Biology and Ecology of Algae on Tropical Reefs

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Biology and Ecology of Algae on Tropical Reefs

• Jennifer E. Smith, Ph.D.
• National Center for Ecological Analysis and
  Synthesis
• University of California Santa Barbara

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Slime ?
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Incredible Diversity

• gt 500 species of marine algae in Hawaii, many new
  species and genera collected every year
• gt 60 species of corals
• Many exciting research opportunities
• Contact me later for more info

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Degraded Reef
Healthy Reef
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Overview of Lecture

• General information
• Taxonomy morphology
• Importance
• Ecology
• The reef environment
• Human impacts

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General Info

• Algae are photosynthetic autotrophs
• Through the process of photosynthesis, they
  convert sunlight into chemical energyglucose,
  starch other carbohydrates

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General Info-cont.

• Kingdom Protistanot true plants
• No real tissues or organs
• Older evolutionary lines
• Huge diversity
• Taxonomic dumping ground

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General Info cont.

• Air vs. water habitat, organisms utilize
  different strategies

Land Plants
Marine Plants
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Importance of Algae

• Primary Producers
• Shelter and Habitat
• Cement and Structure
• Sand
• Nitrogen fixation
• Bioindicators
• Biomedical uses
• Economics

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Primary Producers

• Capture energy from the sun
• Chlorophyll and other photosynthetic pigments
• Use this energy to fix carbon into complex
  carbohydrates
• Serve as the base of the food web
• Supply energy for entire ecosystems

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Shelter Habitat

• Three dimensionality
• Complexity
• Commercially important species (lobster, crab,
  fish, etc.
• Endangered species
• Juveniles

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Cement Protection

• Crustose coralline algae (heavily calcified
  crusts) are the glue of coral reefsfill in the
  gaps and meld together
• The algal ridge/reef crest continually grows
  upward towards the sun
• Provides physical protection to islands
• Prevents erosion from wave action

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Sand Producers

• Up to 90 of the sand in the tropics is produced
  by algae
• Halimeda
• Crustose coralline algae

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Nitrogen Fixation

• Cyanobacteria
• Specialized structure Heterocyst that fixes
  atmospheric Nitrogen (N2) into useable forms
• Available for uptake by reef species
• Important source of new nitrogen on reefs

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Medical Other Uses

• Novel Compounds
• Micosporine-like Amino Acids sun screens
• Antifouling compounds
• Ship hulls
• Medical Supplies (contact lenses, pace makers,
  pins, etc.)
• Antioxidants
• Cure diseases cancer
• Resistance to bacteria, antibiotics

seaweeds in the ocean can avoid infection by
fungi and bacteria by producing their own natural
antibiotics. The seaweeds live in constant
contact with potentially dangerous microbes,
suggesting they are under pressure to evolve some
kind of resistance
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Commercial Uses Economics

• 145 species of algae are cultivated for food-Nori
  (Porphyra, etc.)
• 101 cultivated for phycocolloids (agar and
  carageenan)
• Each year 13 million tons of seaweed produced in
  farms yields an excess of 6.2 billion dollars
• 50 produced in the tropics
• Kappaphycus and Eucheuma

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Bioindicators

• Algae are like all plants and require nutrients
  (nitrogen and phosphorous) to grow
• What happens when you add fertilizer to your
  garden? Weeds?
• Algal blooms can be the result of
  eutrophication-nutrient pollution, runoff, sewage
  etc.

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Taxonomy

• Three major groups of marine algae
• Division Chlorophyta-green algae
• Division Phaeophyta-brown algae
• Division Rodophyta-red algae
• Many other obscure groups that photosynthesize
  but do not form large multicellular marine plants
• Blue-green Algae
• Bacteria-Division Cyanophyta
• Dinoflagellates
• Division Pyrrophyta-zooxanthellae, and many more

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Chlorophyta

• Most diverse group of algae-over 7000 species
  worldwide
• Approximately 60 species in Hawaii
• Range in size from a few microns to over 3 meters
  long
• Single to multicellular
• Fresh water and marine species
• Very simple to very complex

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Phaeophyta

• From less than a centimeter to over 30 meters
  long
• No unicellular representatives
• Mostly all species are marine
• 3000 species worldwide
• Approximately 40 species in Hawaii
• Alginate and Alginic Acid are important
  commercial products

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Rhodophyta

• Single to multicellular
• Few millimeters to few meters
• Fresh water and marine
• Approximately 5000 species, 360 in Hawaii
• Carrageneen and agar are important commercially
• Deepest alga ever found at 364 meters was a red
  crust

