Sandy Shores
 
 

Sandy shores (sand beaches) are mainly found at sites of higher physical wave energy. In the study area sand beaches extend over 146 km of coastline.
In some cases coral reefs run parallel to the coastline in the sublittoral of sandy shores. At a part of the sandy shore sites, a mixed sandy/rocky zone is present in the mid and lower eulittoral. Sometimes rocky outcrops can also be found near the littoral fringe. Further landward from the littoral fringe there regularly is a belt of small sand dunes, which are up to 200 centimetres high. This belt of dunes is often followed by a transition to flat sand sheets.
The sediments of most sandy shores mainly consist of medium grained quartz sand and some shell fragments, which lead to a calcium carbonate content of 5 – 7%.
The vegetation of sandy beaches is mainly formed by shrubs (up to 60 cm high), perennial grasses and some parasitic plants. In detail the most important species are:

  • Suaeda maritima
  • Seidlitzia rosmarinus
  • Bienertia cycloptera
  • Sporobulus iocladus
  • Halophyrum mucronatum
  • Cyperus conglomeratus
  • Cynomorium coccineum
  • Cistance tubulosa

The typical animals living on sandy beaches in the study area are crabs such as Ocypode rotundata, gastropods, polychaetes such as Owenia sp., marine snails and bivalves such as Dosinia hepatica. Most of them life either close to the littoral fringe or down the beach beneath the sand, where over 200 species of macroscopic animals have been recorded.

Most of the sandy shores in the study area were heavily affected by the 1991 Gulf War Oil Spill. Nearly every biota was killed at the hydrocarbon - polluted sites. From the mid eulittoral to the littoral fringe the sandy substrate was considerably oiled. At many sites the upper eulittoral was covered by a closed solid asphalt-like layer.

 
   
     
 
tarcover
Continous band of oil and tar two years after the Gulf War Oil Spill  
 

The fauna of the lower eulittoral seemed not very much affected by the oil. But in the upper eulittoral, especially where tar crusts have accumulated, no living animal was visible in 1992.
By the time the oil tend to percolate into deeper layers of the substrate. This increases the thickness of the oiled horizons.

 
 

oildepth

Oil distribution within the sediment of a sandy beach in 1992 and 2001 (Barth 2002b)

 
 

On the surface wave action was often able to break and rework the tar crusts within the first 2-4 years. At many sites clean sand has accumulated on top of the oiled substrate between HWS and HWN until 1994.
These clean sand layers provide almost normal living conditions to many plants and animals. Therefore recolonisation took place there quite early and species diversity and abundance was relatively high again four years after the Oil Spill.

sandcover

Two years after the

oil spill, new clean

sand has

accumulated on top

of an oil - polluted

beach.

 
 

In general, the recovery was most rapid in the mid and lower eulittoral. Also in the upper eulittoral of lower wave energy sites the recovery was good, despite the fact, that there the amount of oil did not decline significantly until 2001. In those cases recovery is due to the recolonisation of biota in the clean sand layers on top of the contaminated substrate.
At most sandy beaches, especially where wave energy is higher, the strong oxygen influx into the sand by wave action led to nearly complete oil degradation until 2001. Therefore, oiled layers weren’t visible anymore at many sites.
Where tar crusts sealed polluted sediments, hydrocarbon degradation was hampered by oxygen deficit and the oil was still there in 2001. Due to more recent oil spills the thickness of the tar crusts at some sites, especially on beachrock outcrops, even increased.

 
 

The studies showed, that diversity and abundance of life are closely related to the extend of hydrocarbon pollution. Where oil degradation worked quickly, full recovery was possible within four to five years after the 1991 Gulf War Oil Spill. In accumulated clean sand on top of oiled layers species recolonised even earlier. But oiled sediments under clean sand layers as well as those under tar crusts were lifeless until 2001.

 
   

(Barth 2002, Abuzinada&Krupp 1994) (photos: F. Krupp)

 
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