Sand banks contribute to the production of coastal waters by making a habitat for benthic microalgae in the sublittoral zone: food web analyses in Aki-Nada using stable isotopes

Abstract

There are many sand banks in Seto Inland Sea, making patchy shallow zones less than 10 m deep. Due to the shallow environment, the surface sediment on the sand banks in the Hojo area, in the southern part of Aki Nada, Shikoku Island, Japan, often has a larger amount of benthic microalgae than other areas. We hypothesized that benthic microalgae contributed to the secondary production of coastal waters around sand bank areas, and investigated the food-web structure of the Hojo area using stable isotopes in early summer, mid summer and fall. Mean carbon isotopic signatures of several consumers in early summer (Ϫ16.9 to Ϫ15.1‰ for polychaeta; Ϫ17.3 to 13.9‰ for brachyuran crabs; Ϫ17.2 to Ϫ15.3 for fish) and fall (Ϫ16.2 to Ϫ14.3‰ for shrimps; Ϫ14.0 to Ϫ11.2‰ for brachyuran crabs) were more enriched than that of the particulate organic materials of the surface water around sand banks (mainly phytoplankton) (Ϫ20.5Ϯ0.0‰ in early summer and Ϫ18.3Ϯ0.1‰ in fall). Organic materials attached to cobbles, representative of benthic microalgae, showed similar or more enriched signatures than consumers (Ϫ14.7Ϯ0.0‰ in early summer and Ϫ10.3Ϯ0.0‰ in fall). These results suggest that benthic microalgae on the sand bank contribute greatly to the secondary or higher production of coastal waters in Hojo area.

Photosynthetic property and primary production of phytoplankton in sublittoral sand bank area in the Seto Inland Sea, Japan

“…The ratios of fish catch to primary production calculated for our study area were high compared to other studies such as 1.8% in the Seto Inland Sea (Uye et al 1987) and 1.2% in the North Sea (Steele 1974), although fish catch is not necessarily equal to fish production. In sublittoral areas, benthic algae attached on the sand banks have been suggested to contribute substantially to the production (Yoshino et al 2006). Stable isotope analyses by Yoshino et al (2006) suggested that fishes were sustained by benthic algae through polychaetes in the study area.…”

“…In sublittoral areas, benthic algae attached on the sand banks have been suggested to contribute substantially to the production (Yoshino et al 2006). Stable isotope analyses by Yoshino et al (2006) suggested that fishes were sustained by benthic algae through polychaetes in the study area. Benthic algae were observed in the gut contents of many polychaete species in the Hojo area (Fukumoto 2000).…”

“…On a smaller scale, little is known for production in specific topographic structures such as sand banks. Stable isotope analyses by Yoshino et al (2006) showed that benthic algae attached on sand banks can contribute considerably to the coastal production. In this study, we estimated primary production of phytoplankton in a sand bank area by measuring the photosynthetic-light intensity (P-I) relationships of phytoplankton.…”

“…The Seto Inland Sea is the largest semienclosed coastal sea in Japan and is known as a treasury of fishery resources (Hashimoto and Takeoka 1998). There are a number of sand banks in the Seto Inland Sea, making patchy shallow zones less than 10 m deep (Yoshino et al 2006). Sand banks have long been viewed as important fishery grounds (e.g.…”

Distribuição espacial da biomassa microfitobentônica no perfil batimétrico da região de Ubatuba, SP

“…O microfitobentos desempenha um importante papel na cadeia trófica, servindo como fonte alimentar para o meiobentos, foraminíferos e algívoros, formando assim uma das bases da teia alimentar, que alcança os níveis mais altos do macro e megabentos, como crustáceos e gastrópodes que pastejam e processam o sedimento epibentônico. Portanto, é necessário o conhecimento da distribuição microfitobentônica para entender melhor a distribuição dos taxa algívoros e demais níveis tróficos (Sundbäck & Person, 1981;Montagna, 1984;Santos et al, 1995;Miller et al, 1996;Macintyre et al, 1996;Gillespie et al, 2000;Pellizzari et al, 2005;Eichler et al, 2006;Yoshino et al, 2006;Netto et al, 2007;Ubertini et al, 2012).…”