coral reef final

list and describe the 5 classes within the phylum Cnidaria.

1. Hydrozoa - alternate between polyp and medusa stages

2. Anthozoa - only occur as polyps

3. Scyphozoa - true jellyfish

4. Cubozoa - box jellies, cuboidal medusa form, groups of tentacles from each edge

5. Staurozoa - no alteration between forms, only attached medusa stage

what are the two subclasses of the class Anthozoa?

1. Hexacorallia - 6 fold symmetry, colonial, many secrete CaCO₃ skeleton

2. Octocorallia - 8 fold symmetry, colonial, generally ahermatypic, skeleton is typically spicules or sclerites

what are the 3 relevant orders of subclass Hexacorallia?

1. sea anemones - ahermatypic

2. black coral - ahermatypic

3. hard coral - hermatypic

what are the 5 orders of subclass Octocorallia?

1. blue corals - hermatypic

2. pipe organ corals - hermatypic

3. soft corals - ahermatypic

4. sea pens - ahermatypic

5. gorgonians - ahermatypic

explain Darwin’s paradox on reefs.

his question: How can such high production exist in such low nutrient conditions?

answer:

• amount of photosynthetic tissue is so high, so primary productivity is high (zooxanthellae, phytoplankton, CCA, macroalgae)

but photosynthesis requires nutrients…

• effective capture of nutrients through efficient phytoplankton capture (“wall of mouths” (fish))

• rapid recycling of organic matter from dissolved to particulate (DOM to POM) including the sponge loop

• external nutrient inputs including the island mass effect and seabird derived nutrients

explain the symbiosis between corals and zooxanthellae.

1. zooxanthellae gets protection in the form of living inside host tissue, coral gets UV protection

2. zooxanthellae get nutrients like N and P, coral gets sugar important for growth and reproduction

3. zooxanthellae get CO₂ from coral respiration, coral gets O₂ from zooxanth. photosynthesis

label this diagram of coral anatomy.

give an example of relationships within the coral holobiont

zooxanthellae

• algae get protection and shelter, coral gets sugars and UV protection

bacteria

• bacteria get protection and shelter, coral gets nutrient cycling

viruses

• gene transfer

fungi

• antimicrobial activity

what is morphological plasticity with one example

ability of an individual coral to change its physical form or structure in response to environmental conditions

example: corals in low-light conditions may develop a flattened, plate-like morphology to maximize light absorption

what are the 3 coral feeding strategies?

1. autotrophic- energy from zooxanthellae

2. heterotrophic- energy from capturing food

3. mixotrophic- most Scleractinian corals combine methods, gain flexibility this way

what are 3 reason coral mucus is released?

1. prevents against environmental stresses - dessication, radiation, sedimentation

2. capture food

3. release carbon

list and describe the 6 coral asexual reproduction methods?

1. fission = intra-tentacular, new polyp is formed by the oral disc (mouth)

2. budding = extra-tentacular, new polyp is formed from tissue between existing polyps

3. polyp balls = polyps form on the underside of parent and eventually break off

4. asxual brooding = asexual production of planula larvae that are genetically identical to the parent colony

5. polyp bailout = under environmental stress, polyps can break their connective tissue, emerge from their corallite, and float off

6. fragmentation = breakage of small sections of coral

define the two types of coral sexual reproduction.

1. brooders

internal fertilization

sperm released via the mouth of male corals, taken in via the mouth of female polyps

embryo maintained within the coelenteron until settlement-competent larvae can be released (already contain zooxanthellae)

2. broadcast spawners

external fertilization

eggs and sperm are released into seawater where fertilization occurs

gametes meet in water to form ciliated, free-swimming planula larvae (do not contain zooxanthellae)

compare brooders and broadcast spawners (advantages of each)

spawners:

• safety in numbers (more sperm and eggs released)

• greater genetic diversity (carried in currents over distance)

• requires less energy

brooders:

• fewer but better developed planulae

• less chance of getting eaten (can settle immediately)

• can release planulae at any time, already in planktonic stage

label the life cycle of a coral

synchronous mass spawning events (coral)

• maximizes chance of fertilization and increases genetic variability

• seasonal. water temperature initiates gonad development

• half of all GBR corals release gametes at the same time

planulae

ciliated larvae, drift in open water for days to weeks before settling down, main means of long-distance dispersal of corals, how corals can cross genetically

coral growth

calcium is taken up from the water to form the coral skeleton in the form of CaCO₃

what 3 basic reactions does coral growth require?

