1. Tropical Marine Biology Productivity and the Coral Symbiosis

2. Maritime coastal
- greenish
- particulate
Caribbean
- blue
- clear

3. BLUE CLEAR water reflects blue of the sky
water refracts sunlight (more blue light)
no interference from green plants
CLEAR
little particulate matter
few phytoplankton in the water

4. PHYTOPLANKTON microscopic algae - flourish in colder ocean waters
live in upper 60m - the PHOTIC ZONE
give local Maritime waters their colour

5. as you descend through water column
lose more and more light
reds go first (lower energy)
gives a blue cast to everything
much more pronounced locally than in the Caribbean
we have far more photosynthetic organisms in the water
absorb the light (red & blue ) for photosynthesis

6. Tropical waters are still very PRODUCTIVE bottom of food chain events
So- the blue colour & clear water of tropics due to few photosynthetic organisms in tropical waters
Tropical waters are still very PRODUCTIVE
bottom of food chain events
primary production
production of organic material from inorganic

8. Primary Production trophic pyramids - find plants at the bottom
use SUNLIGHT energy to fix CO2 into organic molecules
Primary Production
plants consumed by primary consumers etc.
less total biomass as you go up the pyramid
increase size of organism as you go up the pyramid

9. eximine coral reefs ecosytem:
“how does this flourishing ecosystem survive with so few producers - the plants ?”
clear water, few phytoplankton ???

10. In the reef system primary production is mostly BENTHIC (bottom)
Open ocean (or local Maritime), primary production is mostly PELAGIC (water column)

11. Much of the productivity from corals
Cnidaria - from the Latin “nettle” – a plant
have often been mistaken for plants
attached to a substrate
do not wander about
same colour as many
marine plants
same branched nature
and growth habit

12. were originally classified as plants
by the naturalist John Ray ( )
In 1723, Jean Peyssonel
decided they were animals

13. naturalist John Ellis
a microscope modified for aquatic work

15. found the animal polyps on many reef organisms
then considered to be animals for a while - with no plant component
improvements in microscopy confirmed their animal nature, with polyps filtering out plankton with their tentacles
subsequent studies showed that the reef is composed of many organisms, as well as the Cnidarians

16. The Royal Society Coral Reef Expedition 1896-1898
Funafutii Atoll (Ellice Islands)
analysis of cores - mostly:
1. Calcareous red algae
2. Calcareous green algae (Halimeda)
3. Foraminifera (20-40m protists, porous CaCO3 shell)
4. Corals
Top 18m of the core was 80-90% Halimeda

17. Calcareous red algae

18. Calcareous green algae (Halimeda)

19. Foraminifera

20. Corals

21. so where were the primary producers ??
20C - new understanding of trophic pyramids, attention turned to reef productivity
very productive (produce lots of biomass)
lots of life
lots of diversity
productivity couldn’t be due just to the calcareous green and red algae
so where were the primary producers ??

22. Extensive examination of atolls (Eniwetok)
lots of encrusting algae on the surface of corals, but also ...
examine corals in more detail
true nature of the Cnidarians
algae growing inside the cells of the coral polyp

23. These algae - ZOOXANTHELLAE
enough algae inside the coral polyp to account for massive primary production
their presence explained the plant-like growth habit of the Cnidarian -
to increase surface area for light absorption
Also explained the colours of the corals

24. 1950s - Tom & Gene Odum
suggested the coral polyp and the alga were in some sort of mutualistic relationship
the polyp itself is a miniature ecosytem
the two organisms exchange nutrients and other benefits

25. Corals are predacious animals - suspension feeders
two main methods of prey capture
nematocysts
mucus

26. extend tentacles - mostly at night
zooplankton are most plentiful (move up from deeper waters)
whole surface of the coral becomes a trap for plankton
paralyze prey
sting with NEMATOCYSTS
trap prey
sticky MUCUS on
tentacles

27. tentacles produce WAVE-LIKE action sweeping the mucus and prey into the mouth
down the pharynx (gullet) to the gastrovascular cavity for digestion
prey digested, mucus recycled, solid, undigestible material (eg silt) ejected

29. Keep tentacles retracted during the day
help corals avoid predation
protect from UV
Corals also get some nutrients from seawater
dissolved amino acids
glucose
inorganics
not usually much, except in locally polluted areas

30. Most hermatypic scleractinian corals
structure of the polyps and skeleton of the coral is a simple combination
Most hermatypic scleractinian corals
colonies of polyps
linked by common gastrovascular system (coenosarc)
polyp made up of two cell layers
outer epidermis (or ectoderm)
inner gastrodermis (endoderm)

31. non-tissue layer between gastrodermis and epidermis = mesoglea
made of collagen & mucopolysaccharides
"lower layer" of epidermis = calicoblastic epidermis
secretes the calcareous external skeleton
"upper layer" of epidermis is in contact with seawater

32. The corallite is the part of the skeleton deposited by one polyp
The skeletal wall around each polyp is called the theca
The coral structure also includes calcareous plate-like structure known as septa
The septa radiate from the wall towards the center of the corallite

33. One of the epidermal cell types is the cnidocyte
contains organelles called nematocysts
discharge toxic barbed threads
capture zooplankton prey

35. gastroderm cells line the body cavity
capable of phagocytosis (food particles)
contain the intracellular algae
extend into tentacles
zooxanthellae not in direct contact with the cytoplasm of the coral gastroderm cell
zooxanthellae reside inside a vacuole
the symbiosome (animal origin)

36. Much of the food needed by the polyp comes from the SYMBIONT
Many corals have different growth forms - can vary with local environment - light, depth etc.
Local environment affects distribution of the zooxanthellae

