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Chapter 13 — Transcript

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0:00Hello, I'm Dr. Jeff Ashley and welcome
0:02to chapter 13. Let's get started.
0:05Chapter 13 deals with this word that
0:07I've been discussing throughout the
0:08course and it's called
0:10productivity. In particular, I am
0:13referencing biological productivity. And
0:15in this chapter, we'll get a closer look
0:17at what that means and the energy
0:19transfers involved in food webs. So,
0:21let's start off the with the word
0:23productivity. And I'm going to add
0:25another adjective to that, primary
0:27productivity. This refers to the rate at
0:30which energy is stored as organic matter
0:33and this includes largely those
0:35organisms that are photosynthesizing
0:37using solar radiation to create body
0:39mass or organic matter. It also includes
0:43a subset but much lesser of those
0:45organisms that can utilize chemicals in
0:48order to
0:49chemosynthesize getting energy from
0:51chemical reactions instead of the sun.
0:5599.9% of the ocean's biomass relies
0:58directly or indirectly on photosynthesis
1:00of food. So, as we saw, the unique
1:03creatures and bacteria that utilize
1:05chemicals in the deep ocean vents are
1:08important. They are minimal to the sum
1:11of primary productivity. So, I just want
1:14to remind you of what photosynthesis is.
1:16So photosynthesis is taking energy from
1:20the sun, sunlight and oxygen and
1:23creating biomass or organic molecules
1:27that end up being constituents of the
1:30cell's body. While
1:32photosynthesis creates organic molecules
1:35or biomass, the reverse happens as well.
1:39Those organic molecules can then be
1:41chemically degraded with carbon dioxide
1:44being liberated and also water. And this
1:47is called respiration. So we kind of
1:49have a two-way street here of
1:50photosynthesis creating organic matter
1:53but the reverse is that organic matter
1:55then can be utilized and then liberated
1:59as carbon dioxide. So who are doing the
2:02primary productivity? Well, it's the
2:05primary producers. these organisms
2:07called in general phytolankton, but
2:09we'll get into the different classes of
2:11phytolankton and be more detailed in a
2:13moment. So, how do we measure prim
2:16primary productivity? One way, and we've
2:18seen this before, is to capture plankton
2:20in what's termed plankton nets. These
2:23are nets that are dragged behind a
2:24research vessel and collect the surface
2:28specimens that represent phytolankton.
2:30These nets are all constructed of a
2:32particular net or pore size allowing
2:35water to flow through but capturing
2:37small organisms like phytolankton. The
2:40organisms are captured in a glass or
2:43plastic vessel here in the bottom and
2:45they're concentrated. Those organisms
2:48then can be analyzed for the
2:52abundance and the types of organisms.
2:54One unique way that we can measure pro
2:57primary productivity is once we have
2:59those phytolankton captured, we can give
3:01them a source of carbon and we can give
3:04them not carbon 12 which is the most
3:06abundant isotope of carbon but carbon 13
3:09and we can measure that radioactive
3:11carbon and its uptake into the
3:13incorporation of the uh cells or
3:16biomass. So this chapter has a lot of
3:18deja vu because we've talked about a lot
3:20of the things that drive primary
3:22productivity.
3:24We've seen this before. One other way to
3:26measure primary productivity or how much
3:28phytolanton are growing and accumulating
3:30biomass is to use satellite imagery.
3:33Remember the SEAW whiffs data we saw
3:35that uses colorization to denote either
3:38sediments in the water and they're
3:39usually brown or phytolanton pigments
3:42such as chlorophyll a. So here we see a
3:45blast from the past chapters and we said
3:48that along the coastline where nutrients
3:50are delivered and sunlight is abundant
3:52in these uh typically shallow areas that
3:54those are the two ingredients need to
3:56fuel primary productivity sunlight and
3:59nutrients. So here we have a seaw data
4:02scan that's showing in red the abundance
4:05of phytolankton at its maximum and then
4:08lower areas certainly offshore where
4:10there's uh fewer nutrients in lower
4:13abundance of primary productivity. Just
4:16a sidebar while perusing the data here I
4:19came across this really cool study that
4:22used ice cores to determine historic
4:24productivity levels. So the techniques
4:28that I just talked about are current
4:29use. You can go out in a ship and look
4:31at primary productivity on a Tuesday say
4:35in 2025. Um but how do we go back and
4:38how do we then correlate what's
4:40happening chronologically or
4:42historically? So this article was really
4:44cool and it looked at phytolanonic
4:47blooms off the coast of Greenland. And
4:49we'll see that these are Aries, although
4:51they're cold, they are sunlit for some
4:53degree of the annual cycle. And
4:56phytolankton need that sun and have
4:58abundant nutrients in these waters and
5:00can fuel what we call a phytolanktonic
5:02bloom. So here we have a bloom. They
5:05looked at a specific class of biological
5:08compounds that are discharged by
5:10phytolanton and aerosolized or end up in
5:14the air. Once they end up in the air,
5:16these molecules then by wind transport
5:19are deposited on land like in the ice
5:22covered uh area of Greenland. Remember
5:25back to sediments. This is the same
5:27thing that happens with sediments. As
5:29sediments fall to the seafloor over
5:32time, they just keep accumulating and
5:34they push down. And if you go further in
5:37depth, you're going back in time. Well,
5:39the same thing can be done with ice
5:41cores instead of sediment cores. And
5:44this is what the researchers did. By the
5:46way, if you click on this image, it will
5:48take you to the article. So, taking
5:50these long ice cores, they were going
5:52back in time to look at these compounds
5:54that were aerosolized in phytolanktonic
5:57bloom times. And they can determine the
5:59productivity way back when, decades ago.
