Follow this link to:
Saltmarsh retreat zone (front page of Mangrove Cove Monitoring web site)
Mangrove expansion photopoints
Time changes everything
When the Management Plan for Mangrove Cove was written in 2005, analysis of the extent of mangroves and samphires on the site was undertaken. Aerial photography from 2002 was classified into mangrove, mud flat and saltmarsh. The same three classifications have been used for the analysis of aerial photography from 2011.
Maps of the vegetation, (top: 2004, middle: 2011 and bottom: change map)
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Table showing area of each habitat, 2004 and 2011
2002 |
2011 |
Comparison |
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| Habitat | m 2 |
% |
m 2 |
% |
% |
| Mangrove | 2784 |
10% |
4726 |
17% |
170% |
| Mudflats | 19828 |
71% |
20849 |
74% |
105% |
| Supratidal | 3255 |
12% |
2215 |
8% |
68% |
| Samphire | 1460 |
5% |
30 |
0% |
2% |
| Transition | 753 |
3% |
291 |
1% |
39% |
28080 |
100% |
28111 |
100% |
100% |
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0.11% total area change due to georeferencing errors. |
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Definitions
Mangrove means a cover of mangrove that no other vegetation or mud can be seen through, from the air
Samphire means a mid dense or denser cover of chenopods including Sarcocornia sp, Tecticornia spp and Suaeda sp.
Mudflats means unvegetated mud
Supratidal means the area above normal high water
Transition means areas where the habitat is mixed - thinning saltmarsh with areas of mud showing through, very dark or pitted mudflat that could be changing toward or away from saltmarsh habitat, and areas of either saltmarsh or mudflat with occasional baby mangroves.
Discussion
The different habitats and vegetation associations have changed at different rates. For example, if we look at the mangrove cover, 2727 m2 of mangrove has not changed at all. No area that supported mangroves in 2002 has lost any cover. About 966m2 of what was mudflat in 2002 now supports mangroves, and 239 m2 of samphire was completely over-run by mangroves in the same period. Of the areas that were transitional in 2002, 508 m2 have converted to mangrove. A large area that was considered to be supratidal now supports mangroves (1121 m2). Overall, by 2010 mangroves covered 170% of the area they covered in 2002.
While some of the samphire areas have been over-run by mangroves (239 m2), a much larger area (871 m2) of samphire has died and been replaced by mud flats, and some (279 m2) of what was previously dense samphire is transitioning towards mud or mangroves. This vegetation association is the most labile of all, with only 30 m2 of samphire remaining unchanged over the period. Samphire covers only 2% of the area it covered in 2002.
While a large area of mudflat (966 m2) has been colonised by mangroves, there are no areas of mudflat that have been colonised by samphire. Despite losing some area to mangroves, there is more mudflat in 2010 than there was in 2002 (105%) because quite large areas that were samphire (871 m2) or transitional (250 m2) have converted to mudflat.
Areas that were transitional in 2002 have all converted to mudflat (250 m2) or mangrove (508 m2) and the new areas of transitional cover have been sourced from areas that were samphire (279 m2). The overal quantum of transitional cover is now only 39% of the area this type of habitat covered in 2002.
The area that was classed as supratidal has shrunk, because some of it has converted to mangroves (1121 m2).
The reasons for habitat change can be quite complex, however the prime reason in this case is lokely to be relative sea level change. The relative sea level at Port Adelaide has been changing rapidly. Reasons may include being in the graben zone of the horst and graben formation that results from the Para Fault and other local fault lines, oxidation and compresssion of underlying quaternary coastal alluvial deposits, and actual sea level rise due to warming oceans.
Subsidiary causes for the observed changes include shadowing and competetion once mangroves move into an area, and possibly changes to the supply and texture of silt to the area.
More mangroves in Jervois Basin
Jervois Basin is the old name for the reach of the Port River that lies between the Jervois Bridge and the Railway Bridge. While the entirety of the river would have been lined with mangroves when Europeans settled, they were quickly removed. In the last few years they have begun to establish themselves at several locations in the Port River and the Jervois Basin is no exception. Besides Mangrove Cove itself, other seedling mangroves can be observed growing along the foreshore of NewPort Quays between Mangrove Cove and the new marina, and across the river at "Rotten Row" there is a small patch of mangroves growing in the quiet corner formed on the southern side of the eastern landfall of the Jervois Bridge. Several of these small mangroves are now large enough to detect with aerial photography (2011) and so they can be observed as they attempt to reclaim the shores of the river.
Follow this link to:
Saltmarsh retreat zone (front page of Mangrove Cove Monitoring web site)
Mangrove expansion photopoints