Student Worksheet
Threats to Marine Ecosystems

Atlantic Puffins (Fratercula arctica).

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The term biodiversity comes from the words biological and diversity and means "the variety of life on Earth". It includes all living things, including plants, animals and micro-organisms, and their unique characteristics.

Species diversity is the most common type of biodiversity talked about, but there are several different levels of biodiversity:

  • ecosystem diversity refers to the variety of habitats, living communities and ecological processes
  • species diversity refers to the variety of species in a given area
  • genetic diversity refers to the diversity of the genetic characteristics within a species.

Oceans are marine ecosystems that contain water with more than 0.5 parts per thousand of dissolved salt. Ocean, or marine, biodiversity includes all living things (plants, animals and micro-organisms) found in the ocean.

Tealia anemone (Tealia sp.).

Tealia anemone (Tealia sp.).

Why is biodiversity in our oceans important? There are many ways to look at this. Biodiversity represents living things, and all life is precious. Life in the oceans has evolved some incredible adaptations to survive in that environment, and provides us with endless fascination. Marine biodiversity also provides us with numerous recreational opportunities such as swimming, snorkelling, scuba diving, fishing, boating and others.

But not only that; marine biodiversity provides us with a major part of the world's food supply. At least half of the oxygen we breathe comes from the photosynthesis of marine plants. And through this process they also remove large amounts of carbon dioxide from the atmosphere. Ocean biodiversity also helps regulate our climate through the cycling of gases, and provides great potential for the discovery of medicines and raw materials.

The ocean depends—like all ecosystems—on the combined contributions and interactions of the individual organisms that live within it. The loss of species can change how it functions. And, the greater the amount of biodiversity in an ecosystem, the better it is able to adapt when the environmental changes.

Activity 1: Dissolved Oxygen Levels in the Ocean

Dissolved oxygen (DO) is the amount of oxygen dissolved in one litre of water. It is usually measured in milligrams or millilitres. The same way that land animals need oxygen to breathe, so do the animals and micro-organisms that live in the ocean. Because the oxygen is dissolved in the water, animals need specialized structures to extract it. Fish, for example, have gills for this purpose.

Oxygen is supplied to the ocean from two sources: the air above the surface, and photosynthesis by tiny plants in the water called phytoplankton. The amount of oxygen that is dissolved in ocean water is closely tied to temperature. Colder water can hold more dissolved oxygen than warmer water, if other factors remain the same. Other factors that affect oxygen levels include salinity, pressure, tides, currents and the amount of photosynthesis that is going on.

Although all organisms in the ocean consume oxygen, it is microbes in the water column that can have the biggest impact on oxygen levels because they break down organic materials falling from the surface. Sometimes, when there is a great deal of photosynthesis occurring at the surface, and microbial activity in the water below is high, the amount of oxygen can fall to very low levels.

Wolf Eel (Anarhichas lupus).

Wolf Eel (Anarhichas lupus).

When dissolved oxygen levels fall below 30% or .3, some species begin to be affected. Levels of .2 or lower are generally referred to as hypoxic, meaning "depleted in oxygen", and affect the survival of many species.

Saanich Inlet, a marine area off the coast of British Columbia, is naturally depleted in oxygen in deep areas because of decomposition by microbes. Underwater sensors in the inlet measure water chemistry and send the data, including measurements of dissolved oxygen, to scientists on shore.

1.1 Go to Google Maps and enter 48.651317N latitude and 123.486347W longitude. Where is this location and what is the name of the body of water?

1.2 Watch this video about the Victoria Experimental Network Under the Sea (VENUS):
Video: The VENUS Undersea Laboratory (1 min. 42 sec.)

Why are scientists studying data on oxygen levels in Saanich Inlet?

1.3 Go to the VENUS web site to compare data on temperature and dissolved oxygen levels in Saanich Inlet. And then follow these steps:
a) From the VENUS home page, click on the link called Data Plots.
b) Select the column "Data from Saanich Inlet – VIP Study Area".
c) Click on the box that says "Last Year" and "By Water Property".
d) Go to the bottom of the page, underneath all the data plots, and make sure the data for the temperature and dissolved oxygen plots has been checked and is valid.

1.4 Print the two data plots and record the depth at which the monitoring station is located.

1.4.1 At what time of year is the level of dissolved oxygen lowest?

1.4.2 At what time of year is the level of dissolved oxygen the highest?

1.4.3 At what time of year is the temperature of the water lowest?

1.4.4 At what time of year is the temperature of the water the highest?

1.4.5 Does the water ever become hypoxic?

1.4.6 Does there appear to be any similarity in the temperature and dissolved-oxygen-level trends over the course of the year?

1.4.7 Does the water temperature follow the same general trend as the air temperature in summer and winter?

1.4.8 What might this suggest with respect to the effects of global warming on oxygen levels in the ocean?

Activity 2: Dead Zones

Watch the video about VENUS research on oxygen levels in the ocean
and then answer the questions below.
Video: Research on Dead Zones and the VENUS Lab (2 min. 31 sec.)

2.1 How is research done in Saanich Inlet useful for other places in Canada and the world?

Human activities can also contribute to dead zones. Go to Wikipedia and search for "dead zone (ecology)", and then answer the following questions:

2.2 What are three human activities that can contribute to dead zones?

2.3 What are some actions that can be taken to protect ocean life from these impacts?

Activity 3: Human Impacts on Ocean Health

3.1 Report

Killer whales (Orcinus orca).

Killer whales (Orcinus orca).

Your task is to research an impact on marine biodiversity and complete a written report based on a minimum of three sources of information. The report must be two to three pages and include an overview of the problem you are researching, specific examples and data, a summary of the data, recommendations of what must be done to counteract the problem and a list of references.

3.2 Presentation

Prepare a presentation based on your report, using slides, photos, video, audio, posters or some other teacher approved media.

Additional Resources