13 April 2009

Between the Gulf of Mexico tides

I grew up along the Aegean coasts of the Mediterranean where tides are imperceptible. I had only read about tides, but not experienced them until about 20 years ago during a vacation in Florida when I first noticed the rising and the receding of the sea at a beach. Last week at the west coast of Florida I spent many hours watching, photographing, collecting, examining and measuring intertidal snails and also performing simple experiments with them à la Darwin.

Here is the north shore of the Dunedin Causeway at high tide. The causeway connects the Honeymoon Island to the mainland.


And the same coast at low tide.


Only now am I finally beginning to grasp the significance of the daily tides in the lives of the intertidal animals in general and snails in particular. Reading the books like the classic Between Pacific Tides of Ricketts et al. certainly helps, but mostly in an abstract sense; one needs to be at a coast right at the edge of the sea during both high and low tides and to pay attention to the creatures both during immersion and emersion to begin to acquire a slight understanding of how the intertidal ecosystems may have evolved and how they continue to function.


Of course, it is not just the tides that rule the lives of the coastal species. Also important are the microtopography, insolation, wave exposure, availability of food, and the presence predators, parasites and competitors. I will probably think of more factors to add to this list later.

1 comment:

Anonymous said...

The total tidal range on Nevis is only about one foot which is maybe even less than in the Aegean.

My having grown up on Britain, which has large tidal ranges, there being such a small tidal range on Nevis really takes getting used to. There's not much of an intertidal zone at all there.

Also the tides there are diurnal rather than semidiurnal.


Susan J. Hewitt