Abstract
The influence of soil temperature on rhizome depths of four intertidal seagrass species was investigated in central Queensland, Australia. We postulated that certain intertidal seagrass species are soil temperature-sensitive and vertically stratify rhizome depths. Below-ground vertical stratification of intertidal seagrass rhizome depths was analysed based upon microclimate (soil temperature) and microhabitat (soil type). Soil temperature profiles exhibited heat transfer from surface layers to depth that varied by microhabitat, with vertical stratification of rhizome depths between species. Halodule uninervis rhizomes maintain a narrow median soil temperature envelope; compensating for high surface temperatures by occupying deeper, cooler soil substrates. Halophila decipiens, Halophila ovalis and Zostera muelleri rhizomes are shallow-rooted and exposed to fluctuating temperatures, with broader median temperature envelopes. Halodule uninervis appears to be a niche specialist, with the two Halophila species considered as generalist niche usage species. The implications of niche use based upon soil temperature profiles and rhizome rooting depths are discussed in the context of species' thermal tolerances and below-ground biomass O2 demand associated with respiration and maintenance of oxic microshields. This preliminary evidence suggests that soil temperature interaction with rhizome rooting depths may be a factor that influences the distribution of intertidal seagrasses.
Highlights
Understanding what influences the distribution of species in intertidal zones has implications with regard to climate change with subsequent repercussions for how we consider restoring these habitats
As an initial step to investigate this hypothesis, we examined linkages between below-ground vertical stratification based upon microclimate and microhabitat
Four species were examined in this study, of which, H. uninervis is tropical in extent, with Z. muelleri, H. ovalis and H. decipiens being both temperate and tropical species (Green & Short, 2003; New Phytologist (2017) www.newphytologist.com
Summary
Understanding what influences the distribution of species in intertidal zones has implications with regard to climate change with subsequent repercussions for how we consider restoring these habitats. Shafer et al (2007) identified eight factors that can be attributed to intertidal seagrass zonation from the literature, with no one factor appearing to control all species’. Of these eight factors, three (desiccation, air exposure and high irradiance) are most commonly investigated regarding potential constraints leading to intertidal zonation (Fig. 1). Three (desiccation, air exposure and high irradiance) are most commonly investigated regarding potential constraints leading to intertidal zonation (Fig. 1) These eight factors have been discussed within the literature, a full understanding of the causes of intertidal zonation of seagrass species still eludes researchers. As Shafer et al (2007) suggest, it may be a combination of factors, including growth strategies, that explain intertidal seagrass zonation
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