Ask a Marine Scientist:

answers to Plants and Algae questions!

Index To Questions

Phytoplankton and Earth's Oxygen
Average Concentration of Plankton
Uses for Seaweeds
Kelp Reproduction
Largest Seaweed
Red Algae
Red Tide
Photosynthesis in seaweeds
Algae Structure
Anti-sinking methods
Plant Life in the Oceans
Flora and Fauna
Deep Sea Plants
Seagrass Epiphytes
Seaweed Adaptations
Seaweed Starches
Green Sand
Ocean Plants
Red Algae 2
Sea Sacks

Phytoplankton and Earth's Oxygen - Received from Brendan in Duncan, BC

Q: Hello, My name is Brendan Newbury. I was at your marine station on Nov.9 to Nov.11 with the Duncan Christian school biology trip. We now have to do a big poster on habitat loss. We also have to do a poster on the fact that the ocean creates 90% of earths oxygen. I was wondering how the oxygen from the ocean gets to the land. I was also wondering which plants are the largest producer of oxygen. What are the most common causes of habitat loss in the ocean? Could you please tell me where some of the major habitat losses are and why this is happening?

A: In the ocean, oxygen is produced as a byproduct of photosynthesis by phytoplankton (single celled sea plants) and algae (multicelled sea plants). Although individual alga are much larger than plankton, the latter have a staggeringly larger biomass and so produce the most oxygen. Considering the Earth is more than 70% water and phytoplankton are found throughout the ocean, it's not surprising that they make up 90% of the Earth's oxygen production.

The oxygen produced by phytoplankton is released as a gas. Some of this is absorbed back into the ocean, but most flows into the atmosphere. From there it becomes available for use by all oxygen breathing organisms.

Some common causes of habitat loss in the oceans are oil spills, industrial and residential waste, overzealous ecotourists, and exotic species introduction. Most habitat loss takes place around port cities or any area with high human traffic. Most people don't understand how delicate marine systems are. The damage to or removal of a single species, even if they aren't the most abundant, can devastate an area. A good example is the removal of sea otters from the kelp forests off California. Without otters to prey upon them, sea urchin populations skyrocketed. Since they feed on kelp, the kelp forests were decimated and turned into a wasteland. All the other organisms
that relied on the kelp for food, protection, or habitat either died out or left the area. For other examples, check out the Greenpeace or the World Wildlife Fund.



Average Concentration of Plankton - Received from Barbie in New York

Q: What is an average concentration, in cubic litres, of plankton in the ocean? By average, I mean near-coastal waters not necessarily undergoing a bloom. Is there a "general" or average ratio of phyto- to zooplankton in this hypothetical average ocean water? Could you also give me a range (blue water vs. upwelling/bloom)?

A. As far as I know, there is no "average" value for the concentration of phytoplankton in coastal or oceanic waters. The distribution of plankton in the oceans is very patchy and constantly in flux, two reasons why there probably are no such values. Plankton is highly seasonal, with a large bloom in the Spring followed by a smaller one in the Fall (in the northern hemisphere) . Furthermore, the concentration of plankton is also a function of nutrient concentrations, water clarity and temperature, which further complicate the synthesis of any generalized, static values.

With the advent of satellite imaging techniques, some crude measurements of phytoplankton productivity have been made for various regions of the oceans. Productivity (<100 mg C/m2/day) are encountered in the convergent gyres, whereas higher values (>250 mg C/m2/day)are found in the temperate oceanic areas and the coastal zones. The coastal upwelling regions have values of up to 1000 mg C/m2/day.

Please note that these are approximated values for productivity, which is a measurement of the amount of carbon incorporated into cellular material per unit area of ocean per day. You may also see measurements expressed as (mg Chl/litre/day) which is based on analysis of chlorophyll-a (which is present in all algal cells) concentration in samples of seawater.

