Bermuda Natural History

Geologic History

The information for this summary is from a lecture given at BBSR by David Malmquist.

Bermuda is a volcanic sea mountain that formed from the mid-Atlantic ridge approximately 100 million years ago. Through the processes of plate tectonics and sea floor spreading, this volcano moved to the west of the mid-Atlantic ridge and became extinct. About 30 million years ago, the volcano erupted again, probably due to it floating over a hot spot in the Earth's crust. Afterwards, the volcano became extinct again, and has remained so to this day. Bermudians do not seem to worry about an eruption anytime soon! Actually, there are two calderas, or mouths, of the volcano. There are both located under water - one is at Hamilton Harbor and the other is at Castle Harbor.

Over the millions of years, a limestone cap has formed on top of the volcanic rock. The origin of this limestone is living organisms - those that make up and live in the coral reef. There are two categories here: reef builders and reef breakers. Reef builders, which include coral and the algae that live symbiotically with them, produce a calcium carbonate skeleton. Reef breakers, such as parrotfish, come along and eat the algae that is living on the coral. In the process, they inevitably break off and ingest some of the calcium carbonate. This calcium carbonate passes through the gut of the fish and comes out as sand (lime sand, to be exact). Over time, as sea level fluctuated, this sand was pushed up onto the volcanic rock and sand dunes were formed. Through the processes of dissolution and cementation, this sand became rock (limestone). Dissolution and cementation involve acidic rain (all rain is naturally, slightly acidic because of dissolved carbon dioxide from the air) falling on the sand and dissolving it. When the water evaporates, limestone is formed.

To summarize, Bermuda is an underwater volcano with a limestone cap. When one looks at the natural terrain today, only the limestone cap is visible. Of course, one can also see plenty of sand (yes, it is pink!) and also some rich, red soil known as terra rossa soil. You may be wondering why the sand is pink. It is because of organisms called forams, whose shells are pink and are mixed in with the sand formed by the reef builders and breakers.You may also be wondering where the terra rossa soil came from. Believe it or not, scientists believe that much of it is atmospheric dust that has been blown to Bermuda from the Sahara desert (by hurricanes in the summer) and from the Great Plains of North America (by westerly winds in the winter)! There is also evidence (the presence of a lot of phosphate) that bird guano has contributed to the formation of terra rossa soil. Another interesting geologic phenomenon on Bermuda is the existence of many caves. These formed when acidic rain dissolved some of the limestone as it percolated dwon and then out to sea. This would lead to there being a long tunnel. Then, the tunnel ceiling collapsed in some places, but not in others, forming caves.

Flora and Fauna - a History and Brief Description

The following information about coral is from a lecture given at BBSR by Sheila McKenna.

Of course marine life is very important in Bermuda. Although Bermuda is not very far south, its water is kept warm by the Gulf Stream. Therefore, coral and many tropical fish can survive here, having migrated north from the Carribean. Bermuda's reef is the northern most coral reef in the world! The series of islands is surrounded by one big coral reef, known as an atoll because .... The reef holds many wonderful organisms. The primary creatures are of course the corals themselves. Living with the coral organisms, in a symbiotic relationship, are algaae called zooxanthallea. The coral provide a place to live and shelter for the algae and the algae provide nutrients for the coral, through photosynthesis. Bermuda's water is lacking in nutrients, so without the photosynthetic algae, the coral would not be able to survive. Living among the coral, are many different sea creatures, from sea anemones to sea cucumbers to a myriad variety of fish. Coral reefs are considered important ecosystems by environmental scientists. They are often compared to tropical rainforests in terms of biodiversity.

I have chosen to concentrate on the terrestrial ecology of Bermuda. The flora and fauna on land are fascinating and, unfortunately for the native species, offer a perfect example of the harm that introduced species can do to an ecosystem. You may wonder how did any species get to this remote series of islands. Plants were the first terrestrial organisms to colonize Bermuda, their seeds carried by wind, water, or bird. Eventually, some birds made their home there, while others still just pass through on their migratory path. A lizard (the skink) even made its way there without human help. Since humans first discovered the Bermuda islands, they have brought in many other organisms. For more information on this see Native and Endemic Species of Bermuda, Nonnative Species, and Environmental Problems of Bermuda.

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