Spatiotemporal variability in a copepod community associated with fluctuations in salinity and trophic state in an artificial brackish reservoir at Saemangeum, South Korea

Abstract

Saemangeum Reservoir in South Korea is an estuarine system enclosed by a dyke construction, where seawater inflow and retained water outflow are managed by the opening/closing of sluice gates installed in the southern part of the dyke. An exchange of the reservoir water can cause spatiotemporal fluctuations in the salinity and trophic state, which are major drivers determining variation in the composition of biological communities in estuarine systems. Here, we investigated the seasonal and spatial variability in the copepod community and environmental conditions (water temperature, salinity, transparency, chlorophyll a concentration, total nitrogen, total phosphorus and Carlson’s trophic state index) based on seasonally conducted field monitoring in the Saemangeum Reservoir from July 2013 to January 2018. In addition to the role of temperature, salinity and chlorophyll a concentration in structuring the copepod community and diversity, the biological indices of copepods with respect to salinity range and trophic state, were evaluated. The spatiotemporal variability in the salinity and trophic state variables showed contrasting patterns, and chlorophyll a concentration was negatively affected by salinity, indicating that the reservoir water was being highly exchanged with opening of the sluice gates. The mean trophic state index values, however, were constant in the eutrophic state (50―70). Dominant copepods were Acartia (A. hudsonica, A. sinjiensis, Acartia spp.) and Oithona (O. davisae and Oithona spp.), which are common species in eutrophic neritic water. Variation in the copepod community was mainly associated with the seasonal succession of the dominant species rather than a spatial gradient (from around the estuary to the sluice gates); however, site-specific differences in frequencies of several non-dominant species could be detected around the estuary (Sinocalanus tenellus) and the sluice gates (Centropages spp., Tigriopus spp. and Labidocera rotunda). The copepod diversity increased with species-richness from around the estuary to the sluice gates, which could result from variation in the site-specific location of non-dominant species. The frequency of particular species was also able to discriminate in terms of the salinity range (oligohaline: A. pacifica, S. tenellus and A. sinjiensis; mesohaline: Pseudodiaptomus inopinus; and polyhaline: C. abdominalis and Centropages spp.) and the trophic state (mesotrophic: C. abdominalis, Calanus sinicus and Centropages spp.; and hypereutrophic: S. tenellus, P. inopinus and Sinocalanus spp.). The findings from this study not only identify the factors determining spatiotemporal variation in the copepod community in the Saemangeum Reservoir, but also expand the applicability of copepods as biological indicators of conditions associated with salinity range and trophic state in other enclosed estuarine systems.

Application of Next-Generation Sequencing for the Determination of the Bacterial Community in the Gut Contents of Brackish Copepod Species (Acartia hudsonica, Sinocalanus tenellus, and Pseudodiaptomus inopinus)

“…Based on these feeding characteristics, target copepod species can influence the composition of gut bacterial community through their feeding activities. However, the composition of food environment may vary depending on the water quality factors such as salinity at each habitat [ 24 ], so if the food sources are changed, even if it is the same copepod species, the gut bacterial community can be also changed.…”

“…Compared with open systems (e.g., the coast), physicochemical properties such as seawater input, water current, and overall salinity distribution were regulated by the reservoir because of the construction of a dyke with sluice gates. This regulated environment allowed the tracking of relatively stable environmental gradients [ 24 ], and was suitable for monitoring copepod distribution, interaction with different environments, and the responses of the gut bacterial community. We extracted the gut contents from three copepod species ( Acartia hudsonica , Sinocalanus tenellus , and Pseudodiaptomus inopinus ) that had different adaptations to salinity.…”

Effects of cold storage and salinity on Acartia sinjiensis (Copepoda: Calanoida) egg hatching

“…The culture water was passed through a 300‐μm sieve, followed by a 40‐μm sieve. Acartia sinjiensis is a common species in coastal areas and estuaries (Choi et al, 2019; McKinnon et al, 2003), and previous studies have reported that up to 1000 individuals or more occur at salinities below 10 psu (Oda et al, 2018). This salinity was, therefore, selected as the lowest salinity of the experiment.…”

Kondisi plankton pada tambak ikan kerapu di Desa Mesjid Lama Kecamatan Talawi Kabupaten Batu Bara, Sumtera Utara

“…Selain berperan dalam struktur trofik di lingkungan perairan (López-Ibarra et al, 2018;Paujiah et al, 2013), Kopepoda juga berfungsi sebagai rantai penghubung antara fitoplankton dan tingkat trofik yang lebih tinggi (Sellner & Sellner, 2016). Kelimpahan dan sebaran kelompok Krustasea dipengaruhi oleh kondisi lingkungan perairan seperti suhu, salinitas dan ketersediaan pakan, sehingga kelimpahannya tidak tetap karena berkaitan dengan musim dan lokasi, serta sering dikaitkan dengan kesuburan perairan (Oda et al, 2018). Beberapa spesies Kopepoda pada umumnya melimpah pada perairan yang memiliki kandungan salinitas > 20 ppt (Mulyadi dan Murniati, 2017).…”