Climate and Life on Earth: Marine ecology 2

Question 1

List the three major types of coastal tropical ecosystems

Answer 1

• mangroves
• seagrass meadows
• coral reefs

Question 2

Describe mangroves and seagrass beds

Answer 2

• high biomass of primary producers
• actively sequester huge amounts of carbon

Question 3

Describe seagrass meadows - the basics

Answer 3

• support high biodiversity
• bottom-up and top-down controls in their productivity

Question 4

Describe coral reefs - the basics

Answer 4

• extraordinary biodiversity
• threatened by overfishing, rising sea temperatures and coastal pollution

Question 5

Many parts of the tropical oceans are virtual deserts, because

Answer 5

the permanent thermocline prevents vertical mixing and the return of nutrients from deep waters.

Question 6

Describe the hot-spots of productivity throughout the tropics

Answer 6

• sometimes due to upwellings
• specialised communities of primary producers (e.g. coral reefs)

Question 7

Describe mangroves

Answer 7

• trees that grow in coastal brackish or saline habitats
• flowering plants
• trap sediments around their roots (salt mostly excluded)
• need special adaptations, such as lenticels or pneumatophores
• some spp have the ability to excrete salt through the leaves

Question 8

Describe true mangroves

Answer 8

belong to a single genus: Rhizophora

Question 9

Describe mangrove roots

Answer 9

often anoxic

Question 10

Give an example of a mangrove species

Answer 10

Rhizophora mangle at Aldabra Atoll by Seychelles Islands

Question 11

Describe seagrass meadows - the specifics

Answer 11

• span both temperate and tropical locations
• flowering plants
• 72 spp globally
• 4 families

Question 12

Describe temperature seagrass beds

Answer 12

• species-poor
• often dominated by eelgrass: Zostera marina

Question 13

Describe tropical seagrass beds - the basics

Answer 13

more species-rich

Question 14

Describe seagrass

Answer 14

• no stomata
• thin cuticle
• true roots and a vascular system (take up nutrients from the sediment, unlike algae)
• spread rapidly via rhizomes
• flower (produce pollen and seeds)
• can grow at depths of up to around 55 m, mostly < 30m
• directly grazed by green sea turtles and sirenians
• world’s oldest plant: 200,000 year-old clones in Med

Question 15

sirenians

Answer 15

manatees and dugongs

Question 16

Describe seagrass morphology

Answer 16

• roots
• rhizome
• flower
• leaves

Question 17

Describe small-bodied seagrass

Answer 17

• small, thin leaves
• small rhizome
• “Guerrilla strategy”
• short-lived
• fas turnover
• low biomass
• exploits new space
• abundant flowering
• many small seeds
• seed bank

Question 18

Describe large-bodied seagrass

Answer 18

• large, thick leaves
• large rhizome
• “Phalanx strategy”
• long-lived
• slow turnover
• high biomass
• holds space
• patchy flowering
• few larger seeds
• seeds germinate rapidly

Question 19

List some Floridian small seagrasses

Answer 19

• paddle grass (Halophila decipiens)
• star grass (Halophila engelmannii)

Question 20

List some intermediate Floridian seagrasses

Answer 20

• widgeon grass (Ruppia martima)
• shoal grass (Halodule wrightii)

Question 21

List some large-bodied Floridian seagrasses

Answer 21

• manatee grass (Syringodium filiforme)
• turtle grass (Thalassia testudinum)

Question 22

Describe tropical seagrass meadows - the specifics

Answer 22

• high biomass systems
• high productivity
• grow in coastal areas (incl. intertidal zone)
• cope with some water turbidity and brackish water
• grow alongside other tropical habitats like reefs
• important nursery grounds for commercially important fish spp.

Question 23

Describe tropical seagrass meadows and barrier reefs

Answer 23

• protect by trapping sediment, absorbing excess nutrients and reducing turbidity in coastal waters
• gain protection from wave action
• synergism

Question 24

List some estuary seagrass species in the tropical indo-pacific

Answer 24

• Halodule spp.
• Halophila ovalis
• Halophila spp.
• Enhalus acoroides
• Ruppia maritima

Question 25

List some shallow coastal/back reef seagrass species in the tropical indo-pacific

Answer 25

- Thalassia hemprichii - Syringodium isoetifolium - Thalassodendron ciliatum - Cymodocea spp. - Halodule spp. - Halophila spp.

