JELLYFISH LAKE - BIOLOGICAL EVOLUTION

As rising oceans and incoming tides carried percolating sea water into the lakes, they also allowed microscopic organisms to flow through the small limestone pores. Among those microscopic organisms were the larva of a variety of invertebrate organisms and fish. One of those larval organisms was a jellyfish of the genus Mastigias. These jellyfish feed by capturing small zooplankton with their cnematocysts (stinging cells). Once trapped inside the lake, Mastigias found that there was not enough plankton to support their predatory habits. Luckily, this versatile creature it was armed with a more creative method of feeding.

Mastigias jellyfish (along with hard corals and giant clams), harbor an interesting group of algae cells in their tissues called zooxanthellae. The algae cells collect sunlight and photosynthesize creating an excess of sugars and proteins. The Mastigias release an enzyme which forces the zooxanthellae to give up this valauble resource. In exchange for this free meal the jellyfish carry the algae cells throughout the day, to the areas of the lake with the highest concentration of sunlight. Their migrations are not only horizontal but vertical as well. When the sun sets, the Mastigias sink down to the bottom of the lake to collect nitrates and phosphates to fertilize their algae cells. Thus the jellyfish have made a fascinating evolutionary transition from aggressive predators to passive farmers.

The relationship between the jellyfish and algae cells is known as mutualism. Most animal populations are constrained by their food supply. As the Mastigias population in this lake is limited only by sunlight and nutrients the numbers of individuals will be staggering.

As the Mastigias began to rely only on sunlight for their food supply they no longer had the need to produce metabolically expensive tentacles and stinging cells. The slow elimination of these structures through evolutionary time is a classic example of regressive evolution.

You may also encounter a large see-through Cnidarian known as a moon jellyfish (Aurelia). They are primarily nocturnal so will not be encountered in great numbers. Although they still make their living by capturing microscopic animals, their stinging cells are not powerful enough to harm a human being.

Know more about Jellyfish Lake...
  •  Geology
  •  Biological Evolution
  •  Ecology
  •  Conservation
  •  Visiting Jellyfish Lake