10:45 AM - 12:15 PM
[AHW18-P14] Spatial distribution of free-living nematodes in a brackish lake–Lake Ogawara, Japan
Keywords:Brackish Lake, Environmental indicator, Meiobenthos, Nematoda, Spatial distribution
Benthic organisms sieved to a size of 1 mm-42 µm are called meiobenthos. Meiobenthos play key roles in benthic ecosystems as consumers of bacteria and detritus, and as a food source for macrobenthos and fish. In other words, the sequence of detritus→bacteria →meiobenthos is the primary pathway of energy transfer in benthic ecosystems. In general, free-living nematodes (“nematodes”) are the most abundant among meiobenthos in terms of quantity and biomass, with 60%-95% of meiobenthos taxa and 50%-90% of their biomass composed of nematodes (Giere 2009).
Nematodes are widely distributed from marine to terrestrial waters. However, studies of nematodes in brackish lakes are scarce worldwide, and their species composition and distribution are not well understood. The distribution of nematodes varies with the environment and is intricately intertwined with environmental factors. Therefore, nematodes are considered an effective group of animals as environmental indicators and for monitoring environmental changes. While a few studies have been done on the relationship between nematode species and environmental conditions, the feeding type index(FT-index) of nematodes and the Maturity Index (MI) have been considered to be useful in assessing anthropogenic effects (Ridall and Ingels 2021). This indicator is still used today because of its simplicity, and there are few general-purpose indicators other than the FT-index and MI due to the lack of information on nematode biology. Therefore, the purpose of this study was to obtain basic data on the distribution of nematodes in a brackish lake.
The brackish lake studied was Lake Ogawara, Aomori Prefecture, which is a cool-temperate climate and is located in the northernmost part of the main island of Japan. In the Lake Ogawara, the deterioration of water a quality due to eutrophication, and the decrease in the catch of inland fisheries such as Corbicula japonica have become problem. Surveys were conducted in Sep. 2022, and surface sediment (-3 cm) was collected from 36 points throughout the Lake. The collected sediment samples were brought back to the lab and stored at -80°C. Nematodes in the samples were extracted by density separation and the washing methods, and identified to the family level by morphological observations with an optical microscope.
The population density of nematodes in Lake Ogawara ranged from 1-408 inds. /10cm2. The species composition differed greatly between the southern and northern parts of the lake, likely influenced by salinity, water depth, sulfide concentration, and sediment composition. The population density of nematodes decreased significantly at depths deeper than 12 m. At the time of the survey, a halocline was formed around 12 m, below which dissolved oxygen concentration was almost 0 mg/l and sulfide concentration exceeded 1 mgS/L. Therefore, the distribution of nematodes is considered to be affected by a halocline. This is the first study on the spatial distribution of free-living nematodes in an oligo/mesohaline brackish lake ecosystem.
Acknowledgement: This work was supported by JSPS KAKENHI Grant Number 22H02479.
Nematodes are widely distributed from marine to terrestrial waters. However, studies of nematodes in brackish lakes are scarce worldwide, and their species composition and distribution are not well understood. The distribution of nematodes varies with the environment and is intricately intertwined with environmental factors. Therefore, nematodes are considered an effective group of animals as environmental indicators and for monitoring environmental changes. While a few studies have been done on the relationship between nematode species and environmental conditions, the feeding type index(FT-index) of nematodes and the Maturity Index (MI) have been considered to be useful in assessing anthropogenic effects (Ridall and Ingels 2021). This indicator is still used today because of its simplicity, and there are few general-purpose indicators other than the FT-index and MI due to the lack of information on nematode biology. Therefore, the purpose of this study was to obtain basic data on the distribution of nematodes in a brackish lake.
The brackish lake studied was Lake Ogawara, Aomori Prefecture, which is a cool-temperate climate and is located in the northernmost part of the main island of Japan. In the Lake Ogawara, the deterioration of water a quality due to eutrophication, and the decrease in the catch of inland fisheries such as Corbicula japonica have become problem. Surveys were conducted in Sep. 2022, and surface sediment (-3 cm) was collected from 36 points throughout the Lake. The collected sediment samples were brought back to the lab and stored at -80°C. Nematodes in the samples were extracted by density separation and the washing methods, and identified to the family level by morphological observations with an optical microscope.
The population density of nematodes in Lake Ogawara ranged from 1-408 inds. /10cm2. The species composition differed greatly between the southern and northern parts of the lake, likely influenced by salinity, water depth, sulfide concentration, and sediment composition. The population density of nematodes decreased significantly at depths deeper than 12 m. At the time of the survey, a halocline was formed around 12 m, below which dissolved oxygen concentration was almost 0 mg/l and sulfide concentration exceeded 1 mgS/L. Therefore, the distribution of nematodes is considered to be affected by a halocline. This is the first study on the spatial distribution of free-living nematodes in an oligo/mesohaline brackish lake ecosystem.
Acknowledgement: This work was supported by JSPS KAKENHI Grant Number 22H02479.