51 terms

MSC 111 Chapter 11

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plankton
- drift with the water
- phytoplankton and zooplankton
- variety of sizes
- responsible for producing oxygen, recycling nutrients, and providing biomass to support higher trophic levels.
- The oceanic plankton comprise a diverse group of organisms that drift or float, including bacteria, algae, protozoans and larval forms of many invertebrates and pelagic fish. Though mostly microscopic, the term plankton includes organisms covering a wide range of sizes, including large organisms such as jellyfish.
phytoplankton
- holoplankton
- contain chlorophyll and require sunlight in order to live and grow
- primary producers
- produce about half the Earth's biomass
-their small size allows them to stay in suspension near the sea surface while the large surface area relative to their size (volume) maximizes the capture of light and the uptake of nutrients.
zooplankton
- plankton heterotrophs
- small protozoans to large mesozoans
- include holoplankton, meroplankton (nekton), and benthic
- Although zooplankton are primarily at the mercy of ambient water currents, many have some limited ability to swim and can even move rapidly over short distances in pursuit of prey or to avoid predators.
classifications of plankton based on size ( µm- microns)
microplankton (net plankton)- 20 to 200 microns
nanoplankton- 2 to 20 microns
picoplankton - 0.2 to 2 microns(dominated by species of cyanobacteria and as a group has only had their importance recognized for the past several decades and account for most of the productivity in the oligotrophic gyre centers)
more kinds of plankton
- Bacterioplankton refers to the bacterial component of the plankton found in both seawater and freshwater. In these environments they occupy a range of ecological niches and include both primary producers and primary consumers.
- Mycoplankton include the fungi and fungus-like organisms that occupy the plankton
- both are saprotrophic meaning they remineralize organic material and are responsible for recycling nutrients
Diatoms
- phytoplankton
- golden brown algae
- live in nutrient abundant environments
- They are unicellular in nature though many species will aggregate to form long filamentous chains
- they are golden brown due to a yellow brown carotenoid pigment
- live in a variety of environments (ocean, freshwater,in damp surfaces, in soils, in the pelagic zone or on the sediment in shallow areas that receive sunlight)
Frustule
- siliceous shell of a diatom
- it is made up of two unequal sized halves
- biogenic silica that makes up the cell wall is synthesized intracellularly by the polymerization of silicic acid monomers. This siliceous material is then extruded to the cell exterior and added to the wall.
two kinds of diatoms
Centric: diatoms with radial symmetry (open ocean)
Pennate: diatoms with bilateral symmetry that elongated and found in coastal waters on the shelf (neritic and benthic)
diatom reproduction
- asexual reproduction
- In most species, when a diatom divides to produce two daughter cells, each cell keeps one of the two frustule halves and grows a smaller half within it.
- when it reaches a minimum size (30 to 50 percent of the original it forms and auxospore that increases cell size
Diatom blooms
- bloom when their is an abundance of light and nutrients
- diatoms have a fast growth rate
- as the populations grow, diatoms will get smaller due to cell division and depleting nutrients
Diatom ooze
- found at the bottom of the seafloor, in sediment
- frustules of many diatoms packed together
- ooze comes from dead diatoms
Dinoflagellates
- two whip-like flagella used for locomotion
- abundant in warm waters where the dissolved silica is low
- asexual reproduction
- mixotrophic: phytoplankton and heterotrophs (can ingest food particles)
- responsible for red tides (some species of dinoflagellates release toxins) which are their blooms that actually turn the water red
zooxanthelle
- dinoflagellates
- live as endosymbionts
- especially with coral
- In corals, the zooxanthellae get a protected environment and the raw materials for photosynthesis. In return, they fix carbon dioxide, release oxygen, and produce glucose and amino acids, which are the end-products of photosynthesis. The coral uses these products to make proteins, fats, and carbohydrates, and produce the calcium carbonate that forms the coral polyps' skeletal framework.