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Taxonomic Divisions and Photosynthetic Pigments
Taxonomic Group Photosynthetic Pigment
Cyanobacteria chlorophyll a, allophycocyanin, phycocyanin, phycoerythrin
Green Algae (Chlorophyta) chlorophyll a, chlorophyll b, siphonoxanthins
Red Algae (Rhodophyta chlorophyll a, allophycocyanin, phycocyanin, phycoerythrin
Brown Algae (Phaeophyta) chlorophyll a, chlorophyll c, fucoxanthin and other carotenoids
Dinoflagellates (Pyrrhophyta) chlorophyll a, chlorophyll c, peridinin and other carotenoids
Vascular Plants chlorophyll a, chlorophyll b
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Light in the Marine Environment
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Morphology
Form Simple Complex
Sheet
Cylinder
Complex
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Morphology Cont.
Branching Patterns
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Algal Functional Form
Functional Form Size Division of species in Hawaii
Macroalgae gt 2 cm C, P, R gt225
Crustose Coralline Algae Variable (lt1cm/year) R gt25
Turf Algae lt 2 cm C, P, R gt275
Coral/Zoox lt cm to gt5m Anthozoa, Pyrrophyta Coral 60 Zoox ?
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Algal Functional Forms
TURF ALGAE
CORAL
CRUSTOSE CORALLINE ALGAE
MACROALGAE
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Algal Ecology

• Factors that can influence growth
• Water motion
• Disturbance
• Temperature
• Salinity
• Substrate
• Competition
• Predation

• Factors necessary for growth
• Light
• Nutrients

Physical factors
Biological interactions
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Coastal Marine Ecosystems

• Temperate (cold water)
• High nutrient levels-upwelling, cold nutrient
  rich seawater
• Dominated by producers
• Algae form the ecosystem
• Productive
• High herbivory
• High net export of energy

• Tropical (warm water)
• Low nutrient levels-no upwelling
• High herbivory
• Corals form the ecosystem
• Highly productive
• Low algal abundance
• Low export of energy from system

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Where are all the producers???
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The Paradox of Tropical Reefs
Extremely diverse and highly productive
ecosystems thriving in nutrient poor seashow
does this work??? and where are all of the
algae???
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The Coral/Algal Symbiosis

• Self-contained unit
• Highly efficient nutrient cycling
• Coral fertilizes the zoox (with NH4 as excretion)
  and the zoox feeds the coral (translocation of
  complex sugars-photosynthate)
• Evolved to thrive in nutrient poor waters
• Very little outside energy needed

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The solution for other algae

• Low Nutrients
• Slow growth rates, high efficiency (high surface
  to volume ratio), grow in areas where nutrients
  are relatively high
• Herbivory
• Intense diverse-keeps standing stock low
• Avoid consumption by herbivores
• Chemical (toxins) or physical defense (calcium
  carbonate, or cryptic growth form),
• Grow fast

Nitrogen Phosphorus-low
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Relationship between functional form and ecology
Functional Form Nutrient Efficiency Herbivore Defenses Adaptations to Exposure
Macroalgae Low Some, chemical occasional CaCO3 Some
Crustose Coralline Algae Low Yes, CaCO3 Yes, crust
Turf Algae High None, fast growth rates No, fragile
Coral High Physical CaCO3 Some
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Functional Forms the Reef
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The Reef Flat

• Refuge from herbivory
• Intense solar radiation
• Shallow, nutrient rich, moderate hydrodynamic
  forces
• Substrate basalt, limestone, rubble, sand and
  mud
• Macroalgae dominate

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Reef Flat Algae
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The Reef Crest Algal Ridge

• Extreme hydrodynamics
• High Flux-nutrient delivery
• Intense herbivory
• Severe physical conditions light, temp.,
  desiccation
• Crustose coralline algae

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Reef Crest Algae
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Reef Slope

• Intense herbivory
• Low hydrodynamic forces
• Low nutrients, mild fluctuation in physical
  factors
• Corals dominate
• Algae are cryptic, fast growing (turfs) or
  chemically defended

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Reef Slope Algae
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Keeping the Balance on Reefs

• Intense grazing of algae by fish and
  invertebrates keeps algal standing stock
  low-helps to maintain the competitive dominance
  of corals
• Clear, low nutrient water prevents algae from
  growing overly fast favors the abundance of
  nutrient efficient species-symbioses

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Coral Reefs are Fragile Ecosystems

• Because these unique ecosystems have evolved
  under specific conditions they are susceptible to
  small changes
• Global population 6.3 billion
• 3.8 billion live within 100 km of the ocean, gt
  60 of total
• This number is expected to double in the next 30
  years
• Tremendous pressure on marine resources
  associated ecosystems

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Coral Reef Loss Causes

• Natural
• Storm disturbance, hurricanes, tsunamis
• Predation COT
• Changes in sea level
• Disease

• Anthropogenic
• Overfishing
• Eutrophication
• Sedimentation
• Pollution
• Global warming
• Destructive fishing practices
• Trampling
• Exotic species

