338
Nutrition of Corals
the cell membrane. They are also capable of sedimentary filter feeding,
using for thus the ciliar apparatus and mucus nets. Lastly, they are highly
specialized predators, possessing mechanisms for catching, swallowing and
digesting the moving animal preys. The polyps of scleractinian corals have
the largest ratio of catching area of the body to its biomass among all other
aquatic animals. It seems, therefore, very possible that their apparent
evolutionary success and their flourishing in biotopes of the tropical shelf are
to be ascribed precisely to their capability to use most sources of energy
available for sessile animals: light, plankton and dissolved organic matter. In
spite of the remarkably strong competition for solid bottom substrate in
tropical shelf zones, corals had been during former geological periods and
are at present time among the dominating elements of the benthic fauna.
The problem of the feeding of corals has been a topic of discussion for
over 60 years (Muscatine 1973). Early investigations of the feeding of
actinians and corals in 1905-1910 demonstrated that coral polyps, like the
actinians, actively capture animal food, such as pieces of meat or planktonic
crustaceans. In has been established that in their gastral cavities food was
crushed by the joint action of moving mesenterial filaments and digestive
enzymes. The particles formed were then phagocytosed and transported into
the polyp's tissues by wandering cells. All kinds of plant food including
zooxanthellae were rejected by them (Vaughan 1912; Boshma 1925b). But
also at that time Gardiner and later Gravier (1913) concluded that even if
capable of predation, coral polyps got their basic nutrition anyway from
their algal symbionts with which their cells were literally packed. This quite
reasonable conclusion was later countered by the famous investigator of
coral physiology, Sir Maurice Yonge (1930a,b). He insisted on the predatory
feeding of corals as being the dominating one and did not recognize the role
of the algal symbionts in coral nutrition. His arguments were that corals
have a large catching surface and extremely developed structures for
predation, and so the polyps supporting these without any profit would be
unreasonable, moreover, that the animal tissues in polyp comprise over 90%
of the total biomass. The polyps also actively rejected in his experiments all
kinds of plant food. He strongly insisted on the correctness of his opinion
even in the 1960s and early 1970s, when it looked already somewhat stronge,
especially after the conclusive experiments of Franziskett (1970), proved the
importance of autotrophic feeding of corals. The opinion of such an
acknowledged expert as Maurice Yonge opposing autotrophic feeding of
corals definitely retarded at that time the development of the idea about
their symbiotic nature. But the appearance in the early 1970s of numerous
publications about photosynthesis in corals, which proved the translocation
of photosynthates from zooxanthellae to polyps, finally have led to the
recognition that the energy budget in them is based upon the autotrophic
production of their algal symbionts. Moreover, common opinion after
Fanziskett (1970) started to reject the opposite conclusion that corals really
did not need any other sources of energy at all except the one
Nutrition of Corals
the cell membrane. They are also capable of sedimentary filter feeding,
using for thus the ciliar apparatus and mucus nets. Lastly, they are highly
specialized predators, possessing mechanisms for catching, swallowing and
digesting the moving animal preys. The polyps of scleractinian corals have
the largest ratio of catching area of the body to its biomass among all other
aquatic animals. It seems, therefore, very possible that their apparent
evolutionary success and their flourishing in biotopes of the tropical shelf are
to be ascribed precisely to their capability to use most sources of energy
available for sessile animals: light, plankton and dissolved organic matter. In
spite of the remarkably strong competition for solid bottom substrate in
tropical shelf zones, corals had been during former geological periods and
are at present time among the dominating elements of the benthic fauna.
The problem of the feeding of corals has been a topic of discussion for
over 60 years (Muscatine 1973). Early investigations of the feeding of
actinians and corals in 1905-1910 demonstrated that coral polyps, like the
actinians, actively capture animal food, such as pieces of meat or planktonic
crustaceans. In has been established that in their gastral cavities food was
crushed by the joint action of moving mesenterial filaments and digestive
enzymes. The particles formed were then phagocytosed and transported into
the polyp's tissues by wandering cells. All kinds of plant food including
zooxanthellae were rejected by them (Vaughan 1912; Boshma 1925b). But
also at that time Gardiner and later Gravier (1913) concluded that even if
capable of predation, coral polyps got their basic nutrition anyway from
their algal symbionts with which their cells were literally packed. This quite
reasonable conclusion was later countered by the famous investigator of
coral physiology, Sir Maurice Yonge (1930a,b). He insisted on the predatory
feeding of corals as being the dominating one and did not recognize the role
of the algal symbionts in coral nutrition. His arguments were that corals
have a large catching surface and extremely developed structures for
predation, and so the polyps supporting these without any profit would be
unreasonable, moreover, that the animal tissues in polyp comprise over 90%
of the total biomass. The polyps also actively rejected in his experiments all
kinds of plant food. He strongly insisted on the correctness of his opinion
even in the 1960s and early 1970s, when it looked already somewhat stronge,
especially after the conclusive experiments of Franziskett (1970), proved the
importance of autotrophic feeding of corals. The opinion of such an
acknowledged expert as Maurice Yonge opposing autotrophic feeding of
corals definitely retarded at that time the development of the idea about
their symbiotic nature. But the appearance in the early 1970s of numerous
publications about photosynthesis in corals, which proved the translocation
of photosynthates from zooxanthellae to polyps, finally have led to the
recognition that the energy budget in them is based upon the autotrophic
production of their algal symbionts. Moreover, common opinion after
Fanziskett (1970) started to reject the opposite conclusion that corals really
did not need any other sources of energy at all except the one