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10 Seagrasses

10 Seagrasses. Thalassia testudinum bed off Fort Jefferson, Dry Tortugas http://www.unf.edu/coas/biology/SeagrassImages/SeagrassPageRoss08.dwt. I. Introduction A. Angiosperms 1. Not true grasses, but related to lilies 2. Flowers a. Inconspicuous (at ends of blades)

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10 Seagrasses

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  1. 10 Seagrasses

  2. Thalassia testudinum bed off Fort Jefferson, Dry Tortugas http://www.unf.edu/coas/biology/SeagrassImages/SeagrassPageRoss08.dwt

  3. I. Introduction • A. Angiosperms • 1. Not true grasses, but related to lilies • 2. Flowers • a. Inconspicuous (at ends of blades) • b. Pollen carried by currents

  4. Halodule wrighti Milne, 1995, Marine Life and the Sea, p. 149

  5. B. Anatomy • 1. Flat bladed • 2. Rhizomes • a. Horizontal stems under sediment • b. Anchor and connect plants • c. Mechanism for bed expansion • d. Transplant nutrients to edge of bed

  6. B. Anatomy (continued) 3. Roots a. Extend from rhizomes b. Functions (1) May not acquire significant amounts of nutrients from sediments (2) Associated with nitrogen-fixing bacteria (3) Anchor plants

  7. Seagrass Meadow Nybakken & Bertness, 2005, p. 234

  8. II. Important genera in Gulf of Mexico • A. Thalassia testudinum • 1. Turtle grass • 2. Clusters of 3 to 7 broad leaves • 3. Sheaths at bottom of leaves

  9. Turtle grass Thalassia testudinum Clusters of three to seven broad leaves. Leaves have sheaths R.L. Lehman, Seagrass Taxonomy http://www.tpwd.state.tx.us/publications/nonpwdpubs/media/seagrass_taxonomy.pdf

  10. II. Important genera in Gulf of Mexico (continued) • B. Halodule • 1. Shoal grass • 2. Two to three teeth at ends of blades

  11. Shoal grass Halodule Two to three teeth at ends of blades R.L. Lehman, Seagrass Taxonomy http://www.tpwd.state.tx.us/publications/nonpwdpubs/media/seagrass_taxonomy.pdf

  12. III. Characteristics of beds/meadows • A. Well defined edges • B. Maximum depth determined by distance light can penetrate • C. Beds expand over time through asexual growth • D. Environmental impact • 1. Form mats that trap sediment • 2. Reduce strength of waves and currents • 3. Conventional wisdom: Nursery grounds for fish and invertebrates • a. Supporting evidence from tropical regions • b. Not strongly supported in temperate regions (Heck DISL)

  13. E. Among the most productive marine ecosystems • 1. 1 - 2 kg (dry weight)/ square meter • 2. 500 - 4,000 gm C/ square meter/ year in temperate regions • F. Epiphytes • 1. Algae that grow on blades • 2. Biomass of epiphytes can be more than biomass of the seagrass blades • 3. Compete with seagrasses for nutrients in water • 4. Consumed by herbivores

  14. IV. Trophic Paradox • A. Few herbivores graze directly on seagrasses • 1. Vertebrates • a. Pinfish • b. Green turtle • c. Manatees • 2. Sea urchins

  15. IV. Trophic Paradox (continued) B. Most of the primary production enters detrital food webs 1. Detritus of seagrasses is also not consumed by invertebrates 2. Marine invertebrates do not have the digestive enzymes to breakdown cellulose and other structural carbohydrates of flowering plants 3. Detritus is broken down by bacteria & fungi

  16. Food Web in a Seagrass Community Castro & Huber, 2003, Marine Biology, p. 287

  17. IV. Trophic Paradox (continued) C. Evolutionary significance 1. Terrestrial & freshwater angiosperms are grazed by insects and vertebrates 2. Ancestors of seagrasses were terrestrial plants a. Seagrasses appear to have escaped the herbivores that grazed on their ancestors when they colonized the marine environment b. Insects have not successfully invaded marine habitats (There is not a good explanation for this)

  18. Associated organisms • Invertebrates • Mollusks • a. Scallop – Argopecten • (1) Swims by “clapping” valves • (2) Mantle contains many blue “eyes”

  19. Bay Scallop, Argopecten irradians Ruppert & Fox, 1988, Seashore Animals of the Southeast, Plate B 23

  20. Mollusks (continued) • b. Whelks – Buscyon spp. • (1) Prey upon clams which they open by using their foot and shell • (2) Up to 16 inches in length • (3) Lay eggs in strings that look like poker chips

  21. Lightning Whelk, Busycon contrarium Amos & Amos, 1989, Atlantic & Gulf Coasts Audubon Nature Guide, Plate 34

  22. Mollusks (continued) • c. Sea hare - Aplysia • (1) Rabbit-like appearance • (2) Herbivores • (3) Swim using modified mantle • (4) Release dark ink when threatened

  23. Sooty Sea Hare, Aplysia brasiliana Ruppert & Fox, 1988, Seashore Animals of the Southeast, Plate B 11

  24. Mollusks (continued) • c. Pen clams – Atrina spp. • (1) Large, thin flexible shells bend when adductor muscles contract • (2) Symbiosis • (a) Many organisms only found on exposed portions of shells • (b) Commensal pea crabs and shrimp in mantle cavity

