DNA metabarcoding illustrates biological pollution threats of Red Sea - Dead Sea water conveyance to Dead Sea biodiversity
Introduction
Anthropogenic modifications of geological features such as the opening of the Suez Canal have considerably impacted the marine environment. That opening was followed by important species migration from the Red Sea to the Mediterranean, two bodies of water that differ hydrographically and in biodiversity (Golani, 1998). That Lessepsian migration promoted the establishment and spread of alien species, recognized as ‘biological pollution’ (Galil, 2012). The invasion of organisms has had a significant impact on the ecosystem of the Mediterranean Sea and also affected tourism, fisheries and coastal installations. Counting the macrophytes, invertebrates and fish, 443 species have been recorded to have entered through the Suez Canal (Galil et al., 2015). The various ecological changes reflect the results of human influences on the natural environment (Mavruk and Avsar, 2008). The present study will focus on a planned civil work in the same area that will put two different seas in contact again: Red Sea - Dead Sea Water Conveyance. The geophysicochemical divergence between the connected seas and the project goals of the Suez Canal compared to the Red Sea – Dead Sea Water Conveyance are i different, but the risk of biological pollution could be comparable, and will be studied in this work based on environmental DNA, eDNA.The Dead Sea, a hypersaline lake bordered by Jordan, Israel and the West Bank, is one of the world's saltiest bodies of water. With the surface and shore at 430 m below sea level, it is located on the lowest elevation on Earth. Its waters contain about 348 g/L total dissolved salts and have a pH of 6.0, harsh conditions even for the best salt-adapted microorganisms (Oren and Gunde-Cimerman, 2012). Anthropogenic intervention has severely disturbed its ecosystem mainly due to the diversion of the Jordan river. A comparison of the Dead Sea level between the beginning of the 20th and 21st centuries shows more than 25 m of level dropped (Gavrieli et al., 2005) and a drop rate exceeding 1 m per year in the last decade (Lensky and Dente, 2015). In fact, in 2008 the Dead Sea had already lost 33% of its surface area (Sharp, 2008). The dissolution of the salt layer by undersaturated groundwater has undergone the formation of numerous collapse sinkholes along the Dead Sea coast (Abelson et al., 2006) to a rate of 150–200 sinkholes per year (Yechieli et al., 2006).
Despite its name, the Dead Sea indeed contains life. The extreme geophysicochemical characteristics of this natural lake represent a unique habitat for extremophiles (Jacob et al., 2017). The microorganisms in the Dead Sea have been studied since the 20th century using culture-dependent method. The metagenomic analysis has been recently used to establish the diversity of the Dead Sea microbiota and to do its inventory with the use of the 16S ribosomal RNA. Prokaryotic sequences resulted to represent 97% of all sequences with 52% represented by Archaea and 45% by Bacteria (Jacob et al., 2017). A minor proportion of eukaryotes was also detected (3%) (Jacob et al., 2017). The Eukaryote community of the Dead Sea is composed almost exclusively of fungi and has been studied with enormous interest given their special adaptation to the extreme salinity. Recently, it has been seen that the community is retracting together with the water level. The turnover is very rapid. In only 15 years it decreased by 17 times (Perl et al., 2017). Inventories also revealed seasonal variations (Kis-Papo et al., 2001).
The Red Sea-Dead Sea Water Conveyance (RDSC thereafter) is a project that proposes to construct a pipeline of 180 km to save the shrinking Dead Sea using water from the Red Sea. The RDSC also plans to use the difference in elevation between the Red and Dead seas to produce desalinated water and hydroelectric power to improve livelihoods. While RSDS project will contribute to restore the Dead Sea as its original level, the addition of chemically different water will likely affect the chemistry of the sea (Qdais, 2008). Different environmental impacts will affect both sides of the pipeline. The mixing of seawaters could modify the water column stratification and the evaporation rate. Also, it will affect the composition of the Dead Sea brine (Gavrieli et al., 2005). Different studies were conducted to evaluate the impact of the proposed RDSC on the dead sea's limnology, geochemistry and biology (Gavrieli et al., 2002). Simulation experiments under field conditions to understand the biological effects of dilution of Dead Sea brine with seawater have developed massive blooms of the halophile green alga Dunaliella (Oren et al., 1995) as well as dense communities of red halophilic Archaea depending on the limiting phosphate availability (Oren et al., 2004; Bardavid et al., 2007).