37. single-celled alga, with 2 flagellae
Zooxanthellae:
ZOO - animal
XANTHE - gold-coloured
single-celled alga, with 2 flagellae
a dinoflagellate
spherical, um dia
Most dinoflagellates are free-living
unusual group of algae
feeding modes ranging from photosynthetic autotrophy to heterotroph

38. Many dinoflagellate produce toxins
e.g. ciguatoxin causes ciguatera "fish poisoining”
Other toxic dinoflagellates responsible for algal blooms
e.g. red tides (Gymnodinium)
paralytic shellfish poisoining (Alexandrium)

39. coloured tinge to the coral brown to yellow brown
dinoflagellates
chlorophylls a and c
lack chlorophyll b
characteristic dinoflagellate pigments
diadinoxanthin and peridinin
~ 3 x 106 cells/cm2
coloured tinge to the coral
brown to yellow brown

40. Zooxanthellae can live outside their host
essential in some species for finding a host
Dinomastigotes stage
motile free-living state, have two flagellae
Coccoid stage
living in animal cells, lack flagellae
In culture, zooxanthellae alternate between coccoid and dinomastigote stages

41. Almost all zooxanthellae are in the dinflagellate genus Symbiodinium
taxonomy of Symbiodinium in a state of flux
Symbiodinium microadriaticum assumed to be the one species found in almost all corals

42. great genetic diversity in zooxanthellae clearly more than one species
Recent work
great genetic diversity in zooxanthellae
clearly more than one species
at least 10 different algal taxa
zooxanthellae found in closely related coral species not necessarily closely related themselves
zooxanthellae found in distantly related coral species may, in fact, be closely related

43. Acquisition of Zooxanthellae by Corals either
1. open (or indirect) transmission or acquisition
from the environment or
2. closed (or direct) transmission or acquisition
- via gametes or
- during asexual reproduction

44. Indirect acquisition Coral bleaching Shifting symbioses
provides potential for host to establish a symbiosis with a different strain or species of zooxanthellae than was in symbiosis with the host’s parents
Coral bleaching
may also allow establishment of new symbiosis with different zooxanthellae strain,
has been proposed as a possible adaptive mechanism to environmental change
Shifting symbioses
controversial topic

45. can demonstrate mutualistic relationship feed 14CO2 to the coral
In all hermatypic corals endosymbiotic algae provide an important source of nutrients
can demonstrate mutualistic relationship
feed 14CO2 to the coral
quickly taken up by alga and ends up in the polyp
feed zooplankton raised on 15N to coral
quickly taken up by polyp and ends up in the alga

46. clear they exchange a lot of material benefit each other
reef-shading experiments
3 months in the dark
algae expelled from the polyps
later the polyps died
Most coral polyps have absolute requirement for alga - but not vice-versa (but the free-living alga does get eaten !)

47. MUTUALISM - benefits for algae?
shelter
protection from nematocysts, & other predation
receive waste products of polyp - CO2 & N
N is v.limiting in marine environment
the major limitation to plant growth
algal blooms occur in response to
small changes in N
pressure exists to optimize N scavenging
favours such a mutualistic relationship
Disadvantage
algae restricted to shallow tropical waters

48. MUTUALISM - benefits for polyp?
food (CHO) O2
greatly increased efficiency in precipitating CaCO3
without the alga, coral could not have such a high rate of metabolism and build such extensive reef structures

49. Polyp can survive extended periods with no external food source
Tight internal N-cycling and algal PS
Polyp lays down extensive lipid reserves to be drawn on in times of starvation
High light and high food availability
ejection of pellets containing viable algal cells
Control of algal cell number ?
Algae divide within host polyp

50. Analyze algal cell
C,H,O from PS
N,P,S, from host (normally limiting)
Symbiosis controlled by host
Polyp controls permeability of algal membrane
“signal molecules”

51. Freshly isolated zooxanthellae
Incubate in light with 14CO2
Release very little organic C into medium
Add some polyp extract - releases lots of organic carbon into medium
Other cnidarian extracts work

52. Alga donates most of it’s fixed C to polyp used for resp, growth, etc.
Polyp respires
releases CO2 to alga
Polyp excretes N waste - NH3
used by alga
Polyp also releases PO4, SO4, NO3 to algal
1000x more conc. than in seawater
Algae grow faster - helps polyp

53. Calcification - growth of the reef
Algal PS: 90% fixed C to coral host
Used for metabolic functions
Growth, reproduction &
Calcium deposition
What sort of calcium ?
CaCO3

54. In ocean, mostly find 3 forms of CaC03 Calcite
Mostly of mineral origin
Aragonite
Fibrous, crystalline form, mostly from corals
Magnesian calcite
Smaller crystals, mostly plant origin

55. Examples: Molluscs calcite & aragonite Corals just aragonite
Some green algae just aragonite
Red algae magnesian calcite
Sponges aragonite (with
silica)
Some bryozoans all 3

56. Corals remove Ca++ & CO3-- from seawater Combines them to CaCO3
transports them to base of polyp
Calcicoblastic epidermis
minute crystals secreted from base of polyp
Energy expensive
Energy from metabolism of algal PS products

57. CO2 and seawater What forms of C are available to the coral ?
Organic and inorganic forms
DIC - dissolved inorganic carbon
CO2 (aq)
HCO3-
CO3--

58. DIC comes from: Weathering dissolution of oceanic rock
Run-off from land
Animal respiration
Atmosphere
etc.

59. DIC in ocean constant over long periods
Can change suddenly on local scale
E.g. environmental change, pollution
Average seawater DIC = mmol/Kg
Average seawater pH =
pH affects nature of DIC