Coccolithophore
- golden brown algae
- phytoplankton
- each cell contains two brownish colored chloroplasts that surround the nucleus
- a series of interlocking plates called coccoliths cover the cell
- the coccoliths are produced inside and pushed out
- can alternate a coccolith-bearing "armored" phase and a naked phase where the plates are not present
- almost exclusively marine (not in true polar regions)
- common in warm tropical waters and in high latitudes during the summer
- ive close to the surface in nutrient-poor waters and tend to be the dominant of the larger phytoplankton groups in the nutrient-poor gyre centers.
Importance of picoplankton
- able to produce and recycle dissolved organic matter (DOM) efficiently under circumstance where other larger phytoplankton are limited by nutrients and predators.
Microbial loop
picoplankton can eat and produce dissolved organic matter and then are eaten by zooplankton
when phytoplankton or bacteria die and become DOM
look at figure 5 and page 2 in chapter to better understand this concept.
Phytoplankton in the ocean
Phytoplankton abundance is usually greatest in the subsurface at a depth where both light and nutrients are available in sufficient quantities for photosynthesis to take place, even if neither variable is optimal.
Nutrients in the ocean
depleted at the surface layer since phytoplankton (N, Si, P) take them and then the phytoplankton die, their skeletons sink, animals respire break down the skeleton and have the nutrients released, highest near the pycnocline where the sinking slows
Pycnocline
separates the surface layer from the deep layer
- pronounced pycnocline prevents mixing
- Phytoplankton usually reach an abundance maximum in the subsurface since both light and nutrients are required for photosynthesis. In temperate regions where the thermocline weakens because of seasonal cooling at the surface, the loss of density contrast across the associated pycnocline will allow more nutrients from at depth to be mixed upward into the photic zone, stimulating primary productivity
Phytoplankton and photosynthesis
- Phytoplankton capture the energy of the Sun through the pigment chlorophyll for use in photosynthesis, which converts inorganic carbon dioxide and water to the high-energy organic compounds (simple sugars) that form new plant material.
- primary production: the amount of organic matter produced by phytoplankton at the base of the food chain that controls the overall abundance of life in the oceans.
- If plants are abundant, higher organisms will be abundant too.
Gross primary production versus net primary production
gross primary production: the total amount of organic material produced by organisms
net primary production: the amount of organic matter left over after plant respiration- this makes up the base of the trophic pyramid
Net Primary Production = Gross Primary Production - Respiration [by plants]
Light-dark bottle technique
- The water is placed into two bottles, one that is clear and admits light and one that is opaque and prevents any light from entering. Both bottles are lowered on cables to the depth at which productivity data are desired and allowed to remain there at the ambient light levels for a fixed period of time.
- In the light bottles, both respiration and photosynthesis will be occurring simultaneously. Since total photosynthesis minus respiration gives net photosynthesis, the light bottles provide a measure of net primary production. In the dark bottles, only respiration is occurring. Gross primary production can therefore be obtained by adding oxygen consumption in the dark bottle to net oxygen production in the light bottle.
- Limitations include the sensitivity and dependability of the methods used to measure the dissolved oxygen content. A greater problem is that it often requires several days of incubation for oxygen levels in the two bottles to change enough to give reliable productivity estimates.
Another method for measuring primary production
Instead of measuring oxygen changes, an alternate method is to measure how much carbon is being actively assimilated by the photosynthesizing plants. This can be done by allowing a volume of water with its natural plant population to incubate after introducing bicarbonate ions (HCO3-) that contain a known amount of radioactive 14C. The radioactivity levels of all plants subsequently filtered from the water give a combined measure of the uptake of 14C by the living cells during photosynthesis, which is essentially a determination of primary productivity. The technique of using 14C incorporation to infer primary production was developed in the 1970's and is the most commonly used method today because it is sensitive and can be used in all ocean environments. As 14C is radioactive, it is relatively straightforward to precisely measure its incorporation in organic material using devices such as scintillation counters.
