KOROR STATE GOVERNMENT MARINE TOUR GUIDE ... - C3

Typical lagoon golden jellyfish (left) from Risong, a close relative of Ongeim’l Tketau’s
golden jellyfish (right). The rounded end of the jellyfish is commonly called the ‘bell’ and
the frilly looking structures trailing the bell are called ‘oral arms’. This name reflects their
function. They are covered with stinging cells and thousands of small mouths (hence the
term oral). As the medusa swims forward by contracting its bell, water flows across the
oral arms and small organisms (plankton) are captured by stinging cells and ingested by
the mouths. The structures trailing from the ends of the oral arms are called ‘clubs’ and
are generally much shorter in lake medusae. Their function is unknown.
Interestingly, the ancestors of the golden jellyfish that live in the lake can be seen today
inhabiting coves around the archipelago. Lagoon and lake golden jellyfish share many
features including their source of energy. Like corals, both lake and lagoon jellyfish get
most of their energy from microscopic algae living in their tissues. Like land plants, the
algae use the energy of sunlight to produce the sugars (energy) necessary to grow and
reproduce. They share some of the sugars they generate with their jellyfish hosts. These
algae also confer both types of jellyfish with their color, which is reflected in their
common name, the golden jellyfish.
The fact that both lagoon and lake golden jellies have algae also indicates that the
commonly repeated story - that the lake jellyfish’s relationship with algae originated in
the lake in response to a lack of food (i.e. the original founding jellyfish lacked algae) - is
a myth. The original colonizing jellyfish already depended upon algae for energy.
Similarly, the jellyfish in the lake did not lose their sting as their dependence upon algae
for energy evolved. Both lake and lagoon golden jellyfish have a mild sting. These
stinging structures are used to capture tiny (planktonic) prey, which constitute a part of
their diet.
So what makes the lake jellyfish different from their ocean ancestors?
The golden jellyfish’s reliance on algae and, thus, sunlight for energy has influenced
their behavior. For example, both lake and lagoon jellyfish rotate in a counter-clockwise
direction as they swim which ensures algae in all tissues are exposed to the sun.
55