Phytoplanktongcate.org/marineBio/Chapter_5_The_Microbial_World...Oceanography 10, T. James Noyes, El Camino College 10A-1 Oceanography 10, T. James Noyes, El Camino College 10A-1 Phytoplankton

Oceanography 10, T. James Noyes, El Camino College 10A-1


Phytoplankton

About Phytoplankton

Phytoplankton are tiny (one-celled) algae, plant-like organisms that use sunlight as an energysource to make their own food in a process called photosynthesis (“making with light”). Tocarry out photosynthesis, they need large amounts of water and the gas carbon dioxide, bothabundant in the ocean, to make carbohydrates (the “food” molecules).

Sunlight + Water + Carbon Dioxide Carbohydrates + Oxygen("Sugars")

They also need small amounts of nutrients, molecules thatthey use to build their bodies or molecular “tools” that areneeded to carry out photosynthesis, but are not used up in theprocess. (A hammer is a tool that can be used in the processof building a chair, but the hammer is not part of the chair atthe end of the process. It can be re-used again and again tobuild more chairs. A spatula is used to make food – e.g., ahamburger – but does not become part of the hamburger, andcan be used to make many hamburgers.) Examples of nutrients used in photosynthesis includenitrates and phosphates.

There are many different kinds of phytoplankton. Some have calcium carbonate shells (e.g.,coccolithophores), some have silica shells (e.g., diatoms), and some have no hard shells at all andcan swim (e.g., dinoflagellates). Silica dissolves more rapidly in warm water than cold water, sosilica-shelled phytoplankton tend to prefer living in colder surface water. Calcium carbonatedissolves more rapidly in cold, carbon-dioxide-rich water (more acidic), so calcium-carbonate-shelled phytoplankton tend to prefer living in warmer surface water1. Silica is also considered anutrient, because there are many places in the ocean where there is not enough silica dissolved inthe water for silica-shelled phytoplankton to grow, so like other nutrients its absence limits thegrowth of phytoplankton.

Coccolithophore (Calcium Carbonate Shell)Courtesy of Dr. Markus Geisen, Public Domain

Diatoms (Silica Shells) / Public Domain

1 There are many examples of calcium-carbonate-shelled phytoplankton and zooplankton who live in cold water,and silica-shelled phytoplankton and zooplankton who live in warm water, so this is a preference, not an absoluterule.

In photosynthesis, the carbon inthe carbon dioxide is combinedwith water to create a carbo-hydrate (“hydro” means water).The oxygen in the carbondioxide is simply released.



Sunlight and nutrients are the hardest things forphytoplankton to obtain, so wherever there are bothsunlight and nutrients, phytoplankton will be abundant.Animals will be attracted there too, becausephytoplankton are at the bottom of the ocean food chain.In other words, animals (e.g., zooplankton) in the oceaneat phytoplankton or they eat animals which eatphytoplankton. The phytoplankton make their ownfood, so we call them “primary producers:” they make(“produce”) organic material from inorganic material(carbon dioxide, water). This is the first or “primary”step in the food chain. Animals are secondary, tertiary,etc. producers depending upon their level in the foodchain. They make the organic material of their bodiesfrom organic material that they eat.

Why Phytoplankton Are Important

As discussed previously, phytoplankton are at thebottom of the ocean food chain. So, without them,ocean animals would have little food, and there wouldbe fewer fish and other animals for us to catch and eat.Oceanographers can observe where phytoplankton arecommon in the ocean using satellites (they typically make the waterlook more “green” instead of “blue”), and thus predict where lots of fish and other animals willbe found.

