210
Reef Zoobenthos
and sedimented detritus, dissolved organic matter, various plant materials -
seaweeds, grass, microphytobenthos and periphyton. A significant part of
benthic fauna is represented by predators, as well as by parasites, symbionts
or commensals living with other animals (Gibbs 1978), Numerous benthic
animals are symbiotic with algae. A tentative classification of the main
components of reef benthic communities in relation to their econiches is
given in Table 5.4. It demonstrates among them an abundance of groups
using external sources of energy: light and food sources which arrive to the
reef from the surrounding oceanic waters, such as plankton, detritus and
dissolved organic matter. Besides the involvement with external energy,
benthic communities by using these external food sources introduce into the
coral reef ecosystem also external nutrients - nitrogen and phosphorus -
providing thus their positive balance (d. Sect. 2.2.2). And the fact of an
abundance of filter-feeders within the benthic communities themselves is an
indirect proof of the abundance of plankton in reef waters (d. Sect. 3.4).
Above, the drastic influence of grazing on the composition of reef benthic
communities was also mentioned. Indeed, its stress is very high there
because of a high density of predators - fish, polychaetes, gastropods, stars,
urchins. In the course of evolution benthic animals developed numerous
morpho-physiological and behavioral adaptations to escape grazing (Bakus
1969). These adaptations and also the availability of refuges enable them to
escape grazing and also to preserve a high specific diversity (Grassle 1973).
Among these adaptations there could be mentioned:
1. A high motility and a quick reaction in many free-living invertebrates and
in those living in shells and tubes, which help them to escape the
predators' attack.
2. Protective coloration, mimicry (nudibranchs, gastropods, crabs) and
warning coloration (nudibranches, holothurians).
3. Coloration polymorphism, which prevents the imprinting of a permanent
image of the prey in the predator.
4. Large size of animals decreasing the possibility of being grazed
(tridacnids, holothurians, asteroids, large gastropods).
5. Defence of the body with the aid of nematocysts or poisonous culverian
filaments (actinians, hydroids, holothurians, nudibranchs).
6. Firm outer skeleton (molluscs, crabs, urchins, asteroids), firm tunics
(ascidians, holothurians) internal sharp spicules (sponges, octocorals),
brittle body (brittle stars, crinoids).
7. A bad test, bad smell or toxicity of tissues and of covers of the body.
Of the latter kind of adaptations toxicity is extremely widespread among the
reef fauna (Bakus 1969, 1981; Cameron 1976). Out of reef sponges
investigated 75% were poisonous for man, and of coelenterates 100%, of
annelid worms 60%, of crustaceans 75%, of urchins 54%, of fish about
80%. Such groups of sessile reef benthic animals as sponges, hydroids, and
Reef Zoobenthos
and sedimented detritus, dissolved organic matter, various plant materials -
seaweeds, grass, microphytobenthos and periphyton. A significant part of
benthic fauna is represented by predators, as well as by parasites, symbionts
or commensals living with other animals (Gibbs 1978), Numerous benthic
animals are symbiotic with algae. A tentative classification of the main
components of reef benthic communities in relation to their econiches is
given in Table 5.4. It demonstrates among them an abundance of groups
using external sources of energy: light and food sources which arrive to the
reef from the surrounding oceanic waters, such as plankton, detritus and
dissolved organic matter. Besides the involvement with external energy,
benthic communities by using these external food sources introduce into the
coral reef ecosystem also external nutrients - nitrogen and phosphorus -
providing thus their positive balance (d. Sect. 2.2.2). And the fact of an
abundance of filter-feeders within the benthic communities themselves is an
indirect proof of the abundance of plankton in reef waters (d. Sect. 3.4).
Above, the drastic influence of grazing on the composition of reef benthic
communities was also mentioned. Indeed, its stress is very high there
because of a high density of predators - fish, polychaetes, gastropods, stars,
urchins. In the course of evolution benthic animals developed numerous
morpho-physiological and behavioral adaptations to escape grazing (Bakus
1969). These adaptations and also the availability of refuges enable them to
escape grazing and also to preserve a high specific diversity (Grassle 1973).
Among these adaptations there could be mentioned:
1. A high motility and a quick reaction in many free-living invertebrates and
in those living in shells and tubes, which help them to escape the
predators' attack.
2. Protective coloration, mimicry (nudibranchs, gastropods, crabs) and
warning coloration (nudibranches, holothurians).
3. Coloration polymorphism, which prevents the imprinting of a permanent
image of the prey in the predator.
4. Large size of animals decreasing the possibility of being grazed
(tridacnids, holothurians, asteroids, large gastropods).
5. Defence of the body with the aid of nematocysts or poisonous culverian
filaments (actinians, hydroids, holothurians, nudibranchs).
6. Firm outer skeleton (molluscs, crabs, urchins, asteroids), firm tunics
(ascidians, holothurians) internal sharp spicules (sponges, octocorals),
brittle body (brittle stars, crinoids).
7. A bad test, bad smell or toxicity of tissues and of covers of the body.
Of the latter kind of adaptations toxicity is extremely widespread among the
reef fauna (Bakus 1969, 1981; Cameron 1976). Out of reef sponges
investigated 75% were poisonous for man, and of coelenterates 100%, of
annelid worms 60%, of crustaceans 75%, of urchins 54%, of fish about
80%. Such groups of sessile reef benthic animals as sponges, hydroids, and