Associations between biota and substrata on rocky seashores in temperate southern Australia

Author: Nathan Janetzki

Janetzki, Nathan, 2019 Associations between biota and substrata on rocky seashores in temperate southern Australia, Flinders University, College of Science and Engineering

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Empirical fieldwork enhances our understanding of the associations between intertidal assemblages and the physical attributes of rocky substrata. Research investigating associations between intertidal biota and rock type has largely overlooked established assemblages on rock platforms and later-successional (i.e. >1 year) assemblages on boulders. Moreover, data for the hardness, temperature behaviour and mineralogy of different seashore rocks is often lacking. This makes it difficult to reliably associate these physical attributes with any rock-related differences in the structure, richness and abundances of individual taxa for rocky seashore assemblages. Here I have addressed these knowledge gaps by investigating under-studied biota and rock physical attributes for rocky seashores in temperate southern Australia.

Field-based surveys were used in Chapter 2 to quantify the hardness of seven rock types and to investigate associations between established platform assemblages and rock hardness. No general association between intertidal biota and rock hardness was identified, with most hardness-related biotic differences specific to the bioregion sampled. A boulder transplant experiment was used in Chapter 3 to investigate changes across later-successional (i.e. 5-6 year) assemblages on limestone and siltstone boulders. Limestone supported assemblages with a greater richness and taxonomic abundances than siltstone, with these biotic differences most-strongly correlated with the greater surface complexity of limestone. These results show that rock type is associated with the development of different assemblages on boulders from earliest colonisation and recruitment until the later stages of succession six years later.

The temperature behaviour, in relation to mineralogy, for boulders of six rock types was established in Chapter 4 using a common-garden experiment. This experiment showed that during sunny weather each rock type had patterns of temperature difference which consisted of warmer and cooler areas at the scale of millimetres to centimetres. The maximum temperature of boulder surfaces differed consistently between rocks, with purple and grey siltstone the hottest and white limestone and quartzite the coolest. The temperature maxima were associated with the major mineral and trace element content of rocks, with rock types with the hottest temperatures having the highest metallic content. The biological relevance of this small-scale temperature heterogeneity on boulder lower surfaces was investigated in Chapter 5. Seashore sampling showed that three snail species were strongly associated with lower-surface temperature patterns. Snails generally occupied cooler areas on boulder surfaces, with stronger associations detected on hotter versus cooler rock types. Overall, these studies contribute much to our understanding of rock physical attributes how intertidal biodiversity is associated with different rocks and their physical attributes as substratum.

Keywords: seashore, intertidal, rock, boulder, invertebrate, algae, community ecology, thermal imagery, mineralogy

Subject: Environmental Science thesis

Thesis type: Doctor of Philosophy
Completed: 2019
School: College of Science and Engineering
Supervisor: Peter Fairweather