As part of photosynthesis, phytoplankton add oxygen to ocean water. A lot of this oxygen leaksfrom the ocean into the atmosphere. At least half of the oxygen that you and I breathe wasproduced by phytoplankton. In addition, phytoplankton remove carbon dioxide from oceanwater to carry out photosynthesis and make their shells (e.g., calcium carbonate). Humans haveadded large amounts of carbon dioxide to the atmosphere by burning fossil fuels like oil andnatural gas, increasing it by over 33%. Carbon dioxide is a “greenhouse gas:” it absorbs infrared“light” (“heat”) radiated from the warm Earth towards outer space, “trapping it” and thuskeeping the world warmer than it would otherwise be. This “greenhouse effect” is actually agood thing, because it keeps our planet from becoming a giant ball of ice. However, by addingso much extra “greenhouse gas” to the atmosphere, humans are likely to have caused the usually

Think of nutrients as “fertilizing” the phytoplankton.Nutrients are not “food” or “eaten” by phytoplankton.(Phytoplankton make their own food.) As you willobserve under the microscope, phytoplankton have notentacles, arms, or other structures with which to grabthe extremely tiny nutrients. Instead they rely uponchance: nutrient molecules drift into their bodiesthrough the holes in their shells or cell walls.

big fish

small fish

zooplankton

phytoplankton

SimplifiedOcean

Food Chain

Photographs fromNOAA, Dept. of Commerce



fast warming over the past century. A large amount of the carbon dioxide that we add to theatmosphere leaks into the ocean where it no longer adds to the greenhouse effect. By removingit from ocean water, phytoplankton create more “space” in the ocean water, allowing the oceanto absorb more carbon dioxide. Most phytoplankton bodies end up being eaten or decomposedand their carbon is released back into the ocean water, but a few become part of the sediments onthe bottom of the ocean; this permanently removes the carbon from the ocean-atmosphere systemand thus “cleans up” some of our carbon dioxide pollution.

Over vast amounts of time, the phytoplankton bodies in the sediments can become fossil fuelslike oil and natural gas. Diatoms, in particular, are thought to contribute, because they contain adrop of oil in their bodies, a way for them to store food and lower their density so that they canfloat in the sunlit waters at the surface of the ocean. So, you may be “burning” somephytoplankton when you drive your car. Don’t forget to say “thank you.”

Bacteria

Bacteria are small, single-celled organisms2 (even smaller thanphytoplankton). Bacteria use a huge number of chemical processes3 toextract the energy necessary to sustain their lives from inorganic andorganic matter, including dead, decaying material and fecal matter thatanimals cannot use as food. The bacteria decompose (“breakdown”)dead, decaying material into carbon dioxide and nutrients likephosphates and nitrates, making them available to phytoplankton to useagain. This is important: without bacteria “recycling” nutrients, there would be fewerphytoplankton in the ocean, and therefore fewer animals as well. However, many bacteria needoxygen to decompose “breakdown” organic matter, so if too much dead organic material ispresent in ocean water, it can lead to the growth of lots of bacteria which use up the oxygen inthe water; animals who cannot leave suffocate (die because they cannot breathe).

In recent years, bacteria have been found to play 2 other important roles in ocean ecosystems.First, some bacteria can carryout photosynthesis4 (make their own food using the energy of theSun). Second, bacteria are more abundant than previously thought, because many phytoplanktonbodies are “leaky.” Phytoplankton gain water, carbon dioxide, and nutrients by simply lettingthem drift into their bodies, and remove wastes by letting them drift out of their bodies on their

2 Bacteria are single-celled organisms that do not have a “nucleus,” a structure in the cell which protects its DNA.Instead, bacteria DNA drift within the cell, making it easier for them to become damaged (mutate). This can, ofcourse, be very harmful, but upon occasion the mutation is useful. In essence, bacteria evolve faster than otherorganisms. For this reason, you should always take ALL of the antibiotics prescribed by your doctor, even if youstart feeling better. You need to make sure that you kill ALL of the disease-causing bacteria. If you only kill mostof the them, then the survivors – the most resistant ones – will start breeding, helping the species evolve resistanceto the antibiotics and making antibiotics less-useful for everyone in the future.3 Each species of bacterium specializes in using one chemical process or a few. They have evolved these differencesover time.4 This is not really shocking, because the fossil record suggests that some did this in the past. What scientistslearned is that some still carry out photosynthesis. In the past, one bacteria hit upon the incredibly useful chemicalprocess of photosynthesis, giving it a huge survival and reproductive advantage (more food and energy). Thisbacteria then evolved into all the diverse forms of life that use photosynthesis today, including both phytoplanktonand photosynthetic bacteria.

