Oceanological and Hydrobiological Studies International Journal of Oceanography and Hydrobiology Volume 49, No. 1, March 2020 ISSN 1730-413X pages (34-48) eISSN 1897-3191 Dominant species drive seasonal dynamics of the sh community in the Min estuary, China by Abstract Fishery resources are currently facing multiple stresses Jun Li, Bin Kang* such as over shing, pollution and climate change. Looking into processes and mechanisms of the dynamic sh community through detailed quantitative analyses contributes to e ective conservation and management of shery resources. The Min estuary plays an important role in maintaining sheries in southeastern coastal China, therefore the sh community in the brackish area was investigated and analyzed in this study. A total of 127 DOI: 10.1515/ohs-2020-0004 species belonging to 91 genera, 49 families and 14 orders Category: Original research paper were sampled in 2015. Eight indices re ecting four aspects of sh communities were determined, i.e. species richness, Received: May 5, 2019 species evenness, heterogeneity and taxonomy. Di erences Accepted: August 21, 2019 between the indices were nonsigni cant, suggesting that the use of a single diversity descriptor could not provide a full explanation. Nine dominant species in the Min estuary showed seasonal turnover by rational use of resources and Jimei University, 185 Yinjiang Rd., co-occurring species showed correspondingly adequate 361021 Xiamen, China habitat preferences and feeding habits to avoid competition. The species Harpadon nehereus occurred as the dominant species in three seasons except spring. High values of niche overlap among common or rare species and lower values of niche overlap among all dominant species e ectively brought the diversity of the sh community into a state of equilibrium. Key words: composition, diversity, ecological niche, interspeci c competition, migration * Corresponding author: bkang [email protected] The Oceanological and Hydrobiological Studies is online at www.oandhs.pl ©Faculty of Oceanography and Geography, University of Gdańsk, Poland. All rights reserved. Oceanological and Hydrobiological Studies, VOL. 49, NO. 1 | MARCH 2020 35 Fish community in the Min estuary Introduction Species of a given assemblage constituting the largest biomass in an ecosystem is considered a China has one of the longest coastlines in the dominant species that can affect the distribution of world, stretching over 14 500 km from the border other organisms and define that ecosystem and its with North Korea in the north to Vietnam in the south characteristics. A dominant species may be more (Liu 2013). Estuaries with mixed waters constitute effective in obtaining resources, resisting disturbance a complex of different habitat types with sudden or deterring competitors compared to other species changes in temperature, salinity and depth, and are (Miller et al. 2015). In addition, information on spatial regarded as feeding grounds and nursery areas for niche overlap and segregation among species is both migrant and resident species (Blaber 1997; Elliott essential for further understanding the population et al. 2007; Kerr et al. 2010; Potter et al. 2015), thus structure and dynamics (Cohen 1977; Navarro et al. supporting high levels of fisheries (McLusky & Elliott 2013). Species with similar habitat preferences tend 2007). Meanwhile, estuaries are also excellent sites for to engage in biological interactions and co-occur people to live and access to rivers and oceans helps to together ( Mahon et al. 1998; Tews et al. 2003). Spatial develop trade and communication. As anthropogenic patterns of fish movement can be determined by a impact continues to spread, it is crucial to improve number of factors, including the size of individuals the management of resources to protect and and modes of reproduction (Dunlop et al. 2009; preserve habitats and maintain ecosystem functions Enberg et al. 2010; Heino et al. 2015), interspecific and (Banks-Leite et al. 2014; Lundquist et al. 2017). intraspecific competition for resources (Shulman 1985; In response to oceanographic dynamics and Marshall & Elliott 1997; Svanbäck et al. 2008), habitat variation in solar irradiation, rainfall and wind composition ( Kamrani et al. 2016; Maree et al. 2016; conditions, estuaries show very strong environmental Polansky et al. 2018), and abiotic factors ( Bacheler et al, gradients, limiting some fish species to a particular 2009; Payne et al. 2013; da Silva Jr et al. 2016). However, section, which contributes to complex spatio-temporal knowledge of niche partitioning among sympatric fish patterns in fish communities (Nicolas et al. 2010; de species in estuaries has remained scarce. Moura et al. 2012; Basset et al. 2013). Furthermore, The Min