Terrestrial Laser Scanning Reveals Seagrass Microhabitat Structure on a Tideflat

Michael Hannam,L Moskal

doi:10.3390/rs70303037

Abstract

Local-scale environmental heterogeneity can provide microhabitats that influence the spatial distribution of competing species. Microhabitats may influence the distribution of seagrasses along elevation gradients, but difficulty measuring intertidal microtopography has hindered quantification. Using a terrestrial laser scanner (TLS), we mapped and monitored a 1.84 ha study site for three years to understand spatial and temporal patterns of sediment microtopography. We performed high-accuracy GPS surveys and vegetation surveys of a native and an invasive seagrass. TLS provided sub-decimeter scale precision in digital elevation models (DEMs) of the tideflat. The location and shape of microtopographic features were stable from year to year, but the magnitude of local relief varied. A simple index of topographic context predicted the shoot density of the native seagrass, Zostera marina and the invasive seagrass, Zostera japonica, but the shoot density of the invasive seagrass was better predicted by the shoot density of Z. marina than by topographic context. Microtopographic relief at this site appears to exert a strong influence on the meter-scale distribution of seagrass. We demonstrate the potential for TLS mapping of habitat-relevant microtopography in a soft sediment intertidal environment where TLS faces substantial challenges but promises unique insights.

Highlights

Spatial environmental heterogeneity can lead to spatial patterns in species distributions, allow for coexistence of species competing for the same limiting resource [1], and influence biodiversity [2].Fine-scale topographic heterogeneity can be influential in intertidal communities
Position Index (BPI) mapping, and comparison of digital elevation models (DEMs) among years. We limited these analyses to the area that was scanned in all three years (Figure 1) We visually examined empirical semivariograms of terrestrial laser scanner (TLS)-derived DEMs to assess the scale of topographic patterns at the site
We have demonstrated the potential for Terrestrial Laser Scanner (TLS) mapping of habitat-relevant microtopography in a soft sediment intertidal environment

Summary

Introduction

Spatial environmental heterogeneity can lead to spatial patterns in species distributions, allow for coexistence of species competing for the same limiting resource [1], and influence biodiversity [2]. Fine-scale topographic heterogeneity can be influential in intertidal communities. Small crevices and tidepools can provide thermal refugia [3]. Microtopographic relief can trap water during low tides providing additional habitat for desiccation sensitive species [4,5,6], and affecting spatial patterns of herbivory [7]. Recent work has shown that microtpopgraphic relief can influence competitive interactions between these species [8], but the relationship between microtopography and the distribution of these species has not been quantified or critically tested

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Results

Discussion

Conclusion