Some bacteria can “fix”nitrogen gas, making itinto a nutrient usable byphytoplankton. This ishow soils naturally getnitrogen. Recall thatthe atmosphere isnearly 80% nitrogen.



own (not unlike a small child in a public swimming pool). Unfortunately, phytoplankton alsolose about ¼ of the potentially useful “dissolved organic carbon” (DOC) that they make too. Ifthey used the DOC to grow and for energy, then there would be more food for animals andtherefore more animals, but unfortunately they “lose” a significant amount of what they make.Many bacteria can extract energy from this material, so the leaky phytoplankton lead to morebacteria in the ocean. The big discovery was that there are many, very small animals whospecialize in eating bacteria (bacteriovores), and that these animals are eaten by zooplankton(who are eaten by small fish, who are….). Thus, bacteria make sure that the food “lost” byphytoplankton is not lost from the food chain, and therefore they increase the number of fish5

and other animals in the ocean (more food for us). This pathway in the food chain is commonlycalled the “microbial loop” (the purple lines in the food web below).

Bacteria, fungi6, and viruses7 areabundant in ocean water.However, because they are sosmall, they are hard to captureand study. Aside from what Idiscussed above, relatively littleis understood about their role inocean ecosystems. It is anactive area of research, and Iexpect some big discoveries inthe not-too-distant future thatwill radically alter what I teachabout them.

5 In the 1970’s, the first satellite estimates of the amount of phytoplankton in the ocean suggested that there were“too many” fish in the ocean. (There was not enough food for all the fish.) It took a while for oceanographers tounderstand the role of bacteria in the ocean food chain.6 Fungi are related to plants, but do not carry out photosynthesis. Most obtain their energy from decomposing deadmatter (like bacteria).7 Viruses are strands of RNA (DNA-like material) that invade cells, take over their DNA, and use the cell’s ownbody to produce more virus particles. These virus particles are then released, and try to infect more cells.

phytoplankton

zooplankton

small fish

big fish

bacteria

& Bacteria

OceanFood Chain

wastes

dead, decayingmaterial,

bacteriovores

nutrients

Recent studies have shown that there are about 50 million virus particles per milliliter of ocean water(less than a teaspoon). These viruses kill about 20% of the bacteria in the ocean everyday!



Sunlight and Floating

Sunlight is, of course, more abundant at the topof the ocean. As sunlight goes downwardthrough ocean water, it is absorbed by the water,warming the surface of the ocean but leaving thedeep ocean cold and dark. Anything that helpsphytoplankton float like unusually cold and saltywater (high density water) at the surface of theocean and upwelling (water moving upwardfrom the deep to replace surface water pushedaway by winds) leads to the growth of morephytoplankton. In fact, many phytoplankton are moredense than water (because of their hard calciumcarbonate or silica shells), so they sink. They rely uponwaves or other mixing mechanisms to bring them backup towards the sunlight at the surface. Their bodies areshaped so that they fall slowly, allowing them to waitfor that lucky wave. There is at least one advantage tofalling: their bodies are exposed to more nutrients.

