Regional Background

Archaeological and Historical

The Mediterranean Sea, situated strategically at the crossroads of east-west and north-south economic and cultural interchanges, is unique in the world in its concentration of multi-disciplinary diversity (Fischer &  Garrison 2009) .  Archaeologically and historically, the Adriatic and Mediterranean represent a privileged maritime mode of communication, travel, and cultural/economic interaction between two continents and numerous nations with diverse cultural traditions, languages, religions, and ethnicities.  Currently 21 states and 5 territories border the Mediterranean Sea in close proximity in Europe and Africa, and six countries border the Adriatic, with the coastline here dominated by Italy on the west and Croatian mainland and archipelago on the east.   Over the millenia, the use of the Mediterranean by these diverse cultural entities has resulted in the accumulation of valuable historical/archaeological assets on land and in the sea as the sea advanced over human settlements and works over the millenia.  The Mediterranean Sea has been called “A vast museum …. that is rewriting history as we know it.” (Papadimas 2009) .  Because terrestrial sites have been extensively described, studied, and interpreted over the last several decades, the future of Mediterranean archaeology is considered by many researchers to be in the sea.  The underwater assets in the Adriatic Sea include shipping and harbor infrastructure (anchorages, docks, dry docks and dock foundations, navy yards, quays, piers, breakwaters, haulage chutes), shipping artifacts themselves (shipwrecks and their cargo), fishponds, town infrastructure (foundations, pavements, walls), residential structures (buildings and foundations public and private, caves, nymphaei, quarries), tombs, and plumbing installations (from variously planned drains and gullies to elaborate aqueducts, wells, cisterns, and sewers) (Auriemma 2001; Antonioli et al. 2007; Florido et al. 2011) .  Many terrestrial assets also attest to the maritime cultural and population concentration, beginning with archaeological cave and midden sites dating to the Pleistocene (Della Casa 2001; Shea 2008) .  These assets provide invaluable information about human societies, especially the maritime orientation of Mediterranean cultures, including perspectives on the seascape in relation to human culture, economy, religion, and myth; the seafaring culture, the nature of shipboard societies, in which the usual status relationships of gender, age, wealth, and race/ethnicity are in part freed from “mainstream” society; and the cultural evolution of ship form technology and its roots in the social structure and its relationship to the aquatic economic resource (Flatman 2003) . These assets also provide invaluable information about past sea levels, the process and dynamics of recent sea level rise, and past impacts of climate change.  They also are an important source of biological information, as all submerged human works constitute three-dimensional habitat structure that supports unique marine biological communities of often higher biomass, diversity, and productivity than adjacent unaltered habitat, and in some cases newly described species (Herdendorf &  Berra 1995; Herdendorf, Thompson &  Evans 1995; Duplessis &  Reiswig 2004) , and archaeological sites and historical archives provide a wealth of information, including long-term time series from midden deposits, on the state of the marine environment and past human impacts on marine fisheries and ecosystems (Erlandson &  Rick 2010) .


Geological

The physical assets of the Mediterranean showcase both the dynamics and products of all geological processes in action at all levels of complexity.  These assets present both opportunity and challenge to interdisciplinary researchers (Fischer &  Garrison 2009) .  The diverse marine environments in the Mediterranean, increasingly accessible due to technological advances, will increase in importance in the project of building fundamental geological understanding of the region.  These include submarine fans, clathrates, cold-seep fauna, brine genesis, mud volcanoes, sediment diapirs.  The tectonic organization of the Mediterranean Basin is a complex and diverse “carnival of microplates” in which both ends of the tectonic process – seafloor spreading and subduction – are ongoing vigorously within the basin and can be studied in more detail now that new technologies have increased the accessibility of the sea floor.  Basic geological questions at present include the relative importance of isostatic factors, tectonic dynamics, and marine processes in determining the relative vertical movement of land and sea surface at any location, the rate and causes of salinization of freshwater aquifers, the mapping of the Holocene evolution of the shoreline, the geological/atmospheric/marine processes instrumental in the Messinian crisis, the interaction between paleoclimates and geographical/geological processes in the creation of opportunities for and challenges to biotic evolution and the biotic connectivity with adjacent seas.  In the Adriatic, the Dinaric karst, which covers half of the Croatian territory, is a unique geological, hydrological, and biological asset that extends into the marine realm, where over 235 submarine and coastal caves have been mapped on the Croatian coast alone, of which 126 are completely marine, 75 are anchihaline, and 13 are outlets for submarine freshwater springs (vruljas) (Suric et al. 2005a, b; Suric et al. 2009; Suric &  Juracic 2010; Suric, Loncaric &  Loncar 2010; Suric et al. 2010) . Nearly 60% of these caves contain speleothems, which are definitive evidence of terrestrial origin and formerly lower sea levels.  Another important asset within the karst region is the presence of submerged notches along the Northern Adriatic limestone coasts, which have been surveyed at -0.35 to -2.8 m depth, and whose width is approximately equal to the local tidal range, indicating an erosional process, perhaps in part biogenic, relating to tidal action.  The absence of a modern notch, however, may be due to ongoing tectonic downdrop, or less aggressive weathering processes currently than during the time of notch formation, thought to be during the so-called Medieval Warm Period (Antonioli et al. 2007; Antonioli et al. 2009; Furlani et al. 2009; Furlani et al. 2011) .  Notches, regardless of mechanism of origin, are one of the most useful geomorphological markers for the study of sea level changes.  All geological assets are also unique biological habitat that supports distinctive biological communities, e.g. those of marine caves, which may include endangered species (Bakran-Petricioli &  Petricioli 2008) .  