Blue water (usually tropical areas) is characterized by having very low concentrations of suspended material and nutrients in the water. The subsequent lack of phytoplankton cells in the water is one of the main reasons why the water is so clear in those areas.

I'm not sure about specific ratios, but I do know that there is considerably less biomass as you go from one trophic level to another. At any given time there is considerably more biomass (i.e. grams of carbon per meter squared) in the phytoplankton than in the zooplankton. Estimates of zooplankton abundance are complicated by a whole series of additional factors. Zooplankton concentrations are dependent directly on phytoplankton abundance but there are behavioural and fluid dynamic considerations as well. Many forms of zooplankton have the ability to swim, and many species have daily cycles of migration up and downwards through the water column. If you consider currents and other features of water dynamics that affect the swimming motions and feeding mechanisms of these animals (remember, they feed on the phytoplankton), you begin to see that the measurements and equations for approximating zooplankton concentrations are rather complex.

I hope that answers your questions. If you have any more, let us know!



Uses for Seaweeds - Received from Justin in Oklahoma

Q: Could you please tell me about how seaweed is used medical or any links to seaweed

A. Seaweed has many different uses in biology and medicine. Agar is a substance that is used in the culture of bacteria and other microorganisms. Petri plates are lined with agar gels and incubated. Hospital laboratories frequency use agar plates to identify types of infectious bacteria. Agar plates are also used for other biological studies of fungi, bacteria and viruses. Agarose is another substance that is extracted from seaweeds and commonly used. Agarose gels are used in chromatography to purify proteins, DNA and other substances.

Here is a website that describes other uses of seaweeds

I hope this helps you out.



Red Algae - Received from Mr. Nurimba in Shanghai, China

Q: What is Rhondophyceae ? also known as Chondrus crispus, c.Dceblatus,
Eucheuma cottonil, E-spinosum. Is it a type of sea weed ? I was told that they are available in Indonesia and the Philippines. It is said that they can be used commercially as a kind of syrup. Pls provide any info that you have. Many thanks.

A: Rhodophyta is the division name for red algae, where Rhodophyceae is the class name for red algae. There are over 10,000 described species of red algae found worldwide. The four species you listed the genus and species names for are different types of red algae. I was able to find information on Chondrus crispus, Eucheuma cottonii and Eucheuma spinosum. However, I was unable to find information on Chondrus dceblatus, perhaps it has recently changed names, red algae have an extremely challenging and always changing classification system.

Eucheuma is a genus of tropical red seaweed that grows on limestone-rich substrates, especially coral reefs. This seaweed is eaten in China, Malaysia and other southeastern Asian countries. It is also harvested for a raw material called carrageenan, which is used as a thickener in many of today's food and dairy industries. Carrageenan is the "syrup" substance you had asked about.

Chondrus, the irish moss, was the traditional red seaweed grown and harvested for its carrageenan content. However, recently the carrageenan industry have focused on more productive carrageenan producing red algae, such as Eucheuma.



Kelp Reproduction - Received from George on Earth

Q: How does kelp reproduce?

A: Kelp reproduction is much different from that of land plants. Kelp undergoes something called alternation of generation. In this example, I'll discuss the bull kelp Nereocystis. The form of kelp that you are more likely to see is the large sporophyte stage. This stage of the plant has a full complement of genetic information (diploid), and produces spores called zoospores with half of the genetic information (haploid), just like animal sperm and eggs. A typical bull kelp can produce up to 3.5 trillion zoospores in one year. These zoospores settle to the bottom and grow into microscopic male and female haploid gametophytes. The male gametophyte produces mobile sperm that seek out the eggs that are kept on the female gametophyte. Once fertilized, the zygote (the baby kelp with a full set of genetic material) grows into the giant sporophyte and the cycle begins again. The sporophyte stage only lives for one year, but considering the number of zoospores they can produce, it's long enough.



Largest Seaweed - Received from Alex in California

Q: What is the largest sea plant?

