Estimation of primary production of the waters around rack oyster farm at Wando, Korea
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To establish a comprehensive management strategy, as part of the optimization of cultural practice for an oyster rack culture system, we used a numerical model to estimate the primary production in the waters on the eastern coast of Wando island, South Korea. The estimated primary production ranged from 17.12 to 1052.55 mgC m−2 day−1 (204.22 ± 224.75 mgC m−2 day−1 in average). Except for the times of peak phytoplankton blooms, the estimated primary production (PP) was consistently under 200 mgC m−2 day−1, which is more similar to the value of PP measured off the western coast of South Korea than the southern coast. No clear relationship was observed between nitrogen content and rainfall with the exception of heavy rainfall events, indicating that precipitation might not be the main source of nutrients in these waters. No clear influence was observed from Doam tidal discharge, located 24 km north from these waters due to main tide comes in this area from the channel between Gunwe-myeon in Wando island and Pukpyeong-myeon in Haenam-gun. Because of the shallow water depth and strong tidal current, resuspension of sediments, which causes an input of nitrogen into the system, could be easily caused by even mild wind and the infrequent passing of ships. Microscopic examination of the phytoplankton composition showed additional contribution of benthic species such as Paralia sulcata into the waters, which increase the productivity of oyster farms in the waters. The availability of nitrate and phosphate for primary production was temporarily limited throughout most of the spring and autumn blooming season.
KeywordsPacific oyster Primary production Oyster rack culture Wando
Analysis of variance
Dissolved inorganic nitrogen
Dissolved inorganic phosphorus
Maximum sustainable yield
Oysters are suspension feeders that graze phytoplankton in the surrounding water column. This feeding behavior is facilitated by the cilia located on the gill filaments. These filaments generate water currents over the gills, select for food particles from the water column, transport food particles towards the mouth, and reject pseudofeces onto the mantle (Newell and Langdon 1996). Since the velocity field for feed behavior is highly restricted within organism’s microenvironment (Uslu and Pekkan 2016), primary production could be a key factor in determining the productivity of oyster farms.
The present study site is located on the tidal flat of the eastern coast of Wando, which is positioned in narrow waterway between Wando and Gogeum Island. This area was previously well known for Porphyra aquaculture. Annual production in this region accounted for ~ 22% of national production in South Korea; however, an environmental change linked to changing demographic and industrial development means that Porphyra aquaculture has ceased in the tidal flats in Wando (Lee 2006; Han and Cho 2013). As an alternative fishery in the tidal flats, oyster rack culturing was introduced as a pilot project in 2013 (Cho et al. 2013a). Here, we optimized several conditions to achieve the maximum sustainable yield (MSY) in these oyster rack cultures (Han and Cho 2013).
To ensure the successful management of oyster culture, many factors must be considered, but primary production is one of the most vital to achieving the MSY. Since oysters are filter feeders that rely solely on the surrounding environment as an energy source, an accurate estimation of primary production (PP) is essential to evaluate the potential yields in oyster farm (Lee et al. 1991). In this study, we estimate the PP to optimize the cultural practices (e.g., cultural density, nursery technique) that can yield crucial information on the best practices for managing an oyster farm.
Estimation of primary production
To estimate primary production, a numerical model was developed to predict photosynthetic rate from water temperature, solar irradiation, and chlorophyll-a content (Jeong et al. 2009). The model is briefly described below.
Solar irradiance and attenuation coefficient (k)
Relationship between irradiation, water temperature, and photosynthesis
Primary production was estimated following Steemann Nielsen (1975) using a hyperbolic function between irradiation and photosynthetic rate, which was saturated from 20.6 × 1015 to 90 × 1015 quanta cm−2 s−1 at 20 °C. The saturation point of the hyperbolic relationship increases with increasing water temperature (Steemann Nielsen 1975). Here, the relationship was modified to a biquadratic model between water temperature and saturated irradiation.
Daily primary production
All data were represented, and estimated PP data were analyzed using ANOVAs to characterize spatial distribution. Post hoc analyses were carried out using the Tukey test with a 95% significance level.
Results and discussion
Precipitation can influence the success of oysters (Calvo et al. 1999; Soletchnik et al. 2007), and the input of freshwater can increase PP in coastal waters by the input of land-driven nutrient into the coastal region (Choi et al. 1997). However, no significant regression was observed between salinity and precipitation (P > 0.05) in the present study, which indicates that rainfall is not the main contributor of nutrients to the studied waters. The relatively consistent salinity (30–33 psu) might be influenced by the input of freshwater from adjunct land areas.
The major source of freshwater near the study site is effluent from the tidal gate at Doam-myeon, located ~ 24 km north of the study area. An analysis of tidal residual flow indicates that the effluent from the tidal gate flows mainly out toward Deukryang Bay (Lee and Park 2006), which is located across the channel between Gogeum Island and Maryang-myeon in Gangjin-gun. This flow pattern of the effluent could prevent an abrupt change in salinity after a large rainfall event, which could cause a mass mortality of the rack oyster cultures. The tide with the greatest channel influence on the study area comes from the channel located between Gunwe-myeon in Wando and Pukpyeong-myeon in Haenam-gun, and this waster is weakly mixed with the tide from the Doam effluent between Goma and Sahoo Island.
Pearson correlations coefficients between water qualities
According to the generalized equation for photosynthesis reported by Odum (1971), the availability of nitrate and phosphate for primary production was temporarily limited during the spring and autumn blooming season (Fig. 3). The nutrient availability was limited to a much greater degree in 2012 than in 2011. The hydrodynamic and geological features of this region contribute to the low availability of nutrients in these wasters. The majority of freshwater from the discharge of tidal gate was mostly flowed out toward Deukrayng Bay, meaning that most land-derived input of freshwater in this region consists of runoff, stream water, and hatchery discharge. However, the nutrient load of adjacent basin did not significantly affect the water quality in the study area, as the pollution load showed half dilution within a radius of 300 m (Kang et al. 2015).
Despite the studied waters being located in semi-enclosed ria coast surrounded by several islands, hydrodynamic and geological features make the waters in this area favorable to oyster farming with relatively higher PP. Sediment resuspension might contribute nutrients input that enhance primary production, which satisfied the nutrient demand during the times when phytoplankton blooming are absent; however, during the spring and autumn when phytoplankton blooms occur, this process cannot provide sufficient nutrients for PP due to insufficient nutrient input from the adjacent basin and terrestrial sources.
We wish to acknowledge the fish farmers in Yeongheung-ri Wando for allowing us to use their tidal flat farming ground and their assistance throughout the study.
This research was a part of the project titled “Development of sustainable aquaculture techniques for tidal flat oyster” funded by the Ministry of Oceans and Fisheries, Korea.
Availability of data and materials
WGJ and SMC designed the study. WGJ carried out the model for primary production. SMC carried out the field survey and drafted the manuscript. Both authors read and approved the final manuscript.
Experimental protocols followed the guidelines of the Animal Care and Use Committee of Kunsan National University.
Consent for publication
Both authors declare that they have no competing interests.
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
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