ch15 - 15 Sea Grass Beds, Kelp Forests, Rocky Reefs, and...

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15 Sea Grass Beds, Kelp Forests, Rocky Reefs, and Coral Reefs Notes for Marine Biology: Function, Biodiversity, Ecology By Jeffrey S. Levinton ©Jeffrey S. Levinton 2001
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In Chapter 15 we will cover • Kelp Forests • Coral Reefs • Seagrasses?
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Laminaria hyperborea - British Isles http://www.solaster-mb.org/mb/phaeophyta.htm
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Laminaria kelp forest, as is often found in New England
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Diver in Macrocystis kelp forest, California
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Kelp Forests Dominated by brown seaweeds in the Laminariales Found in clear, shallow water, nutrient rich and usually < 20°C , exposed to open sea Generally laminarian seaweeds have high growth rates , often of the order of cm/d “Forests” can be 10-20 m high or only a meter in height
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Complex life cycle Laminarian kelps have a complex life cycle alternating between a large asexual sporophyte and a small gametophyte Zoospores Diploid sporophyte Sporophyte development Antherozoids Microscopic, haploid Male gametophyte Egg fusion Sori of unilocular sporangia Microscopic,haploid Female gametophyte
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Kelp Forests are Diverse Kelp forests have many species of seaweeds, even if sometimes dominated by one species Many invertebrate species present, especially sessile benthic species living on hard substrata - suspension feeders common
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Kelp Forest Community Structure Herbivory - herbivorous sea urchins Carnivory - sea otter Enhydra lutris can regulate urchin populations Result: trophic cascade. Add otters, have reduction of urchins and increase of kelp abundance. Reduce otters: kelp grazed down by abundant urchins Recent history: Otters hunted to near extinction, their recovery has strong impacts on urchin/kelp balance
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Evolutionary consequences of herbivory • North Pacific - otters reduce urchins - low herbivory (0-2%/day) - relatively few defenses evolved by kelps against herbivory • Australasia - less predation on urchins - higher herbivory (5-7%/day) - phlorotannin concentrations in kelps were on average 5-6 x of N. Pacific Steinberg, Estes, Winter, 1995, Proc. Nat. Acad. Sci. 92: 8145-8
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Kelp Forest Community Structure Storms: remove kelp El nino: storms + warm water -> kelp mortality
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Alternative stable states in a California kelp forest Harrold and Reed 1985 Ecology; Ebeling et al. 2004 Marine Biology
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Kelp Forest Community Structure Nereocystis - winner in succession?? Urchins die -> kelp recruitment - several species Although Nereocystis is often an upper canopy species, with fronds at the surface, it is often an annual and dies back each year Laminaria gradually shades out other seaweeds wins if no dense urchin populations Succession:
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Kelp Forest recap • Clear, nutrient-rich, cool < 20C • Trophic cascade: otters,urchin, kelp (plus Orca) • Barrens versus rich kelp forest - stable states, owing to urchin behavior • Succession in Alaska - light competition leading to dominance by Laminaria
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ch15 - 15 Sea Grass Beds, Kelp Forests, Rocky Reefs, and...

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