12: The Rocky Intertidal- Group Project

Summary

The purpose of the lab is twofold. First, we will become more acquainted with many of the algae and animals that we will learn more about in future lectures and labs. Seeing them in their natural habitat, with their usual neighbors, will allow us to get a much more realistic idea of the local rocky habitat and the community structure of the area. Secondly, we will try to begin using scientific methods to understand the distribution of creatures and how that might be related to the physical environment around them.

Background

The rocky intertidal zone is perhaps the harshest environment in which an organism can be found. The high-energy, wave-swept area is constantly being bombarded with crashing waves. Any organisms in this area must be able to deal with tremendous pressures and mechanical stress. The tidal cycles also expose these marine organisms to anything from concentrated salinities to completely fresh water. Evaporation can bring tide pools up to a very hypersaline level (100 ppt), about 3x as salty as normal seawater, while rain or river run-off can instantly plunge the area into hyposaline, or fresh water. The timing of the tidal cycle can also drastically alter the temperature of the intertidal region. A low tide on a sunny day can elevate the tide pools to well over 38ºC (over 100ºF), while a low tide during a snowstorm can drop the temperature well below freezing. These incredible physical variations make the intertidal region a difficult place for life, but life abounds! The algae, plants, and animals of the intertidal have a wide assortment of physiological and behavioral adaptations, which enable them to thrive in this seemingly inhospitable region. Algae, for example, can settle in microhabitats that are, on a very fine scale, protected and less harsh, or they can tolerate the extreme physical stress of direct wave action. Some algae species can lose as much as 90% of their cellular water to evaporation during a low tide and still survive! Animal adaptations follow the same sorts of examples as the algae: those that use microscale habitats and those that can tolerate tremendous water loss and wave action.

The rocky intertidal is the best-studied marine ecosystem. This is partly due to the fact that many biologists don’t like to get wet! Due to the tidal cycle, for roughly half of a 24-hour period, the intertidal, or littoral zone, is not covered by water. Because of this emersion, the algae, plants, and animals of the littoral region are easily viewed and studied. Another important aspect of the temporary lack of water in this aquatic system is that many of the sampling techniques that were designed for terrestrial ecology can be used in the intertidal zones with ease. However, what we see during the low tide is essentially a habitat in hibernation until the next flooding tide, or immersion. Most of the organisms in the intertidal do not do much during the low tide. They are typically sessile, or benthic forms, and are active only during the high tides, so what we learn about the intertidal during low tide is only half of the story. During the high tide, larger, mobile aquatic predators, such as fish, are common; later, they follow the water out with the receding tide. In contrast, during low tide, other terrestrial and aerial predators are common in the exposed littoral areas. These include many insects, mammals, and birds, all of which are important predators of intertidal algae and animals.

Quadrats

You will place quadrats out in the field, and they will be the source of your data to try to answer your question. You will compare the biodiversity or % cover of your different areas and see what patterns can be discovered. To do this, you will use your data to count the number of creatures inside the quadrat or estimate the % of the quadrat that is covered by species if you are unable to count individuals. Work as a team to count the creatures and get your data.

Each Group will turn in one assignment. Only one person in the group needs to turn it in, but make sure every student's name is clearly listed on the first page.

Activities

• You and your group (maximum of 4 people) will set out to describe both the physical world and the biological components of one of the microhabitats or zones in the intertidal area. Examples of these include: the upper, mid, and lower zones, low energy inshore protected areas, shallow cracks/crevasses, deep tide pools, higher energy outer areas, front of boulders, backs of boulders, etc.
• Each group should clearly decide what the hypothesis that they are testing will be.
• Your group will pick one of these locations, and you will design a rapid sampling strategy utilizing some combination of line transects and/or quadrat sampling techniques. This will not only provide some good information about the habitat in question but will also allow you to take a close look at many of the algae and animals of the intertidal area.
• When designing your sampling protocol, make sure to address the need for replicates. If you are running a line transect with quadrats, how many separate quadrats will you need to make sure you are allowing for the natural variation in the habitat and organisms? How do you also deal with the limited amount of time available to you, both within the lab, but also limited by the tide itself?

Check out this video to get some help graphing your data

Guides of Intertidal Creatures:

• Northern California Tide Pool Creatures- Short picture guide of some of the common animals and algae.
• https://seanet.stanford.edu- A great website made by researchers at Hopkins with lots of good photos and information about the animals and algae.
• Common creatures previously found at Hopkins.

The Write-up:

1. List of all Group Members and which sections of the write-up they worked on.
2. A map of the study location (use lines, arrows, etc., to show where you were in the field).
3. One short paragraph explaining the observations you made that led to your question. What things do you notice about the distribution of algae and animals that led you to your question?
4. What were the questions and hypotheses that your group decided to research?
5. One short paragraph and graph reviewing any abiotic (physical, like temperature or pH) measurements you took in your areas. This can include actual measurements (temperature, pH, salinity data), visual, weather, tide, historical data, etc. This can also include a simple graph of the data.
6. A graph of the organism data (either bar graphs or pie charts, depending on your data) that shows the results of your samples. Use averages for your graphs by taking the averages of the replicates at your locations.
7. What was the answer to your question? Was the data you collected able to answer your group's question?
8. All Group Members: What would be your next question based on what you learned? What challenges did you find? What would you do differently next time? All group members should contribute to this section.

Thumbnail image: “Rocky intertidal surveys” by USFWS Pacific Southwest Region, CC BY 2.0