Abstract
Eurythenes S. I. Smith in Scudder, 1882 are one of the largest scavenging deep-sea amphipods (max. 154 mm) and are found in every ocean across an extensive bathymetric range from the shallow polar waters to hadal depths. Recent systematic studies of the genus have illuminated a cryptic species complex and highlighted the benefits of using a combination of morphological and molecular identification approaches. In this study, we present the ninth species, Eurythenes plasticus sp. nov., which was recovered using baited traps between the depths 6010 and 6949 m in the Mariana Trench (Northwest Pacific Ocean) in 2014. This new Eurythenes species was found to have distinct morphological characteristics and be a well-supported clade based on sequence variation at two mitochondrial regions (16S rDNA and COI). While this species is new to science and lives in the remote hadal zone, it is not exempt from the impacts of anthropogenic pollution. Indeed, one individual was found to have a microplastic fibre, 83.74% similar to polyethylene terephthalate (PET), in its hindgut. As this species has a bathymetric range spanning from abyssal to hadal depths in the Central Pacific Ocean basin, it offers further insights into the biogeography of Eurythenes.
Highlights
While the deep sea is one of the largest ecosystems on Earth, it has traditionally been perceived as a homogenous environment, with few barriers to gene flow (Madsen 1961; Charette & Smith 2010)
We examined the morphological characteristics and sequence variation at the mitochondrial 16S ribosomal DNA (16S) and cytochrome oxidase I (COI) regions of Eurythenes specimens collected from hadal depths in the Mariana Trench, Pacific Ocean and considered their taxonomic placement within the gryllus-complex
As a scavenger at upper hadal depths (6010 – 6949 m) in the Mariana Trench, E. plasticus sp. nov. is not exempt from ingesting microplastics that are bioavailable within the hadal zone
Summary
While the deep sea is one of the largest ecosystems on Earth, it has traditionally been perceived as a homogenous environment, with few barriers to gene flow (Madsen 1961; Charette & Smith 2010). The deep sea, has a high degree of topographic complexity including mid-oceanic ridges, submarine canyons, seamounts, and subduction trenches, which could act as barriers. These barriers potentially restrain gene flow and promote allopatric speciation (Palumbi 1994). Our initial understanding of E. gryllus as a single cosmopolitan deep-sea species is reconceptualised when viewed as a species-complex This provides a much more nuanced picture of their distribution, amphitropical at bathyal depths, and reveals a patchwork of distribution patterns with the complex’s radiation.
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