Duffy J E
Institute of Marine Sciences, University of North Carolina at Chapel Hill, 28557, Morehead City, NC, USA.
Oecologia. 1990 Jun;83(2):267-76. doi: 10.1007/BF00317764.
Herbivorous marine amphipods have been implicated as important grazers on filamentous and ephemeral algae, and thus as beneficial to macrophytes in reducing overgrowth by epiphytic competitors. In North Carolina, USA, amphipods comprise 97% of all macroscopic animals inhabiting the abundant brown seaweed Sargassum filipendula, and peak in abundance between late winter and early summer. I used outdoor tank experiments to test the species-specific impact of common phytal amphipods on the growth of Sargassum and its epiphytes. The results show that seaweed-associated amphipods are a trophically diverse group that could either increase or decrease host fitness depending on their feeding preferences. The amphipods Ampithoe marcuzii, Caprella penantis, and Jassa falcata each significantly reduced growth of epiphytes on Sargassum plants relative to amphipod-free controls, while Ericthonius brasiliensis had no significant effect on Sargassum or its epiphytes. However, amphipod grazing was not necessarily beneficial to Sargassum. A. marcuzii consumed Sargassum in one outdoor tank experiment, reducing its mass by 11%, while Sargassum plants without amphipods grew by 81%. Epiphytes (mostly diatoms and the filamentous brown alga Ectocarpus siliculosus) and detritus remained abundant on these plants suggesting that A. marcuzii preferred the host to its epiphytes. Similarly, when given simultaneous access to Sargassum and to several common foliose and filamentous epiphytes in the lab, A. marcuzii ate Sargassum almost exclusively. The other three amphipods ate no macroalgae. In contrast to A. marcuzii, C. penantis consistently reduced epiphytes with no negative effect on Sargassum. Thus the species composition of the amphipod fauna can determine whether these animals increase or decrease seaweed fitness.
食草性海洋双足类动物被认为是丝状和短暂性藻类的重要食草动物，因此对大型植物有益，可减少附生竞争者的过度生长。在美国北卡罗来纳州，双足类动物占栖息在丰富的棕色海藻马尾藻上所有宏观动物的97%，且数量在冬末和初夏达到峰值。我通过室外水槽实验来测试常见的附生双足类动物对马尾藻及其附生植物生长的物种特异性影响。结果表明，与海藻相关的双足类动物是一个营养多样化的群体，根据它们的摄食偏好，可能会增加或降低宿主的适应性。相对于无双足类动物的对照组，双足类动物马尔库齐长臂虾、尖尾歪尾蟹和镰形真宽水蚤均显著降低了马尾藻植物上附生植物的生长，而巴西艾氏长臂虾对马尾藻及其附生植物没有显著影响。然而，双足类动物的啃食对马尾藻不一定有益。在一项室外水槽实验中，马尔库齐长臂虾啃食了马尾藻，使其质量减少了11%，而没有双足类动物的马尾藻植物生长了81%。这些植物上的附生植物（主要是硅藻和丝状褐藻硅鞭藻）和碎屑仍然丰富，这表明马尔库齐长臂虾更喜欢宿主而非其附生植物。同样，在实验室中同时提供马尾藻和几种常见的叶状和丝状附生植物时，马尔库齐长臂虾几乎只吃马尾藻。其他三种双足类动物不吃大型藻类。与马尔库齐长臂虾不同，尖尾歪尾蟹持续减少附生植物，对马尾藻没有负面影响。因此，双足类动物群的物种组成可以决定这些动物是增加还是降低海藻的适应性。
