1

Biology and Ecology of Algae on Tropical Reefs

Biology and Ecology of Algae on Biology and Ecology of Algae on Tropical ReefsTropical Reefs

Jennifer E. Smith, Ph.D.National Center for Ecological Analysis and Synthesis

University of California Santa Barbara

Slime ?Slime ?

Incredible DiversityIncredible 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…

Healthy ReefHealthy ReefDegraded ReefDegraded Reef

Overview of LectureOverview of Lecture

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

General InfoGeneral Info

• Algae are photosynthetic autotrophs

• Through the process of photosynthesis, they convert sunlight into chemical energy—glucose, starch & other carbohydrates

2

General InfoGeneral Info--cont.cont.• Kingdom Protista…not “true

plants”– No real tissues or organs– Older evolutionary lines– Huge diversity– Taxonomic dumping ground

General Info cont.General Info cont.Land Plants Marine Plants

•Air vs. water habitat, organism’s utilize different strategies

Importance of AlgaeImportance of Algae

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

Primary ProducersPrimary 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

•Sun Light + 6H2O + 6CO2-----> C 6 H12 O 6 ("sugars") + 6O2•Raw Materials-----> Plant Tissue + Oxygen

Shelter & HabitatShelter & Habitat

• Three dimensionality

• Complexity• Commercially

important species (lobster, crab, fish, etc.

• Endangered species

• Juveniles

Cement & ProtectionCement & 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

3

Sand ProducersSand Producers

• Up to 90% of the sand in the tropics is produced by algae

• Halimeda• Crustose coralline

algae

Medical & Other UsesMedical & 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…

Commercial Uses & EconomicsCommercial Uses & Economics

• 145 species of algae are cultivated for food-Nori (Porphyra, etc.)

• 101 cultivated for phycocolloids (agar and carageenan)

• Each year 13 million tonnes of seaweed produced in farms yields an excess of $6.2 billion dollars

• 50% produced in the tropics

BioindicatorsBioindicators• 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.

TaxonomyTaxonomy• 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…

ChlorophytaChlorophyta• 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

4

PhaeophytaPhaeophyta• 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

RhodophytaRhodophyta• Single to multicellular• Few millimeters to few

meters• Fresh water and marine• Approximately 5000 species,

360 in Hawaii• Carageneen and agar are

important commercially• Deepest alga ever found at

364 meters was a red crust

Taxonomic Divisions and Taxonomic Divisions and Photosynthetic PigmentsPhotosynthetic Pigments

chlorophyll a, chlorophyll bVascular Plants

chlorophyll a, chlorophyll c, peridinin and other carotenoids

Dinoflagellates (Pyrrhophyta)

chlorophyll a, chlorophyll c, fucoxanthinand other carotenoids

Brown Algae (Phaeophyta)

chlorophyll a, allophycocyanin,phycocyanin, phycoerythrin

Red Algae (Rhodophyta

chlorophyll a, chlorophyll b, siphonoxanthins

Green Algae (Chlorophyta)

chlorophyll a, allophycocyanin, phycocyanin, phycoerythrin

Cyanobacteria

Photosynthetic PigmentTaxonomic Group

Light in the Marine EnvironmentLight in the Marine Environment

MorphologyMorphology

Complex

Cylinder

Sheet

ComplexSimpleForm

Morphology Cont.Morphology Cont.Branching Patterns

5

Algal Functional FormAlgal Functional Form

245C, P, R< 2 cmTurf Algae

Coral: 60Zoox: ?

Anthozoa,Pyrrophyta

< cm to >5mCoral/Zoox

15RVariable (<1cm/year)

Crustose Coralline Algae

200C, P, R> 2 cm Macroalgae

# of species in Hawaii

DivisionSizeFunctional Form

Algal Functional FormsAlgal Functional Forms

CRUSTOSE CORALLINE ALGAE

CORAL TURF ALGAE

MACROALGAE

Algal EcologyAlgal Ecology

• Factors necessary for growth– Light– Nutrients

• Factors that can influence growth– Water motion– Disturbance– Temperature– Salinity

– Competition– Predation

Physical factors

Biologicalinteractions

Marine EcosystemsMarine 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

Where are all the producers???Where are all the producers??? The Paradox of Tropical ReefsThe Paradox of Tropical ReefsExtremely diverse and highly productive ecosystemsthriving in nutrient poor seas…how does this work???

…and where are all of the algae???