the ocean is a carbon reservoir
carbon can stay in the deep ocean for a thousand years
calcium carbonate (marine skeletal organism) can stay buried for millions of years
Measuring primary production from space
refer to Ch.11 page 3
the ocean exerts different colors based on the amount of chlorophyll a
- The color of the ocean is affected by particulates and dissolved substances in the water and the absorption of light by water itself. Water is transparent at blue and green wavelengths, but strongly absorbs light at longer wavelengths. Chlorophyll-a has a primary absorption peak near 440 nm causing a shift in color as pigment concentrations increase. After making appropriate corrections, measurements of ocean color can be interpreted to reflect differences in the concentration of chlorophyll-a, which is an indirect measure of the abundance of phytoplankton, and hence of primary productivity.
Copepods and krill
zooplankton
meroplankton
larvae of oysters, crabs, sea urchins and most fish
copepods and euphausiids
crustaceans and herbivores that eat more than half their body weight
- Both animals have specialized appendages which generate localized currents that direct food to their mouth.
-Being crustaceans, copepods and euphausiids pass through a number of intermediate growth stages as they grow to adults, each separated by a molt during which their outer exoskeleton is shed and a new larger one grown.
krill
In the Arctic and Antarctic, the euphausiids known as krill occur in such enormous quantities that they provide the main food source for baleen whales which gulp mouthfuls of water and then expel it through net-like sheets of baleen in their mouths to filter out the krill to eat. The population of Antarctic krill, a species known as Euphausia superba, is so large that it has long been viewed as a potential international fishery. However, krill are much smaller and have a stronger, saltier taste than shrimp and must be pre-peeled for mass-consumption because their exoskeleton contains fluorides, which can be toxic in high concentrations. Krill are mostly harvested at present for the production of fish-meal used in the aquaculture industry.
chaetognaths
- zooplankton, carnivores
- arrow worms
- have hooks at the end of their head, small (2 microns), found in all marine environments
- hermaphroditic: have eggs (planktonic) and sperm
- do not have a well define larval stage
- some are benthic and can be found attach to rocks
Unicellular protists
- shell or hard parts of these organisms are sediment on the ocean floor
- two most significant are foraminifera and radiolarians
- Foraminifera eat a variety of foods ranging from dissolved organic molecules, bacteria, diatoms and other single celled phytoplankton, to small animals such as copepods.
- the two catch their prey by pseudopodia, extensions that come out of their tests (shells)
- All of the planktonic varieties, which are vastly outnumbered in terms of species by those which live on the seafloor, are made of calcite and contribute about half of all calcareous material to deep sea sediments as they sink after death.
Radiolarians
- produce intricate skeletons made of opaline silica, typically with a central siliceous capsule dividing the cell into inner and outer portions of endoplasm and ectoplasm
- eat diatoms and other small zooplankton
- Their skeletal remains make up a large component of the siliceous ooze found on the seafloor.
Ctenophores
- large zooplankton
- transparent jellies that float on the sea surface
- slowly propelled by eight rows of beating cilia though some possess tentacles that trail behind.- use cilia for locomotion
- bioluminescent blue and green can only be seen in darkness
- carnivorous
salps
- large zooplankton
- among the highest growth rates of any multicellular animal and when food is plentiful, such as in a phytoplankton bloom, they can bud off clones that grow rapidly and quickly strip the phytoplankton from the sea.
- Salps move by contracting and pumping water through their gelatinous bodies. The salp strains the pumped water through its internal feeding filters, feeding on phytoplankton. Salps are common in equatorial, temperate and polar seas, where they can be seen at the surface, singly or aggregated together in long, stringy colonies
Jellyfish
- not related to ctenophores and salps
- two-layered body wall that surrounds a digestive cavity with only one opening, around which are tentacles that bear nematocysts, or stinging cells
- The tentacles capture swimming or drifting particles and prey and move them into the mouth, through which wastes are also eliminated.
