Coral-Algal Symbiosis Quiz

deepwater

Most corals are ______ and thus do not have zooxanthellae

Hexacorallia, Scleractinia

What subclass and order are hard corals in?

corallite

The entire cup piece of skeleton that the polyp sits in

calyx

The depression in the cup in which the polyp sits

6

Hard corals have multiples of _ tentacles

nematocysts (stinging), spirocysts (stickiness), ptychocysts (holdfasts in tube anemones)

Three types of cnidocytes and their function

epidermis and gastrodermis (endodermis)

Names of two tissue layers

mesoglea

Glue between the tissue layers

In the gastrodermis

where are zooxanthellae located?

4-5

How many stomach cells per zooxanthellae?

epidermis

Calicoblasts contained in this layer

Calcification

Zooxanthellae uptake CO2, helping with this process

hermaphroditic, broadcast

Most corals are this sex type and this spawn type

Solitary means not colonial, free-living means detached from substrate. Produce anthocauli buds

Solitary vs. free-living

intratentacular

Which type of budding is characteristic of brain corals?

when somatic mutations carry over through asexual budding and one colony has multiple genotypes; when two larval recruits fuse together rather than outcompeting each other

Two times when corals are called “chimeras”

“adaptively polytrophic” or “mixotrophic”

Corals are often called either of two names because they are both autotrophic and heterotrophic

78-99%; helps limit growth

How much of the symbiont sugar is given to the coral? Why might this be?

• Scan and trap: movement to alter water flow (Xenia)

• Sieving: pinnicules that strain water

• Aerosol capture: direct capture by nematocysts

• Mucosal capture

Four food capture mechanisms

Orders

Diversity within Symbiodiniaceae is equivalent to this taxonomic level

symbiozomes

Specialized vacuoles that contain symbionts

• 1% SDS + DNAB

• Proteinase K Digest

• CTAB

• Organic Extraction

• 1st ethanol precipitation

• 2nd ethanol precipitation

• Ethanol wash and resuspension of DNA

Steps of DNA Extraction

soap, binds and pulls apart lipids, lysing cell membranes

What is SDS, what does it do

NaCl and EDTA. EDTA chelates four divalent cations which helps keeps enzymes inactive to freeze cell activity. NaCl keeps ionic concentration high enough for EDTA to work without binding to it.

What is DNAB, what does it contain, what does it do?

Generic Protein digester. Helps break down difficult cell wall of the symbiont

What is Proteinase K, what does it do?

CTAB, water, yeast tRNA. CTAB is a long molecule with one polar end and one nonpolar end. The polar end grabs cell bits and will bring them to the interface when we chloroform. Yeast tRNA boosts amount of nucleic acid, there’s a base number needed to precipitate DNA. doesn’t contaminate sample since from yeast and is RNA instead of DNA

What does CTAB mix contain, what does it do?

Similar to EDTA, chelates divalent cations. Molecule that keeps DNA stable by getting rid of divalent cations which normally activate enzymes.

What is TE/ TEDTA, what does it do?

Rubisco

What’s the most abundant enzyme on earth?

Atmospheric dissolution, respiration, coral skeletogenesis (CO2 produced from calcification- possibly in the space where hydrogen ions are pumped?), conversion of bicarbonate by carbonic anhydrase

Where is CO2 for photosynthesis from?

carbon sinks

Coral reefs are not these

Junk food; glucose and glycerol. Need N, P, Fe, other nutrients so get those from heterotrophy.

What is photosynthate? Why do corals need other stuff?

On cloudy days, symbionts can’t provide enough. Corals must use lipid reserves or do heterotrophy.

What was the main takeaway from the carbon budget study?

Oligotrophic areas! Pass nutrients and waste between coral and symbiont

Why do corals need to recycle nitrogen? how do they do it?

Collection of coral animal, algal symbionts, and the microbiome

Holobiont

Symbiont passes fixed carbon to coral, coral passes CO2 to the symbiont. Coral gives fixed carbon to the microbiome (via mucus), microbiome help fix N, gather Fe and P, and can make antibiotics

Holobiont passing nutrients and carbon

Corals fill entry niche with helpful bacteria (probiotics) so that bad ones can’t be there

How does the microbiome prevent harmful bacteria?

can be passed to an adjacent cell or spat out into ocean.

What happens when a symbiont divides?

coccoid

Symbionts are called this when in corals, not free living

Corals often uptake the most when they are young and small near the sediment.

