Eckman J E, Duggins D O
Skidaway Institute of Oceanography, P.O. Box 13687, 314616, Savannah, GA, USA.
Friday Harbor Laboratories, 620 University Road, 98250, Friday Harbor, WA, USA.
Oecologia. 1991 Sep;87(4):473-487. doi: 10.1007/BF00320409.
Experiments conducted on rocky bottoms at 7-11 m depth in the San Juan Archipelago, Washington assessed effects of canopies of understory kelps on growth of benthic suspension feeders, determined the mechanisms responsible for effects, and assessed the influence of kelp canopies on survivorship of benthic fauna. Kelp canopics influenced growth rates of diverse suspension feeders. At several sites the musselMytilus edulis, the barnacleBalanus glandula, and the serpulid polychaetePseudochitinopoma occidentalis grew faster on the bottom beneath kelp canopies than on nearby exposed substrata. The cheilostome bryozoanMembranipora membranacea showed a mixed response to kelp canopies, growing faster in exposed regions at one site, but faster beneath canopies at another. There were no differences in growth of 2 other species (the cheilostome bryozoanCheilopora praelonga and the spongeMyxilla incrustans) between kelp and no-kelp treatments; however, some processes influenced by plant canopies affected their growth. Specific mechanisms responsible for kelp effects on growth were assessed in a series of field experiments usingPseudochitinopoma, Membranipora, Cheilopora andMyxilla. Particulate deposition on the bottom, which is more intense beneath canopies, negatively affected growth of all 4 species. Kelps also reduced rates of flow and prevented devented development of microalgal turfs beneath the canopy.Pseudochitinopoma grew faster in the weaker flows below canopies and bothCheilopora andMyxilla grew faster where there were no microalgal turfs. These other effects of kelp canopies were at least as important to growth (in the cases ofCheilopora andMyxilla) or more important to growth (in the case ofPseudochitinopoma) than were the general, deleterious effects of higher sedimentation beneath canopies.The lower growth rates caused by higher sedimentation beneath kelp canopies did not result in higher rates of animal mortality. Surprisingly, kelp canopies typically did not influence mortality due to predation. For 7 of 12 taxa, mortality rates did not differ between kelp-covered and exposed treatments. Significantly higher mortality occurred outside canopies for only 4 of 12 taxa, and for at least 2 of these 4 differences probably were not related to predation.Mytilus, a species rare at these depths, exhibited higher mortality beneath kelp canopies due to predation by crabs. Other macrophytes in fresh and salt water, as well as some benthic animals that create complex, 3-dimensional habitats, should influence benthic organisms and assemblages in ways analogous to the kelps acting through their effects on flow, particle transport, and shading.
在华盛顿圣胡安群岛水深7 - 11米的岩石海底进行的实验，评估了下层海带的树冠层对底栖悬浮取食者生长的影响，确定了造成这些影响的机制，并评估了海带树冠层对底栖动物生存的影响。海带树冠层影响了多种悬浮取食者的生长速度。在几个地点，贻贝紫贻贝、藤壶纹藤壶和多毛纲龙介虫西方拟甲壳虫在海带树冠层下方的海底比在附近暴露的基质上生长得更快。唇口目苔藓虫膜孔苔藓虫对海带树冠层表现出混合反应，在一个地点的暴露区域生长得更快，但在另一个地点的树冠层下方生长得更快。另外两个物种（唇口目苔藓虫长唇苔藓虫和海绵硬皮海绵）在有海带和无海带处理之间的生长没有差异；然而，受植物树冠层影响的一些过程影响了它们的生长。在一系列使用西方拟甲壳虫、膜孔苔藓虫、长唇苔藓虫和硬皮海绵的野外实验中，评估了海带对生长产生影响的具体机制。海底的颗粒沉积在树冠层下方更强烈，对所有这4个物种的生长产生负面影响。海带还降低了水流速度，并阻止了树冠层下方微藻草皮的形成。西方拟甲壳虫在树冠层下方较弱的水流中生长得更快，长唇苔藓虫和硬皮海绵在没有微藻草皮的地方生长得更快。海带树冠层的这些其他影响对生长至少同样重要（在长唇苔藓虫和硬皮海绵的情况下）或比对生长更重要（在西方拟甲壳虫的情况下），比树冠层下方较高沉积的一般有害影响更重要。海带树冠层下方较高沉积导致的较低生长速度并没有导致动物死亡率升高。令人惊讶的是，海带树冠层通常不会影响因捕食导致的死亡率。对于12个分类群中的7个，在有海带覆盖和暴露处理之间死亡率没有差异。在树冠层外，只有12个分类群中的4个出现了显著更高的死亡率，并且对于这4个中的至少2个，差异可能与捕食无关。贻贝，一种在这些深度罕见的物种，由于螃蟹的捕食，在海带树冠层下方表现出更高的死亡率。淡水和咸水中的其他大型植物，以及一些创造复杂三维栖息地的底栖动物，应该会以类似于海带通过其对水流、颗粒运输和遮光的影响来影响底栖生物和群落的方式产生影响。