1. photosynthesis (zooxanthellae)

2. respiration

3. calcification

what are some potential reasons why the Coral Triangle is so coral-rich, the “global epicenter of marine biodiversity”?

1. tectonic activity has created complex, shifting habitats that promote species diversification

2. ocean currents converge, bringing larvae from Indian and Pacific oceans (genetic exchange)

3. warm, stable conditions support high productivity and long-term survival

list and differentiate the 3 types of reefs?

1. fringing reefs = close to shore, shallow or no lagoon

2. barrier reefs = parallel to shore, separated by wide, deeper lagoon

3. coral atolls = roughly circular, surrounding a lagoon

label the zonation of a fringing reef

label the zonation of a barrier reef

Darwin’s theory of atoll formation

proposes that coral atolls develop around sinking volcanic islands.

as the island subsides, corals continue to grow upward, forming a progression from fringing reef to barrier reef, and eventually to an atoll once the island is fully submerged

what are 4 factors that make reef flats such a challenging environment?

• physical stress - heat, drying, light and air exposure

• pulse events - rain, winds, storm

• no time to recover

• limited refuge

which zone of the reef is the ideal habitat for coral growth?

shallow fore-reef slope

functional redundancy

multiple species perform similar ecological functions, so the loss of one species may be partly compensated for by others

groupers

includes largest reef fish

protogynous - sex change FTM

usually invertebrate and fish predators

snappers

fish and invertebrate predator

occupy reefs and adjacent coastal habitats

parrotfish

dominant herbivores (scrapers and excavators)

protogynous - sex changes FTM

damselfish

herbivores

“garden” algae patches

how is high reef-fish diversity maintained within local communities?

1. niche partitioning - species reduce competition by using different resources, habitats, or times within the same environment

2. lottery hypothesis - larval arrival influences which similar competitor occupies a vacant space

3. variable recruitment - larval supply, settlement, and early survival vary through space and time

4. predation and disturbance

5. habitat complexity

what are three reasons that reef fish are so colorful?

1. to hide in plain sight - bright colors help them hide in a colorful environment

2. helps identify their own species

3. aposematic coloration - warning colors to deter predators

sponges (phylum Porifera)

filter water and play an important role in recycling nutrients and organic matter

sponge loop: sponges rapidly absorb DOM then release it as solid cellular waste that feeds the reef

sea cucumbers (phylum Echinodermata)

act as bioturbators - keep sediments healthy and oxygenated

play a key role in nutrient cycling

heavily exploited

sea urchins (phylum Echinodermata)

play a critical role in the grazing and removal of algae

giant clams (phylum Mollusca)

largest bivalve, have zooxanthellae

CaCO₃ shells contribute to reef framework and can provide a substrate for settlement of reef organisms

under pressure from overfishing

what are broad based assessments and two examples?

show how typical of the area the site is, how complex or simple the communities are, can yield semi-quantitative comparative data

ex: manta tow, timed/ metered swims

what are three examples of percent cover estimates?

1. PIT

2. LIT

3. photo quadrant analysis

point intercept transect (PIT)

identify cover at defined points

ReefCheck method: 20 meter lines, data taken every 0.5 meters

line intercept transects (LIT)

continuously identify cover under straight transect

compare LIT and PIT (advantages/ disadvantages)

PIT

• rapid, allows more replicate transects in dive time

• less detail, no information on sizes

LIT

• high detail, information on sizes

• slower, time intensive may mean less replicates

belt transect

not just benthic like PIT/ LIT, gives density and relative abundance of fish and invertebrates

ReefCheck method: 5 meters wide, 20 meters long

what is the difference between belt transect and PIT/ LIT survey methods?

belt transect gives information on fish and invertebrates, where PIT/ LIT are solely benthic

underwater visual census (UVC)

measuring fish communities, have a 3D cubelike space to measure

count all target individuals and estimate length

can be used with biomass formula to calculate biomass

label the life cycle of a coral reef fish

spawning aggregations (fish)

spatially and temporally discrete gatherings for the purpose of reproduction

fishing during this season is harmful

why do so many marine species spawn in aggregations?

• concentrate the gametes for broadcast spawners

• utilize the dispersal capacity of water currents

• reduce predation risk if higher numbers in limited time frames

pelagic larval duration (PLD)

starts at hatching and ends at the arrival on the reef

lasts 3-6 weeks

feed on zooplankton

delays can happen when larva cannot find a suitable habitat to settle

settlement

post-larvae (juveniles) identify suitable habitat to settle, mortality rates within the first year are high (80-90%)

ontogenetic habitat shifts

changes in the physical environment or habitat use that occur as a reef fish grows from a juvenile to an adult

give two examples of mutualism on the reef.

