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Unformatted text preview: Cnidarians: Ecosystem engineers!
UCSB Moorea Coral Reef Long-term Ecological Research Cnidarians
Lecture 2 May 19, 2008 Professor Hofmann
Mr. Ray's Classroom Outline for Lecture 2 Intro to Phylum Cnidaria The members of the group Evolutionary relationships Distinguishing characteristics Glass sponges Demosponges Calcareous sponges Ctenophores Cnidarians Bilaterians (protostomes and deuterostomes) Functional information Nematocysts Feeding Symbiosis in cnidarians Examples of diversity Phylum Ctenophora 1 Who are they? Phylum Cnidaria contains about 10,000 species Jellyfish Sea anemones Corals Hydrozoans Anthopleura elegantissima Ptilosarcus gurneyi All cnidarians have... A basic radial symmetry Only 2 layers of living tissue Epidermis and gastrodermis A middle gelatinous layer the mesoglea in between the 2 living layers of tissue Tentacles surrounding the mouth Only a single opening to the digestive system "blind gut" these crazy things called nematocysts that account for the "stinging" activity that is associated with these animals Lion's Mane Jelly Cyanea capillata Phyllorhyza punctata Polyorchis penicillatus 2 The Cnidarian Lifestyle Some swim, some don't Simple carnivores Very low metabolic rates Can survive in cold and nutrient poor waters (polar) Cnidarian physiology: Gastric cavity is region of gas exchange and digestion Lack a circulatory system Gastric cavity can be highly branched in large cnidarians Although a "gut" is present, lacking an anus is, well, a problem. Extracellular digestion Cells in gastroderm contain digestive enzymes "Muscles" A diffusion based system
Antarctic jellyfish Desmonema glaciale General Anatomy Gastrovascular cavity Digestion Cnidarian Bauplan
Radial Symmetry Biradial Quadriradial Multipurpose cavity Gas exchange (no gills) Circulation Morphology of body Body "Blind gut" Radiating, non-centralized nerve net Ring of tentacles Feeding Sensory structures "Gut with tentacles" 3 Functional morphology Cnidarian body wall crosssection
A. gastrovascular cavity B. gastrodermis C. mesoglea D. cnidocysts E. epidermis (integument) Desmonema glaciale under sea ice 4 The stinging cells, cnidocytes Cells are at the end of tentacles Eject a nematocyst Literally, `threadbags' Can inject a toxin into prey Really toxic: Box jellies
Chironex fleckeri Northern Australia Fairly fatal poison 3 meter tentacles An advance in the nerves department... Unlike sponges, cnidarians have nerves and muscles First animal (Metazoan) to have one Not a true "nervous system" Mesh of overlapping nerves Examples of nerve nets 5 Cnidarian Life Cycle Hydrostatic skeletal system Medusa ("jellyfish") Young medusa (oral surface) Mouth/ anus Planula larva Tentacles Mouth/ anus Polyp Mature polyp Bud Cnidarian Diversity Scyphozoans ("jellyfish") Anthozoans (corals and anemones) Hydrozoans Members of Class Scyphozoa The "jellyfish" or G: cup animals Thick mesoglea Large, effective swimmers All marine Aurelia labiata, moon jellies Monterey Bay Aquarium 6 Scyphozoan Life cycle Alternation between polyp and medusa Portuguese man-of-war Often called "blue bottle" in Australia Physalia physalis Fig. 32.11 Tentacles By-the-wind Sailor Velella velella http://www.mbayaq.org/efc/living_species/default.asp?hOri=1&inhab=465 7 Class Hydrozoa Often colonial polyps The only freshwater cnidarians Members of the Hydrozoa Freshwater hydrozoan Hydra
Copyright 2002 Olympus Optic al Co.,Ltd. Obelia polyps Members of Anthozoa G: flower animals Corals & sea anemones Corals: Reef building organisms Corals Spatial dominance Grow by vegetative propagation of polyps Some also contain endosymbiotic photosynthetic dinoflagellates (zooxanthellae) Significant ecological diversity Tropical scleractinian corals dominate tropical reefs 8 2. Demographic analyses Coral Life Cycle
Photo: A. Morse Figure 31.20 Corals
Diploria labyrinthiformis Planula larvae Coral Spat
Photo: A. Morse Adults corals Juvenile Corals ( 4 cm diam) Symbiosis Marine symbioses in cnidarians Intra- and extracellular association with unicellular photosynthic organisms Gives cnidarians their green or brownish color Coral-zooxanthellae Symbiosis
Most reef-building corals normally contain:
1-5 x 106 zooxanthellae/cm 2 of live surface tissue >1010 algal symbionts/m2 Marine cnidarians have dinoflagellates as endosymbionts, zooxanthellae Mutualism: Host obtains trophic benefits, nutritional benefits Symbiont gains shelter and access to sunlight
Sinauer Associates, Inc. Relatively small biomass in relationship to their ecological effect = keystone species on coral reefs At right: A coral with zooxanthellae photographed under blue light, which made the zooxanthellae's chlorophyll fluoresce red Isolated zooxanthellae from coral tissue 9 Marine biologists debate the nature of coral bleaching Two schools, generally speaking: Stress response Adaptive Bleaching Hypothesis (ABH) Premise: bleaching is a regulated mechanism that corals use to switch out symbionts in response to variable environmental conditions "High risk ecological opportunity"
Copyright 1996-2003 Australian Institute of Marine Sc ienc e Environmental Causes? Elevated surface seawater temperatures (SST) Short attention span theatre! Ecosystems in the balance Palumbi Lab at Hopkins Marine Station http://www.stanford.edu/g roup/Palumbi/oceanpostc ards.html 2001 California Ac ademy of Sc ienc es 10 Class Cubozoa Box jellyfish Very toxic sting "Sea wasps" of Australia, Chironex fleckeri (nasty) Carybdea marsupialis, around Santa Barbara (not a bad stinger) Four tentacles Have eyes! Phylum Ctenophora Comb jellies Very similar to cnidarians But, They possess two openings to the gut No nematocysts Feed with sticky ctenes or material on body All marine and carnivorous
Carybdea sivickisi Possess eight rows of cilia-like projections, ctenes Tentacle sheath Gut Ctenes Mnemiopsis sp. Web Resources Monterey Bay Aquarium jellyfish site http://www.mbayaq.org/efc/efc_se/se_jla.asp Antarctic cnidarians http://scilib.ucsd.edu/sio/nsf/fguide/cnidaria.html UC-Berkeley museum site http://www.ucmp.berkeley.edu/cnidaria/cnidaria. html Special hexacoral site http://hercules.kgs.ukans.edu/hexacoral/anemon e2/index.cfm Pharynx Tentacle Mouth Mouth
The advent of the anus: one mouth, two anal pores 11 ...
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- Spring '08