6:03What they found was when they went back
6:05in time, they found those phytolanomic
6:07blooms more abundant. there were more
6:09primary production episodes happening
6:12versus today. And in the article, if you
6:15want to read it, they surmise that this
6:17is due in part to global increases in
6:19temperature which decrease the
6:21availability of nutrients in this
6:23certain area. Okay, so we kind of
6:25understand what primary productivity is.
6:27It's building biomass. But there's two
6:30kinds. So it's subdivided into gross
6:32primary productivity which is the total
6:35amount of organic matter produced by
6:37phytolankton by photosynthesis per unit
6:40of time total amount. But remember that
6:42photosynthesis happens but the reverse
6:45happens as well respiration. So net
6:47primary productivity takes into consider
6:50respiration. It's the production of
6:51organic matter that goes into growth and
6:53reproduction products and not that used
6:56for maintenance through respiration. So
6:59it pulls out that respiration process
7:03and gives you something called a net
7:04primary productivity value. So this is a
7:07little harder to do to get net primary
7:09productivity. We looked at the examples
7:12before and that was gross primary
7:14productivity where you had
7:15photosynthesis and also respiration
7:18happening there. But here we want to
7:20pull out respiration. So how is it done?
7:22Typically it's done using this
7:24oceanographic technique called the light
7:26light dark bottle. So in essence, it's
7:29easy to measure gross primary
7:31production, but how do you measure
7:33respiration in order to get that net
7:35primary productivity? Well, here's how
7:37you do it. So you collect water
7:40samples at the surface that contain
7:43growing phytolanton. And again, it's
7:45photosynthesizing because there's light
7:47and there's nutrients and also they are
7:49respiring. So they're losing some of
7:51that organic matter to respiration.
7:53You take that sample and you fill light
7:56bottles and dark bottles and you put
7:58them at a depth. So each of these
8:00bottles is at a certain depth. You go
8:02lower and lower and lower. What is
8:04happening in the light bottles? Well,
8:06they're light bottles. So they light can
8:08penetrate them. So both photosynthesis
8:10and respiration are happening. That is
8:13if it's in the sunlight zone. So here's
8:15net photosynthesis happening. But beyond
8:18that we call the oxygen compensation
8:20depth. You have no light. So all you
8:22have is respiration happening here.
8:25There's no photosynthesis. Again in the
8:27light bottles both photosynthesis in the
8:30euphotic zone or sunlight zone is
8:31happening and respiration is happening.
8:34So again how do we tease out the
8:35respiration? Ah that comes from the dark
8:37bottles where only respiration is
8:39happening. So you can measure the
8:41respiration rates at various depths in
8:44the sunlight zone and also in the nonlit
8:47zone. Using that researchers can then
8:49get net primary productivity. It's a
8:51little more complicated than this, but I
8:53just wanted to give you a feel for how
8:54you would get this more difficult value
8:57called net primary productivity. So,
8:59what are the factors that affect primary
9:02productivity? And I'm just going to say
9:04productivity sometimes for short.
9:06Nutrient availability as we said and
9:08primarily that's nitrate compounds,
9:10phosphor phosphorus compounds, iron and
9:13silica. There are other trace elements
9:16and compounds that are needed but these
9:17are the four most important ones. Where
9:20are these nutrients coming from? They're
9:22coming from lithogenous or land-based
9:24sources and mostly delivered from from
9:27rivers through runoff to coastal
9:29systems. So productivity is very high
9:31along the coastal areas like continental
9:34margins. One important thing that you
9:36may have seen in biology is called the
9:38red field ratio. And redfield determined
9:40that all plants, but especially
9:42phytolantonic plants need a ratio of
9:45these three essential nutrients. They
9:48need carbon and they need lots of it
9:50because they're incorporating that into
9:52their bodies as organic molecules. They
9:54need nitrogen compounds and they need
9:56phosphorus. So these are the three big
9:58players. They need it in a certain ratio
10:01though. They need a lot more carbon than
10:03nitrogen and they need a lot more
10:04nitrogen than phosphorus. So the ratio
10:06is approximately 106 to
10:0916:1. This is sort of the recipe. In
10:12order for you to photosynthesize and
10:14have primary productivity, you have to
10:17give your algaal samples this ratio of
10:21macronutrients. So, as I said, nitrates
10:23and phosphates are coming from
10:25land-based activities such as gardens
10:27and agricultural practices. They also
10:30come from untreated and mildly treated
10:32wastewater treatment plants. And that's
10:34human waste because we are delivering
10:36our waste products that contain nitrogen
10:39and phosphorus as well. And if they're
10:41not eradicated from that waist stream
10:43before it gets into a water body, we end
10:45up having some nutrients uh being
10:49vetored that way. So they're washed into
10:51coastal areas and that can cause this
10:53thing called utrification. And I spoke
10:55to you before about this and now we get
10:57to explore it a little bit. Utrification
10:59is an enrichment of ecosystems with
11:01chemical nutrients that fuel primary
11:04productivity. We also have to have
11:06sunlight. So here we have a depiction of
11:08three different terms that are used.
11:10Utrophic designates an area that is
11:12enriched with nutrients more than it
11:14needs and it's fueling phytolanonic
11:17blooms. On the other side of the
11:18spectrum there's igotrophic where it's
11:20nutrient poor. Phytolankton don't have
11:22enough of these nutrients to fuel
11:24primary productivity. And somewhere in
11:26between we have areas that are
11:28misotrophic. As I mentioned before
11:30nutrients are important but the other
11:32thing is the availability of solar
11:34radiation. And where does that happen?
