DOI: 10.26650/ase.2026.1893232 ISSN: 2602-473X

Seasonal Niche Decoupling and Thermal Alignment of Two Co-occurring Ectoparasites (Diplectanum aequans and Lernanthropus kroyeri) in Cultured European Seabass, Dicentrarchus Labrax

Phan Quyet, Hijran Yavuzcan Yıldız
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Co-occurring ectoparasites represent a challenge in intensive aquaculture; however, quantitative tools to assess how parasite species partition their temporal niches remain limited. The seasonal dynamics of two coexisting gill ectoparasites, Diplectanum aequans and Lernanthropus kroyeri, infecting farmed European seabass (Dicentrarchus labrax) were evaluated using two complementary indices: a Seasonal Niche-Decoupling Index (D) and a standardized Thermal Alignment Score (S). The D index quantified temporal separation in parasite dominance, while S was defined as the Pearson correlation coefficient between seasonal parasite abundance and water temperature. Although both parasites were present year-round, their population dynamics exhibited contrasting seasonal patterns. D. aequans peaked in spring, whereas L. kroyeri predominated in winter, resulting in a pronounced but incomplete temporal separation (D = 0.483). Standardized thermal alignment analysis indicated that D. aequans exhibited a strong negative alignment (S = −0.76), whereas L. kroyeri showed a weak positive alignment (S = +0.19). These findings suggest that temporal niche partitioning may facilitate the coexistence of ectoparasites under continuous infection pressure in intensive aquaculture systems. Under projected warming scenarios, the seasonal window of D. aequans may contract, whereas L. kroyeri may expand its temporal niche. The applied indices provide a practical and transferable framework for evaluating seasonal parasite dynamics and may support improved parasite management strategies in aquaculture.

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