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C. den Hartog and R.C. Phillips
be possible to make any sensible interventions in order to reverse the gradual
deterioration of the seagrass beds.
9.7 Conclusions
A general picture is sketched of the 'ideal' zonation pattern as found along the
coasts of the world. This picture has been worked out in more detail for the
intertidal seagrass beds that are composed of Zostera species along the
temperate coasts, and of Halodule and Halophila in the tropics. These genera
can dominate in the sublittoral where the larger sublittoral seagrasses are
absent.
Intertidal seagrass beds usually have less species and have less structural
elements developed than the sublittoral beds. An important part is played by
the dominant seagrass, as its activity rhythm determines whether associated
species can live in the seagrass bed as permanent inhabitants or not. Where
species live only temporarily in the bed, the species richness of the bed is
largely dependent on the quality of other habitats in the immediate vicinity. It
means that large, uninterrupted beds are not necessarily richer in associated
species than small beds that can form mosaics with other communities.
Since seagrasses display high primary productivity and have a relatively
rapid leaf turnover rate, they produce a prodigious amount of dissolved and
particulate organic matter which forms the basis for the detrital foodweb.
This is by far the most important and complex trophic pathway in the seagrass
beds. The other trophic pathway, direct consumption, is generally less
important.
Most of the questions in relation to the dynamics of the seagrass beds are
still unanswered, despite their relevance iflost beds are to be restored. Finally,
it has been pointed out that seagrass beds are declining the world over. A
number of cases of almost 'terminal' loss of seagrass are discussed. Even when
'purely natural' causes are involved, the conditions are often human-related,
as in the case of the greatest seagrass loss ever recorded, e. g. more than
lOOOkm 2 in Hervey Bay, Queensland, Australia.
References
Bauersfield P, Kleer RR, Durrant NW, Sykes JE (1969) Nutrient content of turtle grass
(Thalassia testudinum). Proc Int Seaweed Symp 6:637-645
Bay D (1984) A field study of the growth dynamics and productivity of Posidonia
oceanica (1.) Delile in Calvi Bay, Corsica. Aquat Bot 20:43-64
C. den Hartog and R.C. Phillips
be possible to make any sensible interventions in order to reverse the gradual
deterioration of the seagrass beds.
9.7 Conclusions
A general picture is sketched of the 'ideal' zonation pattern as found along the
coasts of the world. This picture has been worked out in more detail for the
intertidal seagrass beds that are composed of Zostera species along the
temperate coasts, and of Halodule and Halophila in the tropics. These genera
can dominate in the sublittoral where the larger sublittoral seagrasses are
absent.
Intertidal seagrass beds usually have less species and have less structural
elements developed than the sublittoral beds. An important part is played by
the dominant seagrass, as its activity rhythm determines whether associated
species can live in the seagrass bed as permanent inhabitants or not. Where
species live only temporarily in the bed, the species richness of the bed is
largely dependent on the quality of other habitats in the immediate vicinity. It
means that large, uninterrupted beds are not necessarily richer in associated
species than small beds that can form mosaics with other communities.
Since seagrasses display high primary productivity and have a relatively
rapid leaf turnover rate, they produce a prodigious amount of dissolved and
particulate organic matter which forms the basis for the detrital foodweb.
This is by far the most important and complex trophic pathway in the seagrass
beds. The other trophic pathway, direct consumption, is generally less
important.
Most of the questions in relation to the dynamics of the seagrass beds are
still unanswered, despite their relevance iflost beds are to be restored. Finally,
it has been pointed out that seagrass beds are declining the world over. A
number of cases of almost 'terminal' loss of seagrass are discussed. Even when
'purely natural' causes are involved, the conditions are often human-related,
as in the case of the greatest seagrass loss ever recorded, e. g. more than
lOOOkm 2 in Hervey Bay, Queensland, Australia.
References
Bauersfield P, Kleer RR, Durrant NW, Sykes JE (1969) Nutrient content of turtle grass
(Thalassia testudinum). Proc Int Seaweed Symp 6:637-645
Bay D (1984) A field study of the growth dynamics and productivity of Posidonia
oceanica (1.) Delile in Calvi Bay, Corsica. Aquat Bot 20:43-64