  25. Stiff Pen Shell, Atrina rigida (Cleaned up for photo) Amos & Amos, 1989, Atlantic & Gulf Coasts Audubon Nature Guide, Plate 113

  26. 2. Echinoderms • a. Short-spined sea urchin - Lytechinus • (1) Covers itself with shells • (2) Herbivore

  27. Short-spined Sea Urchin, Lytechinus variegatus Ruppert & Fox, 1988, Seashore Animals of the Southeast, Plate A 31

  28. 2. Echinoderms (continued) • b. Gray (Luidea)and margined Astropecten) sea stars • (1) Tube feet • (a) Without suckers • (b) “Pole” animals through sand • (2) Feed on small clams • (a) Swallow prey whole • (b) Regurgitate shells

  29. Grey Sea Star, Luidia clathrata (left) and Margined Sea Star, Astropecten articulatus (right) Ruppert & Fox, 1988, Seashore Animals of the Southeast, Plate A 28

  30. Astropecten Castro & Huber, 2003, Marine Biology, p. 286

  31. B. Vertebrates • 1. Manatees feed on seagrasses

  32. West Indian Manatee, Trichechus manatus Castro & Huber, 2003, Marine Biology, p. 190

  33. B. Vertebrates (continued) • 2. Stingrays feed on mollusks

  34. Southern Stingray, Dasyatis americana Eat Mollusks in Seagrass Beds Amos & Amos, 1989, Atlantic & Gulf Coasts Audubon Nature Guide, Plate 425

  35. B. Vertebrates (continued) • 3. Pin fish are small omnivores

  36. Pinfish, Lagodon rhomboides Will Feed on Seagrasses Amos & Amos, 1989, Atlantic & Gulf Coasts Audubon Nature Guide, Plate 372

  37. Vertebrates (continued) • 4. Puffer fish • a. Many species… • (1) …are omnivorous • (2) …produce TETRODOTOXIN: a poison that is >1,000 times more deadly to humans than cyanide • b. Powerful teeth can crush shells • c. Up close, it is better to consider them dangerous rather than cute

  38. Mouth of a Southern Puffer Photo by Brian Jones, 2013

  39. …I saw an 18’ long puffer fish neatly tucked into a lobster looking hole...I waggled my hand in front of his face…he launched forward and got hold of my pinkie…This cute little fish has teeth like a parrotfish and the ability to crush rocks if necessary. He bit my gloved hand like a piranha on a dining mission…When I took my glove off, I realized half of my finger was still in the glove…Please be officially advised: Do not mess with the animals… http://www.scubaboard.com/forums/marine-life-ecosystems/40695-puffer-fish-bites-off-divers-finger.html

  40. VI. Reduction of seagrass beds A. Wasting Disease 1. Devastated Chesapeake Bay beds between 1931 - 1932 2. Caused by a fungus-like protist Labyrinthula 3. Similar die-offs occurring in Gulf of Mexico and Florida Keys

  41. Eelgrass blades infected with Labyrinthula, showing complete blackened region across entire blade, black spots and black streaks From Ralph & Short, 2002, Mar. Ecol. Prog. Ser. 226: 265-271.

  42. Collecting blades (left) and removing epiphytes (right) in Florida Keys prior to lab culture From http://www.unf.edu/coas/biology/SeagrassImages/SeagrassPageRoss08.dwt

  43. How Professors Spend Their Summer Vacations South Alabama Biology Department faculty T. Sherman (left), A. Boettcher (center), and D. Martin (right) preparing Labyrinthula infected eelgrass for culture and analysis From http://www.unf.edu/coas/biology/SeagrassImages/SeagrassPageRoss08.dwt

  44. Blades (w/ notable necrotic regions) are plated on agar medium to begin the Labyrinthula isolation process From http://www.unf.edu/coas/biology/SeagrassImages/SeagrassPageRoss08.dwt

  45. In several days a consortium of microbes (arrows) grows into the medium from the lesions From http://www.unf.edu/coas/biology/SeagrassImages/SeagrassPageRoss08.dwt

  46. After several rounds of culture a colony of Labyrinthula (surrounding the agar plug) is eventually isolated From http://www.unf.edu/coas/biology/SeagrassImages/SeagrassPageRoss08.dwt

  47. Classic spindle shaped Labyrinthulid cells (400x) From http://www.unf.edu/coas/biology/SeagrassImages/SeagrassPageRoss08.dwt

  48. Reduction of seagrass beds (continued) • Currently there is a slow reduction of beds around world • 1. Description of problem • a. Epiphytes grow over and shade out seagrasses • b. Hypotheses to explain what causes overgrowth of epiphytes • (1) ”Bottom Up” • (2) ”Top Down”

  49. 2. “Bottom up” or eutrophication hypothesis a. Humans have increased levels of nutrients in beds b. Growth of phytoplankton and epiphytes is no longer nutrient limited c. Seagrasses are shaded out

  50. Bottom Up Control Trophic Level Tertiary Consumers Secondary Consumers Herbivores Seagrasses Epiphytes Size of circle represents relative number of individuals Nutrients Nutrients

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