estuary, located in the southeastern part of the sequential immigration and emigration of fish China, is a typical subtropical estuary. The complexity species for spawning, nursing and wintering result and variability of hydrodynamic characteristics of the in pronounced cyclical seasonal changes in the fish Min estuary attract many types of fish and make the fauna composition (Hoeksema & Potter 2006; Eick Min estuary an important fishery resource. The Min & Thiel 2014). Such complexity makes it difficult to estuary is currently an important economic area with manage and control sustainable fisheries and it is increasing industrialization, urbanization, population therefore necessary to understand the processes and growth and rapidly developing agricultural practices mechanisms of dynamic fisheries through detailed (Yue et al. 2015; Gao et al. 2017), which pose a major quantitative analysis of fish communities (Elliott & challenge to the ecological health of the estuarine Hemingway 2002; Franco et al. 2008). Some measures, ecosystem. However, there is still a substantial lack such as species composition, diversity, abundance of detailed information regarding the quantitative and biomass provide information on the structure of composition and seasonal variation of the fish fauna fish assemblages and corresponding environmental in the Min estuary, as well as the internal mechanism conditions, thus offering complementary insights as to how the structure is maintained. The main into fish assemblages for both theoretical and field objectives of the present work were: 1) to describe studies (Magurran 2004; Eick & Thiel 2014). In addition the composition and species diversity of the fish to the classic index, i.e. species richness and, to a lesser community; 2) to identify dominant species based on extent, species evenness, which continue to play a their abundance, biomass and seasonal turnover; 3) to dominant role as substitutes for diversity measures in explain the seasonal variation of the fish community many studies, the use of a multi-component diversity through interspecific relationships and ecological index should be encouraged to properly describe and niche overlap among dominant species. monitor the main components of species diversity, e.g. Margalef’s species richness, the Shannon– Materials and methods Wiener index, Pielou’s index, Heip’s evenness index, the Simpson concentration index, the taxonomic distinctness index, etc., in order to take full account Study area of the ecosystem functions at different management scales (Gaertner et al. 2010; Loiseau et al. 2016). The study was carried out in the brackish area ©Faculty of Oceanography and Geography, University of Gdańsk, Poland. All rights reserved. 36 Oceanological and Hydrobiological Studies, VOL. 49, NO. 1 | MARCH 2020 Jun Li, Bin Kang (25°50’00”–26°20’00”N; 119°30’00”–120°00’00”E) of and semi-diurnal, and salinity significantly increases the Min estuary (Fig. 1). The climate of the area is when the runoff drastically decreases (Fang et al. 2017). characterized by a typical subtropical monsoon with seasonal variations. The mean annual temperature is Sampling procedure 19.85°C with a range of 9.8–32.2°C (Hu et al. 2017). The mean annual discharge of the Min River is 1760 m3 s−1, Fish surveys were performed seasonally (May with a seasonally uneven distribution as a maximum in spring, August in summer, November in autumn value occurs in April–July (average 3200 m3 s−1) and a and February in winter) at 11 sampling locations in minimum in October–March (average 620 m3 s−1; Yang 2015 (Table 1). Bottom trawling was used (horizontal et al. 2007; Hu et al. 2014). The mean depth of the aperture 7.5 m, vertical opening height 3 m, deploy river is 3 m upstream and the maximum depth is 30 m distance 45 m, and mesh size 63 mm at the net downstream (Zhang et al. 2015). The tide is irregular opening and 25 mm at the cod end). The net was operated for half an hour at each sampling site at a towing speed of approximately 3.3–4.3 knots (corresponding to 6.02–7.85 km h−1) to collect fish. Samples from each site were put into an ice container by site groupings for preservation and sent to the laboratory for further analysis. Species were taxonomically identified according to the monographs “Fishes of the Fujian Province” (Part I, II; Fishes of the Fujian Province Editorial Subcommittee, 1984; 1985), and scientific names were checked against www. fishbase.org. At each site, the number of individual species was counted to determine their abundance and each species was weighted to determine the biomass. Data analysis Non-metric multi-dimensional scaling (nMDS) was performed on species biomass across sampling locations in the Min estuary. The resulting ordinations were examined for