4:l
Reef Environments
oceanic waters into the lagoon and back appeared to be the lime rocks of
ancient Pleistocene reefs (Oberdorfer and Buddemeyer 1985).
The salinity in reef waters is controlled by several factors, mainly by
evaporation and by their mixing with the and with fresh water from rivers.
The evaporation occurs on reefs very extensively, especially in overheating
shallows and on flat areas which drain during the ebbs. The refreshing of
reef waters happens most often on reefs near continents or high islands,
such as Tahiti, New Guinea, and Hawaii. The rains are especially intensive
during the winter, increasing the discharge of fresh water by rivers to the
reef areas, and thus decreasing drastically the salinity of reef waters, as it
often happens in the region of the GBR (Wolanski and van Senden 1983).
Periodial drops in salinity are often the cause of the mortality of corals in
the same regions. The seasonal fluctuations of salinity in lagoons of barrier
reefs under the influence of rain and river waters could attain 3-8%0. In the
lagoon of the GBR in summer salinity grows by up to 36%0, while in late
autumn it drops to 28-32%0 (Fig. 2.6), when the surrounding coral sea has a
salinity of 35.4%0 (Brandon 1973). During periods of river floods in winter it
could also drop by 1-3%0 (Wolanski and van Senden 1983). In lagoons of
atolls with an intensive water exchange, like the Bikini atoll, the salinity in
the lagoon is equal or slightly more than in the surrounding ocean (Ford
1949). But in the closed or semi-closed lagoons under the influence of
t/c
JO
26
22
18
JIj
J2
J(J
28
~mn7~---L--------------A-n-~-C-L-·p-{-·ta--t(-·o-n~
J(JO
200
o L--L __ ~====~~~~~~~
Ill-I ]T-JII ff-Y YJ-W 1Y-JI I-XI IlJ-J U-.m JY-Y
7976
7977
Fig. 2.6. Seasonal changes in water temperature (to, C), salinity (S) and precipitation
(Pr) in the lagoon of the GBR, near Townsville in 1976-1977. (After Relevante and
Gilmartin 1982)
Reef Environments
oceanic waters into the lagoon and back appeared to be the lime rocks of
ancient Pleistocene reefs (Oberdorfer and Buddemeyer 1985).
The salinity in reef waters is controlled by several factors, mainly by
evaporation and by their mixing with the and with fresh water from rivers.
The evaporation occurs on reefs very extensively, especially in overheating
shallows and on flat areas which drain during the ebbs. The refreshing of
reef waters happens most often on reefs near continents or high islands,
such as Tahiti, New Guinea, and Hawaii. The rains are especially intensive
during the winter, increasing the discharge of fresh water by rivers to the
reef areas, and thus decreasing drastically the salinity of reef waters, as it
often happens in the region of the GBR (Wolanski and van Senden 1983).
Periodial drops in salinity are often the cause of the mortality of corals in
the same regions. The seasonal fluctuations of salinity in lagoons of barrier
reefs under the influence of rain and river waters could attain 3-8%0. In the
lagoon of the GBR in summer salinity grows by up to 36%0, while in late
autumn it drops to 28-32%0 (Fig. 2.6), when the surrounding coral sea has a
salinity of 35.4%0 (Brandon 1973). During periods of river floods in winter it
could also drop by 1-3%0 (Wolanski and van Senden 1983). In lagoons of
atolls with an intensive water exchange, like the Bikini atoll, the salinity in
the lagoon is equal or slightly more than in the surrounding ocean (Ford
1949). But in the closed or semi-closed lagoons under the influence of
t/c
JO
26
22
18
JIj
J2
J(J
28
~mn7~---L--------------A-n-~-C-L-·p-{-·ta--t(-·o-n~
J(JO
200
o L--L __ ~====~~~~~~~
Ill-I ]T-JII ff-Y YJ-W 1Y-JI I-XI IlJ-J U-.m JY-Y
7976
7977
Fig. 2.6. Seasonal changes in water temperature (to, C), salinity (S) and precipitation
(Pr) in the lagoon of the GBR, near Townsville in 1976-1977. (After Relevante and
Gilmartin 1982)