Genetic diversity, defined as the variety of alleles and genotypes within a population, represents the most fundamental level of biodiversity. Genetic diversity provides the raw materials for species’ evolution and adaptation, closely related to ecosystem processes and human well-being. However, with increasing human pressure and constant climate change, genetic diversity may be negatively affected. For example, since the Industrial Revolution, genetic diversity within populations of wildlife declined by 5.4% to 6.5%. Although conservation efforts are in full swing, global biodiversity conservation policies and actions have largely neglected to conserve and monitor genetic diversity. In the face of such a serious situation, there is an urgent need to understand the genetic diversity of marine life and develop conservation strategies.

A dataset of genetic diversity data is the initial step to deal with problems. Our knowledge regarding comprehensive genetic diversity studies remains insufficient, especially in marine realm. The China Seas, with their diverse climate zones, ecosystems, and coastal currents, boast one of the world’s richest marine biodiversity. In the past two decades, the majority of studies on genetic diversity of marine species in the China Seas primarily focused on small-scale geographical populations of one or a few species, and solely evaluated their genetic diversity, thus lacking a comprehensive summary. The integration of these empirical studies helps to inform the scope, strengths, and omissions of these works, which is crucial to adjust future goals and directions in time.

That's one of the main reasons we set out a dataset of genetic diversity studies in the China Seas. The process of compiling the dataset has not been smooth. The first thing to determined is the keywords of the literature search. With the help of my supervisor Gang, Ni, who  did meta-analysis work, literature search was relatively easy. Quality-control procedures were the most time-consuming process. Facing various publications with different aims, we had to encourage ourself to filter the publications according to the criteria we defined. Finally, the filtered publications accounted for 64.81%, and the dataset consisted of 746 published studies and 840 data sets, including 3658 populations across 343 species.

The status of genetic diversity in the China Sea  are shown as follows:

(1) Publications per year: The number of publications per year increased steadily from 1998 until 2012 and reached a plateau recently. Of these, more studies were published in Chinese (56.03%), while studies published in English accounted for 43.97%.

(2) Taxonomic groups studied: Fish, mollusk, and crustacean groups were the most representative taxonomic groups, accounting for 46.43%, 23.45%, and 14.76%, respectively; while the proportion of each other taxonomic group (e.g. plant, cnidarian, and mammal) was relatively small (no more than 5.24%). Representative species such as the small yellow croaker (Larimichthys polyactis), the hard-shelled mussel (Mytilus coruscus), the swimming crab (Portunus trituberculatus), and the Japanese mantis shrimp (Oratosquilla oratoria) were traditionally important economic fishery species.

(3) Molecular markers applied: According to the six classes of molecular markers we defined, Class I (mtDNA, mitochondrial DNA) was predominantly applied in all studies (47.14%) and also in most taxonomic groups, while the highly praised Class IV (SNP, single nucleotide polymorphism) accounted for a small proportion (4.05%).

(4) Sampling effort: Unbalanced geographic sampling was evident at both provincial and prefecture-city levels. The sampling was concentrated in several provinces, the top three sampled provinces were Shandong (17.71%), Zhejiang (14.63%), and Guangdong (11.92%) provinces. Within each province, some cities were found with extremely high sampled populations, such as Beihai (64.22%) in Guangxi, Qinhuangdao (56.60%) in Hebei, and Dalian (54.24%) in Liaoning. In addition, the high concentration of sampling within one population (27.73%) and three populations (51.55%) suggests an insufficient number of collected populations.

Thanks to the development of technology, increasing high-resolution population-level genetic data sets have been assessed at decreasing costs. At present, according to the dataset, genetic data only cover a small proportion of all marine species in the China Seas. We have to acknowledge that sampling is one of the important impact factors. Limited by high costs, decreasing fishery resources, weather sensitivity, and inconvenient transportation, sampling in the ocean is more challenging than sampling on land. These challenges may greatly impact the study of genetic diversity in the China Seas. The biases towards coastal waters of China and the traditionally important economic fishery species suggest that the need for strengthening the sampling effort of wild populations in the China Seas persists and it will require substantial time and effort to fill the spatiotemporal and taxonomic gaps.

With the increasing amount of genetic data today, it is expected to make full use of existing data by compiling the dataset in a convenient and accessible way. However, information of genetic diversity is not comprehensive in some publications. For example, most geographic coordinates of sampling are provided at the level of prefecture-level cities or provinces, without precise latitude and longitude, which will undoubtedly weaken the hinder of genetic data. This problem is not only in China but also worldwide. As called for, consensus and uptake standards for collection of genetic data still require more attention and improvement.

Although challenges remain, the information and views provided by the genetic data will help to accelerate joint sampling work, strengthen international cooperation, and promote conservation genetics. We sincerely hope to contribute to piecing a more comprehensive and convincing picture of genetic diversity worldwide.