A: The largest seaweed in the world is a brown algae (kelp) called Macrocystis pyrifera (the giant kelp). The longest recorded length is 54 metres long! M. pyrifera is the type of kelp that makes up the majority of the giant kelp forests off the California coast.




Red Tide - Received from Tracy in Connecticut

Q: I would like some information on paralytic shellfish poisoning. Specifically, how it chemically interacts with human cells to cause it's effects.

A: Paralytic shellfish poisoning (PSP) is one of several toxic results of eating seafood contaminated with certain phytoplankton. Others include diahretic and amnesic shellfish poisoning. PSP is a danger when warm ocean and lots of sunlight in mid to late summer cause
huge blooms of these organisms, so much so that they stain the water red (hence "red tide"). These phytoplankton can accumulate in and then infect the people who eat them. The toxin interferes with human nerves, stopping signals from travelling to and from the brain to control the bodies muscles. The symptoms start with a light tingling in the extremities, which eventually progresses until it paralyzes the diaphragm causing suffocation, or the heart causing instant death. PSP is monitored by local coast guard and fisheries department, who post warnings. Heed them. For more information, check out this Red Tide site.



Bioluminescence - Received from Ann in Seattle

Q. What can you tell me about the phosphorescence that you see while paddling or disturbing salt water at night. I was always told that it was caused by a certain type of plankton.

A. "Phosphorescence" is more correctly known as bioluminescence. This means
living (bio) light (luminescence). This is light that is biologically produced and is caused when a light-emitting molecule, called luciferin, is mixed with an enzyme, luciferase, in the presence of
oxygen. (The light produced in bioluminescence looks very similar to the light produced when phosphorous is exposed to oxygen. Thus the common, but incorrect, term phosphorescence).
Bioluminescence is actually quite common and almost all taxonomic groups of animals, and many plants, have some members that bioluminesce. Planktonic dinoflagellates and bacteria are some of the most abundant creators of this biological light and are what is usually responsible for the green glow in a boat's wake or when waves break on a beach. Other animals, including fish and squid, create light by keeping small cultures of luminescent bacteria in specialized organs
distributed over their body. Since the bacteria bioluminesce continuously, their hosts have developed mechanical means, such as flaps of skin that resemble window shades, to control luminescence.

So why do these individuals create light? Reasons for bioluminescence vary depending on the organism, but they generally fall into one of four categories: escaping predators, obtaining prey,
attraction, and advertising. Some organisms use the "quick flash" technique to temporarily blind a predator"a familiar sensation as when faced with an inexperienced photographer let loose with a
flash. Many bacteria actually luminesce because they want to be eaten. They advertise to potential prey hoping to find a comfy home inside a fish's gut.

Answered by Adrienne Mason



Photosynthesis in seaweeds - Received from Jax in England

Q: How do seaweeds photosynthesize underwater?

A: Seaweeds have a variety of adaptations for carrying out photosynthesis under the water. Terrestrial plants evolved from lineages that originated in the ocean, so much of the fundamental photosynthetic machinery originated among the alga. Unlike terrestrial plants, alga do not have true vascular tissues. Since algae live underwater, they are surrounded by water and nutrients. The algae absorb water and nutrients directly from seawater. By maintaining a high surface area to volume ratio (seaweeds are generally flattened) the individual cells that make up the alga can absorb the water and nutrients that they need directly.

The main materials required for photosynthesis are carbon dioxide, water and sunlight. Seaweeds absorb carbon dioxide that is dissolved in seawater. CO2 is sometimes limiting in areas where there is low water velocity or for species that are periodically exposed to air during low tides. Water is not a limiting factor because these organisms are immersed in it. Light is perhaps the predominant limiting factor because with increasing depth, there is an exponential decrease in light availability. Among seaweeds there are a variety of morphological and physiological adaptations for dealing with the problem of light availability.