Biological

The Mediterranean Sea is a biodiversity hotspot, and the Adriatic Sea itself is a hotspot of endemism. Over 17,000 marine species have been documented (Bianchi &  Morri 2000; Sala et al. 2000; Danovaro, Dell'Anno &  Pusceddu 2004; Bianchi 2007; Danovaro &  Pusceddu 2007; Underwood et al. 2009; Coll et al. 2010; Danovaro et al. 2010; Lasram et al. 2010; Fraschetti et al. 2011) , and though the Mediterranean is less than one percent of the total world ocean, these species constitute between 4% and 18% of all marine species known worldwide (Bianchi 2007). The density of species in the Mediterranean per unit area or volume of sea is 5 to 13 times the average species density in the rest of the world's oceans. A large number of species certainly exist in addition, especially among microbes, and taxa of the southern and eastern Mediterranean. Because species accumulation curves have not yet reached a plateau, more species are expected to be discovered continuing into the next decades in most taxonomic groups.  Endemism is high in the Mediterranean, averages 20% over all species, and is considerably higher in some groups, e.g. 48% in sponges, 36% in mysid crustaceans, and 35% in tunicates. A total of 12% of all fish species are endemic.  Within the Mediterranean, biodiversity tends to increase from the south and east, towards the north and west, with the highest species richness observed in the waters surrounding Sicily (approximately 375 species per 1 x 1 degree of longitude and latitude). Diversity tends also to decrease with depth, with coastal and shelf regions containing about 20 the average richness of deeper waters.  The Adriatic has a moderately high density of species due to its shallow depth (Coll et al. 2010) , with richnesses within 1 x 1 degree quadrats approximately 260 for fish.  The Adriatic is considered a hotspot of endemism, e.g. with 45 species of endemic fish per cell along the eastern coast.  Seagrass meadows, salt marshes, maerls, are especially important biological assets, as their functional impacts reach far beyond the beds themselves, and include important functions such as oxygenation of the water, trapping of fine sediments and clarification of the water, stabilization of the shoreline,  photosynthesis, and a high areal rate of primary production that enters the base of the coastal food web, and provision of three-dimensional habitat for a variety of animal species (Schultz 2008; Kruschel et al. 2009; Schultz, Kruschel &  Bakran-Petricioli 2009; Kruschel &  Schultz 2010a, b; Schultz &  Kruschel 2010; Schultz, Kruschel &  Mokos 2011) .

These are just a sampling of the marine and maritime assets that are of cultural, economic, and scientific value in the Mediterranean Sea; terrestrial assets also are crucial, the primary being historical archives of marine and maritime information, both primary and secondary, including digital information databases.  Truly multidisciplinary study of these assets by CIMMAR can help to answer both basic research questions within academic disciplines, and applied questions of cultural and economic importance to Croatian and wider Mediterranean societies, and can help to guide the region through the serious and potentially economically and socially disruptive environmental challenges that are forecast for the 21st century (Olesen &  Bindi 2002; Arnell 2004; Camci Cetin et al. 2007; Bindi &  Olesen 2011; Chenoweth et al. 2011) .


