Comments on ‘Preliminary data on the genetic structure of a highly successful invading population of oyster suggesting its establishment dynamics in the Levant’ by Ateret Shabtay et al., Marine Biology Research, 2014

Abstract

In a recent article, Shabtay et al. use molecular tools to characterize the genetic structure of the population of the Indo-Pacific spiny oyster Spondylus spinosus at five sites along the Mediterranean coast of Israel and at the northern Gulf of Aqaba, Red Sea. The authors state that the results of their analysis provide evidence that coal carriers offloading at a pier next to the Hadera power plant were the probable vectors of introduced S. spinosus into the Mediterranean. To refute the authors' statement factual evidence is offered as to the sources and pathways of the coal imported to Israel and the ballasting/deballasting procedures of the coal carriers in question. In addition, omissions as to the spatio-temporal distributional data concerning the introduction of S. spinosus into the Mediterranean are rectified. The veracity and accuracy of the geographic origin and the pathways of introduction are of major importance for management of bioinvasions. With much at stake for regulators, scientists, the concerned public and the marine environment, it is important that erroneous data are corrected.

Key words:

• ballast
• introduction
• Mediterranean
• Spondylus spinosus
• Suez Canal

In a recent article, Shabtay et al. (2014) use molecular tools to characterize the genetic structure of the population of the Indo-Pacific spiny oyster Spondylus spinosus Schreibers, 1793, at five sites along the Mediterranean coast of Israel and the northern Gulf of Aqaba, Red Sea. The authors state that the results of their analysis enabled them to determine ‘… the mode of invasion of this oyster [S. spinosus] into the Mediterranean Sea’ (Shabtay et al. 2014: 408). ‘Since 1981, a massive import of coal shipped via the Suez Canal has been routinely taking place at the Hadera power plant, which is only 2 km south of Sdot Yam, making these coal vessels a probable vector of the invasive oyster … S. spinosus was most probably transported into the Mediterranean in the ballast tanks of coal ships’ (Shabtay et al. 2014). In this response, it is outlined why this assertion is questioned, if not refuted.

Molecular genetic methods strengthen interpretations of historical, ecological and observational data regarding geographic origins and sources of introduced marine populations and the pathways and vectors by which they have expanded their ranges (Lawson Handley et al. 2011). Examining shipping patterns and the population genetic structure of the invasive Chinese mitten crab Eriocheir sinensis H. Milne Edwards, 1853, Herborg et al. (2007) determined that ‘ballast water transit, is a significant factor in facilitating ongoing dispersal of mitten crabs between Continental Europe and the UK’. Or, they can offer alternative parsimonious scenarios, as in the case of the oyster-associated clam, Gemma gemma (Totten, 1834), in California, USA (Hoos et al. 2010). A frequently used tool for inferring source and reconstructing routes of introduction, molecular genetics ‘are subject to a major limitation: they take poorly into account the stochasticity of the demographic and genetic history’ (Estoup & Guillemaud 2010), and researchers have been counselled to follow an appropriate sampling design in order to avoid ‘incorrect interpretations resulting from sampling errors’ (Muirhead et al. 2008).

Spondylus spinosus was first recorded in the southern part of the Suez Canal over a century ago (Tillier & Bavay 1905), and subsequent studies documented its progress northward towards the Mediterranean (Tomlin 1927; Moazzo 1939; Ben-Eliahu & Ten Hove 2011) – facts left out by Shabtay et al. (2014). In the Mediterranean Sea the species is present along the coastlines of Israel (Mienis et al. 1993), Lebanon (Crocetta et al. 2013), Syria (Bitar et al. 2003), Cyprus (Zenetos et al. 2009) and Turkey (Çeviker 2001). This spatio-temporal pattern is common for introductions through the Suez Canal and along the coasts of the Levant by passive larval movements with the prevailing currents (Galil 2006; Galil et al. 2014). Bearing this information in mind, a more appropriate sampling design would compare the Mediterranean populations with specimens from the Gulf of Suez, the probable ‘launching pad’ of the introduced populations in the Mediterranean (Golani 1993), rather than the population at the northernmost ‘cul de sac’ of the Gulf of Aqaba, and would comprise samples from populations in another Levantine country in addition to the geographically confined Israeli samples.

The authors’ assertion that coal carriers offloading at a pier next to the Hadera power plant are the probable vectors is not borne out by facts. Ballast is carried in bulk carriers when not carrying cargo or when lightly loaded to ensure that the ship’s stress, stability, draft, trim and propeller immersion are within permissible limits (Bulk Carrier Guide 2010). Between 1982 and 1988, the Israeli National Coal Supply Corporation imported 18,444,730 metric tons sourced from Australia, Colombia, England, South Africa and USA (Anna Yadgarov, Head of Commerce, The National Coal Supply Corp. Ltd, pers. comm., 8 May 2014). Nearly two-thirds of that amount was loaded in the Richards Bay coal terminal, South Africa. Two coal carriers were used for hauling coal from South Africa to Israel: the ‘Leon 2’, with a draft of 15.5 m, travelled mostly through the Suez Canal, whereas ‘Hadera’, with draft of 17.4 m, rounded the Cape and entered the Mediterranean through the Strait of Gibraltar (Capt. Adam Herbst, pers. com., 18 May 2014). Both coal carriers arrived at Hadera fully laden and with ‘no ballast on board’ (Capt. Adam Herbst, pers. comm., 18 May 2014). The vessels took on ballast in Israel for their return voyage in dedicated ballast tanks and cargo holds configured to carry ballast water (Wonham et al. 2001; Drake et al. 2002). Claims that S. spinosus was repeatedly introduced into the Mediterranean Sea in the ballast tanks of fully laden coal carriers should have been substantiated by analysing samples of its populations in the vicinity of supposed source regions (i.e. Richards Bay).

Identifying the geographic origin and the pathways of introduction are of major importance for management of bioinvasions. Only when the source and the vector are established, can specific and appropriate measures be devised and implemented. Molecular tools are widely relied upon to provide accurate data concerning these issues, and the veracity and accuracy of scientific articles are generally taken for granted. Therefore, it is necessary to expunge inaccurate, unsubstantiated or misleading statements before they slip into the scientific mainstream and the ubiquitous citation systems. A recently published Proposal for a Regulation of the European Parliament and of the Council on the Prevention and Management of the Introduction and Spread of Invasive Alien Species (European Commission 2013), the EU Biodiversity Strategy (European Commission 2011) and the EC Marine Strategy Framework Directive (European Commission 2008) rely on region-wide databases of invasive alien species to identify and prioritize management decisions. With much at stake for regulators, scientists, the concerned public and the marine environment, it is important that erroneous data are corrected.

Editorial responsibility: Franz Uiblein

Acknowledgements

The author is grateful to Anna Yadgarov and Liora Yarkony, The National Coal Supply Corp. Ltd, Ariel Metzger, Israel Electric Company, and Captain Adam Herbst for supplying data on coal sources and transportation.

Funding

The research leading to these results received funding from the European Community’s Seventh Framework Programme (FP7/2007-2013) under Grant Agreement No. 266445 for the Vectors of Change in Oceans and Seas Marine Life, Impact on Economic Sectors (VECTORS).

Additional information

Funding

Funding: The research leading to these results received funding from the European Community’s Seventh Framework Programme (FP7/2007-2013) under Grant Agreement No. 266445 for the Vectors of Change in Oceans and Seas Marine Life, Impact on Economic Sectors (VECTORS).