- plankton, cannot dominate over currents
meroplankton II
spend only part of their lives in the plankton
- usually eggs, larval stages or juveniles are in the plankton
- includes benthic invertebrates that release their eggs in the surface water and the eggs drift and later settle back at the bottom
- Because survival rates are so low, millions of larvae may be produced, and the meroplankton are an important food source for other zooplankton as well as small fish and other animals.
larvae and juvenile fishes
- young fish will feed on the other zooplankton until they grow large enough to join the nekton and hunt on their own. The success of the juvenile fish in a particular year-class (i.e., those spawned in a single season) will depend on a number of variables including whether the currents carry them into a region containing sufficient zooplankton of a size suitable to eat before the nutrition supplied by their individual yolk sac is fully exhausted.
Diel Vertical Migration (DVM)
marine and freshwater organisms migrate to the surface at dusk to feed and begin to migrate back down the water column beginning at dawn
- a prominent "deep scattering layer" was consistently observed around the world that would shoal during the night and then retreat back to greater depths during the day
- Later, it was found that the echoes being followed largely originated from reflections off the gas-filled swim bladders of small fish following the ups and downs of the plankton community.
hypotheses for DVM
There are several hypotheses as to why DVM occurs. Perhaps the simplest explanation is that it reflects a trade-off for zooplankton between the safety of the dark deep sea and the bounty of food, such as phytoplankton, which tend to remain near the surface (see the figure here which illustrates this). Being near the surface where there is more light makes it easier for a predator to spot you, so zooplankton have been hypothesized to feed at the surface when darkness falls and move to deeper, darker water during the day to avoid predators. This means they can make the most of the available food supply without making themselves an easy meal. Another hypothesis is that it is bio-energetically more efficient for zooplankton and small fish to perform DVM than to just stay consistently at the surface, because metabolic rates will be lower in the cooler deep waters. Of course, any potential energy savings here must be weighed against the energy costs of migrating several hundred meters vertically in the water column twice a day. It should also be noted that there is a growing body of evidence for diel vertical migration in deep sea plankton. Like plankton at the surface, those at depth have been found to migrate up and down in the water column to the rhythm of the Sun despite the absence of light. In addition, the vertical movements of at least some organisms follow the variation in day length with latitude, which raises questions about what the trigger for DVM is if not the availability of light. One suggestion is that a very precise biochemical clock may be involved, and efforts are underway to test this.
Vertical Migration seasonal changes
Seasonal changes in the average depth at which plankton live can occur because of density changes that accompany the seasonal cycle of temperature, for example. As surface waters cool in mid- to high-latitudes, they become denser which can impact the buoyancy of plankton and cause them to live, on average, somewhat shallower in winter than in summer.
Primary productivity
- controlled by the availability of sunlight and nutrients
- Both of these variables can have seasonal expressions depending on the latitude. It should be obvious that sunlight varies little over the course of the year in the tropics, except for relatively minor changes in the length of the day and the angle of the Sun overhead. In contrast, light at high latitudes is seasonally limited, and north and south of the Arctic and Antarctic Circles, respectively, the Sun never rises in winter. Nutrients also can vary over the course of the year
Nutrients in water
- phytoplankton incorporate nutrients as they photosynthesize and remove them from the surface waters of the ocean. As the organic matter produced by these phytoplankton and the organisms that graze upon them sinks through the water column, the remineralization of that organic matter and the process of respiration reintroduces the various nutrients in dissolved form to the water column at depth.
- winds mix the water at the continental shelf
- overturning in the open ocean occurs as a result of dense surface waters sinking, the thermocline weakens and the waters mix
-Cold surface waters are prevalent year-round in the polar regions but can occur seasonally in temperate latitudes as well, especially where winter storms with their strong winds and large waves enhance deep mixing.
phytoplanktons and limitations
- limited by nutrients and sunlight availability
- when nutrients and sunlight are in abundance, phytoplanktons bloom
- As a general rule in tropical and subtropical waters, primary productivity is low and variations over the course of the year are minimal. This is because primary productivity in these warm waters is limited not by the sunlight it receives, but because a well developed thermocline that is stable over the year prevents nutrients from moving up to the surface waters in the photic zone. Hence, productivity in the tropics is usually nutrient-limited on average on an annual basis.
