Chapter 4: Living and Non-living Connections in the Ocean

Ecology shows us how the living world is connected to the non-living world.

image from: Wikipedia Commons

A kelp forest community, image from: Wikipedia Commons

By one author’s definition, ecology is the study of the distribution and abundance of species and the factors that affect them. The factors that affect species’ abundance and distribution can be divided into two categories – abiotic (non-living) and biotic (living.)

Alternatively, Marinebiology.org describes marine ecology as, “the study of populations, and interactions among organisms and the surrounding environment, including their abiotic factors (non-living physical and chemical factors that affect the ability of organisms to survive and reproduce) and biotic factors (living things or the materials that directly or indirectly affect an organism in its environment).”

Either way, this chapter is looking at the things that affect the patterns of where and how living things grow in the ocean.

Organisms and Their Environment

Organisms are individual living things. Despite their tremendous diversity, all organisms have the same basic needs: energy and matter. These must be obtained from the environment. Therefore, organisms are not closed systems. They depend on, and are influenced by, the environment that surrounds them. The environment includes two types of factors that affect organisms abilities to obtain energy and matter: abiotic and biotic.

Abiotic factors are the nonliving aspects of the environment. They include factors such as sunlight, temperature, and pressure.

Biotic factors are the living aspects of the environment. They consist of other organisms, including members of the same and different species.

The Flow of Energy

Image from Our Ocean Planet

A food web, documenting the flow of energy from one trophic level to the next, image from: Our Ocean Planet

Life on Earth is possible because of the flow of energy coming from the sun.  The first law of thermodynamics states that “energy can not be created or destroyed, only transformed from one form to another”.  Energy enters ecosystems in the form of sunlight and is transformed into edible, chemical compounds by producers (plants and algae.) Other organisms, that are not photosynthetic, will obtain energy by eating other organisms – we call them consumers.

Producers

Producers are organisms that produce food for themselves and other organisms. They use energy and simple inorganic molecules to make organic compounds. The stability of producers is vital to ecosystems because all organisms need organic molecules. Producers are also called autotrophs. There are two basic types of autotrophs: photoautotrophs and chemoautotrophs. Photoautotrophs use energy from sunlight to make food by photosynthesis. They include plants, algae, and certain bacteria. Chemoautotrophs use energy from chemical compounds to make food by chemosynthesis. They include some bacteria and also archaea. Archaea are microorganisms that resemble bacteria. 

Consumers

Consumers are organisms that depend on other organisms for food. They take in organic molecules by eating other living things. They include all animals and fungi, and are sometimes referred to as heterotrophs.

Heterotrophs can be classified by what they eat: herbivores or carnivores. Herbivores are grazers, and in the ocean that means they eat phytoplankton. There is a necessary link between producers and other consumers. Marine examples include zooplankton, some baleen whales, and small fish. Carnivores consume other animals. Marine examples include tuna, salmon, many sharks, and killer whales.

Energy is transferred from producers to other organisms in a series of steps. These steps are known as trophic levels. The greatest “biomass”, or mass of organisms, occurs at the lowest levels. Phytoplankton are far more abundant, and collectively more massive, than fish or marine mammals. For each level you go up, the amount of energy present in the level diminishes. When a Right Whale eats one ton of phytoplankton, it does not gain a ton in new mass. Most of the energy is lost to the system, in the form of movement and heat. Typically, only about 10% of the energy is passed into the next level. This loss of energy explains why there are rarely more than four trophic levels in a food chain or web. Sometimes, there may be a fifth trophic level, but usually there’s not enough energy left to support any additional levels.

Factors that Limit Growth

Some factors are density dependent; the factor becomes more significant as a local population of organisms increases. These density dependent factors can limit the growth of a single organism, or of a whole population of organisms. We call these limiting factors. Imagine an automobile factory that loses a shipment of steering wheels. They have enough parts to make thousands of cars but only five steering wheels – how many cars do they make? For any organism or population of organisms there will be one or more “limiting factor” that limits growth. For photosynthetic organisms (like kelp or phytoplankton) are often limited by nutrients such as nitrogen or phosphorus.  Organisms that eat other organisms are often limited by food availability or the abundance of predators that may eat them.

