Productivity and the Coral Symbiosis

Maritime coastal - greenish - particulate Caribbean - blue - clear

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

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

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

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

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

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

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

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

were originally classified as plants by the naturalist John Ray (1627-1705) In 1723, Jean Peyssonel decided they were animals

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

The Royal Society Coral Reef Expedition 1896-1898 Funafuti Atoll (Ellice Islands - Tuvalu)

The Royal Society Coral Reef Expedition 1896-1898 Funafuti Atoll 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

Calcareous red algae

Calcareous green algae (Halimeda)

Foraminifera

Corals

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 ??

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

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

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

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

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

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

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

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

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)

non-tissue layer between gastrodermis and epidermis = mesoglea made of collagen & mucopolysaccharides "lower layer" of epidermis = calicoblastic epidermis secretes the calcareous external skeleton

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

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

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

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)

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

single-celled alga, with 2 flagellae Zooxanthellae: ZOO - animal XANTHE - gold-coloured single-celled alga, with 2 flagellae a dinoflagellate spherical, 8 - 12um dia Most dinoflagellates are free-living unusual group of algae feeding modes ranging from photosynthetic autotrophy to heterotroph

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)

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

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

Almost all zooxanthellae are in the dinflagellate genus Symbiodinium (1959) taxonomy of Symbiodinium in a state of flux 1980 - Symbiodinium microadriaticum assumed to be the one species found in almost all corals

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

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

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

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

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

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

MUTUALISM - benefits for polyp? food (CHO) O2 greatly increased ability to precipitate CaCO3 without the alga, coral could not have such a high rate of metabolism could not build such extensive reef structures

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

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”

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

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 alga 1000x more conc. than in seawater Algae grow faster - helps polyp

FOOD Polyp Protein CHO Lipid AAs Sugars Fatty acids NH3 CO2 O2 NH3 CO2 Growth & metabolism AAs Sugars Fatty acids ATP NH3 CO2 O2 NH3 CO2 O2 glycerol AAs AAs Sugars Fatty acids LIGHT ATP NADPH Protein CHO PO4- PO4- H2O H2O Growth & metabolism SO4- SO4- Alga

Alga stores CHO – starch Broken down at night Polyp stores lipid – fat bodies Energy reserve Algal PS: 90% fixed C to coral host Used for metabolic functions Growth, reproduction & Calcium deposition