11:36We saw that depth increases and then
11:40sunlight decreases. So the uppermost
11:43surface seawater and shallow uh seafloor
11:45is where light can penetrate. Where
11:48light does not penetrate anymore. We
11:49don't have the availability to conduct
11:51photosynthesis and that's called the
11:53oxygen compensation depth. Talked to you
11:56about this term before but the euphotic
11:58zone is the sunlit zone and that's from
12:01the surface to about 100 mters. Although
12:03that varies because we could have
12:05cloudiness or turbidity caused by
12:07sediments or other practices that shade
12:10the sunlight. In the euphotic zone, we
12:14ideally have enough light for
12:16photosynthesis. So, a bit of a review
12:18and then some new stuff here. Review.
12:20Sun affects three major ocean
12:22components. We talked about how sun or
12:25solar radiation affects ocean winds. It
12:28determines the major wind belts that
12:30produce ocean currents and wind-driven
12:32waves. It also heats up that layer on
12:35top of the ocean and that determines
12:37that we get this layering effect or
12:39ocean stratification where we have a
12:41thin layer of surface water warmer than
12:43the cold denser water below. That was
12:45all review. What's new? Well, the new
12:47stuff is in primary productivity
12:49photosynthesis can only occur where
12:51sunlight penetrates the open ocean. So,
12:53we have to bring in another chapter. I
12:55said we dealt with a lot of these
12:56concepts before. Here they are coming
12:58together. Most solar energy falls in the
13:00visible light portion of the
13:01electromagnetic spectrum and we saw that
13:04water appears blue or ocean water does
13:06because blue wavelengths penetrate the
13:08deepest. The longer wavelengths such as
13:10red orange are absorbed first in water.
13:13We also said that color in the ocean
13:16could be determined by many things. It
13:18ranges from deep blue to yellow green
13:20due to selective color absorption of the
13:22different species biological and abiotic
13:25within that water column. Factors
13:27affecting that water transparity or
13:29transparency or clarity are turbidity
13:32from runoff. So sus suspended
13:34lithogenous sediments and also
13:36photosynthetic pigments like chlorophyll
13:38which absorb at certain wavelengths.
13:40Remember the sucky disc that measures
13:42water transparency or turbidity. So I
13:44just have to bring that up again. So in
13:46coastal and upwelling areas that are
13:48productive because there are nutrients
13:50and sunlight we tend to have the color
13:53of light green and this designates
13:55utrophic open ocean lacks productivity.
13:57So on these sea whiffs data the open
13:59ocean where there's no productivity
14:01often appears blue and that's called
14:04igotrophic nutrient poor. So ocean
14:06margins or fringes along the continents
14:09are usually rich in life but there are
14:12stresses on those organisms. Shallow
14:14water depths allow greater seasonal
14:16temperature and salinity v variations.
14:18So organisms have to be tolerant of
14:20that. Water column varies in thickness
14:23near shore due to tides. So they have
14:25tidal effects which may render certain
14:28areas above the water or even below at
14:31certain times of the tidal cycle. And
14:34again, the energy from breaking waves in
14:35the surf zone release large amounts of
14:38energy that may disturb the ability to
14:42um photosynthesize for these organisms
14:44that are non-mobile. However, despite
14:47these stressors, ocean margins are still
14:49highly productive in most zones. Here we
14:52have a satellite image and again uh that
14:54blue designates it's igotrophic or
14:56nutrient poor. There's not a lot of
14:58primary productivity happening. Where is
15:01it all happening? It's happening along
15:02the continental margins. So the light
15:04green and it's pretty hard to see in
15:06certain areas, but they pinpointed a
15:08couple areas here. Light green oceans uh
15:12color is uh representative of high
15:14chlorophyll concentrations. So
15:15chlorophyll is the pigment within these
15:18uh phytolantonic algae. Not only are
15:20nutrients supplied by runoff of
15:22landbased uh activities such as
15:25agriculture, but we talked about how
15:26nutrients from deep cold water can be
15:28upwelled to these coastal areas in
15:31certain uh areas certainly along western
15:33continental margins. This brings up
15:36nutrients to the surface. Perfect. The
15:38recipe is nutrients plus sunlight fuels
15:41that phytolanonic bloom. And if we go
15:44back to the sea whiffs data, we we saw a
15:46lot of those um conditions being ripe
15:49for primary productivity off the coast
15:52of South Africa and also around Tasmania
15:55as well. So who are these organisms that
15:58are photosynthesizing and are called
16:00primary producers? They are anthroita,
16:04which are seedbearing plants,
16:06macroscopic large algae, microscopic or
16:09small algae, and photosynthetic
16:11bacteria. Let's take a closer look at
16:13these categories. Anthroa appear only in
16:16shallow areas. They're primarily
16:18seaggrasses and mangroves. They're
16:20important sources of food and protection
16:21for nearshore animals. They're the first
16:24response when the land delivers a whole
16:26bunch of nutrients. These organisms,
16:28because of their large biomass, capture
16:30those nutrients. And at times, if you
16:33have coastal systems that do have these
16:35types of organisms that it will limit
16:38the nutrients going further offshore. So
16:40it kind of limits the amount of
16:42phytolantonic blooms offshore. It's a
16:44good thing. So marshes and mangroves are
16:47good. They act as buffers capturing
16:50these nutrients. What about the
16:52macroscopic algae? Well, there's green
16:55algae and this is most common in
16:57freshwater. And um interestingly enough
17:01here that a bloom threatened the 2008
17:03Olympic sailing events. And we'll see
17:05them cleaning that up in a moment.
