Lecture 7

10 multiple choice questions, matching images to terms from assignment 1, 5 short answer questions, 3 long answer questions

What is the primary source of suspended sediment in reef waters?

• resuspension of sediment by waves and currents

How do river plumes primarily reduce light availability for coral reefs?

• by increasing wave action and sediment resuspension

Which of the following is not identified as a mechanism corals use to actively remove sediment

• increased calcification

For calcification to take place, which of the following conditions must be met?

• find answer

What happens when carbonic anhydrase (CA) is inhibited during the calcification process?

• calcification rates are significantly reduced

Is it thought that the part of the coral calcification involves the production of an organic matrix

Symbiosis

• a powerful evolutive way to aquire new metabolic capabilities

• two or more organisms that live together in close association for prolonged periods of time

  • endosymbiosis

  • ectosymbiosis

  • obligate symbiosis

  • facultative symbiosis

  • parasitism

  • mutualism

  • commensalism

Coral/zooxanthellae symbiosis

• relationship has been around for at least 240 million years

  • zooxanthellae also live in numerous other invertebrate taxa

• coral can host between 1 and 12 types of zooxanthellae depending on the species and environment

  • corals can harbour one, a subset of closely related, or numerous types of zooxs

  • doubling times of zooxanthellae in hospite is 10-70 days

• abundance can change depending on conditions such as seasons, positions of the coral, and light levels

  • single coral colonies can host various different types of zooxs which may be related to different light levels (this may have implications for maternal passing on zooxs)

Zooxanthellae

• dinoflagellate algae

  • genus Symbiodinium

    • numerous types of zooxs grouped into clades; specialist vs. generalist

• 5-10 μm in diameter

• lack flagella when inside the host

• surround by a cellulose cell wall

• contain chlorophyll a and c

  • + other accesory pigments peridinin and diadinoxathin which lend brownish colour and assist in harvesting light

How do corals acquire zooxanthellae?

• one of two ways:

  • from their parents

  • environmental food chain

Zooxanthellae diversity

• members of the same clade do not necessarily have the same environmental preferences, but we see some general trends

  • still much to discover about relationship between genetics and physiology

• to what extent is coral distribution limited by physiology of zooxanthellae types?

• can corals change zooxs types as environment changes?

Photoacclimation

• zooxs can adjust the amount of chlorophyll a depending on light conditions

  • shading= increase # of zooxs

• position fluorescent pigments behind zooxs to ehance light or above to reflect light

  • MAAs

• coral withdraw tentacles

Nutritional symbiotic benefits

• atrophy

• light enhanced calcification

• heterotrophy

• N conservation and recycling

Autotrophy

• corals receive energy-rich photosynthetic products

• symbiotic relationship allows corals to be polytrophic

  • polytrophic: deriving nourishment from more than one organic substance or food source

N conservation and recycling

• conservation:

  • preferential use of energy rich photsynthetic products rather than amino acids for respiration

• recycling:

  • zooxs use waste from corals to produce amino acids which are passed back to the corals again

• N in short supply, so sharing and recycling is key

Darwin’s Paradox

• high productivity in low nutrient environments

  • seen in corals!

• a story in 2 parts:

  • part 1: the carbon story

  • part 2: the nitrogen story

    • N is required for reproduction/tissue growth/mucus production

    • scavenge nitrogen in various forms

    • corals conserve what they have

    • recycling of N between host and symbiont

Symbiotic relationship benefits for zooxanthellae

• fixed position with access to light for zooxs in water column

  • branch orientation, light scattering by the skeleton or fluorescent pigments in the tissues which optimize harvesting of down welling light

• protection from grazers

• supplementary CO₂ from coral respiration

• coral fluorescent pigments may enhance light capture for zooxs

• CO₂ from respiration can be used for photosynthesis

• stable “culture medium” controlled by the coral thus reducing energy cost to zoox for ionic regulation

Symbiotic relationship benefits for corals

• supplementary O₂ from photosynthesis

• CO₂ from zoox respiration for calcification

• photoacclimation of zooxs

• shade vs. light loving zooxs

• environmental adaptations

Stable isotope analysis

• useful to help us understand animal physiology, diet composition, trophic level estimations, and food web functioning

• stable isotopes of N is used as a “trophometer”

  • faster loss of ¹⁴N than ¹⁵N in metabolism and excretion leaves animals with higher 𝛔¹⁵N values

  • an increase in trophic level from a plant to herbivore or an herbivore to carnivore have been estimated to involve 𝛔¹⁵N increases of 2.2 to 3.4 %_o in the consumer vs. its diet

Fractionation

• in kinetic reactions, the light isotopes usuallt react faster

• in exchange reactions, heavy isotopes concentrate where bonds are strongest

Delta notation

Marine trophic levels and 𝛔¹⁵N enrichment

• each increase in trophic level from phytoplankton → zooplankton → herbivorous fish → carnivorous fish results in ~3.4%_o enrichment in 𝛔¹⁵N

Heterotrophic feeding

• a mode of nutrition where an organism cannot make its own food and must consume or absorb organic carbon and nutrients from other living or dead organisms

  • accounts for between 0-66% of fixed carbon incorporated into skeleton

• important source of N and P which are in low supply from photosynthesis

• heterotrophic carbon is an important energy source when photsynthetic carbon is not available

  • bleaching or turbidity

Multitrophic pathways of corals

• primary producers

• carnivores

• detritus feeders

• dissolved organic carbon scavengers

Carnivorous corals

• suspension feeders

• effective zooplankton feeders

  • capture particles on contact with nematocyst discharges

  • tentacle grabbing

  • mucus adhesion

• ingest particles of varying sizes

• photosynthates from zooxanthellae= “junk food”

  • so external food supplies are a major nutritive source of N, P and carbon for corals

Coral mucus

• used for feeding

• provides protection from pathogens

• food source

• traps particles and retains nutrients

Nighttime feeding

• many coral reefs feed at night

  • voracious predators of zooplankton

• demersal plankton come out at night

  • demersal meaning that they are mobile, benthic organisms which periodically emerge from the benthos and move up the water column

• can digest 0.5-2 prey items per polyp per hour of ingestion

Detrital particulate organic matter

• surface sediments on coral reefs contain bacteria, microbes, protozoa, microalgae, and detrital organic matter

• coral can feed on and benefit from particles in suspension or trapped in sediment

  • especially those corals living in turbid near-shore areas