Amphistegina lobifera Larsen

The most abundant of the alien foraminifer species in the Mediterranean Sea is Amphistegina lobifera Larsen. It shows a wide distribution range in the Indo-Pacific and Atlantic Oceans (Langer and Hottinger, 2000), also abundantly recorded in the Eastern

Mediterranean Basin, Israel (Langer and Hottinger, 2000; Hyams et al., 2002), Lebanon (Moncharmont Zei, 1968) Greece (Cherif, 1970; Hollaus and Hottinger, 1997) and Turkey (Avsar, 1997; Meric et al., 2002, 2004a). In Israel, Amphistegina lobifera is the most abundant foraminifer species found in hard substrate, reaching densities of almost 180 specimens/g (Hyams et al., 2002). Its range of distribution in Mediterranean is mainly restricted to Levantine basin, and in the Central Mediterranean it has been reported only from Libya (Blanc-Vernet et al., 1979; Crapon-De Caprona and Benier, 1985), Tunisa (Glacon, 1962) and Malta (Yokes et.al, 2007).

Figure 1. Satellite photograph of the southwestern coast of Turkey. © SeaWiFS Project, NASA/Goddard Space Flight Center and ORBIMAGE.

A. lobifera is observed almost everywhere on the Aegean and Mediterranean coasts of Turkey, and even in the Sea of Marmara (Meric et al., 2005). It forms extensively dense populations along the coasts of Antalya (SW Turkey) (Meric et al., 2002). The density of living individuals on the rocky substrate can reach 230000 - 310000 individuals/m2 (Figure 2). The high ratio of tests in the sediment (>350 specimens/g; 0.75g tests/g) results in large amounts of sand formation, changing all the habitat type and coastal structure (Yokes and Meric, 2004).

The A. lobifera populations off Kas (Antalya, SW Turkey) have been followed between 2002 and 2008. The rich sediments were located SCUBA diving and core samples were obtained from different locations and depths. The core samples were cut into 2 cm thick slices, one gram of sediment was weighed from each slice and A. lobifera content in each sample were counted (Figure 3). The first scouts of this alien species were found at the bottom of the core samples, represented with very few individuals (Figure 4). Surprisingly, the size of this alien population had not shown much change for a certain period of time. However, at the 25th cm from the core surface, a rapid increase in population density was

Figure 1. Satellite photograph of the southwestern coast of Turkey. © SeaWiFS Project, NASA/Goddard Space Flight Center and ORBIMAGE.

obvious. The cause of this abnormal population expansion is yet unknown, but it indicates that something had happened and The Kraken waked (Yokes and Meric, 2004).

Amphistegina Lobifera

Figure 2. Alive foraminifer individuals on the coasts of Turkey. A). Amphistegina lobifera Larsen population on Cystoseira sp., Bodrum - Mugla, depth: 9m, October 2002. B) Dense A. lobifera population on rocky substrate, Uc Adalar - Antalya, depth 6 m, 1490 alive individuals have been counted on 15.75cm2 of sea bottom. C) Amphisorus hemprichii Ehrenberg population on Halophila stipulacea (Forsskal) Ascherson, Kas -Antalya, depth 26 m, November 2004. D) A. hemprichii population on Cystoseira sp., Kas - Antalya, depth 14m, November 2004.

Figure 2. Alive foraminifer individuals on the coasts of Turkey. A). Amphistegina lobifera Larsen population on Cystoseira sp., Bodrum - Mugla, depth: 9m, October 2002. B) Dense A. lobifera population on rocky substrate, Uc Adalar - Antalya, depth 6 m, 1490 alive individuals have been counted on 15.75cm2 of sea bottom. C) Amphisorus hemprichii Ehrenberg population on Halophila stipulacea (Forsskal) Ascherson, Kas -Antalya, depth 26 m, November 2004. D) A. hemprichii population on Cystoseira sp., Kas - Antalya, depth 14m, November 2004.

The extensive abundace of these two alien foraminifera species results in the accumulation of tests at an extreme rate on the sea floor. Certain stations off Kas were monitored for six years and the deposition of the test belonging to these two species found to be 2-4.5cm/year. The thickness of the deposited test on the rocky sea bottom reaches to 60-80cm locally. Such a population density is not observed elsewhere in the Mediterranean. It is good for the sand dwelling native species, however, the native habitat sturcture in this particular area is rocky structures. Waves carry foraminifera tests to the shores where they accumulate in small bays, thus changing gravelly shores to sandy beaches. This extensive deposition of tests is creating an immense ecological problem by changing the whole habitat structure, while definitely altering the species composition of the coastal ecosystem in the long run. Thus, regardless of its biological characteristics, any alien species shoul be regarded to have a potential to cause some kind of damage to the ecosystem.

The high sea water temperature observed in this region may suggest that Amphistegina lobifera Larsen likes high water temperatures which may limit its distribution in the Mediterranean. According to Langer and Hottinger (2000) the occurrences of living amphisteginids are delimited by the 14°C winter isotherms. Laboratory experiments showed that Amphistegina lobifera Larsen ceased all movements at temperatures below 12°C (Zmiri et al., 1974). However, its presence in the northern Aegean Sea and in the eastern Sea of Marmara shows that this species can adapt to much lower temperatures, thus may be dispersed to western Mediterranean by time, the recent recording from Malta supports the idea that its invasion in the Mediterranean has not yet finished.

Figure 3. Analysis of the sediment. Close-up photography of the sediment in Kas - Antalya. A) Most of the sediment is composed of Amphistegina lobifera tests. B) Core samples were manually collected from different locations and depths by driving PVC pipes into the sand by hammering. D) High accumulation rate of foraminifera tetst results in drowning of rocky habitat in sand. The phanerogams further increase the sedimentation rate as they start growing on the test deposits.

Figure 3. Analysis of the sediment. Close-up photography of the sediment in Kas - Antalya. A) Most of the sediment is composed of Amphistegina lobifera tests. B) Core samples were manually collected from different locations and depths by driving PVC pipes into the sand by hammering. D) High accumulation rate of foraminifera tetst results in drowning of rocky habitat in sand. The phanerogams further increase the sedimentation rate as they start growing on the test deposits.

Figure 4. Analysis of the core samples. Results of two core samples from different depths show similar Amphistegina lobifera distribution pattern. ♦ core sample from 42 m, □ core sample from 46 m. Both core samples show a population expansion at the same time interval.
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