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Coral Structure and Function I. Maritime coastal - greenish - particulate Caribbean - blue - clear.

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Presentation on theme: "Coral Structure and Function I. Maritime coastal - greenish - particulate Caribbean - blue - clear."— Presentation transcript:

1 Coral Structure and Function I

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

3 BLUE –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 less dissolved organic carbon

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 bluish 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 - leaves green

6 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

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8 trophic pyramids/webs - find plants at the bottom –use SUNLIGHT energy to fix CO 2 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 1776 a microscope modified for aquatic work 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

14 The Royal Society Coral Reef Expedition Funafuti Atoll (Ellice Islands - Tuvalu)

15 The Royal Society Coral Reef Expedition Funafuti Atoll (Ellice Islands - Tuvalu)

16 The Royal Society Coral Reef Expedition Funafuti Atoll analysis of cores -

17 The Royal Society Coral Reef Expedition Funafuti Atoll analysis of cores - mostly: 1. Calcareous red algae 2. Calcareous green algae ( Halimeda ) 3. Foraminifera (  m protists, porous CaCO 3 shell ) 4. Corals Top 18m of the core was 80-90% Halimeda

18 Calcareous red algae

19 Calcareous green algae ( Halimeda )

20 Foraminifera

21 Corals

22 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 ??

23 Extensive examination of atolls (Eniwetak – Marshall Islands) 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

24 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

25 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 –“Trophic Structure and Productivity of a Windward Coral Reef Community on Eniwetok Atoll” 1955

26 Corals are predacious animals - suspension feeders two main methods of prey capture –nematocysts –mucus

27 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

28 tentacles produce WAVE-LIKE action sweeping the mucus and prey into the mouth down the pharynx (gullet) to the gastrovascular cavity for digestion

29 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

30 Tentacles mostly 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

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

32 non-tissue layer between gastrodermis and epidermis = mesoglea –made of collagen & mucopolysaccharides

33 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

34 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

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

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37 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)

38 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

39 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

40 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)

41 dinoflagellates –chlorophylls a and c –lack chlorophyll b –characteristic dinoflagellate pigments diadinoxanthin and peridinin ~ 3 x 10 6 cells/cm 2 coloured tinge to the coral brown to yellow brown

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