Question 26

List some deep (70m) coastal seagrass species in the tropical Indo-Pacific

Answer 26

- Halophila stipulacea - Halophila decipiens - Halophila spinulosa

Question 27

Where are mangroves associated with seagrasses?

Answer 27

at tropical indo-pacific estuaries

Question 28

Where are marshes associated with seagrasses

Answer 28

coastal tropical Indo-Pacific

Question 29

Where is kelp associated with seagrasses?

Answer 29

tropical Indo-Pacific

Question 30

Where is the sea turtle associated with seagrasses?

Answer 30

deep coastal tropical Indo-Pacific

Question 31

Where is the dugong associated with seagrasses?

Answer 31

- shallow coastal/back reef tropical Indo-Pacific

Question 32

Where is freshwater input in tropical Indo-Pacific

Answer 32

deep coastal region

Question 33

Describe one of the threats to coastal systems

Answer 33

- eutrophication caused by runoff from agricultural systems - can lead to coastal dead zones

Question 34

Seagrass growth inhibits

Answer 34

Benthic microalgae

Question 35

Describe eutrophication

Answer 35

increased nutrient loading in water leads to blooms of phytoplankton

Question 36

Describe seagrass ecosystem engineering

Answer 36

- Zostera noltii - trap silts

Question 37

Describe blue carbon

Question 38

Describe coastal wetlands in terms of carbon sequestration

Answer 38

- substantial amounts (50-90% in soils) - long‐term carbon sinks - potential carbon sources upon conversion - managed for their carbon sequestration value

Question 39

Describe some taxa not involved in carbon sequestration

Answer 39

coral reefs, kelp, and marine fauna

Question 40

Describe long-term phytoplankton carbon sequestration

Answer 40

- fix CO2 - sink when dead to the bottom of the ocean - deep sediments lock up carbon

Question 41

Describe coastal wetlands

Answer 41

- tidal inundation keeps the soils wet or submerged - inhibits microbial action - slows decomposition - carbon accumulates in soils and remains relatively stable

Question 42

Describe healthy coastal ecosystems

Answer 42

- continuously accrete carbon in the soil - allows them to keep pace with sea‐level rise - potentially limitless capacity to sequester carbon for long periods of time

Question 43

Describe mangrove forest drainage

Answer 43

- microbial action in the soil (previously inhibited by tidal inundation) oxidises carbon - emits it to the atmosphere as CO2

Question 44

Coastal wetland loss and drainage is estimated to be

Answer 44

between 0.7–3% per year (depending on vegetation type and location), resulting in 0.23–2.25 billion Mg of CO2 released

Question 45

Describe coral reefs - the specifics

Answer 45

- temperatures between roughly 18 and 30 degrees - no sudden changes in salinity - high light intensity - low turbidity - oligotrophic waters

Question 46

Describe the two distinct biogeographic coral regions

Answer 46

- Indo-Pacific (roughly 10x biodiversity) - tropical W Atlantic

Question 47

Describe coral spatially

Answer 47

- missing from areas with major river outflows - sensitive to freshwater and silt

Question 48

Describe the types of coral reefs

Answer 48

- fringing reefs (Israel) - barrier reefs (Australia)

Question 49

Describe fringing reefs

Answer 49

found just beyond shorelines

Question 50

Describe barrier reefs

Answer 50

- found just beyond lagoons - start as fringing reefs - get hollowed out as a lagoon forms and becomes occupied by other life-forms, e.g. seagrass beds - reef survives further offshore - grows upwards towards the sunlight

Question 51

Describe coral growth

Answer 51

build massive structures through the accumulation of their limestone skeletons cemented together with sand

Question 52

Describe atolls

Answer 52

- start growing on the shore of a high volcanic island as a fringing reef - island begins to erode and sink - weight of the volcano can cause subsidence - reef grows upwards, forming a barrier reef further offshore - lagoon between barrier reef and high volcanic island becomes wider and deeper - peak sinks beneath the water, leaving only the reef in place - island becomes an encircling barrier reef: an atoll - tens of millions of years to form - only kept at the surface through the action of the coral - e.g. Aldabra in the Indian Ocean

Question 53

What would happen if the coral of an atoll died?

Answer 53

- continue to erode - end up under the sea

Question 54

Describe phylogeny of reef-building corals

Answer 54

- scleractinian (stony) corals - within the class Anthozoa - within the basal phylum Cnidaria - arose during the mid-Triassic The ceonosarc creates a common gastrovascular system so that food can be shared among the polyps – they are all clones.

