lsm3254_lecture 10 tropical marine ecosystems

8/3/2019 LSM3254_Lecture 10 Tropical Marine Ecosystems

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LSM3254 Ecology of Aquatic Environments

Tropical marine ecosystems

Peter ToddDept of Biological Sciences

By the end of this lecture you should be able to:

Learning outcomes:

Define a coral, a coral community, and a coral reef.

Explain coral development and growth; discuss coral reefformation.

Evaluate the physical factors limiting to corals.

Identify seagrasses and the ecological role they play

Describe mangroves and where they are found

Appreciated mangrove adaptations to their stressfulenvironment.

Corals and coral reefs

They are the largest structures on earth of biological origin.

Why are corals reefs important?

They support more plant and animal phyla, and the greatestnumber of symbiotic relationships, than any otherecosystem.

They provide a crucial role as refuges and breeding groundsfor numerous commercially important marine species.

The vast number of chemicals secreted by reef organismshave great potential for the development of drugs or as toolsfor pharmacological research.


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Coral reefs

Goods

foodconstruction materialswhitewashcementornamentstraditional medicinepharmaceuticals

Services

shore protection

pollutant filtersediment bindingsource of beach sandmarine tourismnursery and shelter

What are corals and what are coral reefs?

What is a coral?


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HydroidsJellyfish Corals and anemones

Cnidarians

Hydroids, fire coral.

Jellyfishes.

, , .

Stony coral

Jellyfishes

Fire corals

Corals and anemones

Corals have polyps and may be solitary orcolonial.

They differ from hydrozoans in the

organization of the gastrovascular cavity,i.e. it is divided into mesenteries.

Two major subgroups:

Octocorallia - polyp with eight pinnatetentacles + eight mesentries.

Mesenteries

Includes sea fans, sea pens, soft corals.

Hexacorallia - Polyps with multiples of sixsimple tentacles + mesentries to match Includes sea anemones, stony corals.

Cross section ofgastrovascular cavity


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Soft corals and seapens no skeleton.

Octocorallia

Seafans, sea whips horny (gorgonin) skeleton (Gorgonians).

Blue coral (Heliopora) and organ-pipe coral (Tubipora) calcium skeleton

sea fanSoft coral Sea pen

Hexacorallia

Sea anemones - sessile and (always) solitary,sea anemones are really much like large soft-bodied corals.

Scleractinian corals

Hexacorallia

Hermatypic corals reef

building

Hermatypic coral (Favites)

Ahermatypic corals non reefbuilding Ahermatypic coral (Tubastrea)

Primary producerswithinconsumers

Reef building corals

Corals gain sugars from the zooxanthellae.

Zooxanthellae obtain nutrients from the coral and also gain protection.

Zooxanthellae - algae living inside the coraloften concentrated in tentacles.


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Coral developmentThe scleractinian

coral polypMost scleractinian coralsform sessile colonies made

polyps (usually ~1-20 mmacross)

In a similar way toanemones, they haveupward pointing mouthssurrounded by tentacles

.

Unlike anemones, eachpolyp secretes a calcareousexoskeleton to live in; a cup-shaped structure called acorallite.

Coral with tissue Coral without tissue Extended polyps

CBA

Here it is possible to see a coral with itstentacles withdrawn (A), the same coralcleared of tissue (B), and a similar coralwith its tentacles extended (C).

Some of the more common arrangementsof corallites (the polyps exoskeleton) areshown on the right. The majority of coraltaxonomy is based on corallite features.


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Common forms of reef-building coralsLaminarMassive

Aborescent

Free-living

Massive coral!Poritescoral on theGreat Barrier Reef.


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What is a coral reef?

A calcium carbonatestructure formed byliving organisms mostly corals(and coralline algae phylum).

Definition does notinclude rocky outcrops

with corals attached(although this is a coralcommunity!).

Hanauma Bay,Hawaii

Types of coral reef

Coral reefs

There are three major types of reef fringing, barrier and atoll.

