Transcript Serratia marcescens

Chapter 15
Coral Reef Communities
© 2006 Thomson-Brooks Cole
Key Concepts
• Coral reefs are primarily found in
tropical clear water, usually at depths
of 60 meters or less.
• The three major types of coral reefs
are fringing reefs, barrier reefs, and
atolls.
• Both physical and biological factors
determine the distribution of
organisms on a reef.
© 2006 Thomson-Brooks Cole
Key Concepts
• Stony corals are responsible for the
large colonial masses that make up the
bulk of a coral reef.
• Reef-forming corals rely on symbiotic
dinoflagellates called “zooxanthellae”
to supply nutrients and to produce an
environment suitable for formation of
the coral skeleton.
• Coral reefs are constantly forming and
breaking down.
© 2006 Thomson-Brooks Cole
Key Concepts
• The most important primary producers
on coral reefs are symbiotic
zooxanthellae and turf algae.
• Coral reefs are oases of high
productivity in nutrient-poor tropical
seas. Nutrients are stored in reef
biomass and efficiently recycled.
© 2006 Thomson-Brooks Cole
Key Concepts
• Inhabitants of coral reefs display many
adaptations that help them to avoid
predation or to be more efficient
predators.
• Coral reefs are huge, interactive
complexes full of intricate
interdependencies.
© 2006 Thomson-Brooks Cole
World of Coral Reefs
• Coral reefs are highly productive, but
occur in nutrient-poor waters
• This is made possible by the symbiotic
relationship between coral animals and
zooxanthellae
• These symbionts + algae form the
basis of the community; other reef
animals depend on these organisms
© 2006 Thomson-Brooks Cole
Coral Animals
• Stony (true) corals deposit massive
amounts of CaCO3 that compose most
of the structure of coral reefs
• Hermatypic—coral species that
produce reefs, found in shallow,
tropical waters
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Coral Animals
• Ahermatypic—corals that do not build
reefs, which can grow in deeper water
from the tropics to polar seas
– most do not harbor zooxanthellae
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Coral Animals
• Coral colonies
– large colonies of small coral polyps, each
of which secretes a corallite
– a planula larva settles and attaches
– a polyp develops, and reproduces by
budding to form a growing colony
– polyps’ gastrovascular cavities remain
interconnected
– a thin, usually colorful epidermis overlies
the colony surface
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Coral Animals
• Sexual reproduction in coral
– mostly broadcast spawners—release both
sperm and eggs into the surrounding
seawater
– some are brooders—broadcast sperm, but
retain eggs in the gastrovascular cavity
– spawning is usually synchronous among
Pacific reef species, but nonsynchronous
among Caribbean species
© 2006 Thomson-Brooks Cole
Coral Animals
• Reproduction by fragmentation
– some branching corals are fragile and tend
to break during storms
– if they survive the storm, fragments can
attach and grow into new colonies
– fragmentation is a common form of
asexual reproduction for branching corals
© 2006 Thomson-Brooks Cole
Coral Animals
• Coral nutrition
– symbiotic zooxanthellae
• supply 90% of nutritional needs of stony coral
• zooxanthella provide glucose, glycerol and
amino acids
• coral polyp provides a suitable habitat and
nutrients, absorbed directly through the
animal’s tissues
• zooxanthellae remove CO2 and produce O2
• need of zooxanthellae for sunlight limits
depths to which stony corals can grow
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Coral Animals
• Coral nutrition (continued)
– corals as predators
• small animals paralyzed by the nematocysts
are passed into the digestive cavity
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Coral Animals
• Coral nutrition (continued)
– other sources of nutrition
• corals can feed off bacteria living in their
tissues, which feed on dissolved organic
matter directly from the water
• mesenteric filaments (coiled tubes attached to
the gut wall) can be extruded from the mouth
to digest and absorb food outside the body
© 2006 Thomson-Brooks Cole
Reef Formation
• Involves both constructive and
destructive phases
• Bioerosion—the destructive phase of