Major environmental challenges in the Mediterranean

Scientific consensus indicates that significant global change is occurring and accelerating within the coastal zone worldwide (Garcia-Ruiz et al. 2011) .  The global indicators include: 1) 80% of all marine pollution originates from land-based activities, including sewage, sediment, and runoff from urban and agricultural activities; 2) nearly 50% of the world's coasts are threatened by development-related activities, including tourism resorts, marinas, and urbanization, all of which cause permanent destruction of littoral and sublittoral habitat; 3) the density of humans within the coastal zone is increasing, and is currently at three times the global average; and 4) over half of fisheries worldwide are in a state of collapse or serious depletion.  All these threats have serious economic, cultural, and social implications: goods and services provided to humans by marine ecosystems have been valued at US $21.000 billion annually worldwide, and the continuing loss of these values is in part responsible for many of the current economic losses, crises, and challenges faced by human societies.  Following is a brief summary of current consensus of the major environmental risks and challenges within the Mediterranean and Adriatic seas.

The major short-term threats to biodiversity, at present and over the next 10 years in the Mediterranean and Adriatic, are habitat degradation, exploitation by commercial fisheries, pollution, and climate change. While the first three are direct consequences of the human population concentration within the Mediterranean, the last is a cumulative global phenomenon. Over the next 100 years, the influence of climate change becomes dominant because of its potential to cause fundamental functional shifts associated with depletion or extirpation of cold-temperate species from the basin, the reduction in the agricultural capacity of the terrestrial environment throughout the Mediterranean, including increased desertification in some regions, and projected increases in use of marine resources, and the increasing political and economic uncertainty and resulting deterioration of instruments and infrastructure for biodiversity management, use, and protection.

Habitat degradation is a necessary consequence of the increasing concentration of the human population near the sea and concomitant human interventions that destroy or permanently degrade the required habitat for many components of diversity, such as submerged aquatic vegetation (seagrass, macroalgae, maerl), oyster beds, and reefs. Habitat degradation has occurred throughout the Mediterranean starting well before the 20th century, due to coastal works that eliminate the natural sea bottom and human activities that cause eutrophication, pollution, and increased sediment loads. Most species have narrow habitat requirements, and species diversity is usually highly correlated with the quantity and diversity of high quality habitat.  Breeding habitat is critical for seabirds, most of which are ground nesting and require islands or oceanfront locations not accessible by mammalian predators; these are also prime tourism destinations and residential real estate. Populations of loggerhead sea turtles have also declined in parallel with their nesting habitat of sandy beach where nests can be dug near the wrack line; this habitat is also prime tourism destination. Fish communities are most diverse where bottom habitat consists of a natural mosaic of seagrass, unconsolidated sediment, rocky reefs, and macroalgal beds. These habitats have been eliminated over large areas of the Mediterranean that have been converted to ports, dikes, landfills and artificial beaches. In a process typical of many areas of the Mediterranean, by 1991 approximately 10-15% of the infralittoral zone from 0 to 20 m depth at the Provence-Alpes-Cote d'Azur region of France was irreversibly destroyed by waterfront development.

Closely related to the coastal concentration of the human population, and the high concentration of tourism and commercial fishing activities within the Mediterranean Sea, are ever increasing threats to the submarine archaeological heritage sites of the entire region.  Shallow archaeological sites are seriously threatened by treasure-hunting SCUBA divers, and deep sites are threatened by trawl fishing, which physically breaks apart sites, drags away and scatters objects over large areas, and damages or destroys fragile objects  (Tolson 2005; Morais et al. 2007) .  In the shallow margins of the Italian coastline, where SCUBA depredation has been the most extreme, virtually “nothing is left above 70 meters.”  In the past, archaeologists have argued that the oligotrophic conditions in the Mediterranean, and especially the Adriatic and Aegean seas, result in low rates of biogenic deterioriation of submarine heritage objects and works, especially under lower oxygen concentration at greater depths.  Therefore, these sites, primarily shipwrecks and their cargo, should be managed in situ rather than through the expensive and potentially damaging process of salvage and transport.   However, it is becoming increasingly clear that in situ preservation is not possible, and that deep ocean preservation is a myth, due to the widespread and ubiquitous operation and damage of trawl fisheries throughout the Mediterranean (Tolson 2005) .  The risk that these pose to fragile archaeological sites is so great that some researchers advocate immediate salvage of valuable and newly discovered sites, rather than hoping the site will purely by chance survive the active trawl fishery.  Recovery and salvage even for fragile sites is possible using new technology, by a combination of methods beginning with photomosaic three-dimensional virtual reconstruction of the site, followed by a “hover and recover” strategy using remotely operated underwater vehicles operating at a spatial accuracy of centimeters (Flatman 2003; Tolson 2005) .

