Intertidal Zone Ecosystems, continued

III. Rocky Shores --
        E. Tropical Intertidal Shores -- not as well studied
        1. more herbivorous fishes and crabs; more predaceous fish
        2. intense consumer pressure, desiccation, extreme heat

        3. high intertidal - barnacles; mid to low - mostly encrusting algae (26-90%) with
                few sessile animals; only in low intertidal is there high diversity
        4. no keystone species that prevent overgrowth by superior competitors
        5. persistent herbivory on invertebrates and fleshy algae maintains crustose algae
        6. recruitment may be important

    F. Patchiness -- small scale patterns within bigger picture
        1. temporally and spatially variable
        2. slope
        3. rock texture (rock type, cracks)
        4. wave action (storms…)
        5. desiccation differences (aspect of rock)
        6. clones -- create local patchiness -- actively fight each other

        7. sweeping clear of patches
        8. territoriality
        9. succession in disturbed patches
        10. random events
    G. Succession
        1. quick colonists of disturbed areas -- opportunistic or fugitive species
            a. small filamentous green and red algae
            b. small animals (e.g., hydroids )

        2. seasonal succession
        3. Evidence for inhibition and facilitation model
            a. Inhibition model example
            b. Facilitation model example
    H. Age Structure
        1. major long-lived species are invertebrate animals
        2. sometimes areas are dominated by a single year class -- time when settlement or survivorship was good
        3. may be few young in certain areas 

    I. Tide Pools
        1. many organisms are similar to those of the surrounding rocky intertidal
         2. higher tidal pools - fewer species and lower biomass than lower tidal pools
           

        3. refuges from desiccation
        4. large temperature variations
        5. salinity changes
        6. oxygen concentration changes as heat up
        7. larger pools experience smaller physical changes
        8. grazing effects example

J.      Cobble beaches

1.      prone to disturbance

2.      extreme temperature changes (rock heats quickly)

3.      few organisms

4.      if salt marsh plants colonize, can stabilize and promote species diversity

SOFT BOTTOM COMMUNITIES
IV. Sandy Shores
    A. Types
        1. sand flats -- less exposure, little or no slope, large numbers of macro-organisms are on the surface
        2. sand beaches -- exposed, more wave action, pronounced slope; most organisms are buried
            a. dissipative beach -- wave energy is spread over a wide, flat surf zone; fine sediments
            b. reflective beach -- wave action hits the beach face directly; sediment is coarse; steep slope
    B. Environmental Conditions
        1. no solid place for attachment
        2. wave action -- waves move and sort sand grains
        3. slope
        4. particle size is important -- determined by the previous two factors –
           
        5. swash -- water running up a beach after a wave breaks -- carries particles
        6. backwash -- water flowing back down the beach -- removes particles
        7. deeper sediments -- temperature and salinity are buffered; no UV radiation
        8. oxygen can become limiting
    C. Adaptations of Organisms
        1. ability to burrow within the sediment and remain there
             thixotrophy

           
        2. reproduction - often timed with lunar cycle
        3. predation avoidance
           
        4. respiration - preventing clogging by sand

    D. Types of Organisms
        1. no large flowering plants or algae occur on open beaches
        2. low primary production - only within the upper few cm of sediments
            a. phytoplankton and detritus are the main sources of energy
            b. suspension (filter feeding common) and deposit feeding (less common)

            c. also carrion feeding
            d. few carnivores on the open beach (polychaetes and moon snails); on sand flats are crabs, snails and horseshoe crab, Limulus)
        3. no large sessile animals
        4. polychaete worms, bivalve mollusks (prefer protected beaches) and crustaceans (more abundant on exposed beaches)
        5. number of species increases in less exposed areas, but the highest biomass is in more exposed places
    E. Community Organization on Exposed Sand Beaches
        1. wave action makes it difficult to study
        2. food -- dead algae and animals (POM), DOM, plankton and benthic algae
        3. three-zone division
            a. highest parts similar to the supralittoral fringe 