Fringing reef

The coral reef is a dynamicsystem that includesaccretion and erosion.


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Barrier reef

The lagoon area is not such a good environment foractive coral growth.

Spur-and-grooveformation

McGraw Hill

Coral atolls

1. Starts as a fringing reef around a volcanic island.

2. As the island subsides, corals row upwards.

Formation first described by Charles Darwin

3. Island almost gone, ring of reef now clear.

4. No more island, channels link lagoon to open ocean.

5. Currents, waves, tides, and coral growth, determinewhether the atoll has large landmasses or not.

McGraw Hill


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Reef zonation

Major limiting factors

Temperature: Extended periods at temperatures below 18o Cwill kill most corals - hence why found in tropics. Too hot willalso kill them (bleaching).

Capricorn

Cancer

Global distribution of coral reefs: equator to tropics (23.5o N & S)

Global distribution of coral reefs

Desiccation: Coral are meant to be wet!


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Light: Light enhanced calcification is responsible for most of theskeletal growth of reef-building corals (Goreau, 1959). Generally

require light >1-2 % surface ambient. Ingestion of zooplankton maypartially compensate for low light levels.

depth

Water movement: Coral reefs flourish in areas of high water energy,thought to be a consequence of beneficial flushing of waste, reworking ofnutrients and food, removal of sediment, and the reduction of salinity andtemperature extremes.

Salinity: Extended exposure to freshwater will kill any coral.High salinity is rarely a problem.

Nutrients: Even minor nutrient enhancement (supposedly) cause shiftsin competitive advantage towards species that out-compete corals. Mayalso have a direct impact on coral metabolism and growth.

Super sucked Hawaiian

reefs!

After


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SINGAPORE REEFS - PRESENT STATUS

biodiversity relatively high

255 coral species

However:

60% of coral reefs lost

growth zone reduced

to upper 6m of reef slope

impacts not decreasing

Seagrass systems

Only group of flowering plantsthat are fully submerged inseawater. Highly specialized.

Have true roots, stems andleaves. Have internal systemfor gas and nutrient transport.

Horizontal stems calledrhizomes creep in sediment.Erect leafy shoots projecta ove sea e .

Produce flowers and fruitswith seeds.

Where are seagrass habitats found?

In shallow (usually 30m) coastal waters,usually on sand flats with a mixture of mud.

est eve ope n warm, trop ca waters w ere t ey ormextensive meadows (only a few temperate species, e.g. Zostera).

Widely distributedthroughout tropics.


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Water transfers pollen much like the wind.

Zostera(eel grass) has thread-like pollen that gets caught inthe sti ma of the female lant.

Reproduction

Special adaptations to avoid hybridization, e.g. turtlegrass(Thalassia) pollen and stigma have slime that only sticks to thesame species.

Enhalusflower

ZosteraEnhalusfruit

Productivity

Very high productivity

This is because seagrasses have true roots that can takeup nutrients (seaweeds have to absorb them form the

water).

Plenty of phosphorous have symbiotic bacteria to help fixnitrogen.

Turtle grass has >100 species of epiphytic algae!

Studies on Enhalus acoroidesin Philippines:

Net production =1.4 gmC/m2/d (as high as 8 gmC/m2/d)

Leaf growth = 1.9 cm/d

n re ea omass pro uce every wee s - ea crops year

Biomass and production of rhizomes double that of leaves.

Generally, a veryimportant carbon fixer! Enhalus acoroides

Dr Marco Nemesio Montano, hasdiscovered that the seeds of Enhalusacoroidescould be made into flour, aviable substitute for the ordinary flouruse in baking. In addition, he hasadded pickled Syringodiumleaves toour salad menu. And it tastes good,says Dr Fortes.

Leaf blades provideextensive surface areathat promote growth ofperiphyton (microbiota algae, bacteria, fungi,

McGraw Hill

,organic detritus).

A relatively stable

habitat.

Would this affectphotosynthetic ability?