reef formation
– boring clams or sponges attack exposed
surfaces on the undersides of large corals
– the coral stand weakens, then topples in a
storm or ocean surge
– debris smothers boring organisms, cracks
are filled with CaCO2 sediments, and
coralline algae cement it together
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Coral Reef Types
• Fringing reefs border islands or
continental landmasses
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Coral Reef Types
• Barrier reefs are similar to fringing
reefs but separated from the landmass
and fringing reef by lagoons or
deepwater channels
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Coral Reef Types
• Atolls, usually elliptical, arise out of
deep water and have a centrallylocated lagoon
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Coral Reef Types
• In addition, patch reefs can occur
within lagoons associated with atolls
and barrier reefs
• Darwin’s theory of atoll formation:
– corals colonize shallow areas around
newly-formed volcanic islands to form a
fringing reef
– the island sinks and erodes, and a barrier
reef is formed about the island
– the island sinks completely, leaving an
atoll
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Reef Structure
• Reef front or forereef—portion of the
reef that rises from the lower depths of
the ocean to a level just at or just
below the surface of the water, on the
seaward side
– drop-off—a steep reef-front that forms a
vertical wall
– spur-and-groove formation or buttress
zone—finger-like projections of the reef
front that protrude seaward; disperses
wave energy and helps prevent damage
© 2006 Thomson-Brooks Cole
Reef Structure
• Reef crest—the highest point on the
reef and the part that receives the full
impact of wave energy
– where wave impact is very strong, it may
consist of an algal ridge of encrusting
coralline algae, lacking other organisms,
and penetrated by surge channels—
grooves of the buttress zone
• Reef flat or back reef—portion behind
the reef crest
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Coral Reef Distribution
• Major factors influencing distribution:
– temperature – corals do best at 23-25o C
– light availability – photosynthetic
zooxanthellae need light
– sediment accumulation – can reduce light
and clog feeding structures
– salinity
– wave action – moderate wave action
brings in oxygenated seawater, removes
sediment that could smother coral polyps
– duration of air exposure – can be deadly
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Comparison of Atlantic and
Indo-Pacific Reefs
• Pacific reefs are older and have a
greater depth of reef carbonates
• Buttress zone is deeper on Atlantic
reefs and coral growth may extend to
100 m down
– Pacific coral growth rarely exceeds 60 m
• Algal ridges more common in the
Pacific because of wind and waves
© 2006 Thomson-Brooks Cole
Comparison of Atlantic and
Indo-Pacific Reefs
• Hydrozoan Millipora complanata (fire
coral) is dominant on Atlantic reefs
– Similar species never dominate in the
Pacific
• Gorgonians more abundant in the
Atlantic
• Soft corals (subclass Alcyonaria) more
abundant in the Pacific
• Atlantic corals nocturnal; Pacific corals
diurnal
© 2006 Thomson-Brooks Cole
Comparison of Atlantic and
Indo-Pacific Reefs
• Atlantic corals often reproduce by
fragmentation; Pacific corals by sexual
reproduction
• Coral diversity is far greater in the
Indo-Pacific than the Atlantic
• Greater sponge biomass in the Atlantic
• Pacific has giant clams and sea stars
that prey on corals
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Caribbean
reef
Pacific reef
© 2006 Thomson-Brooks Cole
Reef Productivity
• Source of nutrients
– land runoff for reefs close to land
– source for atolls unclear
– possible explanations:
• nutrients accumulated over time are efficiently
recycled
• reef bacteria and filter feeders capitalize on
nutrients from dissolved/particulate organic
matter
– nutrients brought from other communities
© 2006 Thomson-Brooks Cole
Reef Productivity
• Reef photosynthesis
– photosynthetic organisms: zooxanthellae,
benthic algae, turf algae, sand algae,
phytoplankton, seagrasses
– more dense than tropical ocean, with
greater biomass than reef animals
