Spatio-temporal characteristics of the fatty acid compositions of two macrobenthos (Nuttallia olivacea and Hediste sp.) in the Nanakita River estuary, Japan

This study examined species-specific, dietary responses of two benthic macroinvertebrate species, Nuttllia olivacea and Hediste sp., to spatial and seasonal variations of resource composition in an estuarine tidal flat system of north-eastern Japan. This study measured fatty acid (FA) composition of sedimentary organic matter and macroinvertebrate tissue to estimate relative contributions of organic matter originating from different sources. N. olivacea and Hediste sp. are predominated in macrobenthos communities of sandy and muddy sediments in the studied estuary, respectively. The total FA of sedimentary organic matter was significantly related positively to the total organic carbon (TOC) content of sediment. FAs of diatom, bacteria, and terrestrial–plant origins were found higher values in the sediments with higher TOC. The dietary composition of N. olivacea showed both spatial and seasonal variations, but was consistently linked with diatom, bacteria and dinoflagellates in the sediments. Meanwhile, the FA composition of Hediste sp. demonstrated that the diets of this species depended heavily on diatom, bacteria and terrestrial plant. From these results it was revealed that Hediste sp. was more tightly linked with sedimentary organic matter composition compared with N. olivacea. This result indicates that Hediste sp. has a euryphagic diet and is possible to feed on sedimentary organic matter of various sources in natural environments. Both macroinvertebrate species showed different characteristics in terms of using of food resources and its spatial and seasonal variation. It is considered that the difference in feeding dietary habit of macroinvertebrates is one of the important factors which decide the sediment suitability for macrobenthos.