Researchers at Florida State University have gained a deeper understanding of a strange marine organism found in oceans around the world and what their presence means for the health of marine ecosystems. Scientists once thought that sea bottles — small marine organisms that look like transparent gelatinous matter — compete primarily for resources with krill, which is an important food source for many marine animals. But new research, published in Limnology and Oceanography, suggests that the bottle is actually competing for food with a creature known as a protozoa.
Researchers at Florida State University have gained a deeper understanding of a strange marine organism found in oceans around the world and what their presence means for the health of marine ecosystems. Scientists once thought that the sea bottle — small marine organisms that look like transparent gelatinous matter — competes primarily for resources with krill, which is an important food source for many marine animals. But new research, published in Limnology and Oceanography, suggests that sea cucumbers are actually competing for food with a creature known as a protozoa.
Michael Stukel, a researcher at FSU's Ocean-Atmosphere Prediction Research Centre and an associate professor in the Department of Earth, Ocean and Atmospheric Sciences, said: "These fascinating and exotic animals are becoming more and more numerous in the vast and warming Southern Ocean, so we are trying to understand how their presence changes marine ecosystems. "
Although sea bottles may resemble jellyfish, they are one of the earliest examples of chordate evolution and are therefore more closely related to humans.
These organisms live in oceans around the world and feed on phytoplankton. When their food sources are abundant, the sea bottles reproduce rapidly with the help of unusual breeding cycles, forming large splashes made up of thousands of organisms. They eat algae, then compress them into small particles and sink them to the bottom of the sea, thus achieving the effect of removing carbon dioxide from the atmosphere.
Sea bottles are also a food source for some marine animals, but they do not provide much nutrient. Their importance in the marine food web is overshadowed by krill, a nutritious food for a variety of animals, from tiny anchovies to giant whales. The old theory was that sea bottle breeding squeezed out krill, resulting in more carbon sequestration, but less food for marine life.
But conversely, the bottle may have replaced tiny protozoa, which are not an important food source for the larger creatures in the ocean. Although the bottles are much larger than those of the protozoa, they feed on the same microscopic algae. Imagine an elephant and an ant eating the same food.
To understand what size of prey the bottles ate, the researchers built a circular tank filled with sea bottles and seawater with their prey. They measured the fluorescence emitted by the prey of the sea bottle living in the water and tracked its change over time to understand the size of the prey that was eaten.
Since protozoa are the same size as their prey, they need to use a different method to observe what size of prey they are eating. The researchers filled one bottle with seawater, which contained a typical number of protozoa and prey, and the other filled with diluted seawater, which reduced the frequency of predators and prey encounters. After 24 hours, they could use the same fluorescence measurement technique to see what kind of prey the protozoa ate.
Understanding that sea bottles may compete with protozoa rather than krill gives reason to rethink the role of their reproduction in marine ecosystems.