Introduction

Photosynthesis is probably the single most important living process on Earth. Without photosynthesis, life would be limited to single-celled bacteria. It is through this process that all the life forms we are familiar with get their food and energy. Chemically, photosynthesis is the conversion of light energy into chemical energy. The raw materials are carbon dioxide and water, the energy source is sunlight, and the end-products include glucose (a sugar) and oxygen.

6 CO₂ + 6 H₂O + Light Energy → C₆H₁₂O₆ + 6 O₂

While you’re probably most familiar with this process as it relates to land plants, it is the same process as we see in the Algae. Algae come in multiple forms, from large, familiar multicellular organisms like kelp to microscopic, single-celled organisms, which are the most important photosynthetic group in the ocean. The production of energy-rich organic compounds (like sugar) from carbon dioxide and water, through the process of photosynthesis, is called primary production. Almost all life on Earth is directly or indirectly reliant on primary production for its food. The organisms responsible for primary production are known as primary producers or autotrophs (a self-feeder), and form the base of the food chain.

Activity 1. Photosynthetic Rate

When studying photosynthesis, often the thing we are most interested in is the rate or speed at which it is happening. This is a measure of how much sugar, energy, or oxygen is being produced over time. We could do this by keeping track of any one of the items in the equation above. Knowing any one, we could calculate how fast the process is happening. We typically do this by measuring the amount of oxygen being produced over time or the amount of CO₂ that is being used. This gives us a rate of photosynthesis. Observe the Pasco oxygen and CO₂ demonstrations, which will explore the amount of dissolved oxygen in two different samples of algae-filled water at different light intensities. What would you predict would happen to the photosynthetic rate with no light, low light, and high light? Do the data support your hypothesis?

Activity 2. Understanding Net Production

In biology, especially in studies involving ecosystems or photosynthesis, we use the following formula:

Gross Production – Respiration = Net Production

Let’s break this down:

• Gross Production (GP): This is the total amount of energy or biomass produced by an organism (like a plant) through photosynthesis. It includes all the energy captured from sunlight and converted into chemical energy.
• Respiration (R): Organisms use some of this energy for their own life processes (like growth, repair, and reproduction). This energy use is called respiration, and it reduces the amount of energy available for growth or for the next level in a food chain.
• Net Production (NP): This is the energy or biomass left over after respiration. It represents the amount of energy that can be passed on to consumers (like herbivores) or stored in the organism for growth.

Why It Matters:

When measuring productivity in ecosystems (like a pond or plant experiment), calculating net production helps us understand how much energy is actually available to support other organisms. It's an important part of the energy flow in ecological studies.

Activity 3. Taxonomy and the Groups of Algae

Taxonomy (from Ancient Greek: taxis, "arrangement," and -nomia, "method") is the science of defining groups of biological organisms on the basis of shared characteristics and giving names to those groups. A related discipline is Systematics, which studies identification and taxonomy with regard to the evolution of groups. There are several different taxonomic systems, but by far the most common is one that was developed in 1735 by Swedish botanist Carl Linnaeus. To do this, it uses taxonomic ranks, including, among others (in order from most inclusive to most specific): Domain, Kingdom, Phylum, Class, Order, Family, Genus, and Species. The historical way to form these taxonomic groups was by looking for similarities and differences in the morphology (appearance) of the organisms. Things that are more similar are more closely grouped, and those that are very different are more distantly grouped.

In the algae, there are three main Divisions (same as Phylum above), the green (Chlorophyta), brown (Phaeophyta), and red (Rhodophyta). These three groups are quite different from each other, evolutionarily speaking, and do not have a recent common ancestor, but the groups can look very similar to each other!

1. Working within a group, you will try to form a taxonomic grouping for the various algae. Start by trying to figure out which are the greens, browns, and reds.

2. Once you have them all separated by Division, try to find other, smaller groupings all the way down to the species. What characteristics do you use to group and separate?

3. Using the provided books, keys, and lists, you will try to identify as many of the common species of marine algae as time allows. Write their common and scientific name in pencil on a small piece of paper and put them on top of the specimens once you have a good guess.

4. This exercise is about careful observation and stopping to look at this amazing and often overlooked group of organisms. To aid in your observations and study, you will be making presses of some of the species as well.

Activity 4. Algae Pressing

Algae pressing is very similar to the techniques used to press flowers, and is used widely by scientists as a means of preserving algal specimens and observing their features. Using the printed instructions and directions from the instructor, you’ll make an artistic, permanent press of representative algae from the lab. Work slowly and carefully, and you’ll be surprised how informative (and cool) they will be.

How to Press Algae

1. Obtain a seaweed specimen, remove debris and epiphytes, and blot mostly dry.

2. Get a dry piece of herbarium paper, write your name and any other text in pencil on the dry paper. Writing notes about the collection date, location, etc., is also a good idea.

3. Get your paper wet and carefully lay out your specimen, spreading out the parts carefully so that they are visible and flat. Choose a specimen that is large enough to easily identify, but thin enough that when compressed into a two-dimensional shape, it does not become a shapeless blob. Thus, “bush-like” algae should be thinned (analogous to pruning) to one branch layer thick before pressing. With delicate, finely branched seaweeds, first float the sample in a little water over your paper and then gently lift it out of the water, or gently tilt the paper so the water runs off and the sample stays behind. This technique helps to prevent the branches from clumping together. You can also separate branches with a paintbrush or toothpick.

4. Bring your work to the instructor to be put into the press.

5. Remove the pressed specimen from the press and carefully peel off the waxed paper. If the specimen comes loose from the paper you pressed it onto, you can secure it with a small drop of glue.

Some Common Algae from Monterey Bay

Chlorophyta

Cladophora sp.- Green pin-cushion alga

Ulva (old Enteromorpha) intestinalis

Ulva spp.- Sea lettuce

Codium fragile- Dead man’s fingers

Acrosiphonia sp.- green ponytail

Bryopsis sp.- green hair

Phaeophyta

Cystoseira sp.- small floats

Egregia menziesii- feather boa kelp

Fucus gardneri- rockweed, with midrib

Laminaria spp.

Macrocystis pyrifera- giant kelp

Nereocystis luetkeana- bull kelp

Pelvetiopsis limitata- rockweed w/out midrib

Postelsia palmaeformis-sea palm

Silvetia compressa- rockweed- long and slender (30 cm)

Pteryogophora californica- Stalked kelp

Rhodophyta

Porphyra spp.-nori

Bossiella spp.- geniculate coralline-thick

Corallina spp.- geniculate coralline-fine

Endocladia muricata- Scouring pad algae

Chondracanthus spp.- Turkish towel

Gracilariopsis sp.- Red sand Spaghetti

Lithothamnion sp.- nongeniculate coralline, crustose

Mastocarpus spp.- bumpy/frilly red

Mazzaella splendens- Iridescent dark-purple

Mazzaella spp.- red dichotomous with frills

Prionitis sp.- dark brown with bladelets

Botryocladia sp.- Sea grapes

Microcladia sp.- Fine branching pattern

Gelidium sp.- Highly branched, sometimes thick, used to make agar.

Fauchea sp.- very flat, iridescent.