Trophic niche of the invasive gregarious species Crepidula fornicata, in relation to ontogenic changes

Crepidula fornicata is a common and widespread invasive gregarious species along the European coast. Among its life-history traits, well documented ontogenic changes in behavior (i.e., motile male to sessile female) suggest a potential shift in feeding strategy across its life stages. Considering the ecological significance of this species in colonized areas, understanding how conspecifics share the trophic resource is crucial. Using fatty acids (FA) and stable isotopes (SI) as complementary trophic markers, we conducted a field survey between late winter and spring to investigate the trophic niche of three ontogenic stages of C. fornicata that bear different sexual (male/female) and motility (motile/sessile) traits. Potential trophic sources were characterized by their pigment, FA and SI compositions and showed well discriminated compositions over the studied period. We showed that the biofilm covering C. fornicata shells harbored a higher biomass of primary producers (i.e., chlorophytes and diatoms) than the surrounding sediment. Over the studied period, we observed a covariation between the three ontogenic stages for both FA and SI compositions which suggest that the trophic niche of C. fornicata does not change significantly across its benthic life. During periods of low food availability, slipper limpets displayed an opportunistic suspension-feeding behaviour, relying on both fresh and detrital organic matter, likely coming from superficial sedimentary organic matter. However, during high food availability (i.e., spring phytoplankton bloom), all ontogenic stages largely benefited from this fresh supply of organic matter (pelagic diatoms in this case). The three ontogenic stages showed consistent differences in FA composition, and to a lesser extent in SI composition. These differences persist over time, as they originate from ontogenic physiological changes (differential growth rates, metabolic rate or gametogenesis) rather than diet discrepancies. This study revealed that multiple trophic markers allow high complementary to characterize organic matter as well as food partitioning between conspecific organisms.Crepidula fornicata is a common and widespread invasive gregarious species along the European coast. Among its life-history traits, well documented ontogenic changes in behavior (i.e., motile male to sessile female) suggest a potential shift in feeding strategy across its life stages. Considering the ecological significance of this species in colonized areas, understanding how conspecifics share the trophic resource is crucial. Using fatty acids (FA) and stable isotopes (SI) as complementary trophic markers, we conducted a field survey between late winter and spring to investigate the trophic niche of three ontogenic stages of C. fornicata that bear different sexual (male/female) and motility (motile/sessile) traits. Potential trophic sources were characterized by their pigment, FA and SI compositions and showed well discriminated compositions over the studied period. We showed that the biofilm covering C. fornicata shells harbored a higher biomass of primary producers (i.e., chlorophytes and diatoms) than the surrounding sediment. Over the studied period, we observed a covariation between the three ontogenic stages for both FA and SI compositions which suggest that the trophic niche of C. fornicata does not change significantly across its benthic life. During periods of low food availability, slipper limpets displayed an opportunistic suspension-feeding behaviour, relying on both fresh and detrital organic matter, likely coming from superficial sedimentary organic matter. However, during high food availability (i.e., spring phytoplankton bloom), all ontogenic stages largely benefited from this fresh supply of organic matter (pelagic diatoms in this case). The three ontogenic stages showed consistent differences in FA composition, and to a lesser extent in SI composition. These differences persist over time, as they originate from ontogenic physiological changes (differential growth rates, metabolic rate or gametogenesis) rather than diet discrepancies. This study revealed that multiple trophic markers allow high complementary to characterize organic matter as well as food partitioning between conspecific organisms.

履螺（Crepidula fornicata）是欧洲沿岸常见且广泛分布的入侵性群居物种。在其生活史特征中，已有充分记录的行为个体发育变化（ontogenic changes，即从活动的雄性转变为固着的雌性）表明，其摄食策略可能随生活阶段发生转变。考虑到该物种在被入侵区域的生态意义，了解同种个体如何共享营养资源至关重要。本研究以脂肪酸（FA）和稳定同位素（SI）作为互补的营养标记物，于晚冬至春季开展野外调查，旨在探究具有不同性别（雄性/雌性）和运动能力（活动/固着）特征的履螺三个个体发育阶段的营养生态位（trophic niche）。通过色素、FA及SI组成对潜在营养来源进行表征，结果显示研究期间各来源组成具有显著差异。研究发现，履螺贝壳表面的生物膜中初级生产者（primary producers，即绿藻和硅藻）的生物量高于周围沉积物。研究期间，三个个体发育阶段的FA和SI组成均存在共变关系，表明履螺在底栖生活期间的营养生态位无显著变化。在食物供应不足时期，履螺表现出机会性悬浮摄食行为（suspension-feeding behaviour），依赖新鲜和碎屑有机质为生，这些有机质可能来源于表层沉积有机质。然而，在食物供应充足时期（即春季浮游植物水华），所有个体发育阶段均能大量利用这一新鲜有机质供应（本研究中为远洋硅藻）。三个个体发育阶段的FA组成存在持续差异，SI组成的差异程度相对较小。这些差异随时间持续存在，其根源在于个体发育生理变化（生长速率差异、代谢速率或配子发生），而非饮食差异。本研究表明，多种营养标记物具有高度互补性，可用于表征有机质及同种生物间的食物分配。