Divernet


THE BUILDING OF THE 101-MILE-LONG SUEZ CANAL was one of the great engineering feats of the 19th century.
When it was completed on 17 November, 1869, ships were able to sail directly between the Mediterranean and Red Sea for the first time and, by avoiding the circumnavigation of Africa, weeks were carved off transit times between the major European and Asian ports. This boosted trade and accelerated colonisation of Africa by the European powers.
What the builders of the canal, including construction company chief Ferdinand De Lesseps, almost certainly didnt realise when the final breach was made was that they had started a grand experiment in introducing alien species that continues to the present day.
My introduction to this grand experiment happened in April 2002 during a night dive at a site called Sheep Dip on the south coast of the island of Cyprus. I had been driven by staff of Dive-In, Larnaca, along many miles of bumpy dirt tracks in a well-used pick-up truck to get to the site, so when we finally arrived I was itching to get on with the dive.
After kitting up in the beam of the vehicle headlights, we entered the water and descended over a series of rock ridges to a sandy area with straggly seagrass fronds in 12m of water.
I started to pan around with my torch, enjoying the superb water clarity, when suddenly I lit up an elongated fish about 30cm from tip to tail, hovering almost motionless above the sea grass.
I instantly recognised it as a blue-spotted cornetfish (Fistularia commersonii) in stripy night pattern camouflage, a fish I had come across many times on dives in the Red Sea.
Something seemed not quite right about the encounter. I pointed the fish out to one of the guides, but was met with a shrug and a hand signal to move on. For the rest of the dive I puzzled over why it seemed so odd to see a cornetfish on this dive and made up my mind to do a bit of research when I got back to my hotel, regardless of the hour.
A quick flick though the Mediterranean fish guides at 1am deepened the mystery, because there was no mention of cornetfish among the hundreds of species listed.
Had I been seeing things, I wondered Narked at 12m With identification questions still unanswered, I turned in for the remainder of the night, and the next day questioned staff at the dive shop. I found that they had been seeing these strangely shaped fish for only about a year, but that they were now quite numerous in shallow waters.
I decided then that some more digging in the fish literature was needed back in the UK.
As it turns out, the dive staff and I were seeing an event that has now happened 59 times since 17 November, 1869 - migration of Red Sea fish species though the Suez Canal and successful establishment of breeding populations in the eastern Mediterranean,
a phenomenon called the Lessepsian migration, after Ferdinand De Lesseps.
This invasion is not limited to fish, as a number of Red Sea worm, snail, crustacean and jellyfish species have followed the same route. The blue-spotted cornetfish is one of the latest Lessepsian migrants, and its subsequent occurrence in the Mediterranean is typical of the invasion pattern.
The first Mediterranean cornetfish was trawled from 35m three miles out from Jaffa, Israel in January 2000.
By June 2001, specimens were turning up on the south coast of Turkey, and later that year they were seen in Cypriot waters too.
In 2002 reports were coming in from all around the eastern Mediterranean, including the Aegean. They have now reached the Straits of Sicily, a significant area that marks the boundary between faunas of the eastern and western Med.
Although the Straits of Sicily is the present limit of Lessepsian migrants, the majority of the 59 alien Red Sea fish are confined to the easternmost Mediterranean, particularly the Levantine Basin (offshore Egypt, Israel and Lebanon), the area closest to the outflow of the Suez Canal at Port Said. Here some Lessepsian species can be abundant and, in fact, one of the earliest recorded migrants, the marbled rabbitfish (Siganus rivulatus) is now an important commercial catch.
The Red Sea invaders have had negative impacts on native fish populations. Gold-band goatfish (Upeneus moluccensis), for example, arrived in the late 1940s and displaced their Mediterranean relative the red mullet into deeper and colder waters.
The gold-band goatfish is also a good example of the boom and bust pattern of alien species invasions. From 15% of total mullet catches off the Israeli coast in the 40s the percentage soared to 83% in the warm winter of 1954-1955, but is now down to 30% of catch.
Why are the Red Sea immigrants so successful in the eastern Mediterranean when there are already plenty of native fish, some of them closely related to the Lessepsian species
As it turns out, there are fewer fish species in the eastern Mediterranean than might be expected. The reasons are partly geological and partly due to the way the major currents flow into and out of the Mediterranean.
Nutrient-rich surface water comes in through the shallow Straits of Gibraltar from the Atlantic and makes its way slowly into the western Mediterranean and then via the Straits of Sicily into the eastern Med. By the time it gets there, many of the surface-water nutrients have been used up and cannot subsequently support large quantities of plankton, the base of all marine food chains. This is the reason for the generally superb visibility in the eastern Mediterranean - good for us, not so good for the fish.
The geological explanation for lower-than-expected eastern Mediterranean fish diversity is more dramatic.
Almost six million years ago, the connection between the Atlantic and Mediterranean closed and the Mediterranean dried up, wiping out all marine life, including coral faunas that were as diverse as the reefs in the present-day Red Sea.
When the Straits of Gibraltar formed some 700,000 years later, Atlantic sea water flooded back into the Med, bringing with it Atlantic fish and invertebrates. Thats why todays Atlantic and Mediterranean faunas are similar (excluding Lessepsian species).
The eastern Med was the area furthest from the source of the Atlantic immigrants and many species never made it that far, leaving empty niches that the newly arriving Red Sea species seem to have been able to exploit.
Indo-Pacific fish species turning up where they shouldnt is not just a phenomenon in the Mediterranean.
Humans have been implicated in another and more recent alien invasion. Since the year 2000, lionfish have been appearing all along the south-east coast of the United States, from Florida to New York. Both adults and juveniles have been seen, suggesting that they are actually breeding in the area.
These fish are a long way from home, and how they evaded US immigration to become the latest marine citizens is the subject of a lot of debate.
The best guess is that they are the result of people releasing unwanted aquarium specimens in a misguided act of kindness. Alternatively, small individuals may have hitched a transoceanic ride in ships ballast water.
Have you seen a Lessepsian fish If you have dived anywhere in the eastern Mediterranean, chances are you have.
After doing the initial research on the blue-spotted cornetfish from Cyprus and seeing lists of other invading Red Sea species, I looked back over my logbooks from a trip to southern Turkey in 1996 and found Id seen some of them before: the filefish Stephanolepis diaspros and the soldierfish Sargocentron ruber (both first seen in Turkish waters in 1950).
Others you might have seen include the dusky rabbitfish (Siganus luridus), ponyfish (Leiognathus klunzingeri), brushtooth lizardfish (Saurida undosquamis) and spotted halfbeak (Hemiramphus far).
It seems very likely that there will be continuing migration from the Red Sea and movement of already-arrived Lessepsian species from the eastern Mediterranean into the Adriatic and western Mediterranean.
To what extent the higher diversity of fish in the latter area will prevent establishment of the invaders remains to be seen. De Lesseps unintentional grand experiment goes on.

One
One of the earliest migrants was the marbled rabbitfish
The
The Sargocentron ruber variety of soldierfish.
Dusky
Dusky rabbitfish
Spotted
Spotted halfbeak