Populations and communities

Macroinvertebrate communities within caves and their limiting factors

Caves offer a unique opportunity to study the responses of aquatic communities to changing abiotic conditions and food resources. Surface streams are known to be high in autochthonous and allochthonous materials, but as a stream enters a cave, allochthonous inputs decrease and photosynthetic producers are lost. It is expected that these changes in food abundance and type within caves will greatly influence aquatic communities.

Abiotic changes within caves, include loss of light, stabilisation of air and water temperatures, and a differing dissolved oxygen regime from surface communities. Biotic changes include a reduction in primary production, which may lead to cave communities becoming dependent on allochthonous energy, rather than autochthonous energy. As part of his MSc research, Troy Watson will be focusing his research on how aquatic macroinvertebrate communities change along this light gradient, from full light upstream of the cave entrance, to deep within the cave where light is lost, and again within full light when the stream exits the cave. Troy predicts that cave macroinvertebrate communities will differ from surface macroinvertebrate communities due to these gross abiotic and biotic changes.

Predatory mayfly approximately 100 m into Ruakuri Cave	Mayfly and glow-worm interaction, approximately 250 m into Hollow Hill Cave

Troy's research will address four main questions: 1) how does the light gradient outside and within caves alter the diversity and abundance of macroinvertebrate communities; 2) what are the environmental drivers associated with caves that influence the structure of aquatic populations; 3) how do aquatic invertebrates disperse within caves; and 4) are these dispersal mechanisms within caves different from dispersal mechanisms of non-cave invertebrates?

People involved in this project

University of Canterbury
Troy Watson (MSc Student)
Jon Harding

National Institute of Water & Atmospheric Research (NIWA)
Graham Fenwick