Fish in the Eastern Mediterranean
I recently wrote this letter to a witness of mine, a prodigiously successful pharmacologist who thinks I should have been a scientist. I had been trying to explain to him why there aren't very many fish in the Eastern Mediterranean.
Dear Phil,
I reread my book about why there aren't very many fish in the Eastern Mediterranean. The book is The First Eden by David Attenborough, published in 1987 (Chapter 4; Strangers in the Garden -- Marine Invaders From the East). It actually explains that there used to not be many fish there, but there are more fish now. The gist of it is:
I reread my book about why there aren't very many fish in the Eastern Mediterranean. The book is The First Eden by David Attenborough, published in 1987 (Chapter 4; Strangers in the Garden -- Marine Invaders From the East). It actually explains that there used to not be many fish there, but there are more fish now. The gist of it is:
- Everything in the Mediterranean came in from the Atlantic when the seas rose and breached the cliffs at Gibraltar. There was a beautiful waterfall for 100 years and then the Mediterranean was full.
- The Mediterranean is saltier than the Atlantic because it's shallower and sunnier and thus evaporates faster. All the briny water falls to the bottom. Salty bottom water flows west out of the sea into the Atlantic, fresher water on the top flows east into the sea.
- The sea life in the Mediterranean either rode the waterfall in over the Gibraltar Straits or crawled across the Gibraltar ledge in later millennia. Thus, no deep sea fish from the Atlantic made it into the Mediterranean, which means the deepest parts of the Sea are pretty uninhabited except for mollusks and bacteria.
- Plankton comes in from the Atlantic and floats along the surface feeding many surface fish like anchovies, etc. But when it falls to the bottom it does not make the nice nutrient ooze it makes in the Atlantic because the bottom salty water keeps flowing west out of the Sea altogether. The nutrients are constantly swept away.
- So the Sea has fewer nutrients. This is why it's so pretty and clear. Also, the Sea is too cold for coral to grow. This leaves not very much for fish other than surface fish to eat.
- So, to consider the eastern coast of the Mediterranean, it's briny and not very nutritious on the bottom, and sunny but not particularly warm on the top, and the fish had to swim all the way from Gibraltar to get there. So although there are fish there, they never came close to filling up the eastern sea and became kind of picky eaters, dilettantes, never had to fight for much, food or sun or anything. Lazy fish. Fish living the high life.
- Then de Lesseps built the Suez Canal and connected the only sea saltier than the Mediterranean, the Red Sea, which also happened to be slightly higher in elevation and overpopulated. Tons of tropical fish there were fighting for resources because the Sea was warm enough to support coral and it didn't have the nutrient-sucking problem created by Gibraltar.
- In the 1920s, opportunistic Red Sea fish and crustaceans hitched rides on the bottoms off ships going north, colonized the Bitter Lakes, and reached the frontier of the eastern Mediterranean. Because it was so unpopulated, the Red Sea-ers stayed for good. Homesteading.
David Attenborough notes that for reasons no-one clearly understands except perhaps that the native Eastern Mediterranean fish had not come anywhere near to exhausting their natural resources before the Red Sea-ers arrived, the newcomers have not displaced the natives at all. Everyone lives side by side happily.
Regards,
posted by Anonymous @ 7:41 PM
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