Coral Reefs and Mangroves, parts 2 & 3

I. Ecology of Reef Fishes
    A. Geographical pattern of coral species distribution is reflected in coral reef fishes
        1. reefs have highest diversity fish communities
        2. highest diversities in IndoPacific
    B. Hypotheses to explain reef fish diversity
        1. Competition model
            a. A.K.A. Specialization or Deterministic Hypothesis
            b. Strong competitive interactions have lead to specialization -- narrow niches
            c. Support – positive correlations btwn. fish diversity and habitat complexity
            d. Evidence against -- are many generalist fishes
            e. Implications – recruitment is not limiting; competition is the primary structuring force
        2. Lottery Hypothesis
            a. Fish are not highly specialized but produce large numbers of offspring that by chance can occupy any unfilled space
            b. Outcome of competition is determined by luck of which species recruited
            c. Implications – competition is less important, variable recruitment is the primary structuring force
        3. Predation-disturbance model
            a. A.K.A. Nonequilibrium Hypothesis
            b. Unpredictable events limit population sizes
            c. Populations do not reach equilibrium; little competition
            d. Implications – random events are important; competition is unimportant
        4. Recruitment Limitation model
            a. Recruitment never high enough for adults to reach carrying capacity
            b. Recruitment determines adult population size, not post-recruitment events
            c. Support - in damselfish 90% of variation in adult abundance explained by recruitment
            d. Implications – competition is unimportant, recruitment is the primary structuring force
    C. Movements of Fishes
        1. Most reef fishes are restricted to small parts of the reef and do not migrate
        2. Some are territorial
        3. Nocturnal and diurnal patterns
            a. Migrations from feeding areas to rest areas by some fishes
            b. Fish excretia/fecal material brings N and P to the coral
        4. Movements with tides
    D. Ecological Roles of Reef Fishes
        1. predators - most common
        2. herbivores and coral grazers
            a. ~15% of species
            b. most important are the parrotfishes and the surgeonfishes
            c. without fish grazing, many corals would be outcompeted by macroalgae
        3. omnivores
        4. zooplankton feeders -- few, small schooling fish
    E. Defense mechanisms to avoid predation
        1. Hide

        2. School
        3. Toxins
            a. sea cucumber toxins can kill fish; also sticky materials
            b. fishes
                (1) venom associated with spines
                (2) poisonous material on the body surface (crinotoxin)
                (3) toxic flesh and internal organs
                    (a) causes human disease -- ciguatera
                    (b) accumulation of toxins from a dinoflagellate
        4. Fish coloration
            a. warning coloration
            b. camouflage
            c. visual communication
    F. Cleaning behavior
        1. specialized predation -- some small fishes and shrimp remove ectoparasites from other larger fish
        2. widespread; 'cleaning stations' found on all reefs
        3. cleaner mimics
II. Cryptofauna and Bioerosion
    A. cryptofauna – invertebrates hiding in crevices or the CaCO3 matrix of the reef
        1. two kinds
            a. true borers
            b. opportunists
         2. some cause erosion of the reefs
         3. most are detritivores, eating organic material
    B. Bioerosion not only by the crypofauna, but also by echinoids and grazing fish can be very significant

III. Symbiosis on reefs
    A. Definitions
          1. symbiosis - close interrelationship between two different species
three basic types

                a.       commensalism - symbiosis that is to the advantage of one member and doesn't harm the other
                    (1)    special case: inquilinism - commensalism where one animal lives in the home of another (or in its digestive tract without being parasitic)
                    (2)    partner getting the advantage is the commensal the other partner is the host
                b.       mutualism - symbiosis of benefit to both species; the partners are symbionts
                c.       parasitism - symbiosis in which one species gains and the other is harmed
    B.     Often very hard to measure costs and benefits

