A Lake that Lives When it Dries ?

 

Lemon Lake within Amberjack Preserve in Charlotte County, FL, is a most unusual body of water. It is a natural and thus very shallow FL lake with a tenuous tidal connection via Lemon Creek to Lemon Bay through Wildflower Preserve. But this creek is constricted with mangroves and mud and only the highest tides reach this brackish lake, which is filled also by rain water. Thus periods of drought and/or high evaporation can lead to partial or complete drying of the lake. You might think this would be a disaster, but exactly the opposite is true.

When the lake is full, the fish (mainly small herbivorous sheepshead minnows Cyprinodon), invertebrates and vegetation (mainly ditch grass Ruppia) flourish. Yet they are not easily available to birds since the water is too deep; thus few birds are seen there. During dry-downs the food is both more concentrated and present in more shallow water, providing a banquet for birds. These dry periods can generally be in April or August and the birds come from far and near to feast. This photo taken of a mixed species flock of water birds feeding in late April includes primarily great and snowy egrets and white ibises.

The different lengths of legs and shapes/sizes of bills are quite evident in these avian feeding frenzies. The usual and most reasonable explanation is that such feeding specialization minimizes the competition among species. The black necked stilt is an extreme example with very long legs and a long narrow bill designed for picking up small prey. The roseate spoonbill has a huge, bizarre bill with a flat tip with which is probes the bottom and clamps down on fish and invertebrates based on touch alone. The stilt sandpiper illustrates another very different mode of feeding in which it probes the shallow bottom with a strong bill.

Of course no environmental conditions favor all species- the prey go through cycles of increase and decline. Yet the dry down of lakes is known to benefit nutrient cycling, so in the long term the prey may also benefit from dry periods. I encountered a small softshell turtle walking across the drying mud and this might be one species that may have to simply tolerate the periods of low water.

If you visit a place such as Lemon Lake, remember that the natural cycle of life is for alternately high and low water levels which provide periodic bursts of food production and availability that attract water birds. This is not a zoo but real life, so the birds will not be present at all times. So return repeatedly over time and observe this amazing cycle of life and death.

Bill Dunson

About Bill Dunson

Bill Dunson, born in rural Georgia, skipped 12th grade and went directly to Yale. Bill subsequent-ly received a PhD in Zoology from the University of Michigan, studying softshell turtles. Bill is Professor Emeritus of Pennsylvania State University thanks to a career spent entirely at that institution, teaching and doing research on the physio-logical ecology and ecotoxiciology of reptiles, amphibians and fish. Always curious about nature, Bill has dedicated his life to learning and sharing his knowledge with others. He has served on many advisory boards here in Southwest Florida to preserve the water that gives life to our region.

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