Thursday, April 13, 2017

Sponge Predation by Cowries

Opposed to popular belief, sponges do not actually live in a pineapple under the sea and do not protect secret hamburger recipes from evil copepods. However, we do know that they can often be found nestled in the crevices of coral reefs.

In Kane’ohe Bay, you can find a wide variety of different species of sponge along our coral reefs, but one of these species is of high interest to some of our researchers here at HIMB. This species of sponge, Mycale grandis (Orange Keyhole Sponge) (Figure 1), is an invasive species that was unintentionally brought into our waters as fouling organisms on Australian ships. In other words, the sponge grew on the hulls on these boats and then were brought to Hawaii accidentally. Around 1996, reports began to surface of this newly introduced sponge being found in the Pearl Harbor Bay, but in relatively low concentrations. Soon after, these sponges made their way to Kane’ohe Bay where they were found to have a much more significant abundance and distribution across the coral reefs, specifically in the Southern Bay near Coconut Island.

Figure 1. Mycale grandis, or the Orange Keyhole Sponge. Here, you can clearly see the
“Key Hole” pores covering the sponge.

In 2004-2005, scientists at NOAA performed some research to try and calculate the rate of growth of the M. grandis sponge and found that the sponge abundance increased by about 13% in just the one year. In the second year of research, they came to the same conclusion when they found significant growth at 7 of 11 observation sites, with the most significant growth still being around Coconut Island. This trend has continued throughout the years and can now be seen throughout the Kane’ohe Bay coral reef system.

So, I am sure you are asking, “Why is this important? What’s wrong with this sponge living on our coral reefs?” Well, good thing you asked! As with all invasive species, they create an unnatural competition with native species of sponge and cause a disturbance in the balance of the ecosystem. Here in Kane’ohe Bay, they can be seen growing over some native coral species as well. Simply put, M. grandis moved in to the reefs around Coconut Island and are making the native corals and native sponges uncomfortable!

In effort to stop the invasive sponge from spreading even further into the bay or expanding to other islands, officials tried to remove the sponge mechanically, but found that this method was too time consuming and not efficient as the sponge would grow back very quickly. They also tried to remove the sponge by injecting the sponge with air. This method was very effective but also requires a lot of resources and may not be the most efficient method.

This now brings us to the research being done here at HIMB. Our researchers, Jan Vicente and Andrew Osberg, are considering the possibility of controlling the growth of the invasive sponge by experimenting with Tiger Cowries. These snail-like creatures can also be found along our coral reefs, slowly grazing on algae and sponge. Our researchers are hoping to find out more about the Tiger Cowries preferred diet and if they will eat the M. grandis that is threatening our coral reefs. To do this, they are comparing the M. grandis to various other species of native sponge that can also be found within our coral reefs to see which one the Tiger Cowries prefer to eat. If they have an appetite for the invasive M. grandis, then this could be a big step towards preventing any further growth and expansion of the invasive sponge!

Post by Kevin O'Rourke

Bishop Museum and University of Hawaii–Guidebook of Introduced Marine Species of Hawai’i. N.p., 2002. Web. 2017.

NOAA – Assessment of Invasiveness of Orange Keyhole Sponge Mycale Armata in Kaneohe Bay, Oahu, Hawaii Based on Surveys 2005-2006, Year 2 of Hawaii Coral Reef Initiative. N.p., 2007. Web. 2017.

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