– associations of producers with other
organisms assist in efficient recycling
– turf algae process the most organic
carbon
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Reef Productivity
• Reef succession
– ratio of primary production to community
respiration = P-R ratio
• P = gross photosynthesis
• C = community respiration
– P-R ratio used to measure state of
development of a biological community
© 2006 Thomson-Brooks Cole
Reef Productivity
• Reef succession (continued)
– P-R ratio > 1 = primary production
exceeds respiratory needs
• biomass increases, excess biomass available
for growth or harvesting
– P-R ratio = 1 = steady state
• little biomass remains available for growth
– P-R ratios for coral reefs are typically close
to 1
• high productivity balanced by high respiration
© 2006 Thomson-Brooks Cole
Reef Productivity
• Reef succession (continued)
– increases in productivity are often the
result of eutrophication
• eutrophication—nutrient enrichment
– eutrophication typically manifested as a
dramatic proliferation of algae
• if grazing doesn’t increase, algae can grow
over and smother corals
© 2006 Thomson-Brooks Cole
Coral Reef Ecology
• Coral provides:
– foundation for reef food webs
– shelter for resident organisms
• Reefs form a complex 3-dimensional
habitat for many beautiful and strange
creatures
© 2006 Thomson-Brooks Cole
Coral Reef Community
• Sponges and cnidarians
– sessile organisms, though anemones can
move if necessary
– filter feed; anemones also paralyze and
consume small fishes and crustaceans
• Annelids
– sessile filter feeders include featherduster
and Christmas tree worms
– fireworms are mobile predators
– palolo worms burrow through and weaken
coral and usually deposit feed
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Coral Reef Community
• Crustaceans
– shrimps, crabs and lobsters
– vary from parasites to active hunters
• Molluscs
– gastropods eat algae from coral surfaces
– giant clams are filter feeders, but also
host symbiotic zooxanthellae
– octopus and squid are active predators
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Coral Reef Community
• Echinoderms
– feather stars, sea urchins, brittle stars,
sea stars, and sea cucumbers
– filter feed, scavenge, or eat sediment
• Reef fishes
– most prominent and diverse inhabitant
– diverse food sources, including detritus,
algae, sponges, coral, invertebrates, other
fish
© 2006 Thomson-Brooks Cole
Species Interactions on Coral
Reefs
• Competition among corals
– fast-growing, branching corals grow over
slower-growing, encrusting or massive
corals and deny them light
– slower-growing corals extend stinging
filaments from their digestive cavity to kill
faster-growing corals
– fast-growing corals can also sting and kill
using long sweeper tentacles with
powerful nematocysts
© 2006 Thomson-Brooks Cole
Species Interactions on Coral
Reefs
• Competition among corals (continued)
– slower-growing corals are more tolerant of
shade, and can grow at greater depths
– as a result…
• fast-growing, branching corals on many reefs
dominate upper, shallower portions
• larger, slower-growing corals dominate deeper
portions
© 2006 Thomson-Brooks Cole
Species Interactions on Coral
Reefs
• Competition between corals and other
reef organisms
– sponges, soft corals and algae can
overgrow stony corals and smother them
– algae outcompete corals at shallow depths
unless grazers control the algae growth
• Other competitive interactions
– hydrozoans overgrow gorgonians
– fast-growing colonial invertebrates on
coral surfaces overgrow many species
© 2006 Thomson-Brooks Cole
Species Interactions on Coral
Reefs
• Effect of grazing
– grazing of larger, fleshier seaweeds
permits competitively inferior filamentous
forms or coralline algae to persist
– herbivory decreases with depth
– damselfish form territories where they
exclude grazers and permit abundant algal
growth
• provides habitat for small invertebrates
• overgrows corals; fast-growing, branching
corals are most successful near damselfish
© 2006 Thomson-Brooks Cole
Species Interactions on Coral
Reefs
• Effect of predation
– predation of sponges, soft corals and
gorgonians provides space for
competitively inferior reef corals