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Seagrass beds/meadows support high species diversity of marineinvertebrates (prawns, crabs, sea cucumbers, urchins, mussels, snails).

Seagrass systems slowdown water energy andmovement.

Traps sediment (andlarvae) and stabilisesbottom sediments (thusincreasing nutrients)

Prevents sedimentre-suspension (makes

water very clear).

Here you can see how the network of rhizomes and roots of the seagrassHalophilahelps to consolidate the sandy substrate, thus reducing erosion.

Seagrass systems support endangered species

Reptiles:Green sea turtle Chelonia mydas

Loggerhead Caretta carettaFlatback Chelonia depressaHawksbill Eretmochelys imbricataWart snake Acrochordus granulatus

Mammals:ea cow ugong ugon u y epen en on seagrass

Leaves regenerate very quickly after being nipped


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Seagrass distribution in Singapore

SINGAPORE

- sites with seagrass

- monitored sites

Mangroves What is a mangrove?

A living system dominated by plantsable to withstand saline conditions(halophytes). The word mangroverefers to the habitat in the same wayas we think of rainforest with itsmixture of plant types.

Where are mangroveslocated?

oas a areas. ey eve ops weparticularly in estuaries, shelteredbays and lagoons.

25% - 30% of worlds mangroves are found in SE Asia. Highly diverse.


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Global estimates vary from: 10 million to 24 million hectares.

Mangrove soil

Mixture of sand, slit andclay in different proportions

Perisesarmamangrove crabs

= .

Lots of organic matter.

Constantly waterlogged.

Mud not well oxygenated.

Host a variet of infaunaland interstitial invertebrates

Hydrogen sulphide gas resulting from sulphur- reducing bacteria thrivingin anoxic (no oxygen) conditions. Makes soil slightly acidic and black.

Mangrove trees

Have to deal with

Salt

Anaerobic substrate

Unstable substrate

Pro a ule dis ersal

Tidal stream through a youngRhizophoramangrove.

Mature Sonneratiasp. close tothe shoreline.

Adaptations: salt

Salt secretion. Some specieshave special glands thatexcrete salt from themselves.Such salt crystals are seen onthe surface of leaves.

Ultra-filtration. Some speciesare not capable of secretingsalt, but can selectivelyprevent salt from enterin .

Salt secretion in Avicenniasp


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Adaptations: low oxygen

known as aerial roots orpneumatophores).

Periodically exposedwith special cells(lenticels) to facilitatemovement of air.

Pneumatophores of Avicenniasp

Adaptations: unstable soil

Root system must providegood anchorage in the softmud.

Prop and stilt roots

Kneed roots

Kneed roots in Bruguierasp

Plank roots

Rhizophorasapling withprop rootsPlank roots in Xylocarpussp.

Vivipary = embryo breaks out of theseed coat and fruit wall while still

Adaptations: propagule dispersal

a ac e o e paren p a n

Environmental conditions fluctuateall the time and quick growth of

propagules enhances survival.

Fruits develop to an advancedstage and are shaped such thatwhen they drop, they penetratedeep in the mud and take rootquickly.

Zonation

Pattern of zonation has been related to avariety of either physical parameters or to thetype organisms

Types of zonation:

Depth in the sediment

On tree trunks, pneumatophores, mud lobstermounds, etc.


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Mangroves (what are they good for?!)

Goods

- wood (fuel, building materials,chipboard, paper, charcoal)

-- leaves/fruit (food)

Services

- sustain other resources(fish, shellfish, crustaceans)

- nursery area (shrimp, fish)- shoreline rotection

- coastal stabilisation- sediment trap- pollution filter

Generalized mangrove ecosystem


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Impacts and threats to mangroves

Clearing and conversionto other uses.

Overharvesting

Changes to river drainage

Loss of protection fromcoral reefs

Pollution

Singapore 1950

Singapore 2002 Connection between coral reefs, seagrasses andmangroves


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lsm3254_lecture 10 tropical marine ecosystems

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