5:15 PM - 7:15 PM
[AOS15-P04] Environmental DNA of small pelagic fish was detected even in the deep ocean
Keywords:environmental DNA, small pelagic fish, vertical distribution, Northwest Pacific
Environmental DNA (eDNA) is a newly developed non-invasive survey method which has been used worldwide for ecological surveys of various kinds of creatures including marine fish. Nevertheless, the eDNA method also has its limitations. One of them is the accuracy of the eDNA method in determining the spatial location of the survey object, which is particularly important for small pelagic fish in the vast ocean. There are relatively more previous studies in the horizontal direction, while this study explores this problem in the vertical direction. The research targets here are Sardinops melanostictus and Engraulis japonicus in the Northwest Pacific.
Our research (seawater) samples came from two cruises (KS-18-5, KS-23-11) by Shinsei-Maru and KH-23-2 cruise by Hakuho-Maru. Water samples in KS-23-11 (July, 2023) and KH-23-2 (June, 2023) were collected from 0 m to 1000 m or 10 m above sea bottom when the bottom was shallower than 1000 m. Water samples in KS-18-5 (May, 2018) were collected from 0 to 300 m. Water samples were filtered by Sterivex filters (0.22 or 0.45μm) and the filters were stored at -30 °C, then DNA was extracted from the filter after the cruise. The environmental information was recorded by a CTD instrument.
Target small pelagic fish are believed to inhabit water layers above 200m deep, but surprisingly, their eDNA was even detected in some water samples as deep as 1000m. This means that the eDNA of the target fish has moved downward long distances.
There can be various reasons for this phenomenon, such as the sinking caused by negative buoyancy, transportation by vertical water currents, and indirect transportation by predators. This study combines eDNA with marine environmental data such as water temperature, dissolved oxygen, chlorophyll, etc., and proposes an environment-dependent sinking hypothesis to explain this phenomenon. The eDNA sinking curve constructed based on this hypothesis also relatively successfully explains the vertical distribution of target fish eDNA found in field surveys. Therefore, it can be expected that this study has important reference value for judging whether and how to determine the habitat location of small pelagic fish in a designated survey area through eDNA signals in the vertical dimension.
Our research (seawater) samples came from two cruises (KS-18-5, KS-23-11) by Shinsei-Maru and KH-23-2 cruise by Hakuho-Maru. Water samples in KS-23-11 (July, 2023) and KH-23-2 (June, 2023) were collected from 0 m to 1000 m or 10 m above sea bottom when the bottom was shallower than 1000 m. Water samples in KS-18-5 (May, 2018) were collected from 0 to 300 m. Water samples were filtered by Sterivex filters (0.22 or 0.45μm) and the filters were stored at -30 °C, then DNA was extracted from the filter after the cruise. The environmental information was recorded by a CTD instrument.
Target small pelagic fish are believed to inhabit water layers above 200m deep, but surprisingly, their eDNA was even detected in some water samples as deep as 1000m. This means that the eDNA of the target fish has moved downward long distances.
There can be various reasons for this phenomenon, such as the sinking caused by negative buoyancy, transportation by vertical water currents, and indirect transportation by predators. This study combines eDNA with marine environmental data such as water temperature, dissolved oxygen, chlorophyll, etc., and proposes an environment-dependent sinking hypothesis to explain this phenomenon. The eDNA sinking curve constructed based on this hypothesis also relatively successfully explains the vertical distribution of target fish eDNA found in field surveys. Therefore, it can be expected that this study has important reference value for judging whether and how to determine the habitat location of small pelagic fish in a designated survey area through eDNA signals in the vertical dimension.