Tag Archives: Greece

How Healthy are Mediterranean Rocky Reefs?

Intense exploitation over millennia has depleted Mediterranean Sea species from the large to the small, including the Mediterranean monk seal, sea turtles, bluefin tuna, groupers, red coral, lobsters, and limpets. Although history suggests that these impacts have been significant, it is difficult to evaluate their magnitude because there is no rigorous historical baseline for the abundance of marine species. However, an international group of researchers have now established the first current comparable baseline of ecosystem structure at the Mediterranean scale, focusing on nearshore rocky reefs.

What would a ‘healthy’ Mediterranean rocky bottom look like? There are no pristine sites (i.e. undisturbed by humans) left in the Mediterranean against which to compare the health of current ecosystems. However, research on pristine, historically unfished sites in the central Pacific show that intact, complex reef ecosystems harbour large biomass (ie total weight of all fish in an area) of fishes and high coral cover. It seems reasonable to suppose that large fish biomass equals healthy reef therefore.

The scientists therefore conducted underwater surveys using SCUBA divers across rocky reefs throughout the Mediterranean Sea, including in Spain, Italy, Greece, Morocco and Turkey. They did this both in marine protected areas and open access sites. The surveys showed remarkable variation in the life on these reefs.

The results suggest that the healthiest shallow rocky reef ecosystems in the Mediterranean have both large fish and algal biomass.

Fish biomass was significantly larger in well-enforced no-take marine reserves. However, there were no significant differences between marine protected areas which allow some fishing and open access areas at the regional scale.

Fish data were collected using standard underwater visual census techniques. Sampling stations within sites were spaced at least 1 km apart from the next, except in very small marine reserves. The data revealed three groups of sites mainly constituted by: (1) well-enforced no-take marine reserves with high fish biomass, (2) partial marine protected areas and weakly enforced no-take marine reserves with lower fish biomass, and (3) non-enforced marine protected areas and areas open to fishing.

The sites with the least amount of fish were in Turkey and Morocco. These had among the lowest reported ever in scientific literature for shallow reefs, even lower than the most overfished coral reefs in the Caribbean.

The Scandola Natural Reserve in Corsica is probably the best example of a ‘healthier’ rocky reef, without fishing and with good water quality.

There was an absence of sharks at the study sites. Sharks were much more abundant historically in the Mediterranean and they used to be an important component of nearshore food webs. The largest predators now are male dusky groupers (Epinephelus marginatus).

A major insight is that, at the Mediterranean scale, partially protected Marine Protected Areas which allow some fishing are not effective in restoring fish populations. For this you need well enforced no-take marine reserves.

The researchers hope that their findings will be used to assess the health of any similar habitat in the Mediterranean, and to evaluate the efficacy of marine protected areas.

Further Reading:
Sala E, Ballesteros E, Dendrinos P, Di Franco A, Ferretti F, et al. (2012) The Structure of Mediterranean Rocky Reef Ecosystems across Environmental and Human Gradients, and Conservation Implications. PLoS ONE 7(2): e32742. doi:10.1371/journal.pone.0032742

Survey Reveals Top 10 Dive Sites in Europe

Europe boasts some world class dive sites, with great visibility and masses of underwater life. In a recent poll of SCUBA Travel readers, these were voted the ten best dive sites in Europe. Disagree? Then cast your vote.

    Diving the Booroo
  1. The Zenobia, Cyprus
    The pristine wreck of a huge ferry. Lying on its port side, the wreck starts at about 15 m and descends to 42 m. Fabulous dive. Possibly the best shipwreck dive in the world in recreational depths. 20 m plus visibility and some great swim-throughs. Needs several dives to see anything like all of it.
  2. Blue Hole, Gozo
    A beautiful sharp drop off into the blue hole with what seems like limitless visibility and literally feels like you are on the very edge of the world. A most extraordinary dive.
  3. Cirkewwa, Malta

    Features the wreck of the Rozi MV as well as stunning underwater topography. Visibility is very good and there iss ea life in abundance: barracuda, morays, octopus, cuttlefish and even dolphins.

  4. Booroo, Isle of Man
    The Burroo, with its extremely diverse and plentiful marine life offers a truly magnificent dive. In fact, in areas exposed to the fast flowing current, it is something of a challenge to find a single square centimetre of bare bedrock, so abundant is the life here.
  5. Blockship Tabarka, Scapa Flow, Scotland
    This shallow 18 m dive is a real beauty. One of the block ships scuttled to prevent submarine attack during WW2. Covered in life, a beautiful place. Worth the trip and the one of surprises of Scapa. anemones
  6. Diamond Rocks, Kilkee, Ireland
    Claimed to by on a par with the famous Yongala. It is a cold water dive off Ireland’s west coast. The bay is fairly sheltered and is teaming with life. The terrain is full of rocks and gullies and the water is really clear.

  7. Eddystone Reef, England
    12 miles off Plymouth, England. The reef is from 8 to 60 m. Encrusted with jewel anemones and with the remains of ancient wrecks, including a large 17th century anchor. Stunning.
  8. Secca della Columbara, Italy
    BarracudaOne of the best dives in the Mediterranean. It features a steep, beautifully-decorated, wall; large shoal of barracuda; grouper; giant amberjacks and a wreck. The wreck is a 74 m ship which was carrying slabs of marble. It sank in 2005 and rests at 20 m in two parts.
  9. Fanore, Ireland

    Shore dive in crystal clear Atlantic water with abundant fish.

  10. Chios island, Greece
    Small undersea caves and paths between impressive rocks, colourful reefs and vertical walls.

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Endangered Bivalve, Pinna nobilis, Recovers Off Italy but Suffers in Greece

Pinna nobilis, the giant bivalve, is endangered. Although in some places it has historically been abundant, there has been a lack of up-to-date information about its exact distribution. SCUBA divers therefore went looking for the giant mussel in the Ionian Sea, Italy.
Ionian Sea Map
The results of the study indicate a tentative of recovery of P. nobilis population there, in spite of all the difficulties of a degraded and heavily polluted environment and the damages of illegal fishing methods.

The divers found the pinnids at depths from 3 to 16 m. Their numbers ranged from one individual in 10 hectares, to one every 1.4 hectares. (A hectare is around 2.5 acres or 0.01 square km.)

The survey method employed in this study was non-destructive and relatively simple to perform.

Pinna nobilis lives only in the Mediterranean Sea (which encompasses the Ionian Sea). It likes seagrass meadows and grows up to 120 cm. It sticks up out of the sea bed so is easily seen by divers, once you know what to look for. Although in the Ionian Sea the mussels were found between 3 and 16 m, in other areas of the Med, such as the Adriatic Sea, they live down to 30 m.

In another study, published last month in the Marine Biology journal, Stelios Katsanevakis of the University of Athens investigated the growth and mortality rates of Pinna nobilis in Greece. He found 160 of the mussels and monitored them for 17 months. He discovered that growth rates had a seasonal pattern. The mussels grew slowly during the cold months, and also during August when water temperatures exceeded 29 oC. They grew quickest during late spring and early summer, probably due to an optimum combination of temperature and food availability. Younger individuals grew faster than older ones.

P. nobilis is a protected species in the EU and its fishing is strictly prohibited. However, in the Greek study many deaths were caused by fishing. The mussels were poached exclusively by free-diving and fishing mortality was practically zero at depths below 9 m. Because of this large individuals were restricted to deeper areas.

Journal References:
Environ Monit Assess 2007; 131:339-47.
Marine Biology 2007; DOI: 10.1007/s00227-007-0781-2

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