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 Slime ? Incredible Diversity > 500 species of marine algae in Hawaii, many new species and genera collected every year

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Biology and ecology of algae on tropical reefs l.jpg

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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Incredible Diversity

  • > 500 species of marine algae in Hawaii, many new species and genera collected every year

  • > 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 energy—glucose, starch & other carbohydrates

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General Info-cont.

  • Kingdom Protista…not “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, organism’s 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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  • Sun Light + 6H2O + 6CO2-----> C 6 H12 O 6 ("sugars") + 6O2

  • Raw Materials----->   Plant Tissue + Oxygen

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 reefs…fill 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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  • 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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  • 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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  • 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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  • 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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  • 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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Morphology Cont.

Branching Patterns

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Algal Functional Forms





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Factors necessary for growth



Factors that can influence growth

Water motion







Algal Ecology





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Temperate (cold water)

High nutrient levels-upwelling, cold nutrient rich seawater

Dominated by producers

Algae form the ecosystem


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

Coastal Marine Ecosystems

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The Paradox of Tropical Reefs

Extremely diverse and highly productive ecosystems

thriving in nutrient poor seas…how 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…

Nitrogen & Phosphorus-low

  • 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

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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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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 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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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, > 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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Storm disturbance, hurricanes, tsunamis

Predation: COT

Changes in sea level







Global warming

Destructive fishing practices


Exotic species

Coral Reef Loss: Causes

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  • 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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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

  • Result…Macroalgal dominance & reef loss



Smith et al. 2001. Coral Reefs

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Case Study: Kane’ohe Bay, OahuDictyosphaeria cavernosa

  • During the 1970’s, 3 sewage treatment outfall pipes were put in Kane’ohe 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 1980’s 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 Hawai’i

  • 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 1950’s

  • 5 have become established in Hawaiian waters and pose threats to reefs

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Alien Algae in Hawaii

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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First appeared in Hilo Harbor in early 1900s-shipping/whaling industry, native to Philippines

Introduced to O’ahu and Molokai for aquaculture

Localized spread, not good at spreading b/w islands

Ecological dominant in some places: Waikiki and Kane’ohe

Gracilaria salicornia: “Gorilla Ogo”

Smith et al. Pacific Science. 2004

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Waikiki Alien Algae Clean-up Events 1900s-shipping/whaling industry, native to Philippines

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The SUPER SUCKER 1900s-shipping/whaling industry, native to Philippines

  • Underwater vacuum cleaner to remove alien algae

  • Kane’ohe Bay

  • Ask DAR divers (Cass and Josh) for more info

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Eucheuma denticulatum 1900s-shipping/whaling industry, native to Philippines

  • Cultivated around the tropics & has been introduced to more than 23 countries

  • Introduced to in Kane’ohe Bay 1970s

  • Fish don’t prefer to eat it

  • Moderate response to nitrogen

  • Once established—very competitive

  • Out competing native species

  • Killing coral, reducing diversity

  • Changes habitat—3D

  • Eradication???

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Native Invasive Species: 1900s-shipping/whaling industry, native to PhilippinesCladophora 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 1900s-shipping/whaling industry, native to Philippines

  • 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 algae—Phase shifts (less diverse, less complex and potentially irreversible)

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What can be done??? 1900s-shipping/whaling industry, native to Philippines

  • 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!!! 1900s-shipping/whaling industry, native to Philippines