Long distance biotic dispersal of tropical seagrass seeds by marine mega-herbivores - PubMed (original) (raw)

Long distance biotic dispersal of tropical seagrass seeds by marine mega-herbivores

Samantha J Tol et al. Sci Rep. 2017.

Abstract

Terrestrial plants use an array of animals as vectors for dispersal, however little is known of biotic dispersal of marine angiosperms such as seagrasses. Our study in the Great Barrier Reef confirms for the first time that dugongs (Dugong dugon) and green sea turtles (Chelonia mydas) assist seagrass dispersal. We demonstrate that these marine mega-herbivores consume and pass in faecal matter viable seeds for at least three seagrass species (Zostera muelleri, Halodule uninervis and Halophila decipiens). One to two seagrass seeds per g DW of faecal matter were found during the peak of the seagrass reproductive season (September to December), with viability on excretion of 9.13% ± 4.61% (SE). Using population estimates for these mega-herbivores, and data on digestion time (hrs), average daily movement (km h) and numbers of viable seagrass seeds excreted (per g DW), we calculated potential seagrass seed dispersal distances. Dugongs and green sea turtle populations within this region can disperse >500,000 viable seagrass seeds daily, with a maximum dispersal distance of approximately 650 km. Biotic dispersal of tropical seagrass seeds by dugongs and green sea turtles provides a large-scale mechanism that enhances connectivity among seagrass meadows, and aids in resilience and recovery of these coastal habitats.

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Conflict of interest statement

The authors declare that they have no competing interests.

Figures

Figure 1

Figure 1

Illustration of biotic dispersal of seagrass seeds by marine mega- herbivores. (a) Ingestion of seagrass seeds or propagules by a dugong or green sea turtle allows long distance dispersal of the seed; (b) before settlement and growth into a seedling. Figure created by Samantha Tol, using images provided by Tracy Saxby, Catherine Collier, Diana Kleine, and the Integration and Application Network, University of Maryland Center for Environmental Science (

ian.umces.edu/imagelibrary/

).

Figure 2

Figure 2

Mean monthly (a) number of seagrass seeds (Zostera muelleri, Halodule uninervis, Halophila ovalis, and Halophila spp.) per g DW mega-herbivore faecal matter; (b) proportion of seeds with a split seed coat per g DW faecal matter; (c) proportion of viable seagrass seeds found per g DW faecal matter collected across all sampling sites between September and December 2014. Crosses indicate data outliers for the sampled months and the box plots indicating the median, quartiles and 95 percentiles.

Figure 3

Figure 3

Zostera muelleri seed with a split coat; the seed was removed from a marine mega-herbivore faecal sample collected in Cleveland Bay, north Queensland Australia, in 2014.

Figure 4

Figure 4

Map of intertidal seagrass meadows (green) in the central Great Barrier Reef, Queensland (QLD) Australia where mega-herbivore faecal matter samples were collected between September and December 2014. The inset map shows the location of the central region (red box) of the Great Barrier Reef World Heritage Area (blue). The map is overlayed with a subset of current known seagrass meadows (available from

http://eatlas.org.au/data/uuid/77998615-bbab-4270-bcb1-96c46f56f85a

). This map was created using ArcGIS v10.3 software by Esri software (

http://www.esri.com/software/arcgis/new

). ArcGIS and ArcMap are the intellectual property of Esri and are used herein under license.

Figure 5

Figure 5

(a) A Zostera muelleri seed (with seed coat removed) taken from marine mega-herbivore faeces returned a positive stain, turning the cotyledon pink; (b) A germinated Zostera muelleri seed removed from marine mega-herbivore faeces.

References

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