Many seaweeds maintain their photosynthetic blades near the surface where light intensity is maximal. The bull kelp, Nereocystis leutkeana, has an inflated bulb that floats at the surface. The meristem is located at the base of the blades (fronds) which attach to this bulb. With the chief photosynthetic organs at the surface, light intensity and photosynthetic potential are maximized. There are several other species that employ floats to lift the blades to the surface. Macrocystis integrifolia and Egregia menziesii are two species that also have floats.

With increasing depth, more and more of the visible spectrum of light is filtered out by the water, particularly in the red and blue regions of the spectrum. As a result, many species of algae are limited to shallow subtidal waters. Most green algae, Division Chlorophyta, are restricted to the zone from a 5m depth to the surface. Below this depth, their chlorophyll (which absorb mainly blue and red light) and accessory pigments (carotenoids) are insufficient for capturing the energetic wavelengths of light that are available. The brown algae, Division Phaeophyta, and red algae, Division Rhodophyta, can be found in deeper waters. These seaweeds have additional accessory pigments that allow the plants to capture a wider range of light energy thus enabling these organisms to persist in areas with lower light availability. These accessory pigments are known as phycobilins and absorb energy in the green portion of the visible spectrum. The Rhodophytes can be found deepest due to the presence of phycoerythrin, an accessory pigment that absorbs very efficiently in the green portion of the spectrum. In deep waters, green light is most abundant, and therefore, only the seaweeds with the right combination of pigments for tapping this wavelength can survive. Many of the deeper rhodophytes appear to be black in colour when they are observed during dives. Their dark colour can be attributed to the high concentrations of phycoerythrin in the cells of these seaweeds.



Plant Life in the Oceans (received from skydot(?!) in New Hampshire)

Q: I have been wondering if plant life is part of marine biology

Yes, it certainly is, although most of the plant life in the oceans is very different from most of the plants that you see growing on land.

If you go to the seashore, you'll probably see lots of seaweeds. These are marine algae, and are very important in the food webs of shallow coastal marine communities. The red, green and brown algae produce food by using photosynthesis just like land plants do, except they do not have any specialised tissues for transporting this food (ie, they have no "sap" or transport tissues). Just as animals on land (consumers) depend on plants on land (producers), so do marine animals depend on algae.

A common green algae is Ulva, or sea lettuce. Kelps are in the group known as brown algae, and are especially important in coastal marine areas on the West coast of North America.

Many marine biologists study marine algae, because it is of such great importance to the marine ecosystem.



Flora and Fauna - Received from Samantha Aguilar in Dilley, Texas

Q: What are fauna and flora? Can you help us?

A. Flora and fauna are basically just fancy names for plants and animals. Specifically, flora is the word biologists use to describe the plant life of a given region or habitat; and fauna is all the animal life in a given region or habitat.



Deep Sea Plants - Received from Caitlin in the United States

Q: Does the DEEP SEA zone have any plants?

A: The deep sea is too deep for light to penetrate that plants need to make their food. Plants get their energy from sunlight and through a process called photosynthesis, turn this sunlight into food for the plant. Since there is not any usable light available for plants to photosynthesize in the deep sea plants cannot live there.

There are bacteria that can live as deep as 1500m to 3200m near deep sea hot vents. These bacteria use a compound called hydrogen sulfide, instead of sunlight, to make their food. The bacteria get the hydrogen sulfide from deep sea hot water geysers that release this compound. In fact, because of these tiny bacteria an entire community of animals can survive and thrive in these hot vent areas!



Seagrass Epiphytes - Received from Ahmad Faizal in K.Terengganu, Malaysia

Q: What is the importance of epiphytes on seagrass bed?