17:07There's red algae and this is more
17:09common in oceanographic situations and
17:12rare in freshwater and it's a phylm
17:16rodo rodopita and it's the most
17:19abundant. Um but don't let red think
17:22that they're all red. Uh they're varied
17:24colors. Macroscopic algae can also
17:27include seaweeds, brown algae um like
17:30sargasm. This is sarasm that is um
17:34containing gas bubbles which allows it
17:36to float. The sarasm sea off the coast
17:39of Florida is a great area for
17:41production of this floating biomass that
17:44is highly productive. And if you looked
17:46at one of the current event readings, uh
17:48they looked at sarasm on the increase in
17:51the Caribbean fueled by nutrients being
17:53delivered from South America and Central
17:56America. So here's that image of
17:58macroscopic algae being cleaned up.
18:01Again, what happens is this is a highly
18:04or hyperutrphic system where you have a
18:07whole bunch of nutrients and you have
18:09sunlight. It just chokes the water.
18:11Oxygen levels go way down where fish and
18:14other organisms that need oxygen, their
18:16lives are hampered and it also decreases
18:19the light penetration to the water
18:21column. So, it acts as sort of a a mat,
18:24a non-transparent mat, which disallows
18:27water from penetrating and fueling a
18:29healthy bios. What about the microscopic
18:32algae? We talked about many of these
18:33before, so the names may ring a bell.
18:36Uh, most of these are plonic and they
18:39produce food for 99% of marine animals.
18:41So, they're the base of the food chain
18:43or food web. Uh, they include golden
18:46algae. These are datoms and we talked
18:48about tests being made of silica and
18:50also carbonate. Um and these include the
18:53cockaliths. We mentioned in last chapter
18:55that sometimes things don't happen as we
18:57expect but this is natural in some
18:59events that some organisms like
19:01dinoflagulates cause red tide and they
19:04have toxins in them that can cause fish
19:05kills and also human illness such as
19:08respiratory illnesses. So we said before
19:11that red tides it's a natural condition
19:13but red tides are being more frequent
19:15now because of human induced changes
19:17like delivery of higher nutrients to
19:19coastal systems. In general they're
19:21called habs harmful algo blooms. Some of
19:24these produce toxins that inadvertently
19:27get consumed by fish and shellfish and
19:29if we eat them that vector that poison
19:31is then transferred to humans causing
19:34paralytic shellfish poisoning.
19:36Interesting sidebar here that uh one of
19:38the toxins is called demoic acid and
19:40it's produced by a datom. It causes
19:43confusion, seizures, death in people and
19:45animals and it was what inspired Alfred
19:48Hitchcock to uh film pen and film the
19:53the birds. And this is if you've ever
19:55seen it in 1961, it's a film about these
19:58demonic birds and they probably inject
20:01ingested this demoic acid from fish um
20:04and started to attack humans. So we
20:06mentioned that utrification is an
20:08artificial enrichment or human-based in
20:11influence of waters by previously scarce
20:14nutrients. It can cause harmful algo
20:16blooms or it can cause just blooms that
20:18limit light penetration and decrease
20:20oxygen. can be from sewage, fertilizer,
20:23and animal waste. As we said before,
20:25cultural utrification is this term
20:27denoting speeding up of natural
20:29utrification through human activities.
20:32What are dead zones? Well, dead zones
20:34are hypoxic, oxygen poor water. So, if
20:37you have oxygen rich water, it's called
20:40oxic. If you have oxygen poor, it's
20:42called hypoxic. If you have no oxygen in
20:45those word waters, it's called anoxic.
20:49So dead zones occur usually at the
20:51mouths of rivers because that's where
20:52the nutrients are delivered most and
20:54these are shallow areas where sunlight
20:56is abundant. Often this happens in
20:58spring runoffs when you have ice uh and
21:01snow melting certainly in temperate
21:03areas like the Mississippi and the
21:05Mississippi Delta. You get a flush of
21:07these nutrients in spring. It suffocates
21:10bottom dwellers. So let's just take a
21:12look at how dead zones are formed. So
21:15here we have a nice healthy system where
21:17the oxygen levels are around eight parts
21:19per million and that's around normal and
21:22that allows or uh oxygen needing
21:24organisms like fish to thrive. So here
21:27comes in water river water with uh
21:30nutrients being laden in that water. It
21:32fuels an algo bloom in number two here.
21:35That alum algo bloom, yes, it does allow
21:39for higher organisms to come and feed,
21:41but it happens so quickly and so
21:44abundantly that it's just too rapid for
21:47any of the primary consumers to keep up
21:50and eat that. So, a lot of it dies and
21:52it settles to the bottom without being
21:55eaten. Once it settles to the bottom,
21:57these are now non-living phytolanter and
22:00they start to lice or open up and they
22:02exude their bodies. That's when bacteria
22:05come in and
22:06bacteria utilize oxygen to degrade that
22:09organic matter and turn it into carbon
22:11dioxide. Once the oxygen is lower,
22:14organisms that cannot transport
22:18themselves out of this area die. If this
22:20dead zone is really large, even fish
22:23which are mobile can't escape this. So
22:25they can't escape the zones of low
22:26oxygen. So unfortunately global marine
22:29dead zones have doubled every decade
22:31since 1960. Now you can see around four
22:35to 500 worldwide. The size and number
22:38expected to increase due to human
22:40impacts as population increases and
22:42delivers even more nutrients to these
22:44coastal systems. And also remember I
22:47said these coastal wetlands and these
22:49organisms that can
22:50utilize nutrients. These are also being
22:54destructed due to building and just loss
22:57of these habitats. So that's not a good
22:59thing. As I said, these were the capture
23:00zones for nutrients and limited those
23:03nutrients from getting further offshore,
23:05fueling these phytolanonic blooms and
23:07dead zones. So here we have an image of
23:10dead zones in the northern hemisphere
23:12and you can see the correlation between
23:14higher populations humans and the
23:17proximity to these dead zones. Clearly
23:19it's a humaninduced effect. The Gulf of
23:22Mexico is one of the quintessential
23:24examples of dead zones. It's the second
23:26largest in the world. The dead zone is
23:29about the size of New Jersey and it's
23:31fueled by runoff of nutrients especially
23:33nitrates and this fuel fuels algo blooms
23:36as we said and as we said algae die
23:39bacteria feed on them at the seafloor
23:41and depletes oxygen. This is largely a
23:43seasonal event with these dead zones
23:46heightening their breadth and their
23:48abundance during spring and summer
23:50conditions. So what are ways that we can
23:53combat these dead zones? Certainly in
23:55the Gulf of Mexico, there's been many
23:57proposals controlling nutrient runoff.