The Water Cycle

(text for the water cycle is taken from CK12 Flexbooks)

Whereas energy flows through an ecosystem, water and elements like carbon and nitrogen are constantly being recycled through the environment. This recycling process involves both the living organisms (biotic components) and nonliving things (abiotic factors) in the ecosystem. Through biogeochemical cycles, water and other chemical elements are constantly being passed through living organisms to non-living matter and back again, over and over. Three important biogeochemical cycles are the water cyclecarbon cycle , and nitrogen cycle .

The water cycle does not have a real starting or ending point. It is an endless recycling process that involves the oceans, lakes and other bodies of water, as well as the land surfaces and the atmosphere. The steps in the water cycle are as follows, starting with the water in the oceans:

  1. Water evaporates from the surface of the oceans, leaving behind salts. As the water vapor rises, it collects and is stored in clouds.
  2. As water cools in the cloudscondensation occurs. Condensation is when gases turn back into liquids.
  3. Condensation creates precipitationPrecipitation includes rain, snow, hail, and sleet. The precipitation allows the water to return again to the Earth’s surface.
  4. When precipitation lands on land, the water can sink into the ground to become part of our underground water reserves, also known as groundwater . Much of this underground water is stored in aquifers , which are porous layers of rock that can hold water.

Run-off

Most precipitation that occurs over land, however, is not absorbed by the soil and is called runoff. This runoff collects in streams and rivers, and it eventually flows back into the ocean.  As water flows back into the ocean, it can bring with it large amounts of nutrients, such as nitrogen and phosphorus; as well as pollution.

Transpiration

Water also moves through the living organisms in an ecosystem. Plants soak up large amounts of water through their roots. The water then moves up the plant and evaporates from the leaves in a process called transpiration. The process of transpiration, like evaporation, returns water back into the atmosphere.

The water cycle.

The Carbon Cycle

(text for the carbon cycle came from CK12 flexbooks)

Carbon is one of the most common elements found in living organisms. Chains of carbon molecules form the backbones of many molecules, such as carbohydratesproteins, and lipids. Carbon is constantly cycling between living organisms the atmosphere (Figure right). The cycling of carbon occurs through the carbon cycle .

Living organisms cannot make their own carbon, so how is carbon incorporated into living organisms? In the atmosphere, carbon is in the form of carbon dioxide gas (CO2). Recall that plants, algae, and other producers capture the carbon dioxide and convert it to glucose (C6H12O6) through the process of photosynthesis. Then, as animals eat plants or other animals, they gain the carbon from those organisms.

The chemical equation of photosynthesis is 6CO + 6H2O → C6H12O+ 6O.

How does this carbon in living things end up back in the atmosphere? Remember that we breathe out carbon dioxide. This carbon dioxide is generated through the process of cellular respiration, which has the reverse chemical reaction as photosynthesis. That means when our cells burn food (glucose) for energy, carbon dioxide is released. We, like all animals, exhale this carbon dioxide and return it back to the atmosphere. Also, carbon is released to the atmosphere as an organism dies and decomposes.

Cellular respiration and photosynthesis can be described as a cycle, as one uses carbon dioxide (and water) and makes oxygen (and glucose), while the other uses oxygen (and glucose) and makes carbon dioxide (and water).

The carbon cycle

The carbon cycle. The cycling of carbon dioxide in photosynthesis and cellular respiration are main components of the carbon cycle. Carbon is also returned to the atmosphere by the burning of fossil fuels and decomposition of organic matter.

Formation of Fossil Fuels

Over time, dead plants, plankton and animals that do not completely decompose before they are buried can be buried, compressed and form fossil fuels such as coal, oil, and natural gas.When humans burn fossil fuels, we have an impact on the carbon cycle ( Figure below ). This carbon is not recycled until it is used by humans. The burning of fossil fuels releases more carbon dioxide into the atmosphere than is used by photosynthesis. So, there is more carbon dioxide entering the atmosphere than is coming out of it. Carbon dioxide is known as a greenhouse gas , since it lets in light energy but does not let heat escape, much like the panes of a greenhouse. The increase of greenhouse gasses in the atmosphere is contributing to a global rise in Earth’s temperature, known as global warming .

The Nitrogen Cycle

(text for the Nitrogen Cycle came from Ck12flexbooks)

Like water and carbon, nitrogen is also repeatedly recycled through the biosphere. This process is called the nitrogen cycle . Nitrogen is one of the most common elements in living organisms. It is important for creating both proteins and nucleic acids, like DNA. The air that we breathe is mostly nitrogen gas (N ), but, unfortunately, animals and plants cannot use the nitrogen when it is a gas. In fact, plants often die from a lack of nitrogen even through they are surrounded by plenty of nitrogen gas. Nitrogen gas (N ) has two nitrogen atoms connected by a very strong triple bond. Most plants and animals cannot use the nitrogen in nitrogen gas because they cannot break that triple bond.

