The Ecology Exercise : Read this & turn in questions

I am not the developer of this exercise, for the citation of the authors of this lab please contact me.  I will be happy to credit them.


Student Introduction to the Problem

The Observations

Visits to a study area seven yars apart revealed the following very obvious changes.

.                                                                               first visit                                 second visit

% cover Enteromorpha spp                                               < 5%                                      80%

% cover Ulva spp.                                                               < 5%                                      40%

number of limpets (Patella spp.)/m2                              180                                         12

number of barnacles (Balanus sp.)/m2           1600                                       1000


Your assignment will be to investigate this change and to uncover as much information as possible about its cause(s). The following background information should prove helpful in thinking about the problem:

General Background Information

We are primarily concerned about the intertidal (= littoral) ecosystem. This is the area that is alternately exposed to air and covered by seawater, as the tidal level fluctuates.

The intertidal area is commonly divided into 3 zones: the high zone (which is exposed to air for long periods of time), the mid zone (which is exposed to air and is underwater about equal amounts of time), and the low zone (which is exposed to air only on quite low tides for a short period of time).

Some other terminology may be helpful:

Subtidal Zone-that area always underwater, never exposed to air

Benthic-attached to, or sitting on, the bottom

Plankton-plants and animals that are free-floating in the water column

Phytoplankton-plant component of the plankton

Zooplankton-animal component of the plankton

Biological Background


Algae are divided into 5 main groups; two of these (the blue-green algae and the diatoms) are microscopic and are important members of the phytoplankton, although many species are benthic as well. Large algae (seaweeds) belong to the remaining 3 groups: the green algae, the

brown algae, and the red algae. The groups are divided on the basis of the photosynthetic pigments present in each, the kind of storage products produced, and other biochemical and structural differences. Algae are zoned within the subtidal-intertidal area; that is, different species are characteristically found at different tidal levels. This zonation is related to the physiological

tolerances of various species as well as biological interaction between algal species (competition) and between algae and marine invertebrates (competition for space, grazing).

There are two types of life cycles common among algae. Many species are annuals; they live less than one year. Many annuals die off in the autumn, and new plants are generated from spores that germinate in the spring. Growth is fast but restricted to

one season, generally spring or summer.

Other seaweeds are perennials (they live more than one year). Growth is generally slower but continuous throughout the year. Some perennials may partially die back in autumn and wither, but basal portions regenerate in the spring.

A few of the more common algal species follow:

Green Algae

1. Enteromorpha spp.-This is a fast growing annual, very common on intertidal rocks at all tidal levels; it frequently grows on other plants as well. It is shaped like soft, papery tubes, 5-15 cm long and 3-6 mm in diameter. Reproduction (and settlement) can take place at any time of year.

2. Ulva sp. (sea lettuce)-This is very similar to Enteromorpha but is a flat sheet instead of a tube.

Brown Algae

intertidal zone. Gametes are released in late summer; plants are perennial.

1. Pelvetia sp.-This is a robust, leathery plant, 15-20 cm long, found in the high

2. Fucus spp.-Very similar to Pelvetia; found in the high-mid intertidal zone.

3. Laminaria sp.-Another large, leathery perennial that reproduces in summer; found only in the low intertidal (and subtidal) zones.

Red Algae

1. Porphyra spp.-A papery sheet, found primarily at high to mid tidal levels; this is an annual and is often found growing on other algae as well as directly on the rock surface. Some species are common only in winter and others only in the spring.

2. Chondrus sp.-A short, tough species that forms a carpet at low tidal levels. It is perennial and reproduces in late summer.


Most intertidal animals are invertebrates (animals without backbones). There are many phyla that may be encountered on intertidal rocks; a few of the more common animals are discussed below:

Barnacles (Arthropod crustaceans)

These are stationary once they settle on a rock surface. They are small (< 1.3 cm in diameter) and covered by calcareous plates. These can be opened when the animal

is underwater and feathery appendages filter plankton (primarily diatoms) from the water. Barnacles reproduce in early spring, and produce planktonic larvae. These float in the water column for a while but soon select a spot on the rock surface and attach. Their main predators are drills and starfish. Barnacles rarely live more than 1-2 years. Two species are common in this Bay: Chthamalus sp., which occupies the high

intertidal zone, and Balanus sp., which occupies the mid zone.

Limpets (Molluscan gastropods)

Limpets are intertidal snails having a flat shield-like shell. They are capable of moving up to a meter/day but rarely do so; generally, they return to the same place on the rock (“home”). Their shape and their strong muscular foot (which enables them to cling tightly to the rocks) allow limpets to withstand violent wave action. Limpets are herbivorous, scraping the rock surface for diatoms and newly-germinated sporelings (very small plants); they rarely eat macroscopic (large) algae. Limpets spawn (shed gametes) primarily in winter. The larvae are planktonic for a short time (1-2 weeks) and then metamorphose into a crawling stage that settles on the rock. They rarely live more than 1-2 years, although a few large individuals may be 10-15 years old. Their main predators are starfish and birds (especially oystercatchers).

There are several species of the genus Patella that range from high to low intertidal zones; we will not differentiate between these species.

Periwinkles (Molluscan gastropods)

Periwinkles, or littorines, are small, very abundant snails found primarily at high to mid intertidal levels; there are several species in this group, but these will not be differentiated here. Littorines are highly mobile and do not home. They are herbivorous, primarily on microscopic diatoms and young sporelings, but may graze larger algae as well (although they inflict little damage on large plants). They reproduce in early spring; some species have planktonic larvae (which spend only a short time in the plankton before settling out), and others have non-planktonic (benthic) larvae. Periwinkles generally live 1-2 years; their main predators are starfish, drills, and birds (especially rock pipits and gulls).

Top-Shells (Molluscan gastropods)

Two genera of top-shells (snails) are common in this Bay: Gibbula spp. (which is found in the high-mid zone) and Monodonta sp. (at mid-low levels). These are mobile, non-homing snails. They are herbivorous, feeding primarily on brown algae (Fucus, Laminaria); since a large part of their diet consists of drift algae (macroscopic algae that has been ripped off the rock surface by wave action and is beginning to decay)

they also qualify as scavengers. They reproduce in the spring; larvae spend some time (1-2 months) in the plankton. Top-shells may live to be quite old (1 5-20 years is not uncommon). Their main predators are birds (oystercatchers, rock pipits, and gulls) and starfish.

Drills (Molluscan gastropods)

Drills (Thais sp.) are snails that inhabit mid to low tidal levels. They do not “home” but rarely move more than one m/day. They tend to return to the same spot year-afteryear to reproduce. They lay benthic egg capsules in late winter and early spring. The young hatch from these in several months (there is no planktonic larva); average life span is 4-5 years. Drills are carnivorous and feed on barnacles, mussels (clams) and, occasionally, top-shells; they bore through the shell with a highly modified boring organ and suck out the soft body contents inside (hence the common name “drills”). In turn, they are eaten by birds (gulls and oystercatchers


I will have 112 pages of data about the study area during the relevant time period.  Some of the data are simple measurements.  Other data are the results of experiments.  To get the simple measurement data you just ask and if I have it it’s yours.  To get experimental results you describe to me a protocol you would perform to run that experiment then I give you the data.


Answer the following questions and turn them in at the BEGINNING of class.

Pre lab assignment for Ecology lab


Use the internet as a source


view this site ----

1.  What is a dependent, an independent variable? What is a control?


2.  Draw a food web for our study site including all the species in the information sheet.


3. Draw a time line of a year. Fill in in with what happens in the lives of the species in the information sheet at each part of the year.