– species that feed on fast-growing coral
assist slower-growing species to remain
– corallivores seldom destroy reefs
– small invertebrates are almost all well
hidden or camouflaged, indicating the
prevalence of predation in the reef
© 2006 Thomson-Brooks Cole
Coral Reef Ecology
• Coral reefs - marine habitats with
greatest diversity/abundance of fishes
• Seems to defy competitive exclusion
principle, which suggests that no 2
species can occupy the same niche
– 60-70% of reef fishes are general
carnivores
– about 15% are coral algae grazers or
omnivorous
© 2006 Thomson-Brooks Cole
Coral Reef Ecology
• Hypotheses proposed to explain this:
– competition model—factors such as time
of day or night, size of prey, position in
the water column, etc. provide each
species with a unique niche (hence, no
competition)
– predation disturbance model—assumes
competition, but suggests that the effect
of predation or other causes of death keep
populations low enough to prevent
competitive exclusion
© 2006 Thomson-Brooks Cole
Coral Reef Ecology
• Hypotheses proposed to explain this:
– lottery model—assumes competition
occurs, but suggests that chance
determines which species of larvae setting
from the plankton colonize a particular
area of the reef
– resource limitation model—suggest that
available larvae are limited and that
limitation prevents fish population from
ever reaching the carrying capacity of the
habitat
© 2006 Thomson-Brooks Cole
Threats to Coral Reefs
• Effect of physical changes on the
health of coral reefs
– hurricanes and typhoons topple and
remove coral formations
– El Niño Southern Oscillation (ENSO)
• changes winds, ocean currents, temperatures,
rainfall and atmospheric pressure over large
areas of tropical and subtropical areas
• can cause massive storms
© 2006 Thomson-Brooks Cole
Threats to Coral Reefs
• Coral bleaching
– a phenomenon by which corals expel their
symbiotic zooxanthellae
– most often associated with warming of the
ocean water by ENSO or global warming
– if the stress is not too severe, corals may
regain zooxanthellae and recover
– if the stress is prolonged, corals may fail
to regain zooxanthellae and die
© 2006 Thomson-Brooks Cole
Threats to Coral Reefs
• Coral diseases
– black band disease—a distinct dark band
of bacteria migrates across the living coral
tissue, leaving behind a bare white
skeleton
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Threats to Coral Reefs
• Coral diseases
– white pox—characterized by white lesions
and caused by Serratia marcescens
– other coral diseases:
• white band disease
• white plague
• yellow blotch disease
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Threats to Coral Reefs
• Human impact on coral reefs
– overfishing may occur
– human-sewage bacteria cause white pox
– nutrient-rich runoff (eutrophication)
increases algal growth, which covers and
smothers corals
• e.g. Kane’ohe Bay in Hawaii
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Evolutionary Adaptations of
Reef Dwellers
• Protective body covering
– tough, defensive exteriors help animals
avoid predation, but can limit mobility and
growth
• Protective behaviors
– producing a poisonous coating of mucus
– burying the body in sand to hide
– inflating to appear larger
– hiding at night when nocturnal predators
are active
© 2006 Thomson-Brooks Cole
Evolutionary Adaptations of
Reef Dwellers
• Role of color in reef organisms
– color for concealment and protection
• countershading
• disruptive coloration
• camouflage (bright colors in reef environment)
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Evolutionary Adaptations of
Reef Dwellers
• Role of color in reef organisms
– other types of camouflage
• body shape
– warning coloration
– other roles of color
• defending territories
• mating rituals
© 2006 Thomson-Brooks Cole
Evolutionary Adaptations of
Reef Dwellers
• Symbiotic relationships on coral reefs
– cleaning symbioses
• cleaner wrasses, gobies, etc. feed on parasites
of larger fishes
• cleaning organisms set up a cleaning station
– Other symbiotic relationships
• clownfishes and anemones
• conchfish and the queen conch
• gobies and snapping shrimp
• crustaceans and anemones
© 2006 Thomson-Brooks Cole