232
Coral Reef Fish
prefer polyps of alcyonaceans. There are also omnivorous species of this
genus, their species feeding on zoobenthos, and also herbivores feeding on
macrophytes and periphyton. And to each kind of trophic specialization
corresponds the appropriate construction of the mouth parts, body forms
etc. (Harmelin-Vivien 1981; Reese 1981; Cox 1988). A more detailed
description of the main trophic guilds of reef fish is given below.
6.3.1 Herbivorous Reef Fish
Herbivorous reef fish form one of the most important trophic guilds, which
includes some 10-20% of the total species and 15-50% of total fish biomass
(Tables (6.10-6.13). Sometimes their biomass comprises over 50% even
of the total (Harmelin-Vivien et al. 1988). Plant food (macrophytes,
periphyton) is also used by omnivorous fish as an additional food source. As
to the conditions favoring the flourishing of herbivorous fish in reef
environments, a main one of these could be seen in the domination on reef
of plant material that is readily edible and easily digested by fish, like
periphyton, microphytobenthos, coralline algae, especially the articulated
kind, and mini-thallomic macrophytes (Bakus 1969). Another cause is the
high temperature of reef waters, enhancing the function of enzymes which
participate in the digestion of plant material by fish. Herbivorous fish are the
latest branch of evolution of reefal bony fish. Being descended from ancient
acanthopterigian fish of the Late Eocene (Hobson 1974), they acquired a
small mouth with powerful jaws and firm massive teeth, which later in some
of them fused together and formed plates of "bills" (Scaridae). Among
other adaptations acquired by herbivorous fish are the throat teeth for the
grinding of crude plant material, extremely elastic stomachs, which could
contain a large mass of plant food, and long intestines. But most of the
herbivorous fishes (exept mugilids) do not have the enzyme cellulase that
dissolves the walls of plant cells. Perhaps they use for this purpose the
cellulase produced by their intestine's microflora.
By their mode of feeding herbivorous fish could be subdivided into
browsers, grazers and suckers. The first feed on macrophytes and seagrasses,
the second on scrape periphytonic turfs and crusts of coralline algae, and the
third suck in or gently collect the films of detritus and the fine turfs of
microphytobenthos from the surface of soft bottom sediments. The fish of
the firsh of these groups have a fine-walled but elastic stomach, and of the
second a powerful thick-walled stomach which resembles the muscular
stomach of birds, being destined for crushing coralline algae crusts. The long
intestines and the long time of digestion make for the high efficiency of
herbivorous fishes in digesting plant material. Its assimilability was
evaluated to be within 30 to 60%. Some fish, which have a low assimilability
compensate it by a high feeding rate (Ogden and Lobel 1978). In stomachs
of acanthurids the presence of agarolythic bacteria was recorded, which
Coral Reef Fish
prefer polyps of alcyonaceans. There are also omnivorous species of this
genus, their species feeding on zoobenthos, and also herbivores feeding on
macrophytes and periphyton. And to each kind of trophic specialization
corresponds the appropriate construction of the mouth parts, body forms
etc. (Harmelin-Vivien 1981; Reese 1981; Cox 1988). A more detailed
description of the main trophic guilds of reef fish is given below.
6.3.1 Herbivorous Reef Fish
Herbivorous reef fish form one of the most important trophic guilds, which
includes some 10-20% of the total species and 15-50% of total fish biomass
(Tables (6.10-6.13). Sometimes their biomass comprises over 50% even
of the total (Harmelin-Vivien et al. 1988). Plant food (macrophytes,
periphyton) is also used by omnivorous fish as an additional food source. As
to the conditions favoring the flourishing of herbivorous fish in reef
environments, a main one of these could be seen in the domination on reef
of plant material that is readily edible and easily digested by fish, like
periphyton, microphytobenthos, coralline algae, especially the articulated
kind, and mini-thallomic macrophytes (Bakus 1969). Another cause is the
high temperature of reef waters, enhancing the function of enzymes which
participate in the digestion of plant material by fish. Herbivorous fish are the
latest branch of evolution of reefal bony fish. Being descended from ancient
acanthopterigian fish of the Late Eocene (Hobson 1974), they acquired a
small mouth with powerful jaws and firm massive teeth, which later in some
of them fused together and formed plates of "bills" (Scaridae). Among
other adaptations acquired by herbivorous fish are the throat teeth for the
grinding of crude plant material, extremely elastic stomachs, which could
contain a large mass of plant food, and long intestines. But most of the
herbivorous fishes (exept mugilids) do not have the enzyme cellulase that
dissolves the walls of plant cells. Perhaps they use for this purpose the
cellulase produced by their intestine's microflora.
By their mode of feeding herbivorous fish could be subdivided into
browsers, grazers and suckers. The first feed on macrophytes and seagrasses,
the second on scrape periphytonic turfs and crusts of coralline algae, and the
third suck in or gently collect the films of detritus and the fine turfs of
microphytobenthos from the surface of soft bottom sediments. The fish of
the firsh of these groups have a fine-walled but elastic stomach, and of the
second a powerful thick-walled stomach which resembles the muscular
stomach of birds, being destined for crushing coralline algae crusts. The long
intestines and the long time of digestion make for the high efficiency of
herbivorous fishes in digesting plant material. Its assimilability was
evaluated to be within 30 to 60%. Some fish, which have a low assimilability
compensate it by a high feeding rate (Ogden and Lobel 1978). In stomachs
of acanthurids the presence of agarolythic bacteria was recorded, which