1. goby fish and pistol shrimp

goby uses the shrimp’s burrow to hide from predators

shrimp uses goby as “eyes” since it is blind

2. corals and zooxanthellae

corals get sugars

zooxanthellae get a safe environment, nutrients, and carbon dioxide

3. fish cleaning stations

wrasse fish get food

big fish get cleaned

give one example of commensalism on the reef.

pearlfish and sea cucumbers

• pearlfish enter sea cucumbers anus for shelter from predators

give two examples of predation on the reef.

1. COTS and corals

COTS evert their stomach over coral colonies to consume coral tissue

2. moray eels and fish

eels ambush fish and octopus from holes in the reef

discuss and distinguish the ecological role of the 4 types of reef algae.

1. macroalgae

ecological role: primary producers, food source, build ecosystems (hiding spot for fish)

2. turf algae

mix of juvenile macroalgae, covers most bare space on a reef, can trap sediment

ecological role: primary producers, food source

3. cyanobacteria

photosynthetic bacteria, fast-growing and can compete with coral

ecological role: fix nitrogen into bioavailable form

4. crustose coralline algae (CCA)

encrusting red algae that forms hard sheets over reef surface

ecological role: cements reef elements together

label this diagram of a positive fish-algae-coral feedback loop.

label this diagram of a negative fish-algae-coral feedback loop.

list and describe the four functional groups of herbivores.

1. scrapers

scrape coral and rock, removing turf algae (parrotfish)

1. grazers

crop turf algae (damselfish)

3. browsers

remove standing macroalgae (rabbitfish)

4. detritivores

remove detritus from turf algae (cleaner crabs)

allelopathy

chemical inhibition of one organism by another due to the release of chemical substances

can happen with coral due to algae because algae release metabolites

what type of species need to be prioritized most in management?

species that perform functions with low functional redundancy

define and give 5 explanations for the island mass effect.

observed phenomenon of localized increases in phytoplankton biomass near island and atoll reef ecosystems

1. nutrients that result from decomposing reef animals

2. upwelling of nutrient-rich colder waters toward the surface

3. the mixing effect of waves and currents

4. sedimentation from land erosion

5. human-derived runoffs from ag, urban development, and wastewater

list 4 effects on reefs adjacent to rat-free (more seabirds) islands that studies have shown.

• higher fish biomass

• damselfish grew faster

• grazing rates were higher

• bioerosion was higher

why is the eradication of rats on islands important to reef health?

rats predate seabird eggs and chicks. this disrupts nutrient flows among pelagic, island, and reef ecosystems because seabirds play an important role in nutrient deposition

explain why seabirds are important for reef health?

seabirds feed on fish and marine organisms

when the return to islands, they release guano (poop) that is high in nutrients (N and P)

it accumulates on island soils and is washed into the sea by rainfall

reefs thrive in oligotrophic conditions through tightly regulated nitrogen cycling

nitrogen is used on the reef to support the growth of plankton, corals, and fish

differentiate terrestrial sediments vs carbonate sand.

terrestrial sand = particles are smaller, more compact with low oxygen content, very hard to live in (mud, silt)

carbonate sand = not as compact, animals that live there have a higher risk of being dug up by predators (coral fragments, CCA)

reef bioerosion

biotic breakdown of CaCO₃

differentiate external and internal bioerosion with examples.

external = on the surface (rasping, biting, scraping)

• ex: parrotfish

internal = colonization and growth of penetrating organisms

• ex: boring sponges, christmas tree worm

describe 4 pathways for “sand fate”

1. reef lithification

2. formation of sand flats

3. beach/ island formation

4. beach rock formation

reef lithification

fine CaCO₃ sediments filter into porous structure of reef, bacterial remineralization CaCO₃, sediments compact under pressure resulting in solid limestone deposition

beach rock

mix of gravel, sand, and silt sediments that is cemented with carbonate minerals and has formed along a shoreline

reef accretion

vertical buildup of reef framework

net accretion = (carbonate added to reef) - (carbonate lost)

what 4 inputs cause reef accretion

1. constructive processes (calcification, lithification)

2. reincorporation or infilling of material into the framework

3. destructive processes (physical erosion, bioerosion)

4. displacement of CaCO₃ material (sediment, rubble)

what are the 4 scales of reef stressors?