Where Nutrients Are

Nutrients enter the ocean when they are washed off theland by rain runoff. (The nutrients are in the soil onland. They help land plants to grow.) Thus,phytoplankton like to live near the coast, and nutrientsare hard to find out in the middle of ocean. As deadorganisms and wastes sink towards the bottom of theocean, they are slowly decomposed by bacteria ordissolved by ocean water, releasing nutrients back intothe water in the deep ocean. However, many nutrientsare released down deep, where phytoplankton cannotlive because of a lack of sunlight. Anything that bringsthese nutrients up to surface will lead to the growth oflots of phytoplankton. Upwelling is the most effectivemeans of bringing up nutrients, but upwelling onlyhappens in special places where the winds blow in theright directions. Examples include the Equator, alongwest coasts at mid- and low latitudes, and in the middleof the Southern (Antarctic) Ocean. In most parts of theocean, nutrients are brought up by waves and othermixing mechanisms that stir up the nutrients from below. Waves can only bring up nutrients ifthe surface water is not too warm. Cold, nutrient-rich water brought up from below cannot floatin warm surface water – its density is too high – so it will sink back down rather than mix withthe surface water.

Examples of Upwelling:California

Land

"Gap"

Upwelling

Upwelling Zones:

NOAA, DOC.



Cold Lots of Nutrients

Few NutrientsWarm

Waves have difficultly bringingup nutrients if the surfacewater is too warm. When awave tries to mix the surfacewater, the cold water tries to diveback down, the warm water triesto pop back up.

Why Deep Water is Rich in Nutrients

Deeper water has more nutrients than surface water, because nutrients at the surface of the oceanare being removed from the water by phytoplankton, but nutrients are being added to the deeperwater when dead, decaying matter (e.g., phytoplankton bodies) sinking from the surface aredecomposed by bacteria. Unlike at the surface, nutrients are not being “used up” byphytoplankton, so they slowly build up in deeper water over time.

The water beneath the surface mixed layer (a layer called the “thermocline”) is particularly richin nutrients. At the top of the thermocline, the water is much colder (and often saltier) than thewater of the mixed layer, so it is has a higher density than the mixed layer. Therefore, it givesmore support, so when sinking bodies reach the thermocline, they begin to fall slower. Thebodies “clump up” near the top of the thermocline, so more nutrients are released when they aredecomposed by bacteria.

thermocline

mixedlayer

deeplayer

LOTS ofoxygen

littleoxygen

LOTS ofnutrients

fewnutrients

plenty ofoxygen

plenty ofnutrients

Sinking dead, decaying matter (like the bodies of phytoplankton),carry nutrients away from the surface and into the deep ocean.

Sediments are not nutrients.Sediments are much largerthan the phytoplanktonthemselves!

Deep in the ocean, there are no waves or strong currents. The primarymixing mechanism which stirs the water is the swimming of animals.This mixing is very weak, but over time their swimming helps nutrientscome up to the algae at the surface (VERY slowly)!



Where Phytoplankton Live

Most phytoplankton live, of course, in the sunlit waters near the surface of the ocean where theycan obtain light for photosynthesis. But there are more phytoplankton in some parts of the oceanthan in others.

In the satellite image below, dark blue & purple colors indicate that very few phytoplankton arepresent while red & orange & yellow colors indicate that huge amounts of phytoplankton arepresent. Light blue & light green colors indicate that lots of phytoplankton are present. As youcan see, phytoplankton are very abundant near the coasts, because of all the nutrients that arewashed off the land. Notice, though, that there is more life along the west coasts than east coastsowing to upwelling. For example, compare the west coast of Africa to the east coast of theAmericas across the Atlantic Ocean. Similarly, the light blue tongue across the Equator showsthat there is more life at the Equator, also owing to upwelling. (Notice that upwelling isstrongest along the west coasts near the Equator.)

Red / Orange = Tremendous Amounts of Phytoplankton NASALight Blue / Light Green = Large Amounts of PhytoplanktonDark Blue / Purple = Few Phytoplankton

The satellite image clearly shows that life is more abundant in the colder waters near the Polesthan in the warmer waters closer to the Equator. This often confuses my students, because they(correctly) reason that warmer water is warm due to more sunlight and sunlight is needed forphotosynthesis. What they forget, though, is that warm water has a lower density, sophytoplankton sink more easily in warm water, and the more they sink, the harder it is for themto get sunlight. More importantly, if the surface water is too warm, waves have difficultystirring up nutrient-rich water from down deep. (The deeper water is cold and dense, so whenthe waves try to bring the water up, it immediately sinks back down.) The upwelling in themiddle of the Southern (Antarctic) Ocean adds even more nutrients to the surface water, makinglife more abundant in the Southern Ocean than nearly any other place in the open ocean.



