The sea is deeply ingrained in our perception of Slovenia, as well as in our way of life, which would undoubtedly be different were it not for our connection to it. Warm, sunny spring and autumn days, when the interior of the country is shrouded in cold, clouds or mist, draw crowds to coastal towns for a coffee; life by the sea provides us with seafood, salt, olives and citrus fruits. And last but not least, it connects us to the wider world. But, given all these gifts of life by the sea and with the sea, what do we actually know about the Slovenian sea – or rather, about the marine environment?
Shallowness and enclosure: fluctuations in temperature and salinity
The Slovenian sea is fairly shallow. The seabed, which consists mainly of clayey silt, exceeds a depth of twenty-five metres only in isolated areas. Due to its shallowness, there are significant fluctuations between summer (28 degrees Celsius) and winter temperatures (6 degrees Celsius), as the sea warms up quickly but also cools down rapidly. The shallowness and enclosed nature of the Gulf of Trieste create a sensitive underwater ecosystem that is far more vulnerable to environmental changes and pressures than the deeper parts of the Adriatic. The consequences of global warming and the associated rise in average sea temperatures are evident in the extinction of certain animal and plant species, which are accustomed to cooler sea temperatures and are further threatened by thermophilic species that are expanding their range ever further northwards into the Adriatic. As a result, over the last few years, researchers have observed the death of stony corals in our sea due to rising sea temperatures; these are the only corals in the Mediterranean capable of forming coral reefs. However, our sea is characterised not only by considerable fluctuations in sea temperature but also in salinity; due to river inflows, particularly from the Soča, the Timava and the Po, the salinity of the sea in this part of the Adriatic is lower than the average salinity of the Adriatic Sea.
The Coast
Although short, quite densely populated and, for the most part, altered by human intervention, the Slovenian coastline from Debeli Rtič to the Sečovlje salt pans remains rich and diverse in terms of natural habitats. The area of the high Strunjan cliffs, the highest along the Adriatic Sea, represents, alongside Debeli Rtič, one of the most unspoilt and biologically rich parts of our coastline. It is precisely in these two areas, at Cape Ronek and Cape Debeli Rtič, that we find two major coral reefs. The Sečovlje and Strunjan salt pans are important areas for birds; the coastline between St Catherine and St Nicholas near Ankaran is an example of a Mediterranean salt marsh, whilst in Škocjan Bay the meeting of fresh and salt water creates a unique ecosystem comprising marine areas, brackish lagoons, seagrass beds and freshwater marshes.
Natural wealth: nature trails and parks
All the areas mentioned are protected, and their natural riches are showcased along educational trails that visitors can walk along. Just a few metres from Piran’s Punta, the seabed reaches its greatest depth in the Gulf of Trieste, at 37.5 metres below the surface. This is home to a rich underwater world of diverse habitats, providing a habitat for many plant and animal species. In total, along our 46 kilometres of coastline and within our 406 square kilometres of territorial waters, we have two landscape parks, three nature reserves of national importance, thirty natural features of national importance and nine natural features of local importance. We also have several protected areas at sea, such as the Posidonia meadow, a seagrass that once covered a large part of the seabed of the Gulf of Trieste, but which today can only be found in Slovenian waters along the road between Koper and Izola.
The Marine Strategy Framework Directive
In order to protect Europe’s seas for future generations, the European Commission adopted the Marine Strategy Framework Directive in 2008, which obliges Slovenia to draw up an action plan to achieve or maintain good environmental status in the marine environment. To this end, the first systematic description of the characteristics and state of the marine environment in Slovenia was carried out, and the impacts and pressures on it were recorded. To assess the status, researchers identified eleven descriptors or characteristics which, on the one hand, describe the status of marine habitats and ecosystems and, on the other, describe the impacts and pressures exerted on them by external factors. They monitored biodiversity, the presence of non-native species, fish stocks of commercial species, the marine food web, nutrient pollution, the condition of the seabed, hydrographic conditions, environmental pollution by hazardous substances, the presence of contaminants in fish and seafood, as well as underwater noise and marine litter.
Twenty species of sharks have been observed in our waters
During the preparation of the initial assessment of the status of marine waters, it became apparent that, due to a lack of data and the unreliability of estimates, it is difficult to provide an accurate assessment of the state of the marine environment in Slovenia. The data and assessments collected to date indicate that habitats are generally in good condition, with the sole exception of intertidal zone habitats (the area affected by the tides) due to their high susceptibility to human interference. The status of phytoplankton, zooplankton, macroalgae, seagrasses, invertebrates and fish in the coastal zone is considered to be good, with the exception of individual degraded or polluted areas. The fish population in the coastal waters comprises just over 200 species of bony fish; to date, 20 species of sharks and 14 species of rays have also been observed in Slovenian waters.
We do not have specific data on the population sizes of individual species of cartilaginous fish, which include sharks and rays, but based on observations gathered to date, a downward trend in population numbers can be detected. The only marine mammal found in our waters is the harbour porpoise. Experts estimate that the population found in Slovenian waters numbers between 40 and 100 porpoises, although only a portion of this population visits Slovenian waters regularly. As they are at the top of the food chain, porpoises are highly vulnerable to the condition and quality of the food web, which is threatened by overfishing and the presence of pollutants in the organisms that form their diet. They are also affected by the impact and pressures of underwater noise, which is even more pronounced in our waters due to the enclosed nature of the Gulf of Trieste. Noise affects their sense of balance, spatial orientation, ability to locate prey and communication with one another, and can also cause damage to internal organs. It is also estimated that their population is in decline.