6

The Coral/Algal SymbiosisThe Coral/Algal Symbiosis

• Self-contained unit• Highly efficient-self

contained unit• Coral fertilizes the zoox

and the zoox “feeds” the coral

• Evolved to thrive in nutrient poor waters

• Very little “outside” energy needed

The solution for other algae…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

Relationship between Relationship between functional form and ecologyfunctional form and ecology

No, fragileNone, fast growth rates

HighTurf Algae

SomePhysical; CaCO3HighCoral

Yes, crustYes, CaCO3LowCrustose Coralline Algae

SomeSome, chemical & occasional CaCO3

LowMacroalgae

Adaptations to Exposure

Herbivore Defenses

Nutrient Efficiency

Functional Form

Functional Forms & the Reef Functional Forms & the Reef

The Reef FlatThe Reef Flat

• Refuge from herbivory• Intense solar radiation • Shallow, nutrient rich,

moderate hydrodynamic forces

• Substrate: basalt, limestone, rubble, sand and mud

• Macroalgae dominate

Reef Flat AlgaeReef Flat Algae

7

The Reef Crest: Algal RidgeThe Reef Crest: Algal Ridge

• Extreme hydrodynamics• High Flux-nutrient delivery• Intense herbivory• Severe physical conditions:

light, temp., desiccation• Crustose coralline algae

Reef Crest AlgaeReef Crest Algae

Reef SlopeReef Slope

• Intense herbivory• Low hydrodynamic forces• Low nutrients, mild fluctuation in

physical factors• Corals dominate• Algae are cryptic, fast growing

(turfs) or chemically defended

Reef Slope AlgaeReef Slope Algae

• 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

Coral Reefs are Fragile Ecosystems Coral Reefs are Fragile Ecosystems Human Impacts on Coral ReefsHuman Impacts on Coral Reefs

• Phase shifts from coral to algal dominance• Anthropogenic Causes:

– Eutrophication-nutrient pollution– Overfishing-reduced herbivory– Any “stress” imposed on coral can push the

competitive edge in favor of the algae– Alien Species-unique traits

8

The Relative Dominance ModelThe Relative Dominance Model(Littler and Littler 1984)(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 shiftsResult…Macroalgaldominance & reef loss

HUMAN IMPACT

Nutrient PollutionNutrient Pollution

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

• In the years following this event D. cavernosaA.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?

Case Study:Case Study: Kane’oheKane’ohe Bay, OahuBay, OahuDictyosphaeria cavernosaDictyosphaeria cavernosa

OverfishingOverfishing & & Reduced Reduced HerbivoryHerbivory

Case Study:Case Study: Diadema antillarumDiadema antillarum & & Caribbean ReefsCaribbean 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

Alien Species: Caulerpa taxifolia

• Introduced to the Mediterranean from Monaco Aquarium

• Spread across hundreds of hectares

• Alien invaders are among the leading causes of reduced biodiversity and habitat loss

9

Other ImpactsOther Impacts

• Localized– Sedimentation (smothering),

disease outbreaks (coral death), trampling (abrasion) etc.

• Global– Global warming-increased

temperature (coral bleaching) and carbon dioxide (reduced calcification)

Phase Shifts & Case Studies in Phase Shifts & Case Studies in Hawai’iHawai’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

Alien Algae in Alien Algae in HawaiiHawaii

• 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

Alien Algae in HawaiiAlien Algae in Hawaii

1981

1974

1971

1974

1950

Year

Aquaculture-Intentional

PhilippinesEucheuma denticulatum

Hull Fouling-Accidental

GuamAcanthophora spicifera

UnknownNative toNW & SW

Pacific

Avrainvillea amadelpha

Aquaculture -Intentional

?, Native toNW & SW

Pacific, Indian Ocean,

Australasia

Gracilaria salicornia

Aquaculture-Intentional

FloridaHypnea musciformis

VectorOriginSpecies

Hypnea musciformisHypnea musciformis

• Introduced in the 1970s for experimental aquaculture

• Forms massive blooms on south shore of Maui

• Most likely responding to high nutrient inputs

• Smothers benthos• Economic losses-$20

million per year to Maui

10

Eucheuma denticulatumEucheuma denticulatum

• Introduced in 1970s for aquaculture, Kane’ohe Bay

• 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???• Introduced & cultivated

around world for carragennan

Native Invasive Species: Native Invasive Species: Cladophora sericeaCladophora sericea

• Forms large ephemeral blooms on west Maui

• Summer months• Some years • Large-scale, wide

depth range• Causes & impacts

unknown

SummarySummary

• 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)

What can be done???What can be done???• Better land management practices

– Reduce runoff, manage sewage, time release fertilizers, prevent deforestation, etc.

• Create no-take marine reserves– Increase fish and other herbivore

populations• Prevent introduction of non-native

species• Reef restoration• Education• Conduct research…

QUEST!!!QUEST!!!