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39 Cards in this Set
- Front
- Back
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Seagrass
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-are marine angiosperms (flowering plants) that live in soft sediments and are confined to very shallow water (low water mark to about 3-5m)
-Extend mainly by subsurface rhizome systems -Found throughout tropical and temperate oceans - Grow best in very shallow water, high light and modest current flow |
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Why are seagrasses foundation species?
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-dominate communities and serve as foundation species
-Create vertical structure above sediment surface = habitat complexity -**High primary productivity and structural complexity** ==>result in a very diverse habitat -Provide food and shelter for many species of invertebrates and fish, and food for larger herbivores ==>ex: manatees, sea turtles |
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Seagrass Rhizomes
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-Rhizomes = root complex within the sediment
-Extend laterally and send up shoots -take up nutrients from pore waters in sediment, and can transport nutrients -Lateral spreading of rhizomes is primary means by which seagrasses extend their coverage |
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Reproduction by Flowering
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-less important than lateral spreading by rhizomes
-Seagrasses can flower, and pollen moves between plants in the water currents -Flowers are dull and inconspicuous - |
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Growth conditions of seagrasses
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-rarely found in depths greater than 3m
-Depth limit is related to light irradiance ==>Epiphytes (ex. Bryozoans and microalgae) can reduce light capture and photosynthesis by seagrass blades -Develop more extensively under modest current conditions (possibly because of nutrient delivery) -Obtain most nitrogen from water column (uptake by leaves) ==>have nitrogen-fixing bacteria on their rhizomes |
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Seagrass Bed Succession
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-colonize best when sediments are nutrient rich and physically stable
-most easily colonize sediment after previous colonization by seaweeds |
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Seagrasses production and ecology
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-High primary production, support a diverse group of animal species
-often colonized by a variety of fouling organisms (bryozoans, hydroids, algae, sponges) -Form dense meadows -Deter the entry of snail, crab and fish predators from side -Seagrass beds reduce current flow ==>May encourage settlement of swimming larvae ==>may enhance growth of infaunal suspension feeders near edge ==>phytoplankton may not penetrate far into bed |
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Grazing of seagrasses
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-is variable: in temperate zone, grazing on Zostera marina (eel grass) is minimal
-IN TROPICS several species that are grazed differentially because of different toughness, cellulose content -Green turtles nip the leaf tips, making more soft and digestible new grass ==>have extended hindguts with intestinal microflora (digesting cellulose) -even tough grasses grazed by turtles, urchins, dugongs |
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Seagrass community structure
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-Tropical seagrass beds diverse, often as many as 10 species, mixed with seaweed species
-Epiphytic algae often grows on seagrass blades -Seaweeds, seagrasses, and epiphytic algae grazed by a variety of invertebrates (seek shelter) -Predators such as fishes, crabs, consume invertebrates |
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Seaweed vs. Seagrass Dominance
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-Nutrient enrichment and loss of suspension feeders can cause switch from seagrass to seaweed dominance
-Nutrient enrichment ==>Seaweeds and epiphytic algae can outcompete seagrass for nutrients – results in rapid growth of seaweeds and algae, which shade seagrass -Loss of suspension feeders ==>Results in increased levels of phytoplankton in water column, which reduces water clarity |
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Decline in Seagrasses
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-very vulnerable to **eutrophication**
==>phytoplankton shade sea grasses, strong reductions of eelgrass beds in North America -Possible that overfishing results in reduced grazing and overgrowth of epiphytes, which smothers seagrasses -Dredging, boat traffic can also cause decline -Disease important - fungus caused eelgrass epidemic in 1930s ==>other fungi are now cause of sporadic diseases in tropical seagrasses |
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Kelp forest (rocky reef)
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-rocky reef complex found in cooler coastal waters with high nutrients
-rapid growing seaweeds (brown seaweeds) in shallow waters -“Forests” can be 10-25m high -epifaunal animal dominance in deeper water |
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Subtidal Rocky Reefs
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-communities of algae and invertebrates
-often dominated by colonial invertebrates (colonial bryozoans, hydroids, sponges, sea squirts) -very patchy (rock dominance alternating btw invertebrate assemblages and red algae -large patches of sessile organisms on vertical walls =>patches maintained by disturbances (landslides) =>competition (Larger, thicker, slower-growing species outlive rapid growing species) ==>controlled by predation and grazing (mainly by sea urchins) |
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Intertidal rocky reefs
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-dominated by organisms that occur as individuals (barnacles, mussels, etc...)
