The primary photosynthesizers of the marine environments are not true "plants", but instead are "algae". These algal organisms are classified in the Kingdom Protista, an entirely different kingdom from the plants. The Kingdom Protista is a loose collection of organisms that really defy a general description. Just with the algae alone, there are unicellular, colonial, and multicellular algae. There are algae of many different sizes and shapes and evolutionary origins. There are microscopic algae (phytoplankton) and macroscopic algae (seaweeds). All algae trap sunlight energy and use it to construct carbohydrates (glucose) from the raw materials carbon dioxide and water. This is the process of photosynthesis. Algae are the base of most aquatic food chains as they provide the nutrients that are ultimately consumed by all other organisms in their ecosystem.
If we consider all the photosynthetic organisms on Earth, there are 3 major groups: plants, cyanobacteria, and algae. Plants are defined as multicellular, photosynthetic eukaryotes that protect their developing embryos with parental tissue. Cyanobacteria are the photosynthetic bacteria (also misleadingly known as the blue-green algae). The best definition I can come up with for the algae is: eukaryotic photosynthesizers that are not plants.
The algae which you will be able to see and identify on your field trip (without the aid of a microscope) are the macroalgae or seaweeds. Although seaweeds look similar to plants, they do lack true roots, stems and leaves. Instead they have holdfasts (instead of roots), a stipe (instead of a stem), and blades (instead of leaves). The technical difference between the plant structures and algal structures is the vascular tissue (water and food conducting tissue) in the plant structures. In addition, most seaweeds have a structure (a float or bulb) that keeps the blades near the surface of the water. The float and a flexible stipe are critical especially in an environment where the tides are constantly changing water levels. Cells of seaweeds can absorb nutrients directly from their watery environment. On most seaweeds sporangia (spore producing structures) are visible during the reproductive times of the year. Sporangia look like "bumps" or "spikes" on the surface of the blades.
There are three major phyla of macroalgae (all of course in the Kingdom Protista):
Phylum Chlorophyta : The chlorophytes are also called "green algae". This phylum contains unicellular algae ( e.g. Chlamydomonas spp.), colonial algae ( e.g. Volvox spp.), and multicellular algae ( e.g. Ulva spp.). Based on similarities in metabolism and genetic sequences, the green algae are the most likely ancestors of the Kingdom Plantae. Examples of green algae that you may encounter in the Rocky Intertidal Zone include: Tube Weed or Sea Hair, Enteromorpha spp., Sea Lettuce, Ulva spp., and Green Rope, Acrosiphonia spp.
Phylum Phaeophyta : The phaeophytes are also called "brown algae". This phylum contains all multicellular organisms with most in either a filamentous or leaf-like body form. The brown algae are so named because of their brownish appearance created by the combination of yellowish pigments (carotenoids) and greenish pigments (chlorophylls). Common brown algae in the Rocky Intertidal Zone include: Rockweed, Fucus gardneri , Little Rockweed, Pelvetiopsis limitata , Sugar Wrack or Oar Weed, Laminaria spp., Acidic Seaweed, Desmarestia ligulata , Winged Kelp, Alaria marginata , Ribbed Kelp, Costaria costata , Bull Kelp or Bullwhip Kelp, Nereocystis luetkeana .
Phylum Rhodophyta : The "red algae" are also all multicellular. The color, red, of these species is also due to the presence of a pigment, in this case phycoerythrin, found in the cells. This pigment allows red algae to absorb light even when they live at great depths (as deep as 260 meters). Often the appearance of the red algae is directly related to the depths at which the organism lives as they have the ability to alter their concentrations of pigments to best suit their habitat. Therefore, "red algae" may actually appear green when they live closer to the surface, but look quite red when found at deeper depths. Examples of red algae typically found in the Rocky Intertidal Zone include: Pacific Laver or Red Laver or Purple Laver or Nori, Porphyra perforata , Turkish Towel, Chondrocanthus exasperatus , Turkish Washcloth or Papillate Seaweed, Mastocarpus papillatus , and Iridescent or Rainbow Seaweed, Mazzaella splendens .
Parts of the information from this page were researched in the following:
