Fish-farming can lead to eutrophication of freshwater environments through the increase in organic matter resulting from food supplementation and fish wastes. Eutrophication can induce an excessive development of plants and algae on various substrates, including living organisms (algal epibiosis). Although algal epibiosis has been shown to reduce mobility by increasing drag in marine species, its consequences on host species in freshwater ecosystems remain poorly known. In this study, we investigated the individual (age and sex) and environmental (extensive versus intensive fish-farming) determinants of epizoic algae presence and abundance on European pond turtles (Emys orbicularis). We also explored the potential consequences of algal epibiosis on fitness-related traits of E. orbicularis. Based on a large sample size (1112 turtles from 23 ponds), we found that the abundance of algae growing on turtles increased during spring and summer. However, such increase was different across ages and sex; presumably reflecting the influence of thermoregulation (required to increase metabolic rates to sustain growth and reproduction) and thus, periodical drying of the shell, in reducing algal cover. We also found that intensive fish-farming increased algal epibiosis, especially when fish-farming involved food supplementation. Finally, we found that adult female body condition and reproduction of turtles were negatively linked to algal cover, thereby suggesting a potential negative impact of algal fouling on some fitness-related traits of adult female turtles. Future studies should usefully assess the demographic consequences of algal epibiosis induced by fish farming in this long-lived vertebrate.

养鱼可通过补充食物和浪费鱼类而增加有机物，从而导致淡水环境富营养化。富营养化会导致植物和藻类在各种基质（包括活生物体）上过度生长（藻类生物扩散）。尽管已显示出藻类流行病会通过增加海洋物种的阻力来降低其流动性，但其对淡水生态系统中宿主物种的影响仍然鲜为人知。在这项研究中，我们调查了欧洲池塘龟（Emys orbicularis）上流行的藻类的存在和丰度的个体（年龄和性别）和环境（广泛养殖与集约养殖）的决定因素。我们还探讨了在健身相关性状藻epibiosis的潜在后果E.眼轮匝。基于大量样本（来自23个池塘的1112只海龟），我们发现在春季和夏季，海龟上生长的藻类数量增加了。但是，这种增长在不同年龄和性别之间是不同的。大概反映了温度调节的影响（需要增加代谢率以维持生长和繁殖），并因此在减少藻类覆盖方面定期地壳的干燥。我们还发现，密集的鱼类养殖会增加藻类的流行，特别是在鱼类养殖涉及食物补充的情况下。最后，我们发现成年雌性海龟的身体状况和繁殖与藻类覆盖度负相关，从而表明藻类结垢对成年雌性海龟的某些健身相关性状具有潜在的负面影响。