24:00Preserving wetlands, those buffer zones
24:02before those nutrients get further
24:04offshore. Agricultural fields, you can
24:06plant buffer strips. This is called a
24:08riparian zone. And those buffer strips
24:11contain trees and grasses that can
24:12capture those nutrients before they end
24:14up in receiving water bodies water
24:18bodies like streams and rivers before it
24:21gets to the ocean.
24:24And even improving crop rotation can
24:27decrease the use of nutrients. And also
24:30lastly, enforcing existing clean water
24:33regul regulations is really important.
24:35Not only algae can be primary producers,
24:38but we said bacteria can. And these are
24:39photosynthetic bacteria. They're
24:41extremely small. They exert critical
24:43influences on marine ecosystems. It's
24:47estimated that at least half of the
24:48world's oceans are photosynthetic
24:50biomass from this bacteria. So
24:53regionally you see variations in primary
24:55productivity low values from one gram of
24:58carbon per square meter per year to
25:01around 4,000. Why is there an uneven
25:04distribution? Well, it's the uneven
25:06distribution of nutrients and also
25:08changes in the availability of sunlight.
25:11So here we see some values for primary
25:13productivity and they support the idea
25:15that the open ocean is not so productive
25:17due to the lack of availability of
25:19nutrients. closer to shore where you do
25:21have nutrients and the availability of
25:23light. Even though it's seasonal, you
25:25get higher pro primary productivity
25:27values. Also, only 1% of organic matter
25:30is not decomposed in the deep ocean.
25:33There's this thing called the biological
25:34pump and it moves material from the
25:36euphotic zone to the seafloor.
25:39Subtropical gy thermoclines and also
25:42picnoclines prevent the resupply of
25:44nutrients to the surface in the open
25:46ocean. So here we have three distinct
25:48zones and I'll talk about each one of
25:50these and what's happening uh
25:53productivity-wise in each of these. The
25:55polar or high latitude oceans, the
25:57tropical or low latitude oceans, lots of
26:00sunlight, and the temperate or middle
26:02latitude oceans. Think of us in
26:04Philadelphia. So let's start with the
26:05polar ocean productivity scenario.
26:08There's winter darkness, there's summer
26:09sunlight, and when spring arrives in
26:12April or May, you have the sunlight and
26:15you also have a whole bunch of
26:16nutrients. So that fuels a
26:18phytolanktonic bloom as you see here in
26:20green. That's quickly followed by
26:22primary consumers, those things that are
26:25eating it. So zoplankton, phytolankton,
26:28zoplankton, higher in the food chain,
26:30start to chomp down on
26:32those. This is typical of what you see
26:34in polar oceans. The Antarctic
26:37productivity is slightly greater than
26:39the Arctic and that's because the North
26:41Atlantic deep water upwells near
26:43Antarctica. So it delivers a bit more
26:46nutrients. However, productivity is
26:49decreased slightly because of UV
26:51radiation, bad UV radiation because of
26:53the larger ozone hole over the Antarctic
26:56continent. Little sidebar here, but blue
26:59whales depend upon zoplankton. So they
27:02have um a timed migration to the zop
27:05plankton maximum. So they're going down
27:07to Antarctica and they are uh feeding
27:10upon that. Fast growing calves are
27:12evidence for large biomasses of
27:14zoplankton seasonally in these polar
27:17regions. In tropical oceans this
27:19permanent thermocline warm water sitting
27:22up top cold water is a barrier to
27:24vertical mixing. So we have a low rate
27:27of primary productivity here because
27:29there's a lack of nutrients. You would
27:31think tropical areas, lots of sunlight.
27:33Yep, that's indeed true. But the lack of
27:36cold nutrient water being upwelled in
27:38certainly the open ocean, which most of
27:40the tropical oceans are, decreases that
27:42productivity. However, you do have areas
27:45in the tropical oceans that are high
27:47productivity areas. You get them in
27:49equatorial upwelling areas. So, the
27:52trade winds are conver diverging here,
27:55pushing that water onto either side of
27:57the equator, leaving a gap. I said this
28:00is sort of like the parting of the Red
28:01Sea and water is upwell delivering those
28:04cold nutrient-rich waters. So it does
28:07happen certainly along the equatorial
28:09Pacific and Atlantic and the Indian
28:11Ocean. Also as we know in certain areas
28:14you can have coastal upwelling bring
28:16those nutrients up. Yep. That will fuel
28:17it in tropical areas and coral reefs as
28:21you looked at that activity and the
28:22video coral reefs are highly productive.
28:25they are delivering or recharging and
28:28recycling a lot of nutrients. So
28:30nutrient availability in coral areas is
28:32high. Let's switch to the temperate
28:34area. What's happening there?
