Cyprus is located in the Levantine Basin - Eastern Mediterranean which is one of the most oligotrophic seas in the world, characterized by very low nutrient availability and hence very low primary production (Por, 1978 Krom et al., 1991 Krom et al., 1992 Tselepides et al., 2000). In addition to its ultra-oligotrophism, Levant’s Sea, is characterized of high temperatures (Fig1a + Fig1b) ranging yearly from 16 °C in winter and up to 26 °C in summer (ΕΕΑ, 2002). Moreover, the evaporation and salinity are high (yearly average salinity of eastern Mediterranean >37.5 psu, average salinity of coastal waters of Cyprus 39.1 psu), and also the inflow of fresh water is very limited due to the absence of large rivers. In Cyprus there aren’t rivers in permanent flow and the structure of several restraint river water dams and streams further limits the supply of coastal waters with debris and nutrients. In addition, the construction of the Aswan dam has further reduced the nutrient deposits from the Nile River. On top of everything, the coastal reflux (upwelling) in the Levant Sea is in general weak and as a result of that the nutrients, which are in the bottom of the sea, are unavailable to be at the euphotic zone for primary production.
The special hydrological conditions of Levant Sea and the small width of the continental shelf in combination with low concentrations of available nutrients (in particular phosphorus), have as a result a very low primary production, that is low concentration of chlorophyll / phytoplankton in seawater (Fig 2a + Fig 2b). Krom et. al. (1992) recorded chlorophyll-a concentrations in the deep waters of Eastern Mediterranean between 0.1 μg/L and 0.2μg/L. Especially the waters off the coast of Cyprus, showed some of the lowest chlorophyll-a concentrations (10 - 90 ng / L) ever measured in coastal waters (Bianchi et al., 1996). The oligotrophic character of the Eastern Mediterranean and the differences with the Western Mediterranean have been recorded and confirmed many times in the past but also recently (Crombet et al., 2011; Pujo-Pay et al., 2011). As a result, the quantities of zooplankton and the larger invertebrate and vertebrate organisms (e.g. fish) that rely on it for their diet is also limited compared to other regions.
However, despite its low productivity compared to other seas, the Mediterranean is characterize by very high biodiversity, that is great number of flora and fauna species, which however are found in small abundances. Especially among other European seas, the Mediterranean has the highest biodiversity, since recent estimations based on the existing scientific literature (UNEP-MAP RAC/SPA 2010) state a biodiversity of about 10,000-12,000 identified species (about 8,500 species of macrofauna, over 1,300 species of plants and 2,500 species of other taxonomic groups). This means that the Mediterranean, (with a surface area and volume occupying only 0.82 % and 0.32 % of the surface area and volume of global ocean respectively) corresponds to 4-18 % of all, until now, known marine species worldwide (UNEP-MAP RAC / SPA 2010). It is no coincidence then, that the Mediterranean is one of the 25 global biodiversity recognized centers ("biodiversity hot spot"). The Mediterranean biodiversity decreases from west to east, with 87 % of all known species to occur in Western Basin and only 43 % in Eastern (UNEP-MAP RAC / SPA 2010).
Being a semi-enclosed sea, the Mediterranean is also characterized by a high degree of endemism (it hosts species that are not found anywhere else in the world), where 20-30% of its species are endemic, i.e. Posidonia oceanica a marine angiosperm plant, which is considered as the most important marine ecosystem of the Mediterranean and is a priority habitat of the European Habitats Directive 92/43 / EEC.
Many marine species which are found in Cyprus, such as sea turtles (Chelonia mydas, Caretta caretta), the pen shell (Pinna nobilis), the Mediterranean monk seal (Monachus monachus), etc., are considered endangered and in need of protection, and therefore included in the list of high biodiversity and ecological importance for the Mediterranean.
In addition, in our island there are several important and sensitive biocommunities and habitats such as the meadows of the marine angiosperms Posidonia oceanica and Cymodocea nodosa, forests of the brown algae of the genus Cystoseira, underwater caves, etc., which they are also objects of protection zone and conservation in the framework of European and national laws and international and regional conventions.
Nowadays, coastal - marine environment of the Mediterranean is under many and various pressures from many different sources which are interacting together and lead to weakening or loss of biodiversity. The intensive and over - increasing human exploitation of the coastal / marine environment is the main cause of degradation and destruction of important habitats and species. Among the major pressures on the Mediterranean is tourism, transportation, industry, pollution, overfishing, introduction of non-indigenous species, and also global phenomena such as climate change which interact and reinforce the impact of more local pressures either directly or indirectly.
Mediterranean is particularly vulnerable to the introduction of alien species, several of which are characterized as invasive and cause significant problems for native species and habitats. Today it is estimated that in the Mediterranean there are 1,000 such species and the rate of introduction is believed to be approximate one species every 1.5 week (UNEP-MAP RAC / SPA 2010). The Eastern part of the Mediterranean is facing the biggest problem with alien species due to the existence of the Suez Canal, which is now the most important introduction pathway of alien species originating from the Indo-Pacific and Red Sea ("Lessepsian immigrants").
In this context the most significant pressures on the marine - coastal environment of Cyprus result from tourism and residential development, pollution - mainly eutrophication due to the influx of nutrients from point (measured) and non- point sources, coastal erosion and coastal works, over-fishing, increasing presence of invasive alien species (mainly Lessepsian migrants) etc .
However, the marine environment of our island, despite being subject to various pressures can (both in general but also in comparison to other Mediterranean countries), be considered to be in a good status, due to the low-scale industrial development, the intense hydrodynamism and physical configuration of the coasts (no closed bays, mainly offshore etc). Unfortunately, at present, the knowledge about the marine environment of Cyprus is relatively limited, especially concerning offshore seas. Therefore, investing in more intense and systematic research in the field of the marine environment of Cyprus is an important step towards a holistic protection and management of the natural wealth of our seas.
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