A: Epiphytes of seagrass are algae and other seaweeds and these epiphytes use the seagrass merely for physical support. Epiphytes can be an important food source for animals in and around seagrass beds. Animals can also use the seagrass and epiphytes to hide in and therefore protect them from predation or to stalk prey. However, epiphytes are not necessarily beneficial to the seagrass. Epiphytes growing on the seagrass cover the photosynthetic area of the seagrass blade and therefore reduce the photosynthetic capabilities of the seagrass. In fact, a problem in seagrass beds, in mainly tropical systems, is fouling. Fouling occurs when there is a rapid growth of epiphytes, usually diatoms, that completely cover the entire seagrass blade. This coverage prevents the seagrass from receiving sunlight and thereby inhibits photosynthesis and the seagrass eventually dies. The rapid growth of epiphytes, such as diatoms is usually the result of high nutrients. These high nutrients levels are usually caused by human activities in the area, such as fertilizers from agriculture.


Seaweed Adaptations - Received from Jennifer somewhere out there

Q: In the sunlit layer of the ocean, how do plants adapt? I only need 3 ways.

A: Algae (aquatic plants) have many adaptations to living in the photic zone (sunlit layer) of the ocean. One way is by having different types of light catching pigments. For example, green algae have cholorphyll a which absorbs mainly red and orange light. Whereas red algae have accessory pigments, called phycoerthryn and phycocyanin that absorb blue and violet light. Another way is by having larger blade surface area, and therefore increasing the light absorbing area of the algae. In the photic zone there is a lot of competition for space between different algal species. Some algal species have adapted different ways to push out other species. For example, a brown algae called the Feather Boa (Egregia) actually whips the other algal species out of the space surrounding it.


Seaweed Starches - Received from Emily Alderson in Sidney, BC, Canada

Q: my name is Emily and I'm in grade 8.I am working on a science fair project for the Uvic regional science fair and I have a few questions. my project is on the nutritional values of common seaweeds. Could you please tell me if there is usually starch in seaweed. I did a test [using iodine] but nothing happened. If so, what types of starch, and also what,m if any, types of sugars. How could I find out if the water at the beach where I got the seaweed is polluted? It is too expensive to take it to a water analysis lab. i also dried the seaweeds in my experiment to see what percentage of them were made up of water. Would there be any other substances in the seaweed which could have dried up affecting my results? Thank you very much for reading my questions.

A: Wow it sounds like you have quite the project! First the reaction to your iodine test will depend on what kind of seaweed you tested. There are three types of seaweed red, green and brown. All three types of seaweed have storage polysaccharides (sugars) in them, and it is the glucose polymers (a type of polysaccharide, sugar) that are most similar to the starch of land plants. The kinds of glucose polymers change depending on the group of algae you are looking at. The similarity to the starches of land plants is greatest in the green algae, less in the red, and least in the brown. In the green algae (Chlorophyta), there are polysaccharides that are stored in granular form that react to with iodine to give a blue-black colour. Because of this reaction it appears that the polysaccharides in the green algae are similar in structure to the starches found in land plants. Red algae (Rhodophyta) have floridean starch which is packaged in smaller granules and iodine stains it a red colour. In brown seaweed (Phaeophyta), in particular kelp species classified as Laminarans, have a glucan that is the least similar to land plant starches. To see the reactions of these algal species to iodine it is very important to know the species of seaweed you are testing and whether it is a brown, green or red seaweed. You will probably want to do your iodine tests on fresh seaweed and looking at how the iodine stains the cells, by looking at them through a microscope.

Good luck on your project, it sounds great!


Green Sand - received from D. Besack in PA.

Q: While in N.Carolina in the beginning of August we were on the beach at night and when we walked the sand started to glow green where the pressure from our feet where ever we stepped-also when we splashed in the water the same thing happened. Could you please figure this out? We thought it was so neat!! Thanks for all your help.

A: What you saw in the wet sand and in the water is called bioluminescence.
Bioluminescence is the phenomenon of organisms producing light with an energy-releasing chemical reaction.

