Alone in the dark: Distribution, population structure and reproductive mode of the dominant isopod Eurycope spinifrons Gurjanova, 1933 (Isopoda: Asellota: Munnopsidae) from bathyal and abyssal depths of the Sea of Japan

• Published in: Deep-sea research. Part II, Topical studies in oceanography Vol. 86-87; pp. 103 - 110
• Main Authors: Elsner, Nikolaus O., Golovan, Olga A., Malyutina, Marina V., Brandt, Angelika
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01-02-2013
• Subjects: Asellota; Biodiversity; Eurycope; Eurycope spinifrons; Fecundity; Isopoda; Marine; Munnopsidae; Population structure; Sea of Japan; INW, Japan Sea; Sea of Japan; Population structure; Eurycope spinifrons; Biodiversity; Fecundity
• ISSN: 0967-0645; 1879-0100
• DOI: 10.1016/j.dsr2.2012.07.043

Due to isolation and a period of severe anoxic conditions in geologically recent times, biodiversity is low in the deep Sea of Japan. Among a small group of species inhabiting depths below 2500, only one isopod species, Eurycope spinifrons, was found during the SoJaBio expedition in 2010, but it was the most abundant species of all benthic taxa. E. spinifrons was found with remarkably high numbers of individuals at the sampled stations below 2500m, providing a rare opportunity to investigate aspects of population structure and reproduction of a deep-sea isopod. The distribution, population structure, fecundity and depth dependent density of E. spinifrons were studied. Brooding females were the longest in body size and least abundant, while mancae were the shortest and most abundant. The mean length of individuals showed little deviation among the stations below 2500m, ranging from 4.21±0.29mm in brooding females to 1.20±0.26mm in free-living mancae. Iteroparity is demonstrated for E. spinifrons. It is argued that females have continuous reproduction which increases in the summer. The length of the brooding females is positively correlated with the number of eggs in the marsupium in our sample (r=0.291; p<0.05). Comparing the mean length of E. spinifrons between different stations revealed that specimens sampled at the upper slope (460m) were significantly smaller in every developmental stage than those from stations below 2500m. This finding confirms the existence of a threshold depth below which E. spinifrons was the only isopod species found. Thus, we argue that individuals at deeper stations grow bigger due to reduced competition in the deep Sea of Japan.