The loggerhead turtle visits us from May to October
Of the marine reptiles, the loggerhead turtle is a regular visitor to our waters, appearing from May to October, when our sea becomes their summer feeding ground. The turtle population is most threatened by fishing, as the turtles become entangled in fishing nets, causing severe injuries to their bodies. In recent years, a decline in the amount of phytoplankton has been observed in Slovenian waters; phytoplankton forms the basis of the marine food web, absorbs carbon dioxide from the atmosphere and releases oxygen into it. The amount of phytoplankton depends on the volume of water from rivers flowing into the sea and carrying nutrients with them; therefore a reduction in river flow due to droughts and changes in river regimes also affect the good status of the marine environment. In Piran Bay, the average chlorophyll concentration was around one microgram per litre until 2006; after 2006, this average fell to 0.6 micrograms.
Negative impacts
The presence of non-native species is also an important indicator of the state of the sea. These are currently present to an extent that does not threaten existing habitats or native species; however, this situation could deteriorate rapidly due to the widespread presence of alien species in the Mediterranean.
As mentioned in the introduction, human pressures on the marine environment are numerous and varied, with some linked to the economic use of the sea and others resulting from our way of life. Despite a marked decline in fish landings from 8,000 tonnes to 1,000 tonnes over the last twenty years, fishing remains a significant factor affecting the marine environment. The biggest problem facing fisheries is the overfishing of certain fish species, which is causing their stocks to decline and, consequently, reducing biodiversity and the marine food web.
According to researchers’ estimates, the stocks of anchovy and sardine – both of which are considered the most commercially important species, accounting for approximately 70 per cent of the total catch – are fully exploited, whilst the stock of sea bream is being overfished. Alongside the targeted catch of commercial fish, fishing also presents the problem of by-catch – fish and other marine animals (such as turtles) that become entangled in nets and are discarded by fishermen.
Another significant pressure exerted by fisheries on the marine environment relates to the seabed, as certain fishing gear and certain shellfish harvesting practices cause damage to the seabed. The seabed is the habitat of many organisms that play a vital role in ensuring the good health of the marine ecosystem, as, amongst other things, they filter seawater, contribute to the carbon cycle and help provide nutrients. However, even the seemingly innocuous anchoring of ships and boats damages the seabed, so it is important that, particularly in protected areas – which, unfortunately, are often the most attractive for swimming or the richest in fish – no anchoring takes place.
Litter poses a major problem for the marine environment. In 2015, as part of the ‘Clean Coast’ campaign, volunteers collected 168.60 kilograms of litter – or 14,074 items – at the sites of Strunjan, Fiesa, below Belvedere, Seča and Debeli Rtič as part of the ‘Clean Coast’ campaign. The most common items among the collected waste were cigarette ends, followed by pieces of glass and ceramics, unidentifiable pieces of plastic, cotton buds, pieces of polystyrene, plastic bags and mussel farming nets. Only around 15 per cent of the litter ends up on the shoreline where it can be cleaned up; around 15 per cent floats on the sea surface and in the water column, whilst around 70 per cent sinks to the seabed! One of the biggest pollutants is microplastic – tiny plastic particles which, due to their small size, can enter the food chain of marine organisms. The presence of waste in the digestive tracts of dead sea turtles has already been proven.
Microplastics are formed as a result of the breakdown of larger pieces of plastic waste, whilst these particles also enter the sea via sewage, as microplastics are found in many everyday items, such as cosmetics and clothing. The River Po is one of the major sources of microplastic inflow into the Adriatic Sea, whilst ocean currents carry microplastics from across the entire Adriatic Sea towards the Gulf of Trieste. According to Dr Manca Viršek Kovač of the Water Research Institute of the Republic of Slovenia, a study carried out as part of the DeFishGear project, which covered the entire Adriatic Sea, a significant accumulation of microplastics was found specifically in the Gulf of Trieste. The problem with plastic, which accounts for more than 90 per cent of waste, lies in its accumulation in the environment, as it takes several centuries to degrade!
The future of the sea depends on all of us
Researchers estimate that the biodiversity of Slovenia’s marine environment remains high at present, but it must be protected to ensure its good condition for future generations. The pressures on it are considerable due to its economic use. As we do not live below sea level and are cut off from contact with the underwater environment, it is difficult for us to observe and be aware of the pressures our activities exert on marine ecosystems. Tourism, fishing, urbanisation, maritime transport, the operations of both the Koper and Trieste ports, the farming of marine organisms and the presence of industry represent the main factors influencing and impacting the marine environment. There are pressures causing damage to the seabed, the presence of waste and organic nutrients, the overfishing of animal species, the introduction of non-native species, underwater noise, the loss of natural habitats due to construction and municipal infrastructure, and so on.
Therefore, measures will need to be implemented in the future to ensure its environmentally friendly and sustainable use, which will benefit both coastal and marine ecosystems as the economy, which is, in fact, largely dependent on the good condition of the marine environment. We too can contribute our own small part to the mosaic of marine conservation, particularly in reducing marine litter and respecting protected areas. The marine environment is far too valuable a habitat to lose due to irresponsible human behaviour.
Author: Saša Starec