            b. midlittoral area is more variable -- isopods, sand crabs
            c. infralittoral fringe or surf zone  -- greatest number of species
        4. are many tidal migrations (few sessile organisms)
        5. may be seasonal changes
        6. fauna sparse -- no apparent competition for space
        7. fish and birds may be important predators
    F. Community Organization on Protected Sand Flats
        1. more studied
        2. physical factors --
            a. grain size can set limits
                (1) more deposit feeders in fine sediments that hold more organic matter
                (2) more suspension feeders in coarse sand
            b. seasonal temperature changes -- some organisms migrate from intertidal to deeper water in the winter
        3. biological factors
            a. predation particularly important


            b. deposit feeding


            c. competition
                (1) Competitive displacement horizontally: e.g., competition between two mud snails determines their intertidal distribution
                   
                (2) Competitive displacement vertically in the sand:
                   
                (3) competition between bivalves usually results not in movement, but decreased growth and fecundity (competition for food)
V. Muddy Shores
    A. Physical factors
        1. wave action not important -- muddy flats only form without strong waves
        2. topography is flat and more stable -- organisms build permanent homes
        3. water does not drain from the sediment
        4. the anaerobic sediments are the most important characteristic
            a. just a few cm below the surface the sediments go anoxic

            b. redox (measure of anaerobic conditions) potential discontinuity - rapid transition from oxic to anoxic zone
                (1) upper sediments are aerobic; sediments usually brown or yellow
                (2) at RPD the sediments are gray - reduced energy-containing compounds diffuse upward;
                        bacteria use limited oxygen to oxidize these compounds and gain energy
                (3) lower sediments are anaerobic; decomposition by anaerobic bacteria; sediments are black
                    (a) bacterial chemosynthesis in these deep muds -- produce organic matter
                            from CO2 using energy in reduced compounds
                    (b) so are two layers of production in the muddy intertidal sediments -- primary production at the surface
                            and chemosynthetic production in the mud
        5. horizontal zonation is not pronounced
    B. Adaptations of organisms
        1. burrowing animals are capable of withstanding low oxygen

        2. little selection for withstanding being swept away (no waves)
        3. how do they burrow?

    C. Types of organisms --
        1. often have many plants – diatoms, macroalgae, seagrasses (Zostera)

        2. lots of bacteria decomposing organic matter in mud
            · chemosynthetic sulfur bacteria abundant in anaerobic sediment layers
        3. nematode worms eat bacteria
        4. many deposit feeders: polychaetes, and clams: eat organic matter and bacteria
        5. some suspension feeders, but filter feeders are often excluded
        6. few herbivores, but some polychaetes, mollusks and crustaceans graze diatoms
        7. carnivores --


VI. Intertidal Fishes
    A. Rocky intertidal -- turbulent environment
        1. most are small
        2. generally compressed and elongate body shapes - Blenniidae, Pholidae or depressed shape, Cottidae, Gobiescosidiae
        3. inhabit holes, tubes, crevices or depressions
        4. most lack swim bladders and are associated with the substrate
        5. visual predators
        6. most lay eggs on stones, rocks or vegetation (males may guard them); larvae spend weeks or months in the plankton
        7. generally live 2-10 years and mature in first or second year
    B. Mud flats and sandy beaches --
        1. skates, rays -- prey by excavating the sediment in search of infauna
        2. various flatfishes -- prey on infaunal invertebrates
VII. Birds -- selective foraging; different bill types and leg lengths
    A. Can be important in structuring community
        1. migrating birds
        2. foraging birds on East Coast are estimated to consume 50-70% of the invertebrate populations
        3. more effects of bird predation on mud flats than on sand flats
    B. Bird Islands -- breeding locations

VIII. Human Uses / Impacts
    A. Recreation
    B. Development
    C. Pollution – runoff from shore – eutrophication and toxins; oil spills
    D. Thermal pollution
    E. Erosion
    F. Introduced species (e.g., European shore crab Carcinus maenas; periwinkle Littorina littorea)
    G. Harvesting of organisms
        1. overharvesting of rocky intertidal organisms (sessile, easily accessible)
        2. clams and crabs from soft-sediment areas
        3. Limulus (horseshoe crab) -- amebocyte lysate assay for bacterial endotoxins that cause disease (e.g., botulism, dysentery, spinal meningitis)

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