Blooms

A bloom is the rapid increase in the population of an organism (a “population explosion”).Blooms occur when something needed for growth and reproduction, something that was holdingback or “limiting” the size of the population, becomes more abundant. In the case ofphytoplankton, blooms typically occur when the amount of sunlight and/or nutrients increases.A bloom will stop and the population will shrink when the resource runs out or goes away (like aparty when the booze runs out…). Zooplankton bloom when phytoplankton bloom, becausemore phytoplankton means more food for them. However, most animals cannot reproduce asfast as phytoplankton, so their population grows more slowly and is never large enough to inhibitthe growth of the phytoplankton population until the bloom begins to end on its own.

Humans can cause blooms of phytoplankton byadding additional nutrients to ocean water. (Wecannot affect the amount of sunlight, can we?8)Typically, humans add nutrients by dumpinguntreated sewage or when rain washes fertilizersand animals wastes (e.g., manure from cows, pigs,etc.) off farmland and into rivers9. Wetlands slowdown the water washing off the land and absorbthe nutrients, keeping them from reaching theocean and causing harmful algae blooms.

Harmful Blooms

Offhand, you might expect that causingblooms is a good thing: more nutrientsmeans more phytoplankton whichmeans more food for animals that weeat. However, as we have dumpedmore and more nutrients into the ocean,we have found that they can alsoencourage the growth of harmfulmicroorganisms. Some attack fish andother organisms directly, causingwounds (e.g., Pfisteria piscicida), orinhibiting feeding and/or breathing(produce lots of mucus, clog gills, e.g.,species of Chaetoceros), but manyharm other organisms and theenvironment “by accident.”

8 Well, there was that episode of the “Simpsons” where Mr. Burns blocks out the Sun so that people will buy moreelectricity from his nuclear power plant…9 Storm drains carry yard waste and animal feces, sources of nutrients, into the ocean when it rains as well.However, the nutrients are typically not abundant enough to cause a harmful bloom of phytoplankton.

Sewage comes from all the stuff that youwash down the drains in your house: thekitchen sink, toilet, bathroom sink,bathtub, dishwasher, washing machine,etc. It is a soup of dead, decayingmaterial, wastes, and chemicals. Before itis released into the ocean, the governmentmandates that it must be “treated,” but thistreatment typically focuses more onkilling disease-causing bacteria thanremoving excess nutrients.

National Oceanic and Atmospheric Administration,Department of Commerce



“Red tides” are a classic example. Red tides are a bloom of red-colored phytoplankton10

(typically dinoflagellates); there are so many phytoplankton in the water that they make the waterlook red (or brown or yellowish). Some red tide algae – but not all! – produce chemicals that aretoxic to vertebrates like birds, mammals, and humans. Filter feeders (or suspension feeders) likeclams and other shellfish strain the algae out of the water during a bloom. They eat lots of algae,and the more they eat, the more toxic they become. (This is called “bioaccumulation” or“biomagnification.”) If we or other vertebrates (e.g., seals, sea gulls11) eat the shellfish, we canbecome sick. Illnesses caused by toxins being passed up the food chain in this way includeciguatera fish poisoning (CFP), diarrhetic shellfish poisoning (DSP), and paralytic shellfishpoisoning (PSP). In general, though, it is safe to swim in red tides;you won’t swallow nearly enough water to become poisoned12.However, the algae do leak toxins into the water, and these causesome people to develop rashes. As long as you get out of the waterwhen you notice the rash and wash it off, you should be fine.Breaking waves can catapult these toxins into the air, and some ofthese toxins cause respiratory (breathing) problems for people wholive near the coast.

