Ecology of animals living in intertidal boulder-fields

Professor Gee Chapman


Background
Intertidal boulder-fields consist of loose rocks which are covered during high tide and out of water

Intertidal boulder-fields are habitats consisting of loose rocks, of various sizes, that lie on a rocky, sandy or muddy bottom and which are covered during high tide, but mainly out of water during low tide. The tops of the boulders often support the same types of animals and seaweeds as are found on intertidal rocky shores. The undersurface of a boulder provides a very different sort of habitat, especially in very sheltered areas where they are not frequently overturned by waves. Many types of attached animals, such as sponges and ascidians, live underneath boulders, along with an interesting array of snails, brittlestars, chitons and other mobile animals. Many of these are relatively rare and not commonly found in other marine habitats.

Little is known about the ecology of rare invertebrates, particularly rare marine animals. Because boulder-fields are accessible and support a wide diversity of animals, some of which are common and some of which are quite rare, they are therefore an ideal habitat in which to investigate aspects of rarity in marine invertebrates. In addition, boulders can be disturbed, by natural events, such as storms or by human disturbances, e.g. foraging for food. Measuring effects of such disturbances on rare animals is important for developing plans of management for their protection.

Aims

This broad-scale project has a number of aims. The first is to document the diversity and abundances of animals and plants that live in these habitats. Second, we are comparing natural patterns of variability of these animals at many different spatial scales, from boulder to boulder in a boulder-field, up to comparisons among boulder-fields many kilometres apart. This variation is being compared to that found on rock-platforms to identify any similarity of ecological processes between these two habitats. We are simultaneously examining patterns of change through time, again to compare temporal processes in boulder fields to those on seashores. Third, we are comparing patterns of difference and change of rare species and more common species that live in boulders-fields and other intertidal habitats. This will identify how much of our knowledge of common intertidal animals will be applicable to those rarer animals, for which it is very difficult and expensive to collect relevant data.

Importance
The tops and under-surfaces of intertidal boulders provide very different habitats

This work is important because it will add to our knowledge of a suite of rare Australian animals, many of which are unique to Australia. It will also add to our understanding of how rare marine invertebrates vary in space and time in comparison with common animals and in comparison with rare terrestrial invertebrates. This knowledge will be very important in developing plans to conserve these animals.

Results

We have collected data on patterns of difference and change of the suite of species living under boulders in a number of different boulder fields.

We have also been testing hypotheses about colonization of individual boulders, i.e. that particular characteristics of a boulder or where it is lying in a boulder-field affect colonization and that patterns of colonization are similar for common and rare species. We have also tested whether the sessile animals and plants that live on boulders affect colonization by mobile animals, or that animals readily colonize new surfaces.

This project has generated a lot of data, most of which is being analysed and written up now for publication.