Pseudechinus magellanicus is one of the most abundant sea urchins in southern South America, but many aspects of its feeding ecology in nearshore environments remain unknown. Here, we aimed to analyze the variability of the diet composition along a coastal depth gradient from intertidal tidepools to upper circalittoral zones and examine the relation between seaweed availability and the diet composition at intertidal tidepools. A total of 118 food items, including seaweeds and animal components, were identified. The diet composition showed a large variation between the different coastal habitats present along the depth gradient studied. In tidepools, articulate coralline seaweeds (Corallina spp.), mussel shell fragments and small crustaceans were frequent in the gut contents, suggesting that this species behaves like a general omnivore but can also act as a mussel bioeroder when consuming epizoic algae and microeuendolithic organisms. In intertidal tidepools, the species showed a negative preference toward typical species of late successional stages such as Dictyota dichotoma, Adenocystis utricularis, Codium fragile and Chondria macrocarpa. Sea urchins from kelp forests showed higher dietary diversity than those from intertidal and deeper subtidal habitats, but with prevalence of kelps. At upper circalittoral soft bottoms, diverse detrital items as benthic diatoms, cyanobacteria and drifted algae were observed in gut contents, usually associated with fine sediments, indicating that P. magellanicus captures drifted algae and behaves like a biofilm feeder. This trophic plasticity may allow this species to occupy contrasting habitats and may also contribute to explain its wide distribution in southern South America.

麦哲伦假单胞菌（Pseudechinus magellanicus）是南美洲南部最丰富的海胆之一，但在近岸环境中其摄食生态学的许多方面仍然未知。在这里，我们的目的是分析从潮间带潮汐到上层周缘区域沿海岸深度梯度的日粮组成的变异性，并研究海藻的可利用性与潮间带潮汐池的日粮组成之间的关系。总共确定了118种食品，包括海藻和动物成分。饮食组成显示，沿研究的深度梯度存在的不同沿海生境之间存在很大差异。在潮池中，发出清晰的珊瑚海藻（Corallinaspp。），贻贝壳碎片和小的甲壳类动物常出现在肠道中，这表明该物种的行为像普通杂食动物一样，但在食用表生藻类和微真石质生物时也可以充当贻贝生物侵蚀者。在潮间带潮汐池中，该物种对连续演替后期的典型物种（如双歧线虫（Dictyota dichotoma），乌头腺囊虫（Adenocystis utricularis），脆弱的dium（Codium脆弱）和大角破软骨（Chondria macrocarpa））表现出负面偏好。。海带森林的海胆比潮间带和潮间带深海生境的海胆具有更高的饮食多样性，但海带盛行。在上层周缘软底部，肠道内容物中观察到底栖硅藻，蓝细菌和浮藻等多种碎屑，通常与细小沉积物有关，表明麦哲伦疟原虫捕获了浮藻并表现得像生物膜饲养者。这种营养可塑性可能使该物种占据相反的生境，也可能有助于解释其在南美洲南部的广泛分布。