Abstract
The East China Sea (ECS) off the Coast of Zhoushan Archipelago, Zhejiang
(ECS-CZA) is home to abundant fishery resources and an important
spawning, feeding, and nursing ground for a variety of fish species. Due
to long-term overfishing, the ichthyoplankton structure has been
dramatically altered. Understanding the species composition and
distribution of fish eggs and larvae is one of the most essential tasks
to accurately regulate fishery resources and formulate effective
management policies; however, little is known about the ichthyoplankton
in this region. In this study, an integrated strategy of morphology
identification (MI) and mitochondrial COI DNA barcoding were used to
identify species of fish eggs and larvae collected from the ECS-CZA. MI
revealed 15 fish egg species belonging to 12 families and 12 fish larva
species belonging to 12 families; in contrast, DNA barcoding altogether
identified 30 species, including 18 fish egg species and 13 fish larva
species. One species was shared between the egg and larva samples. Our
study offers useful tools and critical scientific information for
understanding the recruitment, distribution, and conservation management
of various fish species in this marine environment.
Keywords : Zhoushan Archipelago; ichthyoplankton; morphology;
DNA barcoding; recruitment; conservation management
Ichthyoplankton are characterized by species of fish eggs and larvae
during the early developmental stages of fish life history (Borja et al.
2018), and are the basis for the sustainable development of marine
resources and study of fish population dynamics. Understanding the
species composition and distribution of fish eggs and larvae is one of
the most essential efforts to accurately regulate fishery resources and
formulate effective fishery and conservation management policies (Ziober
et al. 2012). Though ichthyoplankton offers a precise evaluation of
species-specific spawning characteristics, egg and larva collection,
particularly the former is greatly neglected due to the limitations of
morphology-based identification.
Due to the insignificant morphological differences in fish eggs and
larvae, the power of morphological identification (MI) of
ichthyoplankton to the species level in terms of resolution is limited
to the life stage and quality of specimens. Recently, the over-reliance
on traditional morphology has lifted with more accurate and specific
criteria for variation (Lewis et al. 2016). New approaches developed in
the classification and identification of fish eggs and larvae include
allozyme (Turan et al. 2005), nuclear DNA (Imsiridou et al. 2007) and
mitochondrial DNA (Fraga et al. 2007). Especially, the DNA-based
molecular tool is efficient in terms of detection, resolution, and
coverage compared to morphology since fish eggs and larvae are cryptic
and difficult to identify through morphological diagnostic features.
DNA barcoding is a molecular technology that has broadly been used in
species identification and determination over the past decade. This
method allows for species identification by taking advantage of a gene
fragment shared by organisms with interspecies differences, e.g.,
mitochondrial cytochrome c oxidase subunit I, COI (Hebert and Gregory
2005; Overdyk et al. 2016). The COI gene is generally regarded as a
species barcode and used for identification in animals having recorded
many successes (Aquino et al. 2011; Zhang and Hanner 2011). For example,
a previous study barcode 26 fish species from 70 larvae samples from
Dongsha Islands, South China Sea (Chen et al. 2013).
The East China Sea (ECS) located in the West Pacific Ocean is surrounded
by China, South Korea, and Japan, and composed of one of the world
ocean’s widest continental shelves (Xu and Oda 1999), and provides
habitats to more than 440 fishes, including many ecologically and
economically important fishery species for spawning, feeding, and
nursery (Cheng et al. 2009). The ECS off the Coast of Zhoushan
Archipelago (ECS-CZA) is located at the openings of Yangtze, Qianjiang
and Yongjiang River and influenced by several ocean currents, including
the coastal current of Jiangsu-Zhejiang, cold water mass of the Yellow
Sea, and warm current of Taiwan. These factors contribute abundant
nutrition and support the most of marine fisheries in the ECS (Li et al.
2007). However, long-term overfishing has harmed the coastal marine
ecosystem in the past decades, and the ichthyoplankton structure has
been drastically altered (Liu 2013).
Despite the importance, little is known about the structure of
ichthyoplankton in the area. To better understand the status of
ichthyoplankton in the ECS-CZA, we used an integrated strategy of
morphology and DNA barcoding to assess the ichthyoplankton species
across the sea. Our findings will have immediate and practical
implications for the value of the study area, in terms of being
spawning, nursing, and feeding grounds for commercial fish species, and
for managing and protecting the ecosystem and its functionality for
supporting the ichthyoplankton community and regional fisheries.