Red Tide, La Jolla, California. Courtesy of P. Diaz (Public Domain)

10 Red tides have nothing to do with ocean tides or the Moon.11 The Alfred Hitchcock horror movie “The Birds” was based on a true story. More likely than not, the real-lifederanged birds had eaten some fish or shellfish who had eaten a lot of toxic phytoplankton.12 In fact, the salt in the water would be worse for your body than the tiny amount of toxin that you would swallow.

Clam



In general, eating fish is safe so long as it was fighting and kicking when you caught it;just be sure to eat the fillets, not the organs or entrails. The most dangerous organisms toeat are filter-feeders like clams, mussels, oysters and so on, because they are more likelyto build up lots of toxins in their bodies. It should be safe to eat them in restaurants,because the United States has good regulations and does a good job of inspectingseafood. Restaurants will import shellfish if the local ones may be poisonous.

Another example of a harmful algae bloom is a “dead zone13.” At the end of the bloom (once thephytoplankton have used up all the nutrients), the water will be filled with a lot of deadphytoplankton. This encourages the growth of bacteria who decompose (“break down”) thebodies. In doing so, the bacteria use up the oxygen in the water. Animals that do not swim away(either because they cannot swim or because they cannot survive in the open ocean), die becausethey cannot breathe.

One of the best known examples of a “dead zone” is the one that occurs at the end of theMississippi River. The Mississippi drains practically the entire middle of the United States,including a vast amount of farmland. The fertilizers that the farmers put on their land to helpthem grow more food per acre and animal wastes from huge “factory farms” are washed off theland and into rivers. These rivers join with the Mississippi, which carries these nutrient-richmaterials into the ocean. The resulting “dead zone” harms the livelihoods of the local fishermen.Harmful algae blooms cost the United States an estimated $100 million dollars each year in lostfisheries and tourism revenues.

“Dead zones” can occur naturally. For example, brief, strong winds along the coast of Oregonoften enhance upwelling, leading to a short, enormous bloom of phytoplankton that ends in a“dead zone.”

NASA

National Oceanic & Atmospheric Administration,Department of Commerce

13 Scientists use the word “eutrophication” to describe this phenomena, and the word “anoxic” (“no oxygen”) todescribe the lack of oxygen in the water.



Even unnaturally large blooms of “good” phytoplankton that do not result in “dead zones” cancause problems. Many ocean animals begin life as zooplankton that feed on phytoplankton.When then grow up, they become nekton or benthos that eat other things (e.g., seaweed,zooplankton, corals). If humans cause an unnaturally large bloom of phytoplankton, too many ofthese animals will survive into adulthood – because they can grow quickly since they haveabundant food when they are “babies” – and they can disrupt their ecosystem by eating too muchas adults. For example, they might eat an entire kelp forest or coral reef before their ownpredators can reduce their population to their original and stable level.

Seasonal Blooms

Phytoplankton are more abundant during some seasons than others, depending upon theavailability of sunlight and nutrients.

In the mid-latitudes, phytoplankton “bloom” during the spring and fall. I think that it is easiest tounderstand why they bloom during these two seasons if you first understand why they do not“bloom” during the summer and the winter. During the winter, there is less sunlight, because thedays are shorter and the Sun does not get as high in the sky14, so the phytoplankton populationdrops. During the summer, there is plenty of sunlight, but the surface water becomes too warm:warm water has a lower density, so phytoplankton sink more easily in warm water: the more theysink, the harder it is for them to get sunlight. More importantly, if the surface water is toowarm, waves have difficulty stirring up nutrient-rich water from down deep. (The deeper wateris cold and dense, so when the waves try to bring the water up, it immediately sinks back down.)In summary, during the winter there is not enough sunlight to support a large population ofphytoplankton, and during the summer waves cannot bring up enough nutrients.