    C.     Examples

IV. Coral Reef Long-Term Dynamics

    A. Succession and Stability
        1. Succession

        2. Large scale destructive forces
            a. Storms
            b. Population explosions of coral predators (e.g., Acanthaster planci)
                (1) is some evidence that these outbreaks have occurred historically --
                (2) unclear whether the outbreaks have increased or what the trigger is
                    (a) predator-removal hypothesis -- starfish predators gone
                    (b) run-off hypothesis --
                        i. juvenile recruitment is enhanced by phytoplankton blooms that follow a year of high rainfall and run-off
                        ii. exacerbated by humans
                        iii. outbreaks of adult starfish follow 3 years later
                        iv. fits the pattern of outbreaks, but no direct evidence
                    (c) adult aggregation hypothesis -- tropical storms; concentrate adults
            c. Regional climatic swings (El Niño) and elevations of water temperature (correlated with coral bleaching)
            d. coral bleaching -- zooxanthellae expelled
            e. Disease producing organisms
                (1) black-band disease
                (2) white-band disease

        3. Human activities
            a. dredging
            b. pollution (Kaneohe Bay, Hawaii)
            c. overfishing
            d. mining of coral
            e. destructive fishing techniques
            f. oil pollution
            g. Jamaican example -
        4. recovery
            a. depends on extent of destruction, rate of recolonization, conditions for establishment, time between disturbances…
            b. long-term prognosis is not good

I. Community Composition and Adaptations
    A. Trees and shrubs -- 12 genera in 8 families (~80 species)
    B. Root types (2)
        1. Shallow extensive roots
            a. air shafts called pneumatophores extend above the surface
            b. Conduct air to roots in anoxic sediments
        2. Distinctive prop roots that run from aboveground parts into the sediments
    C. Salt balance
        1. Internal water storage -- leaves are succulent
        2. Ability to tolerate high salt concentrations
        3. Salt secreting glands
        4. Reverse osmosis in the roots to separate fresh and salt water
    D. Reproduction
        1. vivipary
        2. water-borne dispersal
II. Distribution
    A. Wider distribution than coral reefs
    B. Tropical and subtropical shores that are well-protected from wave action
    C. Can not survive where there are frosts  (are replaced by salt marshes as move north)
    D. Can penetrate upstream along river banks
    E. Absent from many isolated islands and atolls
III. Physical Conditions of Mangrove Forests
    A. Low wave action and roots make for slow water and increased sedimentation - mud
    B. Sediment in a mangal is most often mud
    C. Can cause land to accumulate at 200 m/year!
    D. Reduce coastal erosion
    E. Mangals thrive in areas of high tidal range
    F. Unlike corals, mangroves can thrive in estuaries and in areas of high run-off
IV. Zonation -- no generalized scheme yet proposed
    A. Horizontal – from the sea, inland
        1. Pacific, 30-39 species of mangrove
        2. Americas -- Florida has only 3 mangrove species
    B. Vertical – from sediment into the branches
        1. terrestrial organisms in the upper branches -- e.g., insects; epiphytes
        2. marine organisms in the sediments and bases of trees -- mollusks, crustaceans, fishes; some occupy hard
            substrate of the stilt roots; some occupy the mud
V. Associated Organisms
    A. Epiphytic colonists on above ground tissues
    B. Birds
    C. Nurseries for fishes and crustaceans -- mullet; penaeid shrimps and spiny lobsters
    D. Marine fauna
        1. mollusks
        2. Crabs
        3. Endangered and peculiar fauna
            a. Specialized fish -- mud-skippers (Periophthalmus)
            b. American crocodile
            c. brown pelican
            d. Atlantic Ridley sea turtle
        4. complex interactions poorly understood
VI. Succession and Mortality
    A. Classical view – zonation patterns are part of a sere (successional series)
    B. Both biotic and abiotic factors are important in zonation
    C. Human induced mortality -- has destroyed ~1/2 of the world's mangals
        1. herbicides
        2. filling and dredging; water channelization
        3. cutting for firewood
        4. oil spills -- mangroves are very sensitive to oil residue
        5. fish and shrimp farming -- mangals razed to build ponds to raise shrimp; also pollutes the surrounding water;
            current efforts to make this sustainable

 Return to Marine Ecology Lecture homepage

 Return to K.L. Schulz's homepage