藻（Fucus distichus subsp.）下发现了卷曲卷藻。伊瓦内森斯。在此海拔处， C. Crispus被遮蔽（> 50%；高于 MLLW > 1 m）。我们进行了一项跨越中部区域的冠层去除实验，其中C. 卷曲和F. distichus亚种。 evanescens与低区（无冠层）同时出现。中部区域的树冠移除后，紫外线色素浓度随着潮汐升高而增加。考虑海拔影响后，去除藻冠导致紫外线防护色素浓度比未处理的对照地块高出 2 倍。 这些结果表明，改善太阳紫外线照射可能是作为基础物种的冠层海藻促进岩石海岸林下海藻生长的另一种机制。