At the beginning of the spring, sunlight becomes more abundant, but surface water is still quitecold, so waves can easily stir up nutrients from below. The bloom ends when the surface waterbecomes too warm, making it difficult for waves to bring up more nutrients. During the fall,sunlight is becoming less abundant (bad for phytoplankton), but the real problem is a lack ofnutrients. Once the surfacewater cools down enough, itplunges downwards, and waterfrom below comes up toreplace it. This happens againand again, cooling the surfacelayer of the ocean and bringingup nutrients from below15.Thus, the fall bloom occurswhen the ocean surface coolsdown enough for nutrients to bestirred up by the waves andsinking water, but there is still

14 The sunlight hits the surface at an angle, so more reflects off the surface, and the sunlight entering the water doesnot go straight down, so it does not penetrate as far.15 And the cooler surface layer makes it easier for waves to bring up nutrients as well.

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Spring Summer FallWinter Winter

Tropics

Mid-latitudes

Poles



enough light for them to carry out photosynthesis. The spring bloom is larger than the fallbloom. (If you think about it, this is due to water’s high heat capacity.)

There is never any bloom in the tropics. As we discussed earlier, the tropical ocean has less lifethan any other part of the ocean. (This is why the water of the tropics is “crystal clear” and“blue:” it is sterile, dead. Green murky water is full of algae and life.) Even though sunlight isalways abundant, the surface water is too warm, making it difficult for waves to bring up cold,nutrient-rich water from below.

The largest bloom in the oceans occurs atthe Poles during the summer. The surfacewater never becomes very warm, so wavescan always bring up nutrients from below,and sunlight is abundant. Near the summersolstice, the Sun dips down in the sky butnever sets, providing 24 hours of sunlighteach day.

As you may know, gray whales regularly migrate up anddown our coast. They head up to Alaska for the summerwhen the most food is available16. They need to eat a lot tobuild up their blubber (their food reserves), since they feedless frequently during the rest of the year. Then, the whalesmigrate south, and go past us in the fall so that they canspend winter in the warm, shallow lagoons (estuaries) ofMexico where the females give birth to their calves17. In thespring, they migrate north and go past us18 on the way toAlaska. (They go to Alaska for the summer and Mexico forthe winter. Smart animals, huh?)

16 Unlike most baleen whales, gray whales are primarily bottom feeders. A gray whale opens one side of its mouthas it rubs along the ocean floor, scooping up sediments. It then uses its tongue to force the water and the small,muddy sediments out of its mouth. Small crustaceans that were living in the sediments are caught between theirlong, thin teeth (baleen), and the whale licks them off the inside of its teeth and swallows them. The crustaceans eatplankton remains that sink to the bottom of the shallow waters along the coast.17 There are several explanations for why the whales leave Alaska and go down to Mexico. Baby whales don’t havemuch blubber, so the water may be too cold for them during the winter. In addition, orcas (killer whales) are moreabundant farther north (where most of the food is, as we have discussed). Orca’s kill baby gray whales by holdingthem underwater long enough for them to drown. This would be difficult in the shallow waters of Mexican lagoons.18 Whalers (people who hunt whales) use to have an outpost on Palos Verdes. Gray whales were once called “devilfish,” because they learned that humans are dangerous and the whales became quite violent. They have “unlearned”some of these behaviors, and there are now some populations in Mexico which will allow humans to approach andpet them. One of the primary reasons for hunting whales (in general) was for their oil, needed for lighting andcooking and a host of other needs, until someone figured out how to use oil from the Earth for the same purposes.

Gray Whale. Marine Mammal Commission (Pub. Domain)

Spring

Fall

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Phytoplanktongcate.org/marineBio/Chapter_5_The_Microbial_World...Oceanography 10, T. James Noyes, El Camino College 10A-1 Oceanography 10, T. James Noyes, El Camino College 10A-1 Phytoplankton