The Gulf of Aqaba, also called the Gulf of Eilat where the Red Sea water will be taken for the conveyance, is located at the northern edge of the Red Sea. On the contrary of the Dead Sea, the Gulf of Aqaba exhibits an important species richness of fishes and coral reefs. The hydrographic parameters of the coastal water are 25.88 ± 1.14 (°C), 39.69 ± 0.19 (S‰) and a pH of 8.21 ± 0.01 (Abdel Halim et al., 2016). The Red Sea has a rich diversity with 1448 species belonging to 165 families recorded today (Froese, 2019).
This study based on eDNA presents the potentially harmful species found in the Red Sea that could enter the Dead Sea through the water conveyance due to their small size - they could pass the coarse filters. The species identification in the present study has been developed using the metabarcode COI gene in water samples taken in January 2019.
Section snippets
Water sampling
Water samples from the Gulf of Aqaba were collected on the 14th of January 2019 at three different sites (Fig. 1). Water samples from the Dead Sea were collected on the 25 and 26th of January 2019 at seven different sites (Fig. 1). The coordinates and location features are given in Table 1. Every site was separated by a minimum of 800 m to the next one. Three filter samples were collected at each site. Each sample was 10 syringes of 100 ml of water. Thus, a total of 1 L of water per filter was
Efficiency of the eDNA extraction, HTS and bioinformatics
Prior DNA extraction, the number of Dead Sea samples was 21 (7 sites, 3 samples per site) and the Red Sea samples were 9 (3 sites, 3 samples per site). For each site, the 3 replicates are identified as A, B and C. The DNA quantification revealed a low concentration of DNA in some samples. Samples taken from the same site with low DNA were combined and quantified again. If the DNA concentration was under 0.050 ng/μL they were excluded from the study. Therefore, sites 1 and 2 of the Dead Sea were
Discussion
The present study shows an important contrast in the biodiversity of the Red Sea and the Dead Sea detected through eDNA, consistently with their very different environments and known biota inventories. Fish species won't be able to pass the filters of the water conveyance from the Red Sea to the Dead Sea, planktons, fungi and seeds might be able to enter the Dead Sea and impact the ecosystem. Some prejudicial species may enter the Dead Sea after the conveyance because they are present in the
Conclusion
Using eDNA metabarcoding from small volumes of water samples (1 L) and three sites in the Red Sea and seven in the Dead Sea, 69 and 13 species respectively were identified, although non-fungi Dead Sea species belong to run-offs from other sources. Amongst Red Sea species, many of them are potentially harmful for the Dead Sea ecosystem. The RSDS water conveyance project will modify the hydrographic parameters making hard to anticipate the impact. Further studies are needed to address the
Funding
This work was supported by the Government of Asturias (Spain) with the grant number IDI-2018-000201, and the Ministry of Science and Innovation with the grant PID2019-108347RB-I00.
Availability of data and material
The datasets analyzed in the current study are available on NCBI's Sequence Read Archive repository with the BioProject ID number PRJNA631156 and the BioSample number SAMN14853927. Sample names are identified per collection point. Data will be accessible with the following link after the indicated release date: https://www.ncbi.nlm.nih.gov/sra/PRJNA631156.
CRediT authorship contribution statement
Oriane Georges had the original idea, conducted field work, laboratory research and data analysis, and wrote the manuscript draft. Jose Luis Martinez and Sara Fernandez did metabarcoding laboratory and analysis work. Sara Fernandez led the bioinformatics. Eva Garcia-Vazquez designed the project, contributed to data analysis, especially to BLAST issues; to the interpretation of results, manuscript writing and preparation, and funding acquisition.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
This study has been supported by the University of Oviedo and the Government of Asturias (Spain), grant IDI-2018-000201, and the Ministry of Science and Innovation with the grant PID2019-108347RB-I00. We are grateful to Assaf Zvuloni for sharing his knowledge about the Dead Sea and to Guy Benoish for his help on the field while sampling in Israel. We would also like to thank the reviewers of Marine Pollution Bulletin for their contribution to improve our article.
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