Salient

Victorian Theses

By Matthew Proctor | 24 Mar, 2008

Ingrid Knapp is a student from the School of Biological Science, whose PhD thesis is on the effects of invasive species of sponges on Summer Atoll, about 1000 miles south of Hawaii. She holds a BSc (Hons) from the University of Wales, where her Honours thesis on “Seabird Predation on Small Molluscs” was first in her year, entitling her to skip a Master’s degree, and study directly towards a Doctorate.

Summer Atoll was used by the Americans as a naval base in World War II. During the war, extensive construction took place on the atoll, including a road joining all the islets together, dredging of the lagoon, and construction (and subsequent degradation) of concrete buildings. However, although the lagoon is filled with an unusually high level of sediment, the reef surrounding the atoll is in Knapp’s words “pretty much pristine,” which is surprising given the level of human activity.

The atoll is unusual in that the sponges are apparently just in the lagoon. “They’re pretty much absent from the reef. The reef also lacks a lot of other macrofauna. They haven’t got a lot of crabs or molluscs.”

The bulk of Knapp’s work will be identifying and classifying the various species of sponges to be found on the atoll, and identifying which are native to the atoll, and which are invasive species accidentally introduced by American sailors. By using genetic analysis on the mitochondrial DNA of the introduced sponges, Knapp hopes to identify their source, by comparing samples from the atoll to those from the Caribbean (which she suspects to be the source), mainland Hawaii, and Mexico. Sponges have a very low dispersal rate, so they could not have arrived there naturally.

Because there has been no study on sponges on this atoll previously, Knapp is unsure what effect the introduced species may have had in the 60 years since they were introduced, and to what extent colonies have grown over that time.

“They could be slowly moving towards the reef … We’re looking at whether they’re maintained in the lagoons, or if they have the potential to leave the lagoons. However, the effect of fish and other predators around the reef, who cannot survive in the heavily sedimented lagoon, is not known.”

“Sponges take out oxygen … potentially inhibiting native species… There’s lots of little ones underneath boulders, and we don’t know if they’re native or invasive, and if they’ve been restricted to the boulders if they are native… And we’re just looking at how the sponges survive in the sedimented areas… The effects the sediment has on … the sponge hasn’t really been covered [before].”

Knapp’s main goals are just to look at the effect of such high sediment levels on sponges, and to assess the extent to which the introduced species have escaped the lagoon. She hopes that if they have done so, some kind of management plan can be formulated, although she recognises the potential costs involved.

She is also especially looking forward to diving on the atoll to collect samples. The reef is home to unusually high numbers of large fish, “and 44% of the fish are sharks. That’s pretty cool!”

Apparently no post-graduate students read Salient any more. If you want to restore my faith in the ability of student media to reach a wide audience, and would be happy to discuss your thesis with me, please contact me atmatt@salient.org.nz.