28:36Productivity is limited by available
28:38sunlight. It's seasonal and availability
28:41of nutrients. So what we have here in a
28:43temperate area like off the coast of New
28:45Jersey is we get a winter low where
28:48algae are
28:50uh have a lot of nutrients but they
28:53don't have the sunlight to fuel that
28:55primary production. In spring we still
28:57have those many nutrients there but now
28:59we have the solar radiation to fuel
29:01photosynthesis. We get a summer low
29:03because they have utilized those
29:05nutrients despite having abundant
29:07sunlight. And then we get a fall bloom
29:10usually where the nutrients have been
29:13recycled and it gives you a fueled
29:15second boom or bloom of phytolankton. So
29:18here we see that we see a spring bloom
29:21of phytolankton and then the zop
29:23plankton come in to graze upon them and
29:25then we have the availability of
29:28recycled nutrients coming in and still
29:30availability of sunlight to fuel a
29:32smaller fall bloom of phytolankton.
29:34Let's talk about energy flow in marine
29:37systems. What's a biotic community? It's
29:39assemblage of organisms in a definable
29:41area. An ecosystem, what is that? It's a
29:44biotic community plus its surrounding or
29:47adjacent environment. Energy flow is
29:50unidirectional based on solar energy
29:52input. So, it starts with solar energy
29:54fueling photosynthesis and that then
29:57transfers the energy unidirectionally up
29:59the food chain. Animals do expend
30:02energy. The residual energy dissipates
30:04in ecosystems as heat and also increased
30:07entropy. Remember that from chemistry
30:08class. Just to give you or remind you
30:10some definitions of the players in
30:12marine ecosystems. We have the
30:14producers. They nourish themselves with
30:16photosynthesis or chemosynthesis. In the
30:19case of hydrothermal vents, they are
30:21autotrophic. They are feeding
30:22themselves. Then we have consumers.
30:25They're heterotrophic. They eat other
30:27organisms. Then we have the other
30:28category called the decomposers. They
30:31break down dead or decomposing or waste.
30:34So here we see radiant energy and
30:36nutrients and phytolanton taking off.
30:38That energy is converted to chemical
30:40energy in the form of sugars through
30:42photosynthesis. Then we have metabolism
30:44in fish. It's a consumer. Then released
30:47that chemical energy for conversion to
30:49mechanical energy like swimming and heat
30:52discharge. Then these decomposers work
30:54to break down the remaining energy after
30:56an organism dies, recycling those
30:58nutrients back into the system. Again, a
31:00little bit of the nomenclature or
31:03categories of consumers in the marine
31:06ecosystem. There are herbivores. They
31:08eat plants. There are carnivores. They
31:10eat other animals. Omnivores eat both
31:12plants and animals. And bacterioores,
31:15which eat bacteria. So what is detritis?
31:18It's dead remains and waste products.
31:22Biogeeochemical chemists or
31:23oceanographers really like this because
31:25they look at all of these organic
31:28molecules that contain carbon and they
31:32look at the cycles. These are called
31:33biogeeochemical cycles. Let's just talk
31:36about some of the feeding strategies of
31:37organisms. They are suspension feeding
31:40or filterfeeding organisms like this
31:42that take in seawater and filter out
31:44usable organic matter. Think of a filter
31:47feeder oyster which opens up when it's
31:50submerged in water and it takes in huge
31:53volumes of water, grabs what it needs it
31:56needs and it's usually dependent upon
31:58size and then excretes the rest as what
32:01we call pseudo feces. We have deposit
32:03feeders which take in detritus and
32:05sediment and extract the usable organic
32:07matter. And we have carnivorous feeding
32:10also which capture and eat other
32:11organisms. Here we have a depiction of
32:14what happens to some of the feeding
32:16strategies in the benthic environment.
32:18What are trophic levels? They're
32:20essentially feeding levels or stages.
32:22The chemical energy transferred from
32:24producers to consumers is followed in
32:26these trophic levels. And about 10% of
32:29the energy transferred to the next
32:31trophic level is done. What is gross
32:34ecological efficiency? It's a ratio of
32:36the energy past the higher trophic level
32:38divid divided by the energy received
32:40from the lower level. And this allows uh
32:44ecologists to look at how much energy is
32:46actually transferred up a trophic level.
32:49So again, a lot of that energy is lost
32:52and it doesn't move on to the next
32:54trophic level. Only about 10% of that
32:57food mass consumed by the herbivores is
32:59available for consumption by the
33:00carnivores. As that food mass initially
33:03produced by the phytolankton passes from
33:05herbivore to carnivore on its way up the
33:08food pyramid here, a large percentage is
33:11excreted as feces used during
33:13respiration or dies uneaten. So marine
33:17ecologists start to depict this energy
33:19transfer using depictions like this.
33:22They look at the incoming energy, the
33:24original energy fueling that primary
33:26production. And then they look at that
33:29transfer of units of energy to higher
33:31organisms. And you can see with that 10%
33:34loss uh sorry, you can see with that 90%
33:37loss and only 10% efficiency that you
33:41get representative energy flows like
33:43this. What are food chains as opposed to
33:46food webs? Well, food chains are linear
33:49descriptions of who's eating who. They
33:52start with a primary producer like
33:54datoms here, phytolanton, and then who's
33:56feeding that. We have here in this case
33:58a copapod, a zop plankton. Uh that's a
34:02herbivore. And then we have one more uh
34:05organism here. We have herring feeding
34:07upon the copapod. So if it's a linear
34:10transfer of uh organic carbon in an
34:14example like this, it's called a food
34:15chain. However, when we bring a whole
34:18bunch of food chains together, we can
34:19construct what we call food webs.
