Calcareous assemblages of the southeastern Mediterranean low-tide estuaries — Seasonal dynamics and paleo-environmental implications
Introduction
Estuaries are often heavily populated and represent regions of utmost economic value (e.g. Ducrotoy and Elliott, 2006). Anthropogenic activity and intensive exploitation of these water resources cause disturbance to the biota living in this ecosystem. This includes overfishing, physical habitat modifications, habitat loss, organic enrichment and pollution (e.g. Bar Or, 2000, Bianchi and Morri, 2000, Crossland et al., 2005). Estuaries are also at risk of invasions of alien aquatic species diminishing biodiversity (Occhipinti-Ambrogi and Savini, 2003). Hence, studying these vulnerable ecosystems (e.g. Costanza et al., 1997) and carefully monitoring their fauna are imperative for efficient management and their continuous utilization in the future and for protecting or reestablishing their distinctive biodiversity (e.g. Poff et al., 2007). This is especially significant in small estuaries vulnerable to anthropogenic activity that have a small tidal range known worldwide e.g., South Africa (e.g. Bell et al., 2001, Cooper, 2001), Australia (e.g. Ranasinghe and Pattiaratchi, 2003), southwestern USA (Elwany et al., 1998), and the southeastern Levant (e.g. Reinhardt et al., 2003) and which were studied mainly for their geomorphological aspects but rarely for their biota.
Estuaries represent a dynamic ecosystem characterized by high environmental variability in salinity, temperature, primary productivity, bottom water dissolved oxygen content and sediment type (e.g., Lu et al., 2008, Bárcena et al., 2012). These variables affect the abundance, distribution patterns and the community structure of the calcareous benthic organisms that live there generally in low diversity and with frequent shifts in species dominance (Marques et al., 1993, Cognetti and Maltagliati, 2000).
Among the calcareous organisms living in estuaries molluscs are increasingly employed as bio-indicators of environmental quality. They are used to evaluate water/sediment relation and to determine the state of health of the estuary ecosystem (e.g. Koutsoubas et al., 2000, McLusky and Elliott, 2004, Afli et al., 2008). This group plays a role in cycling nutrients and in exchanging materials between sediments and water column in addition to being a source of food for secondary consumers of higher trophic levels (McLusky and Elliott, 2004).
Ostracods and benthic foraminifera also comprise a significant part of this ecosystem, being increasingly used as environmental bioindicators evaluating water/sediment quality conditions (e.g., Debenay et al., 2003, Debenay et al., 2006) and especially in polluted environments (e.g. Ruiz et al., 2004, Ruiz et al., 2005, Bergin et al., 2006). The sensitivity of these organisms to environmental change might be expressed either by disappearance, replacement, appearance of specific species or by the occurrence of morphological anomalies (e.g. Ruiz et al., 2004, Ruiz et al., 2005 and references therein).
The occurrence of molluscs, ostracods and foraminifera in several microtidal estuaries along the Israeli coast was reported so far only in few papers and mainly in internal reports. Herbst and Mienis (1985) and Mienis and Ortal (2001) studied the distribution of molluscs in Tanninim and Naaman streams, respectively. Reinhardt et al. (2003) studied the dead foraminiferal assemblages of the Tanninim estuary and the Sr isotope composition of shell material (foraminifera, ostracods, molluscs, algae) as salinity proxy. Almogi-Labin et al. (2001) and Siman Tov and Almogi-Labin (2002) characterized different stream mouths and coastal plain inland brackish habitats based on a semi-quantitative survey of live and dead groups of diatoms, thecamoebians, foraminifera, ostracods and molluscs. Almogi-Labin et al., 2002, Almogi-Labin et al., 2004 and Flako-Zaritsky et al. (2011) studied the brackish water foraminifers and ostracods of the inland brackish Enot Timsah pond (32°33.9′N/34°55.41′E; 193537E/717650N new Israeli grid), the current main water source of the Tanninim stream. The distribution of foraminifera, ostracods and molluscs was studied also in the inland Nur pond located adjacent to the Naaman estuary (Almogi-Labin et al., 2007). They focused on salinity alternation between brackish and freshwater during the last few decades based on the faunal distribution. The main variables controlling ostracod species distributions in the Israeli inland aquatic environments (lakes, ponds and streams) were studied by Mischke et al., 2010, Mischke et al., 2014. In these studies an ostracod-based electrical conductivity transfer function was developed and applied onto fossil ostracod assemblages from Pleistocene–Holocene in order to trace the hydrologic history of water bodies in the region.
