[A-CG53] Coastal Ecosystems - 1. Water Cycle and Land-Ocean Interactions

[ACG53-P01] Development of measurement method for bio-irrigation by burrowing shrimp and its evaluation in aquaria

*Keisuke Takeno¹, Makoto Yamada², Ryo Sugimoto³, Yumi Henmi¹ (1.Maizuru Fisheries Research Station Field Science Education and Research Center, Kyoto University , 2.Faculty of Economics, Ryukoku University, 3.Faculty of Marine Science and Technology, Fukui Prefectural University)

Keywords:crustacean, burrow, tidal flat, material cycle, active irrigation

Material cycling between the sediment and the water column is important for nutrient supply to shallow water areas, specifically in tidal flats. One of the factors causing this material cycle is the transport of materials by Submarine Groundwater Discharge (SGD). Recirculated SGD accounts for more than 90% of all SGD and is reported to enhance material transport in coastal areas. Tidal flats are characterized by many burrows formed by benthic organisms such as polychaetes and crustaceans, which facilitate water exchange through their burrows (bio-irrigation). In particular, deep burrows constructed by large crustaceans may have a significant impact on the material cycle in coastal areas as a part of recirculated SGD. However, the influence of bio-irrigation on material circulation in shallow water areas remains poorly understood due to the absence of an established method for quantitative assessment in the field. It has been reported that bio-irrigation can be classified into “passive irrigation”, which is induced by environmental factors such as tidal changes, and “active irrigation”, which is caused by the behavior of the host organism. Therefore, these two types of bio-irrigation need to be measured separately to evaluate the impact of bio-irrigation accurately. A method has been previously developed to measure only the passive irrigation among the two types of bio-irrigation in the field. This study aims to develop a method to measure active irrigation in the field. In addition, its reliability will be validated through controlled aquarium experiments.
We developed a method for measuring bio-irrigation by applying the Granier method, which is used to measure SGD. First, a Granier-type flowmeter was constructed by using a Raspberry Pi Pico microcontroller. The device was then calibrated using a custom- designed apparatus with adjustable flow rates, creating calibration curves to measure bio-irrigation. Active irrigation can be categorized into two types: steady water flow through activities such as respiration and sudden water flow caused by activities such as feeding. Accordingly, calibration curves suitable for these two types of active irrigation need to be developed. We used Neotryoaea japonica, a species of burrowing shrimp, and kept it in a custom-made acrylic aquarium (20×8×60 cm³). The Granier-type flowmeter was installed at the burrow opening formed in the aquarium to measure water flow rates out of the burrow.
In this study, we present the development of the Granier-type flowmeter and its application in measuring active bio-irrigation through burrows in aquariums. Finally, we evaluate its efficacy in quantifying active irrigation based on measurement results.