34:21They're a branching network of many
34:23consumers. Consumers are more likely to
34:26survive with alternate food sources. So,
34:28if herring are feeding upon a whole
34:30bunch of variety of species, it's like a
34:33smorgus board. They have the opportunity
34:36if one of those species is knocked out
34:38to shift their dietary influence or
34:41preference to that organism. It makes
34:43that species more robust and survivable.
34:46So I mentioned this in passing a moment
34:48ago, but a pyramid, what's a biomass
34:50pyramid? It's the number of individuals
34:52in total mass and that decreases as
34:55successively you go up this pyramid.
34:58Organisms do increase in size up that
35:00pyramid. So you start with small micro
35:03or macroscopic organisms, phytolanton,
35:06and then you increase in size. However,
35:08at the top of the biomass pyramid, there
35:10are larger organisms, but there are
35:12fewer individuals. So, total biomass is
35:14the least as opposed to at the base of
35:17the pyramid. I'm going to just run
35:18through this fairly quickly because I've
35:20given you two documentaries within this
35:22course that look at the impact of over
35:25fishing. So, marine fisheries,
35:27commercial fishering versus
35:29recreational, and we largely concentrate
35:31on commercial fishering fishing because
35:33of its industrialization and the methods
35:35used. They're wide scale and they're um
35:39massively efficient. So most of this
35:42happens in continental shelves and
35:44that's because these are productive
35:46areas. Nearly 21% of the areas of
35:48upwelling that make up.1% of the ocean's
35:51surface are utilized for these marine
35:53fisheries. So you can see these
35:55different zones of the ocean that are
35:57utilized for commercial fishing. only a
35:59very small part of the ocean open ocean
36:01being not so productive and not fueling
36:04these food webs is utilized. What is
36:07over fishing? It's when fish stocks are
36:09harvested too rapidly, juveniles are not
36:11sexually mature to reproduce. You also
36:14saw in the video this thing called
36:16maximum sustainable yield. It's sort of
36:18like the golden standard. It's the
36:20maximum amount of fish biomass that can
36:23be removed yearly and still allow for
36:26sustainable populations. MSY is very
36:30difficult to calculate. So it's based on
36:32models and also environmental data. But
36:35sometimes scientists don't get it right.
36:37Also, it's difficult to regulate. If you
36:39do set an MSY, you certainly have to
36:42employ that and regulate it to make sure
36:44that people are not over fishing and
36:46going above that. So here's a rather
36:48depressing figure that looks at the
36:51status of marine fisheries. uh we can
36:54see in yellow that the these uh include
36:5652% that are fully exploited and then
37:0018% are overexploited. We have depleted
37:03marine fish at 9%. Uh there are only 1%
37:08of these populations which are
37:10recovering and you can see on the good
37:12side here that we have moderate and
37:14underexploited but that's a very small
37:16fraction of the total um species that
37:20are available for commercial marine
37:22fisheries. Another depressing fact is
37:2480% of 523 world marine fish stocks are
37:29fully exploited, overexploited or
37:31depleted or recovering. Uh that includes
37:35largely large predatory fish. Uh that's
37:38where we've seen the most reduction in
37:41numbers and exploitation. So people like
37:44large fish. So the three images on the
37:46right are come from a cool study from
37:49Scripps. And this was a graduate student
37:50who looked at this and she delved into
37:53historic photos from marine recreational
37:57anglers in Key West to look at their
37:59catches throughout time. And we can
38:01clearly see that back in the day in the
38:0350s and the 60s, the catches were huge.
38:06They were catching large fish like
38:08tuna. As time progressed to current
38:11days, uh the catches became smaller.
38:15the species became a little more
38:17uniform. There wasn't much variety here
38:19until present day when we see the
38:21catches here are only small fish. This
38:24was a nice study that supported this
38:26issue of over fishing. Not from a
38:29commercial standpoint, but from a
38:31recreational point of view, but did
38:33indicate that the stocks were being
38:36depleted. This is what regular folks
38:38were going out and fishing and catching
38:40at the time. and it was decreasing in
38:42size and decreasing in speciation or the
38:45number of different species. So these
38:47large fish, they're called top
38:48predators. They're also called keystone
38:51species. Very important for the health
38:52of marine organisms. They prevent
38:55smaller fish from overpopulating and
38:57they call sick or old herbivore
38:59populations. Modern fishing has
39:01harvested unfortunately 90% of large
39:04predatory fish. You can see that in
39:06coral reef ecosystems that are affected
39:08by the removal of large predators such
39:10as sharks. Removal of fish that eat
39:12algae can cause algo overgrowth in
39:14reefs. This essentially is fishing down
39:17the pyramid where we have the top
39:18predators being removed and we're going
39:21to end up with the bottom of the pyramid
39:24which are phytolankton, zoplankton and
39:26very small fish. So as we saw in our
39:28documentaries, is it the end of fish?
39:31Because of the removal of larger fish
39:32leaves fewer and smaller individuals,
39:36the offspring are less genetically
39:38variable. So at the current rate, it was
39:40surmised by 2048 that we had fished down
39:43these stocks due to pollution, habitat
39:45loss, but mostly over fishing. We can't
39:48forget recreational fishing, too, but
39:50it's not as large as the industrial
39:52commercial fishering. For some species,
39:54though, it's more of a threat than
39:55commercial fishing. And here are some
39:57examples of species that are affected
40:00largely because of recreational fishing.
