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Lecture 21

BIOL 336 Lecture 21: March 27th 2017

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BIOL 336
Varela Diana

March 27 , 2017 Biol 336- Lecture 21 • 3. Growth of the algal cells as a function of external nutrient levels (Monod) • Loss processes in phytoplankton populations o Recall: r = 𝜇 – 𝜆 ▪ R = net growth rate ▪ 𝜆 = loss processes ▪ 𝜇 = o Loss processes (𝜆) ▪ Grazing ▪ Perennation- formation of dormant cysts ▪ Sedimentation ▪ Death or mortality- was believed until recently that unicellular algae don’t die because they just keep dividing. Is death when they divide? No. It was found that cells could in fact die ▪ Parasitism ▪ Washout- not that common, more common in restricted places (small lake, tidal pools, these places get washed out). Common in the lab in continuous cultures ▪ Competition- nutrients, nitrate, light. All of these define competition between species o A system that starts with high nutrients characterizes a food chain that is typically made of larger cells ▪ Cold waters ▪ Temperature/boreal seas ▪ Coastal upwelling zones o A system that starts with low nutrients, dominated by small cells because they have a higher surface area to volume ratio and therefore can outcompete others and take u more nutrients. Characterized by very long food chains and therefore lots of losses. Many levels before top predator and lots of energy lost in those transfers ▪ Subtropical ocean gyres ▪ Summer/stratified temperate oceans o High nutrients, low Si:N. Food chain is lengthened. Large cells, lots of nutrients, but ratios are very different and therefore a different food chain is created ▪ Coastal/eutrophic waters Topic 16: Macroalgal Ecology (Chapter 22) • 1. Introduction and Definitions o Phytoplankton: unicellular, colonial, filamentous algae; floating or swimming (weakly) o Seaweeds: macroalgae typically attached to substrates o Periphyton: unicellular, colonial, or filamentous algae (diatoms, cyanobacteria, and filamentous eukaryotic algae) typically grown attached to substrates- freshwater and marine o Substrates for seaweed and periphyton: o Periphyton processes: common in all benthic environments, the films you see over many things. Basically an aggregation of a whole little world on its own. Use metals in their processes, grazing happening, and nitrogen cycles. A sort of abiotic interaction that includes algae o By a variety of mechanisms, the periphyton-bacteria-organic microlayer surfaces is scraped or browsed. Diatoms are a prominent constituent o Primary productivity by macroalgae ▪ Equal or greater than that of most productive terrestrial plant communities ▪ Productivity of the Postelsia community: estimated at 14.6 km m yr vs <2 km m yr for rain forests o Fate of macroalgal primary production ▪ ~10% of seaweed biomass is directly consumed by herbivores; and 90% enters the detrital food web (and thus contributing indirectly to animal biomass) o Coastal marine seaweed communities have been in existence for the past 500 million years o Ecologists are interested in factors that influence algal growth, occurrence and distribution patterns o Factors: ▪ Complex interaction of: physical (water motion, tides, desiccation, etc.) and biotic (herbivory, pathogens, interspecific competition, etc.) • 2. Physical factors and macroalgal adaptions o Coastal regions influenced strongly by ▪ Water levels: tides ▪ Water motions: waves and currents o Combined with weather changes and seasonal variations in solar irradiance levels: ▪ Seaweed subject to frequent variations in light, temperature, nutrient availability, and the level of hydration o Seaweeds exposed to air (emersed) for long periods ▪ Lose their source of dissolved nutrients ▪ May become desiccated ▪ May receive damaging levels of solar radiation o Seaweeds covered by seawater (immersed) from the incoming tide a few hours later: ▪ May experience greatly reduced irradiance levels ▪ May be subjected to stressful mechanical forces from wave action o Wave motions also influence the abundance and activities of herbivores and the extent of interspecific competition o Tides ▪ Tidal patterns influence the structure of algal communities by creating an intertidal (or littoral) region ▪ Both, water levels and the types of organisms present define these zones ▪ 3 nearly universal intertidal zones • 1. An uppermost black strip of highly desiccation- tolerant cyanobacteria, a marine lichen (Verucaria) and littorinid snails • 2. A intermediate zone of various seaweeds together with barnacles and limpets • 3. A lowermost zone inhabited by laminarialean brown algae (in temperate and high-latitudes) or corals (in tropical regions) ▪ Aside from these general features: zonation patterns may differ c
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