Why is it beneficial that symbionts live in the sediment?

oxygen

This is toxic under high concentrations and the coral must expend energy to deal with it

Benefits: Solar panels, enhanced calcification, algae can sequester toxic compounds and create fluorescent sunscreens.

Costs: Makes you vulnerable to heat stress, Diseases that affect them affect you, Limited to tropical photic zone, Need to invest in nutrients symbiozomes oxygen detox, regulation of growth

Indirect: Surface area maximization

Benefits, Costs, Indirect Coral Perspective

Benefits: Grazer protection, Consistent Light Exposure, UV protection, Increased Photosynthetic efficiency

Costs: High rent, Landlord can evict you, Limited Nutrient Supply, Slower Growth Rate

Indirect:Dispersal by corallivorous fish and inverts

Benefits, Costs, Indirect Symbiont Perspective

Benefits: Faster Growth Rate, Better Competitor for Space, Recycling Resources, Possible Increased Wave Resistance

Costs: Compounded Sensitivity to Multiple Stressors, Restricted range of tolerance of light, temp, sediment

Benefits, Costs Holobiont perspective

O. ann typically has B shallow, C deep

O. fav typically has A shallow, C deep

Intial Oannularis and Ofaveolata depth findings

Most did change but 3/8 had no sig difference. Controls taken down and back up to ensure movement not involved. Many deep corals bleached initially upon being brought to surface, but recovered with shallow symbionts. Many of the shallows died at depth because no symb change.

Toppling and reciprocal transplant studies.

C, D. vs. A,B,C,D

Most common clades in IndoPacific vs Atlantic

Durisdinium is dominant in the Arabian Gulf, whereas in the Red Sea the distribution is more representative of nearby populations. This is because the Arabian Sea is shallow and experiences a crazy range of temperatures → suggest D is hardier!

How do symbionts in the Arabian Gulf differ from the Red Sea? Why does it matter?

Mauritius escaped bleaching in El Nino due to a typhoon cooling them down, whereas Kenya did not. Kenya had more Durisdinium afterwards.

Mauritius vs. Kenya bleaching study.

18-24 months; study done in a cooler area

How long did a study find Durisdinium to last in corals, and what was a caveat?

Tropical, finicky, slow-growing, near impossible to render aposymbiotic

Why are reef corals not good model organisms?

lose more symbionts during bleaching

Having more symbionts before bleaching means you will

Severity of bleaching (% symbiont loss), and temperature. Often there is a “threshold” to swap to D. Genotype and previous history may be involved in some way.

What does recovered symbiont community composition depend on?

Using chemical bleaching and doing repeat bleaching to see if they would be more bleaching resistant.

How did they confirm it was about Durisdinium and not temperature that made them bleaching resistant?

Yes, slower growth due to less optimal photosynthetic output. However other clades may lower to similar growth rates under higher heat conditions.

Are there tradeoffs for Durisdinium?

Poisons the photosystems

Mechanism for DCMU bleaching

Budding within colony, fragmentation, stress-induced polyp bailout

Three types of asexual reproduction in corals

70%

What percent of corals are hermaphroditic?

Caribbean; Indo-Pacific

The spread of gono/herm and brood/broadcast is more diverse in the ______ than in the ______

• Energetic cost of males (don’t produce offspring so halves potential)

• Cost of passing ½ genes to offspring (meiosis)

Twofold cost of sex

16%

What percent of corals brood?

symbionts

Larvae already have these in brooders

Advantages: Genetic diversity, Higher initial survivorship (k selected), Less time in water column, competent quickly, multiple attempts a year, local dominance

Disadvantages: Short dispersal (low connectivity), More costly and less larvae, Sperm disperses very rapidly once released

Advantages and Disadvantages; Brooder

Day length, temperature, lunar cycle, wind, Genetic control (Circadian rhythm). Possible chemical cues (contagious spawning)

Synchronization cues

Advantages: Genetic Diversity, Long range dispersal, more larvae (numbers game), Genetic connectivity, conducive to hybridization, Effective at low abundances

Disadvantages: Subject to environmental changes, fewer chances, high predation due to long water column times, low initial survivorship

Advantages and Disadvantages; Broadcast Spawners

Long light period, then dark period, then light when the full moon comes out

What specifically is needed with lunar cues during spawning?

The Great Barrier Reef

Where does mass spawning occur?

