Algae (photosynthetic organisms) are an extremely diverse group ranging from single celled organisms to giant kelp that can reach 65m length. There are 550 species of algae recorded in the Greek seas, forming the base of most food webs in the littoral ecosystems. This is due to their ability to convert the sunlight into energy that can be utilized by other marine organisms in higher trophic levels. This takes place where there is enough light penetration for photosynthesis to occur (usually down to 40m), so mainly in the littoral ecosystem.
Seagrasses are rooted flowering plants that have evolved to live in the marine environment. They are also primary producers, forming meadows which are very important to many species of fish, invertebrates and birds. Seagrass beds play a vital role in sheltering the coast from wave action and erosion. In the eastern Mediterranean, four species of seagrass are found; Posidonia oceanica, Cymodosea nodosa, Zostera noltii and Halophila stipulacea. Posidonia seagrass, named after the Greek sea god Poseidon, is of exceptional importance to the eastern Mediterranean, remaining one of the Archipelagos’ research and conservation priorities.
Invertebrates are defined as organisms without a spine. They are the most diverse taxa group on the planet. Over 6500 species of marine invertebrates are found in the Mediterranean alone, including sponges, jellyfish, sea urchins, starfish and squid.
There are over 600 species of fish in the Mediterranean, 86 of which are endemic to the area. They can be seen in various sizes, shapes and colors, due to each species’ unique adaptions which allow them to thrive in their own place in the marine ecosystem. They range from the immense size of the basking shark, which can reach a length of up to 8 m, to the small and intricate sea horses that are just a few centimeters long.
Threats
Due to their close proximity to cities and villages, littoral ecosystems often are affected by anthropogenic activities more than any other marine habitats. Here are the main threats:
1.Large scale fishing
The primary threat faced by littoral ecosystems, is that of physical disturbances which are caused by trawling well as by anchoring (mainly of recreational boats but also by small scale fishing vessels). These physical disturbances contribute to the loss of important habitats such as Posidonia oceanica meadows.
2.Eutrophication and pollution
Eutrophication and pollution from untreated sewage outlets and fish-farm effluents can smother benthic species and reduce water visibility, which in turn decrease the depth to which photosynthetic organisms can survive. Meadows of Posidonia seagrass or Cystoseira algae in particular, are very sensitive to water and sediment enrichment. In bays with low water exchange, even small amounts of nutrient or organic input from anthropogenic sources can induce habitat degradation.
3.Toxic chemicals
The accumulation of toxic chemicals in the water column can inhibit growth rates of marine species and bioaccumulate in the food chain. Mercury is a heavy metal commonly found in a number of commercial fish species, such as swordfish and tuna. These chemicals bioaccumulate throughout the food chain and can be particularly dangerous to wildlife and humans, especially to fetuses, infants, and nursing mothers.
4.Invasive species
A globally growing concern, invasive species can greatly impact areas, causing devastation to biodiversity and benthic community structure. These species are able to outcompete native species for food and space, impeding local species and sometimes even replacing them. Invasive species have become such a threat that more than 5% of the marine species in the Mediterranean are now considered non-native species. As it is impossible for scientists alone to monitor the spread of invasive species, it is important to join forces with all those who spend time at sea and share a passion for marine life, to record the presence of invasive species. For this purpose Archipelagos has set up a citizen science network with the aim of encouraging fishermen, divers, sailors and other sea enthusiasts to identify and report invasive species they might encounter in the Greek Seas and the NE Mediterranean Sea.
5.Climate Change
Climate change raises ocean surface temperature and alters deep-water currents; this affects the spread of some species, with more tolerant species able to survive while fragile, slow growing species are wiped out. It can also lead to a rise in sea levels, resulting in the migration of both invertebrate and algae species further up the littoral zone. Even though the potential future effects of climate change on the Mediterranean Sea are hard to accurately predict, they should not be underestimated.
Actions
Archipelagos have spent more than 10 years collecting data and monitoring the shallow littoral zone communities of the eastern Aegean Sea. The monitoring of the littoral zone will help understand the effects humans are having on the marine ecosystems. The collection of data on the biodiversity and ecology of littoral ecosystems enables us to get an understanding of local conditions, processes and the impacts of threats. This knowledge enables the development of well-targeted and successful management plans.
Archipelagos research on the littoral zone ecosystems focuses on the assessment of the biodiversity of fish, invertebrates and algae. These surveys are carried out with visual census techniques; employing the use of line transects and quadrats. Apart from the biodiversity, other parameters such as light levels, temperature, depth and substrate type are also assessed.
Specific research projects include:
- The assessment of the growth and morphology of the invasive algae species Caulerpa racemosa, as well as its impact on biodiversity. With the use of laboratory and field experiments, the effects of Caulerpa racemosa on the growth of macroalgal and invertebrate communities are also studied.
- The assessment of the cover and evaluation of health of Posidonia oceanica seagrass beds and the impact caused to them by trawling, as well as anchorage of recreational boats.
- Using dropdown camera equipment to map the extent of Posidonia oceanica, followed by lepido-chronological analyses to assess the ecological status of the meadows.
- The assessment of the impact caused by overgrazing by sea urchins on the biodiversity of algae and invertebrates.
- The use of loggers for monitoring the temperature and light intensity.
- The assessment of the impact of island erosion in littoral ecosystems, with the use of sediment traps.
- The use of the Water Framework Directive to monitor littoral pollution, with the use of benthic macroalgae as bioindicators.
- The assessment of recolonization rates and biodiversity in different substrates (artificial and natural).
- Effects of substratum on fish community structure in littoral habitats.
- The assessment of horizontal, vertical and diurnal behavior of plankton.
- The assessment of water quality in the littoral zone.