Cooler temperate waters
- In cooler temperate waters, the changes that accompany the seasons are much more dramatic. Overturn and mixing during the winter when the thermocline breaks down brings large quantities of nutrients to the surface. At the same time, markedly lower light levels prevent phytoplankton from utilizing the available nutrients, leading to low, light-limited productivity in the winter. As spring arrives, however, the days get longer, the light in temperate latitudes becomes more intense, and the surface waters contain abundant nutrients because of overturn and mixing during the preceding winter. This leads to ideal conditions for phytoplankton growth and produces a period of rapid population expansion known as the spring bloom (peaking in April in the figure you should still be looking at).
- As this bloom develops, two things happen that negatively impact phytoplankton growth. First, the increase in sunlight warms the surface water, making it less dense and the water column more stable. This eliminates the overturning and mixing of nutrient-rich deep water to the surface. Second, the phytoplankton rapidly use up the available nutrients in the photic zone as they photosynthesize and grow, which occurs at a time when the deep nutrient supply is increasingly blocked. (causes them to be nutrient limited)
- fall bloom in temperate latitudes: autumn cooling of the surface water breaks down the stratification and allows mixing of deep nutrients back to the surface again. However, a fall bloom will only occur if light levels remain high enough to stimulate photosynthesis as the nutrients again become abundant. Once light levels drop down to full winter values, the system switches from being nutrient-limited to light limited.
Productivity in polar areas
- light limited, except in the summer
- never nutrient limited since the water is never too stratified
- summer: Sun shines most of the day and light levels are at their highest.
Primary, secondary, and tertiary consumers in the ocean follow the cycles of primary productivity
As phytoplankton bloom, zooplankton respond to the increased abundance of their food source with population growth of their own. Grazing pressure by zooplankton will eventually help reduce the size of the phytoplankton pool, thus causing a reduction in food source and the size of the zooplankton population that can be supported. Secondary and tertiary consumer populations will wax and wane as well in size, following the patterns of primary production in a region. For some higher level consumers, this can lead to a life centered on migration, following the blooms in productivity poleward in the spring, and then returning to the lower latitudes in the winter.
food web
from the Sun through the primary producers to the various consumers that occupy the different trophic levels.
energy inefficiency
it is estimated that less than 1 % of the solar energy that makes it through the atmosphere to the ocean surface is absorbed by autotrophs, and much of that energy captured for photosynthesis is used for growth, reproduction and general cell maintenance of the primary producers. Thus only a small fraction of the energy from photosynthesis is available to be passed on to the herbivorous zooplankton (known as primary consumers) that graze upon the phytoplankton. A similar decrease in energy occurs between herbivores and carnivores, and between lower level carnivores and those that occupy higher feeding levels (Figure 14). Studies of marine ecosystems place the average transfer efficiency from one trophic level to the next at about 10 %. This is commonly known as the ten-percent law and means that only about 10 % of the energy available to any trophic level is passed on to the next trophic level
- reason why there are not many trophic levels
trophic pyramid
the transfer of energy (as food) directly controls how much biomass can be supported at the next level, the biomass generally decreases by 10 percent at each level
Importance of decomposer and fungi and bacteria like plankton
- break down and consume marine snow to place organic nutrients back into the ocean system
- The role that bacteria in the picoplankton play in the breakdown of material in the marine snow helps to close the microbial loop discussed earlier.
food web versus food chain
Most predators have evolved to eat multiple types of prey and hence the term food web is more appropriate than food chain to describe the often complicated, interconnecting relationships between organisms.
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