The dynamics determining the establishment and maintenance of epibiotic relationships are fundamental to understand the role of biological interactions in the functioning of marine coastal ecosystems. Epibiosis of barnacles on mussels is a common feature of many intertidal rocky shores. There are several possible explanations for this relationship, but it is unclear whether the association is commensal, antagonistic, or mutualistic. We investigated the diets of barnacles and mussels in an epibiotic relationship (epibiont barnacle and basibiont mussel), and compared them to the diets of conspecifics living on the same rocky shore but independently (free barnacle and free mussel), using stable isotope (SI) and fatty acid (FA) techniques. The SI results indicated that the diet of mussels did not change as a function of epibiosis, while free barnacles were characterized by higher δ¹⁵N values than epibiotic conspecifics, indicating that they were feeding on more recycled food sources. This result was, however, supported by data from only one site. Results from FA were partially consistent with those of SI analysis, indicating that mussel FA profiles did not change between basibiont and free mussels, but that epibiotic barnacles were characterized by a lower amount of polyunsaturated FA than free barnacles. This suggests that the diet of epibiotic barnacles is of lower quality. This could be due to competition for food with mussels, driven by the different mechanisms of food assimilation between epibiotic barnacle and basibiont mussel; or by the different sizes of particles ingested by the two species under epibiosis vs free-living conditions. The discrepancy between the FA and SI results observed could reflect the different integration time of the analytical techniques, with FA reflecting shorter term variability than SI. We conclude that epibiosis represents an unfavourable relationship for barnacles due to the lower quality of food available when colonizing mussel shells, whereas mussels neither benefit nor were harmed by this association. Thus, this relationship is amensalistic: negative for barnacles but neutral for mussels.

确定表观生物关系建立和维持的动力学是了解生物相互作用在海洋沿海生态系统功能中的作用的基础。贻贝上藤壶的流行是许多潮间带多岩石海岸的共同特征。对于这种关系，有几种可能的解释，但尚不清楚这种联系是共鸣，对立还是相互关系。我们调查了表生生物关系中的藤壶和贻贝的饮食（表皮藤壶和basibion​​t贻贝），并使用稳定同位素（SI）将它们与生活在同一多岩石海岸但独立的同种异食（游离藤壶和贻贝）的饮食进行了比较。和脂肪酸（FA）技术。SI的结果表明，贻贝的饮食并没有因流行病而改变，¹⁵N值高于表生生物同种异型，表明它们以更多的回收食物为食。但是，只有一个站点的数据支持此结果。FA的结果与SI分析的结果部分一致，表明贻贝的FA分布在basibion​​t和游离贻贝之间没有变化，但表生生物藤壶的特征是多不饱和FA的含量低于游离藤壶。这表明表生藤壶的饮食质量较低。这可能是由于表生生物藤壶和basibion​​t贻贝之间食物同化的不同机制所致，贻贝对食物的竞争。或两种生物在流行病与自由生活条件下摄入的颗粒大小不同。观察到的FA和SI结果之间的差异可能反映了分析技术的不同积分时间，其中FA反映了比SI短期的可变性。我们得出结论，由于定居贻贝壳时可用食物的质量较低，因此流行病对藤壶而言是不利的关系，而贻贝既无益也无害。因此，这种关系是淡化的：藤壶为阴性，贻贝为中性。