Temporal differences in spawning, gamete dispersal, gamete incompatibility

How is hybridization avoided in mass spawning?

Light Pollution, Increased temperatures (affects both gamete production and spawning cues), hormonal pollution (estrogen decreases number of egg bundles)

Reasons for spawning synchrony breakdown?

Mesenteries

Where does gametogenesis occur?

undeveloped egg. Lipid rich, positively buoyant

Oocytes

Packets of sperm. Neutrally buoyant, mobile

Spermaries

Sperm concentration, Allee effect (parents too spread out), Predation, Sperm motility, Environmental conditions

What factors affect fertilization success?

Cleavage → Blastulation → Gastrulation → Planula

Four stages of external development

CCA, chemical olfaction (bacteria that live on CCA), pink and red, biofilms, sound, vibrational cues

Positive larval recruitment cues

Sedimentation, toxins, macroalgae

Negative settlement cues

Light (they like darker nooks and crannies where predators wont get them), Temperature (can speed up growth but kills if too high), Density of other larvae

Either +- settlement cues

Often more fragging based; need to be careful to vary genotypes when outplanting on reef.

How does Florida differ from other reproductive efforts?

Mega net cradles, shaded boxes, Chucking substrates into the ocean.

Other reproduction efforts

Thylakoid membrane; splits water and makes oxygen; recharges ATP and NADPH for use in the light rxns

Where do the light rxns take place? What do they do?

Light hits photosystem II, which splits water into hydrogen ions, oxygen, and electrons. The hydrogen ions build a low pH. Meanwhile the electrons travel down the ETC and recharge NADP+ to NADPH at Photosystem I. The pH gradient makes H+ want to move through ATP synthase which recharges ADP + Pi to ATP.

Light rxn steps

H2O + 2NADP+ + 3ADP + 3Pi + 8 photons → O2 + 2NADPH +2H+ + 3ATP

Full light rxn equation

Stroma; fixes carbon dioxide into photosynthate

Where does the dark reaction take place? What does it do?

Rubisco binds 3 CO2 to 3 five carbons to make 3 six carbons; Change to 6 three carbons. ATP and NADPH change the structure of the three carbon to make it more high energy and eventually produce 6 G3P. One G3P pops out as the net, while the other are changed to 3 five carbons to start the cycle again.

Dark reaction Steps:

CO2 + 2NADPH + 2H + 3ATP → CH2O + H2O + 2NADP+ +3ADP + 3Pi

Full Dark reaction equation

Rubisco

The most abundant enzyme on Earth. Rate limiter of photosynthesis

carbonic anhydrase

How does CO2 enter the cell

Photochemical quenching- fluorescing photons away

Nonphotochemical quenching- rerouting energy into chemical mechanisms

Two ways corals deal with excess energy?

burn energy by turning diatoxanthin to diadinoxanthin and vice versa

Xanthophyll cycle

Water-water cycle. Burn energy by starting with water and ending with water.

Mehrler cycle

Uses light for Rubisco to fix O2 into CO2

Photorespiration

Xanthophyll Cycle, Photorespiration, Mehrler (water-water) cycle

Three common NPQ mechanisms

Photosystem II has a protein called D1 that repeatedly gets damaged and repaired during normal photosyntesis. However the repair process stops under thermal stress.

How does thermal stress stop photosystems?

Disrupts photosystem function, Damages thylakoid membrane, Rubisco inactivated, Dysfunction of carbon transfer, production of ROS

How does thermal stress disrupt photosynthesis?

• Singlet oxygen (1O2)

• Superoxide (O2-)

• Hydrogen peroxide (H2O2)

• Hydroxyl radicals (*OH)

Common ROS

APX, SOD

Enzymes that corals use to deal with ROS

reactive cascade involving the mitochondria and nitrogen radicals that eventually leads to apoptosis via an immune response.

What do ROS lead to?

• In situ symbiont degradation

• Exocytosis (sometimes healthy form of growth control)

• Host cell detachment

• Host cell apoptosis

• Host cell necrosis (extreme bleaching, tissues slough off)

Mechanisms for symbiont loss

chemicals (DCMU), salinities, nutrients, light

Bleaching is a general stress response and can also happen with

Photic hell

Term describing white inside of corals when bleached, only tough symbionts can survive

about 1-2million per cm² means corals are fully optimized

Average symbiont size 10 micrometers. What this mean?