Elsevier

Marine Pollution Bulletin

Volume 62, Issue 8, August 2011, Pages 1822-1829
Marine Pollution Bulletin

New threats of an old enemy: The distribution of the shipworm Teredo navalis L. (Bivalvia: Teredinidae) related to climate change in the Port of Rotterdam area, the Netherlands

https://doi.org/10.1016/j.marpolbul.2011.05.009Get rights and content

Abstract

The effects of four climate change scenarios for the Netherlands on the distribution of the shipworm upstream of the Rhine–Meuse estuary are described. Global warming will cause dry and warmer summers and decreased river discharges. This will extend the salinity gradient upstream in summer and fall and may lead to attacks on wooden structures by the shipworm. Scenarios including one or two degree temperature increases by 2050 compared to 1990 with a weak change in the air circulation over Europe will lead to an increased chance of shipworm damage upstream from once in 36 years to once in 27 or 22 years, respectively; however, under a strong change in air circulation, the chance of shipworm damage increases to once in 6 or 3 years, respectively. The upstream expansion of the distribution of the shipworm will also be manifested in other northwest European estuaries and will be even stronger in southern Europe.

Highlights

► We examine the distribution of shipworms in estuaries due to global warming. ► Decreasing precipitation in summer and fall decreases river discharge. ► Lower river discharge extends the salinity gradient. ► Longer salinity gradient extends the distribution of shipworms stream upwards. ► Distribution extension increases the risk of damage of wooden structures.

Introduction

Shipworms (Teredinidae) are wood-boring marine bivalves. The shipworm Teredo navalis L. appeared in 1730 in the coastal waters of the Netherlands and was described by Sellius (1733) as Teredo marina. Its origin is unknown, and the species is therefore described as cryptogenic by Hoppe (2002). In the successive years of 1731 and 1732, massive destruction of the wooden constructions that protected the dikes in Zealand and Westfrisland occurred (Vrolik et al., 1860). Authorities attempted to use tropical hardwoods and arsenic and to cover the wooden dike gates with iron plates and nails, but the only (very expensive) solution was changing the mode of dike construction. This began as soon as 1733 by defending the dikes with imported stones, and over the centuries, this has led to the “petrification” of large parts of the Dutch coastline. Later outbreaks of the species took place in the Netherlands in 1770, 1827, 1858 and 1859. Not only were sluices and dolphins in harbors upstream of the Rhine–Meuse estuary found to be infected in 1826, but quays also collapsed. Low river discharges resulting in increased salinity had created favorable conditions for the shipworm. The shipworm is still commonly found in Dutch coastal waters and enclosed salt water bodies in the Dutch Delta Area (Van Benthem Jutting, 1943, De Bruyne, 1994).

If shipworms encounter optimal abiotic conditions, they are able to destroy fir piles 15 cm in diameter in six weeks (Snow, 1917), and even 10 m long, 25 cm thick oak pilings can be turned into rubble in 7 months (Cobb, 2002). In 1995, shipworm damage in the US was estimated to cost approximately US$ 200 million per year (Cohen and Carlton, 1995). Over the centuries, many attempts to protect wood structures from shipworm attacks have more or less failed. They have used copper and lead plating, nails with large flat heads (Teredo-nails), paraffin, tar, asphalt, and paints. The most effective deterrent, creosote, has been banned in many countries because of its toxic and carcinogenic properties (Snow, 1917, Hoppe, 2002). Chemical impregnation with chrome copper arsenate (CCA) or borax (CKB) is widely used as a wood preservative and is effective, although this practice remains controversial among environmentalists (Hoppe, 2002).

