What Makes Sponges Grow?

Sponges are animals that eat tiny food particles as they pump water through their bodies. They are very common on Caribbean coral reefs, and come in all shapes, sizes and colors. There is great variability in their size: some sponges are very small (just a few centimeters) while others are very big, like the giant barrel sponge, which can be six feet wide. Even sponges of the same species can vary greatly in size—but why?

Marine biologist Joseph Pawlik tested which factor is more important to sponge growth: access to food, which helps them grow bigger, or accessibility to predators like angelfish, which can nibble away at sponges faster than they can grow. With his research team, Pawlik tested both possibilities by protecting some sponges from predation by putting them in protective cages, and did this in both deep water, where there are more food particles, and in shallow water. After a year, sponges in cages grew a lot more because they were protected from angelfishes, but sponges did not grow more in deep water. This shows that sponges are more affected by predation than food. Removal of angelfishes by fishing may result in sponges overgrowing and killing the corals that build coral reefs.

This video received honorable mention in the inaugural Ocean 180 Video Challenge in 2014, hosted by the Florida Center for Ocean Sciences Education Excellence (COSEE Florida). Scientists were challenged to bring their latest research papers to life in a short video that not only summarizes their important findings but also highlights the relevance, meaning, and implications of the research to people outside of their area of study. Submitted videos were reviewed by a panel of scientists and communication experts, but the final winners were selected by a diverse (and often very critical!) group of potential future ocean scientists–6th to 8th grade students from classrooms around the world.