Increase in Fish Production Through Bottom-Up Trophic Linkage in Coastal Waters Induced by Nutrients Supplied via Submarine Groundwater

Koji Fujita,Osamu Tominaga,Masaru Takeuchi,Makoto Taniguchi,Hisami Honda,Jun Shoji,Ryo Sugimoto,Toshimi Nakajima

doi:10.3389/fenvs.2019.00082

Abstract

Submarine groundwater is richer in nutrients compared to surface (river) water and therefore has been considered to be an essential component of biological production in marine coastal ecosystems. However, there has been no information on the effects of submarine groundwater on animals at high-order trophic levels. Here we show the first direct evidence that fish feeding and growth are elevated by submarine groundwater discharge (SGD) by on-site experiments and quantitative sampling. An experiment using cages moored on the sea bottom confirmed that the fishes obtained elevated levels of nutrition in the vicinity of SGD. Quantitative sampling at three sites with different hydrodynamic properties showed correspondence of high SGD with high biological production or biomass from producer to secondary consumers. These findings demonstrate nutrients of terrestrial origin provided via submarine groundwater in coastal areas promote marine fish production.

Highlights

Water flowing from the land to the marine coastal area is an essential component supporting the high biological production by supplying nutrients of terrestrial origin (Field et al, 1998)
First direct evidence that fish feeding and growth were elevated by submarine groundwater was obtained by an on-site experiment and quantitative samplings
The quantitative sampling at three sites with different hydrodynamic properties showed that correspondence of high submarine groundwater discharge (SGD) with high biological production from producer to secondary consumers prevails in coastal marine areas

Summary

Introduction

Water flowing from the land to the marine coastal area is an essential component supporting the high biological production by supplying nutrients of terrestrial origin (Field et al, 1998). Freshwater provided from terrestrial areas to coastal areas can be divided into surface water (river water) and groundwater. More studies have been undertaken on how variability in river waters affects biological production in marine ecosystems compared to groundwater supply influences (Moosdorf and Oehler, 2017). A high contribution of nutrients (e.g., 65% of total dissolved inorganic phosphorus (DIP) provided through all freshwater) has been estimated to be supplied via submarine groundwater, which is richer in nutrients, especially phosphorus (Sugimoto et al, 2016). Submarine groundwater is considered to have high potential for promotion of trophic flow in coastal ecosystems

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Conclusion