Exploitation of marine resources has increased exponentially since 1900, with the result that the majority of fish stocks in the Mediterranean lie somewhere between seriously depleted and endangered. Within the Adriatic, nearly half of all stocks, and about 70% of economically important stocks are overexploitated and considered no longer safe to harvest. Many elasmobranchs, previously common in the Adriatic, are now rare due to by-catch and destructive harvest methods such as bottom trawling.

Because of its shallow and semi-enclosed nature, the Adriatic Sea Large Marine Ecosystem (ASLME) is the most impacted ecosystem of the entire Mediterranean. It is especially vulnerable to all forms of chemical alteration. Cultural eutrophication due to agricultural effluents in the Po river is especially a problem, causing jelly fish outbreaks, red tides, hypoxic “dead zones”, and widespread mucilage aggregations, as well as in lower water clarity, which results in lower rates of photosynthesis and regression of all kinds of submerged aquatic vegetation, and degradation of the sediment, which causes further regression of seagrass meadows.  Over the last decades, the inexorable increases in nutrient and organic loads in the Adriatic have triggered increased functional changes, including increases in frequency and the spatial extent of dead zones.  Some researchers have indicated a very high risk that these dead zones expand and coalesce into one very large region of semi-permanent hypoxia that covers virtually the entire northern Adriatic (Riedel, Zuschin &  Stachowitsch 2008)  .  Significant expansion of Adriatic dead zones would be economically catastrophic to the region, and actions to reduce this risk should be a paramount concern for all Mediterranean institutions that are charged with protecting the economic and environmental interests of the region.

The entire Mediterranean Sea is considered to be not only a “hotspot” of biodiversity, but also a hotspot of climate change by virtue of the fact that it is a semi-enclosed basin with low inertia due to the short ventilation and residence times (approx. 70 years) of its water masses. The shallow and semi-enclosed status of the Adriatic Sea itself makes this sub-basin especially vulnerable to climate change. Global climate change can be considered as secular increases in temperature superimposed on natural fluctuations within the climate system, with the Mediterranean influenced strongly by the north Atlantic Oscillation (NAO), an oscillation in intensity of the Icelandic low pressure system and the Azores high pressure system that modulates the strength and frequency of westerly winds and associated weather phenomena in Europe. Climate change in the Mediterranean is predicted to involve rapid reductions in precipitation throughout the region, and a shifting to a permanent increase in aridity, to a state of -10 on the Palmer Drought Severity Index (-4 is considered extreme drought) (Dai, Fung &  DelGenio 1997; Dai &  Trenberth 2002; Dai 2010) . Evidence that this shift is in progress has been presented starting in the late 1990s (Mariotti 2010), and a state of extreme drought is projected to arrive the region in as early as two decades (Dai 2010) . This represents a severe change in the Mediterranean water cycle, and a “pathway toward long-term regional hydroclimatic change” (Mariotti 2010) , that will result in immediate shifts in salinity of the Mediterranean and, along with changes in pH and temperature, changed patterns of thermohaline circulation that could have far-reaching effects on the entire ecosystem, and especially in semi-enclosed, shallow sub-basins such as the Adriatic Sea. These changes could have profound effects on the productivity, food web topography, and on the supply of exploited marine resources in the region, and the tourism value of the entire Mediterranean coastline.

Fundamental changes in composition of the animal community are underway, with tropical and subtropical species migrating into the Mediterranean via the Straits of Gibraltar and the Suez Canal (lessepsian migration), and native cold-temperate species migrating northward within the basin (Nike Bianchi &  Morri 2003; Bianchi 2007; Moschella 2008; Zenetos et al. 2009) . These changes will result in functional shifts in the topography of the food web. Currently there is speculation that “it is impossible at present to foresee to what extent the exuberance of warm-water species will affect the trophic web and the functioning of marine ecosystems in the Mediterranean Sea of tomorrow.”  However, certainly one goal of ecological research is to push the horizons of prediction forward to the extent allowed by current knowledge of how ecosystems operate.