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Phase-Shifts

• Phase shifts can be the result of coral death
  where algae simply settle on open space
• Or the algae may actually kill coral as a result
  of overgrowth, shading and smothering
• Reduced herbivory increased nutrients

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Things that kill coral

• Localized
• Sedimentation (smothering), disease outbreaks
  (coral death), Acanthaster blooms, trampling
  (abrasion) etc.
• Global
• Global warming-increased temperature (coral
  bleaching) and carbon dioxide (reduced
  calcification)

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Things that enhance algal growth/abundance

• Nutrient addition Eutrophication
• Overfishing or loss of grazers

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Nutrient Pollution
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Overfishing Reduced Herbivory
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The Relative Dominance Model(Littler and Littler
1984)

• Phase shifts from coral to macroalgal dominance
  can occur when both nutrient levels and herbivore
  numbers are altered
• Reefs across the globe are experiencing these
  phase shifts
• ResultMacroalgal dominance reef loss

HUMAN IMPACT
Smith et al. 2001. Coral Reefs
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Case Study Kaneohe Bay, OahuDictyosphaeria
cavernosa

• During the 1970s, 3 sewage treatment outfall
  pipes were put in Kaneohe Bay
• In the years following this event D. cavernosa
  A.K.A. the bubble alga began growing
  extensively in the bay
• First large-scale evidence of what nutrients can
  do
• What is the current situation?

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Case Study Diadema antillarum Caribbean Reefs

• The sea urchin D. antillarum was extremely
  abundant
• Early 1980s massive mortality due to disease
• Algal overgrowth of coral occurred across the
  Caribbean
• First large-scale evidence of herbivore effects
  on reefs

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Phase Shifts Case Studies in Hawaii

• Numerous cases
• Each situation is unique
• Often difficult to determine exactly what the
  causes are
• Multiple and interactive effects
• Each situation needs to be studied
• Exotic/alien species

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Alien Algae in Hawaii

• 19 species of non-indigenous seaweeds since have
  been introduced since 1950s
• 5 have become established in Hawaiian waters and
  pose threats to reefs

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Alien Algae in Hawaii
Species Year Origin Vector
Acanthophora spicifera 1950 Guam Hull Fouling -Accidental
Hypnea musciformis 1974 Florida Aquaculture -Intentional
Gracilaria salicornia 1971 ?, Native to NW SW Pacific, Indian Ocean, Australasia Aquaculture -Intentional
Eucheuma denticulatum 1974 Philippines Aquaculture -Intentional
Avrainvillea amadelpha 1981 Native to NW SW Pacific Unknown
Smith et al. Pacific Science 2002
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Hypnea musciformis

• Introduced in the 1970s for experimental
  aquaculture
• Forms massive blooms on south shore of Maui
• Responding to high nutrient inputs
• Smothers benthos
• Economic losses-20 million per year to Maui

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Gracilaria salicornia Gorilla Ogo

• First appeared in Hilo Harbor in early
  1900s-shipping/whaling industry, native to
  Philippines
• Introduced to Oahu and Molokai for aquaculture
• Localized spread, not good at spreading b/w
  islands
• Ecological dominant in some places Waikiki and
  Kaneohe

Smith et al. Pacific Science. 2004
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Waikiki Alien Algae Clean-up Events
Time Volunteers Wt. Removed
gt20 volunteer events, 2002 gt1000 people gt100 tons algae
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The SUPER SUCKER

• Underwater vacuum cleaner to remove alien algae
• Kaneohe Bay
• Ask DAR divers (Cass and Josh) for more info

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Eucheuma denticulatum

• Cultivated around the tropics has been
  introduced to more than 23 countries
• Introduced to in Kaneohe Bay 1970s
• Fish dont prefer to eat it
• Moderate response to nitrogen
• Once establishedvery competitive
• Out competing native species
• Killing coral, reducing diversity
• Changes habitat3D
• Eradication???

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Native Invasive Species Cladophora sericea

• Forms large ephemeral blooms on west Maui
• Summer months
• Some years
• Large-scale, wide depth range
• Causes impacts unknown

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Summary

• Algae are a diverse and important component of
  coral reefs
• They are the base of the ecosystem that supply
  energy for higher trophic levels
• They are important sand producers and reef
  cementers
• Important indicators of reef health
• Human impacts can shift the competitive edge away
  from coral and in favor of the algaePhase shifts
  (less diverse, less complex and potentially
  irreversible)

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What can be done???

• Better land management practices
• Reduce runoff, manage sewage, time release
  fertilizers, prevent deforestation, etc.
• Better management of fisheries
• Create no-take marine reserves
• Increase fish and other herbivore populations
• Prevent introduction of non-native species
• Reef restoration
• Education
• Conduct research

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QUEST!!!
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