New data on marine life on offshore reefs along Israel’s Mediterranean coast shows a worrisome decline in the populations of many species, including sea urchins, shellfish and snails. Possible causes for the decline are climate change, which has raised sea temperatures, and competition from invasive species that arrived from the Red Sea via the Suez Canal.
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The data was compiled by Dr Gil Rilov from the Israel Oceanographic and Limnological Research Institute and published two weeks ago in the periodical Scientific Reports. Rilov based his findings on his own surveys, surveys by other researchers and consultations with experts. A comparison was made to numbers found in the past in the same region, as well as to numbers on other Mediterranean coastlines.
The animals that were studied are located on rocky surfaces called abrasive reefs near the shoreline. Two species of snails and sea urchins which were abundant there have almost completely disappeared.
One particular snail called Stramonita haemastoma (red-mouthed) was renowned in ancient times as a source of purple colors. Between 2009 and 2015 it could no longer be found in the marine park at Achziv, in which it had been abundant only two decades previously. Over the past seven years, not a single specimen has been located on all of Israel’s shores. Three individuals were found in Acre, outside the surveyed area, but those also disappeared. Nor has Rilov found them in Crete and Cyprus in recent years, though he did trace some near Naples.
The purple sea urchin was present at Achziv marine nature reserve 40 years ago, at a density of 12 per square meter. In a survey conducted between 2010 and 2015, only one specimen was found in the survey zone and a few others were found outside the zone. A few more were found near Haifa. Another black sea urchin species, which used to be abundant, also yielded only one specimen.
One important component of the offshore ecosystem was a certain snail called Dendropoma petraeum, a member of the Vermetidae snail family which tightly attaches to rocks by a shell shaped like a pipe. It has almost completely disappeared along the shoreline in recent years. The disappearance of this species is most notable at the Dor-Habonim nature reserve, where 40 percent of rocks were covered by this snail two decades ago. In Cyprus and Crete there are still some relatively large populations of this snail.
In a study of 59 types of molluscs which used to be quite common in this region, it was found that 38 of them could not be found in recent years. Accompanying this decline is an increase of species coming from the Red Sea through the Suez Canal, which may be responsible for pushing out local species. In some rocky areas, less than two percent of snails and shellfish found in recent surveys belonged to local species.
Rilov believes that destruction of habitat and pollution is not the main cause of this depletion. Invasive species are only a partial explanation, since some disappearing species were not in competition with these newcomers.
He is convinced that the most significant factor is the rapid and consistent rise in sea temperatures in the Mediterranean over the last two decades, as part of global climate change. In one case, it was shown that exposing the purple sea urchin to temperatures over 30.5 degrees centigrade was lethal. Every August over the last decade water temperatures were higher than that off Israel’s shores.