1. local

2. global

3. chronic (press)

4. acute (pulse)

differentiate obligate and facultative corallivore with an example for each.

obligate = feeds only on coral (diet at least 80% coral)

• ex: Drupella snail

facultative = feeds on corals and a number of other prey species

• ex: damselfish

differentiate the 4 corallivore feeding mechanisms

1. mucus eaters

little damage to coral

2. tissue eaters

remove only polyps and soft tissue

3. scrapers

remove a bit of underlying skeleton

4. excavators

remove a substantial amount of underlying skeleton

what is the argument for naturally caused COTS outbreaks?

great reproductive potential makes the species prone to population fluctuations

evidence:

• geological studies show large concentrations of skeletal parts in the past

• Pacific Islanders recall past outbreaks

• outbreaks occur naturally on isolated, protected reefs

what are the 2 arguments for human caused COTS outbreaks?

1. larval stage hypothesis: human runoff causes increased COTS larval survival from elevated nutrients and phytoplankton

2. predator removal hypothesis: overfishing of predators of juvenile and adult stages (crabs, tritons, snappers, humphead wrasse)

list 3 COTS predators.

1. humphead wrasse (eat juveniles)

2. giant Triton snail

3. pufferfish

4. triggerfish

list the 2 methods for controlling COTS outbreaks?

1. hand collecting and killing ashore

can be expensive, time consuming, dangerous

2. in situ injection with poison

more cost effective, some poisons like copper sulfate can cause local pollution, vinegar is effective and safer

crown of thorns starfish (COTS)

largest seastar, covered with poisonous spines on upper surface, walks using tube feet

feeds through everting stomach (external digestion)

what are some demographic factors that give COTS high potential for harm?

1. high reproduction rates

2. high feeding rates (eats its own body area each day)

3. adults have few predators

give 2 examples of local + acute stressors.

1. ship grounding/ anchor damage

2. oil spill

3. COTS outbreak

4. coral disease outbreak

5. blast fishing

give 2 examples of local + chronic stressors.

1. sewage/ nutrient pollution

2. persistent sediment runoff

3. overfishing (loss of herbivores)

4. coastal development (marine debris)

give 2 examples of global + acute stressors.

1. marine heatwaves (El Nino)

2. severe tropical cyclones

give 2 examples of global + chronic stressors.

1. long-term ocean warming

2. ocean acidification

3. sea-level rise

list 3 effects of the local stressor of sedimentation.

1. reduced light levels

2. energetic cost to corals through sediment shedding (mucus production)

3. reductions in coral recruitment

list 4 effects of the local stressor of nutrient addition.

1. increased turbidity due to algal blooms

2. increased coverage of algae (turf, macro, cyanobacteria)

3. increased prevalence of coral disease

4. increased risk of COTS

stony coral tissue loss disease (SCTLD)

highly lethal coral disease, first reported in 2014 and is now the most deadly coral disease outbreak in history

tropical cyclone effects

can cause physical damage to reefs, especially branching corals

BUT

when less extreme, can also alleviate heat stress and reduce bleaching risk

list 2 effects of the global + chronic stressor of rising sea levels.

1. reef drowning - if vertical carbon accretion cannot keep pace, reef surfaces become progressively deeper

2. reduced coastal protection - increasing water depth allows larger waves to cross reef flats

coral bleaching

coral tissue becomes transparent due to complete or partial loss of pigmentation from endosymbiotic zooxanthellae

underlying skeleton becoming visible gives it the white appearance

bleaching is not death, but can lead to bleaching-related mortality

mass bleaching

wide-scale (tens to hundreds of km²) phenomena where corals and other symbiotic reef organisms (giant clams, sea anemones, sponges) bleach

often linked to elevated temperatures

thermal acclimation

process where surviving corals previously exposed to elevated temperatures can “remember” the stress and condition themselves to withstand future heat waves

what is unique about heat-adapted genes in corals?

the trait is polygenic, meaning a coral’s heat resilience is not linked to any single gene but to many genes

ecological succession

the gradual process by which ecosystems change and develop over time

early colonizers

species that are specialized to colonize new surfaces

opportunistic, fast growing

climax communities

occur at the end of succession

list the 4 reef colonization (ecological succession) stages in order.

1. bacteria and microalgae

2. CCA, sponges, turf algae

3. macroalgae

4. coral larvae

erosion

what causes coral bleaching?

coral have to expel their zooxanthellae

mainly caused by heat stress from elevated ocean temperatures

can also result from pollution, extreme sunlight, low tides, etc