For the coastal plain of the southeastern Mediterranean shelf, with its dense population and the ongoing disappearance of natural coastal habitats, the need to restore streams is pressing (Bar Or, 2000, Gafny, 2013), particularly estuaries, which received so far only little attention. Due to the limited information on this vulnerable ecosystem and due to plans to rehabilitate this environment we aimed in this study to: (1) identify and describe the distribution of the living foraminifera, ostracods and molluscs over an annual cycle, in six estuaries along the Israeli coast (Fig. 1); (2) determine the relationships between environmental factors and the fauna using multivariate statistical analyses in order to improve their use as environmental bio-indicators; (3) add information on aliens/invasive species and their association with the local ecosystem as part of the efforts to improve environmental conservation; and (4) study the time-averaged death assemblage of the three calcareous groups in order to create a reference baseline for future paleogeographic, paleoenvironmental and paleoecological studies.
Section snippets
Study area
The studied coast of the southern Levant extends 180 km along the southeastern Mediterranean, in a nearly straight NE–NNE direction (Fig. 1). This coastal area includes two main sedimentary provinces: a southern one, part of the Nile siliciclastic (quartz)-rich littoral cell (e.g. Zviely et al., 2007, Hyams-Kaphzan et al., 2008) and a northern one that ranges from Akko promontory northward to Lebanon and is composed of carbonate-rich sediments of local sources forming mainly rocky and coarse
Field sampling
Surface sediments and water samples were collected once in every season over a period of one year (2012–2013) from six estuaries located on the southern, central and northern Israeli coast (Fig. 1; Table 1, Table 2). Samples were taken between 5 and 35 cm water depth, near the riverbanks, a depth interval that was relatively well oxygenated. The samples were taken along an E–W gradient with Station 1 in our notation being the closest to the river mouth and 3 the most inland one (Table 1a).
During
Environmental properties
Water temperature (WT) varies between 12 °C and 22 °C in winter and 26 °C and 32 °C during summer (Fig. 2a; Table 1a). Differences in WT for example in the Naaman are related to differences in sampling time, during the day, in each season. The coldest WT of 12 °C was measured in Poleg 2. The lowest pH was measured in Tanninim 3A (7.48) and the highest in Alexander 1A and Lachish 1W (8.6 and 8.7, respectively). The electrical conductivity varies between 1.35 in Poleg 1W and 42.80 mS/cm in Alexander
Faunal distribution pattern and species richness in low-tidal estuaries
The current study focuses on the lower reaches of the low-tidal estuaries of the southeastern Mediterranean continental shelf, an environment common in semi-arid subtropical regions worldwide (e.g. Bell et al., 2001, Cooper, 2001, Ranasinghe and Pattiaratchi, 2003, Elwany et al., 1998)). The numbers of living species of ostracods, molluscs and foraminifera are low and seem to be associated with the low salinity values of the Tanninim and Naaman estuaries (≤ 7 psu) and the oscillating salinity
Conclusions
A regional reference baseline of foraminifera, ostracods and molluscs was established for the first time, for the low-tide estuaries of the southeastern Mediterranean coast that can be used for any future paleoenvironmental reconstruction. The calcareous fauna that lives there is affected by mainly the natural seasonality combined with anthropogenic interference.
The living benthic foraminiferal assemblage composition is rather similar in most stream reaches, except that of the Naaman. It is
Acknowledgments
This study was carried out with the support of the Ministry of Science and Technology and of the Ministry of Energy and Water Resources (Grant nos. 3-7818 and 212-17-022 respectively). We gratefully acknowledge the technical assistance received from M. Kitin and C. Netzer-Cohen of the Geological Survey of Israel and A. Yurman and M. Bachar from the RIMS diving workshop, of the Department of Maritime Civilizations and the Leon Recanati Institute for Maritime Studies, Haifa University. H. K.
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