The adult shipworm tolerates salinity conditions between 5 and 35 (Nair and Sarawathy, 1971) and thrives and reproduces at salinities of 9 and higher (Kristensen, 1969; Soldatova, 1961 in Tuente et al., 2002). Boring activity stops below a salinity of 9–10. Pelagic shipworm larvae survive at salinities as low as 6, and below that salinity level, pediveligers die within a few days (Hoagland, 1986). It was observed in Germany that a low salinity of 9 prevented the establishment of shipworm larvae (Hoppe, 2002). At water current velocities exceeding 0.8 m1 s−1, shipworm larvae can no longer attach to wood (Quayle, 1992). The optimal water temperatures for growth and reproduction range between 15 and 25 °C. Spawning is initiated when the temperature rises above 11 to 12 °C. These animals may breed from May until October (Grave, 1928). First year animals may reach sexual maturity in six weeks (Lane, 1959). Temperatures up to 30 °C are tolerated. Boring activity decreases below 10 °C and stops at 5 °C (Roch, 1932, Norman, 1977). At temperatures near the freezing point, shipworms hibernate until the water temperature becomes favorable again.

The complete salinity gradient of the Rhine–Meuse estuary is present in the Port of Rotterdam area, and a vital shipworm population exists in the large polyhaline harbors in its western region (Beerkanaal and Calandkanaal). T. navalis settlement in the Port of Rotterdam area decreases with increasing distance from the sea floor in both test panels and beams (Paalvast and Van der Velde, 2011). This was also found by Scheltema and Truitt (1956) in test panels in coastal waters of Maryland in the US and by Tuente et al. (2002) in the harbors of Bremerhaven in Germany.

The situation in the Rotterdam port area, which is one of the largest ports in the world, can be used as a typical example of the estuaries of all large temperate rivers in western Europe. Various climate models (Van den Hurk et al., 2006, Van den Hurk et al., 2007, Boé et al., 2009, Diaz-Nieto and Wilby, 2005) used to predict the effects of global warming on the hydrology of these large rivers show, on average, a serious decrease in precipitation during summer and fall, leading to lower river discharges. Combined with an expected sea level rise, this will lead to increasing salinity over large parts of the estuarine gradient (Beijk, 2008).

Therefore, the following research question was formulated: what is the risk of shipworm damage (i.e., the expansion of its distribution upstream) under present climate conditions and under climate change due to global warming?

Section snippets

Study area

The Port of Rotterdam is situated in the estuary of the Rhine and Meuse rivers (Fig. 1). It stretches over a length of 40 km and covers 10,500 hectares, 3440 hectares of which are covered by harbor waters and 1960 hectares, by rivers and canals. Under average conditions, with a Rhine river discharge at the Dutch–German border (Qbr) of 2200 m3 s −1, the complete salinity gradient from fresh to seawater is found in this part of the estuary. This salinity gradient moves downstream at ebb tide and

Risk of damage under the present conditions

Using the SIMONA modeling system, it was calculated that for the Port of Rotterdam area, a discharge of 700 m3 s−1 or less (crit-Qbr) of the Rhine river at the Dutch–German border under the prevailing climate conditions would lead, within a week, to salinities of the bottom water in the harbors of the Nieuwe Maas in the eastern part of the Port of Rotterdam upstream to the Rijnhaven (Fig. 2A) appropriate for settlement and growth of the shipworm (and, thus, expansion of its distribution

Discussion

The increased risk of the extension of the shipworm towards the eastern part of the Port of Rotterdam as far as the Rijnhaven depends greatly on a temperature increase with changed air circulation patterns. However, under the present situation, at discharges below 1000 m3 s−1, there is salinization above the sea floor in the most downstream part of the eastern portion of the Port of Rotterdam that creates conditions for the shipworm to settle and grow. Using test panels placed on the sea floor,

Conclusion

Climate change with a global increase in temperature of one or two degrees coinciding with a strong change in air circulation that leads to low river discharges in summer and fall will extend salinity gradients upstream in western Europe estuaries and considerably increase the risk of damage to wooden structures by the shipworm in the near future.

Acknowledgements

We thank the Rotterdam Port Authority for financing the use of the SIMONA modeling system.

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