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Kelp Forest Diversity
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-distinct canopy layers, different layer dominated by different kelp species
-invertebrate species present (sessile benthic species) =>suspension feeder (feed on kelp particles) =>grazers (abalones, limpets, sea urchins) |
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Community structure of kelp forest
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-Herbivory - herbivorous sea urchins (feed on kelp)
-Carnivory - sea otter Enhydra lutris can regulate urchin populations -top down- too many carnivores = less urchins = more kelp =>more common, especially when more carnivores around -winter storm remove kelp (lower canopy kelp more resistant) -California kelp forest- barren b/c of storms and urchins taking over and eating newly recruiting seaweeds => has alternating barren and kelp forests |
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succession in kelp forest community
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-depends on a combination of grazing pressure, disturbance and competition for light
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Nereocystis
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-first dominant species in kelp forests
-die out annually even though an upper canopy species |
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Laminaria
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-a kelp forest species
-gradually shades out other seaweeds; becomes dominant if no dense urchin populations present |
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Coral reef
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-built up by corals, coralline algae, sponges, and other organisms
-Order Scleractinia =>Reef-building corals =>have endosymbiotic algae known as zooxanthellae =>high calcification rate => |
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Reef-Building (Hermatypic) Corals
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-Phylum Cnidaria, Class Anthozoa, Order Scleractinia
-Secrete skeletons of calcium carbonate -have endosymbiotic zooxanthellae - |
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nematocysts
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way cnidarian Polyps collect zooplankton on tentacles
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Hermatypic
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-Reef framework building, have many zooxanthellae, high calcification rates
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Ahermatypic
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-not framework builders, low calcification rates
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Growth forms of coral reefs
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-branching grows faster in linear dimension than massive
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Zooxanthellae
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-Found in species of anemones, hermatypic corals, octocorals, bivalve Tridacna, ciliophora (Euplotes)
-Endodermal- found in corals within tissues concentrated in tentacles can live freely outside of coral, that's how polyps from sexual reproduction obtain zooxanthellae |
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Zooxanthellae - Benefits to Coral
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-**Nutrition**- carbohydrate for corals
-Source of oxygen for coral respiration- not most beneficial b/c coral already in oxygenated water -Facilitate release of excretion products- not important bc coral in circulated water. -**Facilitate calcification**- uptake of carbon dioxide by zooxanthellae enhances calcium carbonate deposition ==> if photosynthesis inhibited, calcification rate decreases -Aid in lipid synthesis- structure and energy source for corals |
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Coral benefit to Zooxanthellae
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-Protection from grazing
-Nutrients from coral excretory products |
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Zooxanthellae - Bleaching
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-Bleaching = expulsion of zooxanthellae
-Causes - stress (temperature, disease) -zooxanthellae cells appear to die and are expelled |
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Factors Needed for Coral Growth
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-Warm sea temperature
-High light (symbiosis with algae)- UV portion can be damaging -Open marine salinities -Low turbidity- sediments inhibit photosynthesis -Strong sea water currents, wave action -Reef growth- a balance between growth and bioerosion - pH - Increasing ocean acidity a problem? |
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Coastal reefs
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coral reef type
-Elongate structures that border a coast; range from massive structures |
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Atolls
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coral reef type
-Mostly found in the Pacific Ocean; are horseshoe or ring-shaped island chain of islands atop a oceanic island of oceanic origin |
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Depth Zonation on Reefs
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-Reefs dominated by different coral species at different depths
-affected by: Wave and current strength; Light; Suspended sediment; Competition |
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Reproduction of Corals
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-hermaphroditic
-internal fertilization followed by release of planula larvae (larvae can travel a far distance) -asexually by division of polyps |
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Competition
(Biological Interactions on Reefs) |
-shading, overgrowth, interspecific digestion, sweeper tentacles, allelopathy
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Predation and grazing
(Biological Interactions on Reefs) |
-experiment with urchin removed lead to increase in seaweed and decrease in coral growth
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Climate Change and Coral Reefs
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-Sea surface temperature warming:
==>warming has increased over the past century and correlated with increased bleaching events - |
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Acidification
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-Also related to climate change
-carbon dioxide addition to atmosphere results in reduction of seawater pH -Already evidence of lower skeletal density in one Australian coral over time |
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Coral reef future
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review slides 36 and 36 on lecture 29
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