Department of Biology, University of Washington, Seattle, WA 98195, USA.
Department of Marine Sciences, Central Campus, Des Moines, IA, 50309, USA.
Integr Comp Biol. 2023 Dec 29;63(6):1285-1297. doi: 10.1093/icb/icad125.
Cephalopods are among many marine animals that through some combination of habit and/or habitat have proven difficult to study, especially understanding their trophic positions in marine communities. Stable isotope analyses have provided powerful tools for discovering quantitative aspects about the ecology and food sources of many cephalopod species. Here, we present new gut content and isotopic data (carbon and nitrogen isotopes) from phragmocone-bearing cephalopods (both ectocochleates, as well as those with internal, hard part buoyancy maintenance apparatuses). To this, we also include observations from baited remote underwater video systems to describe feeding habits and potential prey types to correlate with gut contents analyses. These data come from extant Allonautilus, Nautilus, and Sepia species, as well as from extinct nautiloids and ammonites. Extant nautiloids occupy a different isotopic niche than all other cephalopod groups where such data have been published to date. We conclude that these species are obligate scavengers rather than predators on any living species in their environments. Extant Nautilus and Allonautilus also demonstrate different patterns of functional allometry of nitrogen isotope values over ontogeny than do most other cephalopods (or animals in general), by showing decreasing nitrogen isotope levels during ontogeny. This pattern is shown to be different in Sepia and the yet small number of ammonite cephalopods studied to date, supporting the increasingly accepted view that ammonites were far closer to coleoids in basic biology than nautiloids. Overall, phragmocone-bearing cephalopods appear fundamentally different ecologically than cephalopods without this kind of buoyancy system. Of these groups, nautiloids appear to live a low-energy existence that allows them to subsist on energy-poor food sources, such as crustacean molts, as well as being able to scavenge in low oxygen basins where rare food falls, such as dead fish, remain unobtainable by most other animals.
头足类动物是许多海洋动物中的一种，它们由于某种习性和/或栖息地的结合，被证明难以研究，尤其是难以了解它们在海洋群落中的营养地位。稳定同位素分析为发现许多头足类物种的生态学和食物来源的定量方面提供了有力的工具。在这里，我们提出了来自带有角质层的头足类动物（包括外耳动物以及具有内部、硬体浮力维持器官的动物）的新的肠道内容物和同位素数据（碳和氮同位素）。此外，我们还包括了诱饵远程水下视频系统的观察结果，以描述摄食习惯和潜在的猎物类型，以便与肠道内容物分析相关联。这些数据来自现存的 Allonautilus、Nautilus 和 Sepia 物种，以及已灭绝的鹦鹉螺和菊石。现存的鹦鹉螺占据了与迄今为止发表的其他头足类动物不同的同位素生态位。我们得出的结论是，这些物种是强制性的清道夫，而不是它们环境中任何活体物种的捕食者。现存的 Nautilus 和 Allonautilus 在个体发生过程中也表现出不同于大多数其他头足类动物（或一般动物）的氮同位素值功能异速生长模式，即在个体发生过程中氮同位素水平逐渐降低。这种模式在 Sepia 和迄今研究的少数几种菊石头足类动物中表现不同，这支持了越来越被接受的观点，即菊石在基本生物学上与头足类动物的关系远比与鹦鹉螺类动物的关系更密切。总的来说，带有角质层的头足类动物在生态上与没有这种浮力系统的头足类动物有根本的不同。在这些群体中，鹦鹉螺类动物似乎过着低能量的生活，能够以能量贫乏的食物来源为食，如甲壳类动物蜕皮，并且能够在很少有食物落下的低氧盆地中进行清道夫活动，这些食物对大多数其他动物来说是无法获得的。
