The wealth of species of local shellfish and snails on Israel’s Mediterranean coastline has declined by almost 90 percent in recent decades, according to a new study.
The decline represents the largest regional loss of diversity documented in a marine environment anywhere in the world, and scientists believe that the decline is related to global warming, which has led to a sharp increase in the temperature of the Mediterranean Sea. They also expect to find similar declines in other parts of the Mediterranean Basin.
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The study, which was published last week in the Proceedings B biology research journal of Britain’s Royal Society scientific academy, was based on 119 samples of various species of molluscs – a category of animals that includes snails and shellfish. They were sampled at 16 sites along Israel’s Mediterranean coastline, from shallow water up to a depth of 90 meters (295 feet).
The research team compared the numbers of living molluscs that they found with previously reported population sizes, as well as estimates of their prevalence based empty shells found on the sea floor. The drop was greater than anything ever seen before.
The study was led by Dr. Paolo Albano, a marine biologist from the University of Vienna, whose team included researchers from Croatia and the United States, as well as Dr. Gil Rilov of the Israel Oceanographic and Limnological Research Institute in Haifa.
According to the research findings, in the shallower areas, the variety of species plummeted to 12 percent of what existed in the past in the soft sea bottom and to only 5 percent in the areas of sea floor that are rocky. About 60 percent of the species found in the shallower water aren’t surviving to their reproductive age.
At major depths, the rate of decline in the biodiversity was a smaller 50 percent.
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“The magnitude was totally unexpected,” said Albano in an interview with The Guardian following publication of the study. “What I found was a desert, totally devoid of even common Mediterranean species.”
The murex, for example, a gastropod the excretions from which were used in ancient times to make purple clothing dye, was no longer found off the coast, Albano said.
Along Israel’s coast, an environment reminiscent of a tropical region has developed, populated by various invasive species, the scientists wrote. What has evolved is a “novel ecosystem” whose restoration to historical baselines appears unachievable, they stated.
The scientists said they believe the sharp decline in the diversity of species along Israel’s coastline was related to the warming of the Mediterranean. In the past four decades, the temperature of the eastern Mediterranean has risen by about 3 degrees Celsius, reaching water temperatures of 32 degrees Celsius (nearly 90 degrees Fahrenheit) during the summer. Many species have not been able to adapt to such a high temperatures and are therefore disappearing. According to prior studies, there are several species with a greater resilience to heat that have survived in greater numbers.
The disappearance of species may also be related to other causes, including competition with invasive species coming from the Red Sea via the Suez Canal or due to disease or environmental pollution. But the scientists note that many of these native species don’t actually compete with invasive species.
The Haifa Bay was not included in the sampling because it is known as an area that still suffers from pollution from poisonous metals, and other sources of pollution were found to have an effect only at the local level. In the past, disease has only caused harm to a single species, meaning that disease also cannot explain the sharp decline.
The decline in mollusc species is likely to have a major impact on the ecosystem of the Mediterranean, the Guardian noted in its coverage of the study. Molluscs play a major role in regulating the chemistry of the marine environment by recycling nutrients and removing nitrogen and phosphorus, the newspaper explained. Some of the job may be assumed by new invasive tropical species from the Red Sea, but based on preliminary findings, it appears that their role would not be the same, it was noted.
Molluscs also have a role in creating the rocky marine surfaces. One type of mollusc secretes a substance that creates the rocky surfaces that can be seen jutting out of the water near the shoreline. Israel’s coastline has not remained empty of molluscs because there is a substantial presence of invasive species, but they don’t perform the same ecological task.
“In experiments being conducted in our laboratory, we demonstrate that the Mediterranean species are less able to withstand the warming of the water than the invasive species are, and apparently that is why they are becoming rarer,” said Rilov of the Israel Oceanographic Institute. “The present study is definitive proof of the far-reaching effects of climate change and the urgent need for a drastic reduction of greenhouse gas emissions. The drastic change in biodiversity also presents a challenge to the policy of marine nature preservation and for determining criteria for a healthy and functioning ecological system.”