Live Water, Dead Water, Live Water

A quick ecology quiz: Is there more life in cold waters or warm waters?

Our journey has provided some wonderful empirical evidence on this question. When we set out from Cape Town, water temperatures in the Atlantic hovered around 50 degrees Fahrenheit. When we reached Richards Bay in northeastern South Africa, the Indian Ocean clocked in somewhere in the 70s. And as we crossed the Tropic of Capricorn off the coast of Mozambique, the mercury was up around 80 degrees.

So, where did we see the most marine life? Around Cape Town. The ocean is cold there, because it is fed by upwellings from the deep ocean. That deep water is cold, but it is also full of nutrients. As a result, the water around Cape Town is rich with sea birds, Penguins, Fur Seals, and our friend the Great White Shark.

The waters around Richards Bay, on the other hand, appeared virtually devoid of life. The jetties at Cape Town were crowded with cormorants, gulls, and terns. The jetties at Richards Bay were empty.

This pattern is not special to South Africa. The richest marine environments around the world are concentrated in places with cold, nutrient-rich waters -- places like the Arctic, the Antarctic, Georges Bank, the Galapagos, the southern Sea of Cortez, etc.

Happily, warm water doesn't have to mean no marine life. As we moved further into the tropics off Mozambique, we began to see more critters. Flocks of sooty terns diving on shoals of bait driven to the surface by predatory fish. A fairly rare pod of Melon-headed Whales (photos). And several pods of Transtropical Spotted Dolphins and Spinner Dolphins. There's still not as much biomass as down near the Cape, but there's enough to keep things interesting.