There are millions of microscopic algae in the surface waters of the ocean. Some of these algae (mostly one group called the Dinoflagellates) have the ability to emit light for a very brief amount of time (0.1 to 0.5 seconds). They emit light when agitated, which is why you saw them where you stepped and where you splashed around. This is a mechanism that helps protect them from predators - because it reveals the predator to its predator.

There are many organisms that bioluminesce for different reasons, including deep sea fish, jellyfish, and fireflies.
Check out this site for more info about bioluminescence, dinoflagellates, and other bioluminescing organisms:
Monterey Bay Aquarium Bioluminescence research page


Ocean Plants - received from Stephanie in Texas

Q: What kinds of plants are in the oceans? Like what are the plants names?

A: There many different kinds of plants in the ocean. Most of them are seaweeds (marine algae). There are 3 majoy types of seaweeds:
The reds: Rhodophyta (e.g. Chondrocanthus [Turkish Towel] and Porphyra [Nori])
The browns: Phaeophyta (e.g. Macrocystis [Giant kelp] and Nereocystis [Bull Kelp])
The greens: Chlorophyta (e.g. Ulva [sea lettuce])
But, seaweeds aren't the only types of plants in the ocean. There are some vascular plants as well. (Seaweeds do not have a vascular system ("sap") the way land plants do). Intertidal plants like surfgrass (Phyllospadix) and eelgrass (Zostera) are also important ocean plants.
Plants in the ocean are not just the primary producers that are the foundation of the food chain but they also build important habitat for invertebrates and juvenile fish.


Red Algae - received from Lucie in Vancouver.

Q: What are the predators/prey of red algae?

A: Red algae is autotrophic, which means that it turns inorganic nutrients into organic nutrients through the process of photosynthesis. For this reason, i wouldn't really consider red algae to be a predator of anything, and therefore doesn't have "prey". There are however, a number of organisms that prey on red aglae. Some of these include fish, abalone, gumboot chitons, and decorator crabs.


Sea Sacks

Q: What is a sea sack?

A: A sea sack is a type of red algae (Phylum Rhodophyta) called Halosaccion glandiforme. It also goes by the other common names of Dead man's fingers, sea sacs, and salt sacs. They are found from the Aleutian Islands, Alaska to Point Conception, Calfornia. Sea sacs prefer exposed, rocky habitats, in the mid intertidal zone. They are yellowish in colour, and filled with water. You can probably find a picture in any intertidal field guide (can be purchased at a local bookstore). You can find a pictures of sea sacks by "Google-ing" images of 'sea stacks'.

Find out how sea stacks are formed at this site!


Algae structure - received on from Kevin in New York

Q: How does a stipe, blade, and pneumatocyst pertain to marine algae?

A: To make an analogy to land plants: a stipe is like a stem, and a blade is like a leaf. The blade of the algae will be responsible for photosynthetic process, and the stipe provides support and height, in order for the algae to reach near the lighter areas of surface water. For a diagram of the position of the stipe and blade on a common west coast kelp go to our seaweed page. A pneumatocyst (or bulb) refers to a float used to keep the blades of the algae near the surface.


Anti-sinking methods - received on from Kelly in Bristol

Q: Could you tell me some methods that zooplankton use to stop themselves from sinking?

A: For many phytoplankton and zooplankton, it is vital to remain at the surface in order to survive. Phytoplankton need to stay in the photic zone in order to photosynthesize, and the zooplankton need to stay near the phytoplankton in order to feed!

Four mechanisms enable plankton to float:
1. they are less dense than seawater
2. their shape increases drag, thus reducing settling velocity
3. they have some control over vertical distribution using their own locomotion
4. water turbulence to stay suspended

Most plankton are more dense than seawater, but flotation structures, such as long, elaborate spines to increase surface area, and gas-filled sacs. Some plankton can even collect low density ions and expel high density ions. Some zooplankton also have some control over their own locomotion such as jelly bell-pulses and crustacean swimming appendages.


see also: OceanLink's Seaweeds pages

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