Question 55

Describe the morphology of reef-building corals

Answer 55

- simple body plan - two germ layers: ectoderm and endoderm - mesoglea inbetween - muscles formed from the epithelial cells (retract and extend the tentacles) - secrete calcium carbonate skeletons and a corallite

Question 56

Describe coral ectoderm

Answer 56

contains cnidocytes

Question 57

Describe coral endoderm

Answer 57

contains photosynthetic algae

Question 58

corallite

Answer 58

protective cup

Question 59

Describe the ecology of reef-building corals

Answer 59

- exist as single polyps or as a colony connected by coeonsarc tissue - colony can grow for years or decades, forming massive structures

Question 60

Describe Palaeozoic reef-building corals

Answer 60

went extinct during the Great Dying.

Question 61

Acropora

Answer 61

a branching coral

Question 62

Porites lutea

Answer 62

a boulder coral that is resisting coral bleaching quite well

Question 63

Describe coral reef symbiosis

Answer 63

- photosynthetic algae called zooxanthellae in endoderm - coral provides protection for the algae and CO2 from respiration - also contributes other essential nutrients (e.g. nitrogen) from feeding - regulates growth and multiplication of symbionts

Question 64

Zooxanthellae

Answer 64

- dinoflagellates - genus Symbiodinium - essential for coral growth (carbon provision, aiding calcification)

Question 65

Symbiodinium

Answer 65

- free-living at low density in tropical waters - 30% of the biomass of a polyp - symbiont cells separated from host cytoplasm by symbiosomes

Question 66

symbiosome

Answer 66

specialised membranous structure

Question 67

Describe coral polyp dependence

Answer 67

- on algae for nitrogen as well as carbon - symbiont produces amino acids using DIN from water column, and from nitrogenous waste produced by the coral - polyp acquires more than 80% of N from the algae when feeding rates are low

Question 68

DIN

Answer 68

dissolved inorganic nitrogen

Question 69

Describe carbon and nitrogen dynamics within the coral symbiosis

Answer 69

tight recycling

Question 70

Describe coral reef productivity

Answer 70

- very high productivity (similar to the best agricultural systems) - corals keep most of the photosynthetic products; channel around 90% of the C fixed by their symbionts into their own growth (much of it is respired away)

Question 71

Describe algae on reefs

Answer 71

- many kinds - coralline red algae - fleshy green and brown algae - provide a ‘turf’ for grazing fish (e.g. herbivorous surgeonfish) - herbivorous fish support predatory fish

Question 72

Describe coral reef biodiversity

Answer 72

- probably the most biodiverse ecosystem on the planet - take up 1% of the ocean floor - support 25% of marine life - over ¼ of the world’s fishermen in 99 countries fish on reefs

Question 73

List some marine life that corals support

Answer 73

Sponges, echinoderms, nudibranchs, anemones, and lots of fish.

Question 74

Describe fishing on coral reefs

Answer 74

- begin by targeting top predators (groupers, jacks and sharks); easily overfished - ‘fishing down the food chain'; targeting smaller herbivorous fish (e.g. parrotfish)

Question 75

Describe Jamaican coral reefs

Answer 75

- chronic overfishing: began by targeting predatory fish, but then herbivores (e.g. parrotfish) - sea urchin boom: massive numbers of long-spined urchin Diadema antillarum kept fleshy algae in check, despite loss of herbivorous fish. - hurricane damage (1980) destroyed much of the Acropora species (short-lived coral recovery) - sea-urchin die-off (’82-’84): pathogen caused the death of 99% of urchins - loss of urchins and absence of fish caused dramatic bloom of benthic algae; prevents coral recruitment - phase-shift

Question 76

Describe phase-shift

Answer 76

reefs can exist in one of two states and that either is stable

Question 77

Describe El Niño/La Niña events

Answer 77

large-scale climate phenomenon that occurs every 3-8 years

Question 78

... of the Great Barrier Reef has bleached to death since 1995

Answer 78

Half

Question 79

average interval between bleaching events has ... between 1980 and 2016

Answer 79

halved

Question 80

Coral bleaching occurs when

Answer 80

- corals expel their symbiotic algae - exposed to prolonged high temperatures - high UV exposure also contributes

Question 81

What are the two main causes of coral bleaching?

Answer 81

t is thought to have two main causes: Oxidative stress – the algae produce reactive oxygen and nitrogen species. High temperatures cause the algae to become ‘selfish’ and stop exchanging nutrients with the host.