40:02To circumvent this, catch and release
40:04programs help sustain these populations,
40:07as do moratoriums or complete bans on
40:10fishing of those species. So, one
40:12problem that we saw again from those
40:14documentaries is this estimated annual
40:16catch versus a reported catch. And the
40:19reported catch is always underestimating
40:22the actual catch. This is difficult
40:24because we have no way to monitor what's
40:26being caught in the open or coastal
40:28oceans. So these numbers that lead to
40:30these data sets are somewhat unreliable.
40:34And as we mentioned before, incidental
40:36catch or what's termed by catch is
40:38important too. These are non-commercial
40:40species that are taken incidentally or
40:43accidentally by commercial fishers. by
40:46catch may end up being eight times more
40:48than the intended catch and you may be
40:51catching seabirds, turtles, dolphins,
40:53and sharks. These higher keystone
40:55predators, keystone predators, tuna and
40:57dolphins swim together. They're caught
40:59in purse sane nets. Luckily, the Marine
41:02Mammals Protection Act had an appendum
41:04for dolphins and they limited the um
41:09techniques for catching tuna. So, drift
41:11nets and gil nets were banned in 1989.
41:14This figure is a little complex, but you
41:16can just kick back and look at how
41:19industrial and how technological
41:21commercial fishing has become. I was on
41:24the shores of the Chesig Bay one time
41:26looking out upon the bay and saw a whole
41:29bunch of airplanes. These were spotting
41:31airplanes. So, they're used to spot
41:33groups of menhaden, which are small,
41:35very oily fish that are then coralled
41:39into these nets and captured. that they
41:41were using techniques such as this. You
41:44can also use satellite tracking. You can
41:47find uh not only depth finders, but fish
41:49finders. So, it's becoming very easy to
41:52find fish in both coastal systems and
41:55even the open ocean. We mentioned this
41:57before, but again, a great depiction
41:59here in this figure of ghost fishing.
42:01It's the loss of discarded uh fishing
42:04gear. Uh it can continue to catch fish,
42:07marine mammals, and other organisms. And
42:09as we saw early on in the course that we
42:12might use biodegradable materials or
42:14re-engineer such things as crab traps to
42:18allow organisms to escape after a period
42:21of time so they no longer ghost fish. So
42:24to end on a happier note here, what can
42:26we do? Well, fisheries management be has
42:29become a huge discipline within the
42:32larger discipline of oceanography. And
42:35fisheries management folks try to
42:36regulate fishing. They manage
42:39conflicting stakeholder interests
42:40because you got to keep everybody happy.
42:42Um those who are coming to the table,
42:44not only commercial fishermen but other
42:47stakeholders and think about human
42:49employment and we saw that in
42:50documentary you take away fishing or you
42:53ban or you put a moratorum on a certain
42:55species and people get affected. So you
42:58have to create alternatives for that. We
43:01can create self- sustaining marine o
43:03organisms. We can create self-sustaining
43:05marine ecosystems. We can have
43:08international waters that are very
43:10difficult
43:12police. But the downside is
43:14international waters are very difficult
43:15to police. More enforcement is needed.
43:19So the industry while it has fished down
43:21the top predators in the open and
43:22coastal oceans, they're turning their
43:25attention to more deep water fisheries.
43:27This is a depletion of fish stocks
43:29causing fish industry to fish deeper
43:31down where regulations are fewer. An
43:33example of this is Atlantic cod
43:35depletion caused by replacement with
43:37deep water Greenland
43:39halibit. Also, as we saw, the mechanisms
43:42for deep sea fishing are very
43:44environmentally destructive. Bottom
43:47dragging troll nets do have long-asting
43:49damage to the deep sea ecosystem. What
43:51can we do? Well, we can change consumer
43:53choices in seafood. We can consume and
43:56purchase seafood from healthy, thriving
43:57fisheries, although that's sometimes
43:59really difficult as we saw from those
44:01documentaries. We can choose farm
44:03seafood, but again, farmed seafood has
44:06its environmental impacts as well. And
44:08we can certainly avoid overfished or
44:10depleted seafood. Examples are tuna,
44:12shark, and perhaps even shrimp. So, this
44:15is an interesting depiction of what
44:18happens when you increase the ocean
44:21temperatures through global climate
44:22change. And the catches are predicted to
44:26be fewer, so fewer fish, but also fewer
44:30species. So you see you get knocked out
44:32species here as you get increased
44:35temperatures and this happens both in
44:37the subtropic and temperate ocean areas
44:39and also the tropics. So how can
44:41consumers know what to eat and what not
44:44to eat? The Mterrey Bay Aquarium has
44:46been putting out this document and now
44:48it's web- based for you to look at each
44:51species of consumable fish product and
44:54look at whether it's good or not,
44:56whether there's wild or domestic or
44:59farmraised. um alternatives and it gives
45:01you kind of a scorecard for each. So,
45:03it's worth checking out. If you click on
45:05that URL, uh the Monterey Bay Aquarium
45:08representative walks through the utility
45:11of this. Um here are some seafood
45:14choices, uh best choices, moderate
45:16choices, and bad choices. You can just
45:18look at this. This is often
45:20everchanging. So, we see some species
45:22being pulled from this list and put on
45:24another list or being removed totally.
45:27But you can spend some time on this or
45:29go to the Monterey Bay Aquarium website
45:31for a more interactive experience. But
45:33you can see there are good alternatives
45:36uh best alternatives and these certainly
45:39uh are the avoidable ones based on a
45:41depletion of stocks but also sometimes
45:44the accumulation or hyperaccumulation of
45:46contaminants in large keystone species.
45:50The longer lived species tend to
45:52accumulate these bioaccumulative
45:54chemicals to a longer degree. So there
45:56we have it again, a whirlwind tour of
45:59primary productivity and energy
46:02transfer. Hope you enjoyed it.

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