In order for plants to make use of nitrogen, it must be transformed into molecules they can use. This can be accomplished several different ways (Figure below ).

  • Lightning: Nitrogen gas can be transformed into nitrate (NO – ) that plants can use when lightning strikes.
  • Nitrogen Fixation: Special nitrogen-fixing bacteria can also transform nitrogen gas into useful forms. These bacteria live in the roots of plants in the pea family. They turn the nitrogen gas into ammonium (NH ). In water environments, bacteria in the water can also fix nitrogen gas into ammonium. Ammonium can be used by aquatic plants as a source of nitrogen.
  • Release: Nitrogen also is released to the environment by decaying organisms or decaying wastes. These wastes release nitrogen in the form of ammonium.

Ammonium in the soil can be turned into nitrate by a two-step process completed by two different types of bacteria. In the form of nitrate, nitrogen can be used by plants through the process of assimilation . It is then passed along to animals when they eat the plants.

Sending Nitrogen back to the Atmosphere

Turning nitrate back into nitrogen gas, the process of denitrification , happens through the work of denitrifying bacteria. These bacteria often live in swamps and lakes. They take in the nitrate and release it back to the atmosphere as nitrogen gas.

Just like the carbon cycle, human activities impact the nitrogen cycle. These human activities include the burning of fossil fuels, which release nitrogen oxide gasses into the atmosphere. Releasing nitrogen oxide back into the atmosphere leads to problems like acid rain .

The nitrogen cycle includes assimilation, when plants absorb nitrogen; nitrogen-fixing bacteria that make the nitrogen available to plants in the form of nitrates; decomposers that transform nitrogen in dead organisms into ammonium; nitrifying bacteria that turn ammonium into nitrates; and denitrifying bacteria that turn nitrates into gaseous nitrogen.

Biotic Factors in Marine Ecosystems

The most direct way that an organism is biologically controlled by the distribution and abundance of other living organisms is to eat it (food) or be eaten by it (predation.)  A tuna eating a sardine uses the chemical energy from the sardine to move, reproduce, and grow more tuna.  This should be obvious, but there are some equally important but perhaps more subtle ways in which species affect each other.

Keystone Species

Image from Arkive.org

Some species have a disproportionately strong influence on the other living things around them; they are known as keystone species. Keystone species may play an especially important role in its community by creating habitat for other species or by consuming key herbivores that have the potential to graze key habitat down to nothing. Major changes in the numbers of a keystone species affect the populations of many other species in the community. For example, some sea star species are keystone species in coral reef communities. The sea stars prey on mussels and sea urchins, which have no other natural predators. If sea stars were removed from a coral reef community, mussel and sea urchin populations would have explosive growth. This, in turn, would drive out most other species. Sea otters in kelp forest ecosystems are another example.  Sea otters eat sea urchins and other grazers of kelp.  (Click on the link for a video.)  Fast growing kelp provides nurseries for fish and habitat for thousands of species in a kelp forest.  Without sea otters, urchins quickly graze kelp beds into nothing creating areas know as “urchin barrens” which are populated by lots of urchins but almost nothing else.

Competition

Competition is a relationship between organisms that strive for the same resources in the same place. The resources might be food, water, or space. There are two different types of competition:

  • Intraspecific competition occurs between members of the same species. For example, two male birds of the same species might compete for mates in the same area. This type of competition is a basic factor in natural selection. It leads to the evolution of better adaptations within a species.
  • Interspecific competition occurs between members of different species. For example, predators of different species might compete for the same prey. Interspecific competition can lead to the extinction of one of the species competing. The species that is less well adapted may get fewer of the resources that both species need. As a result, members of that species are less likely to survive, and the species may go extinct. Interspecific competition will more often lead to greater specialization. Specialization occurs when competing species evolve different adaptations. For example, they may evolve adaptations that allow them to use different food sources.

The NicheNiche_L

In the Begon et al. have defined the niche as “the limits, for all important environmental features, within which individuals of a species can survive, grow and reproduce.” However, very few species have their ecosystem to themselves. They must share the ecosystem with other competing species all trying to consume the same resources. Competition is the normal state of nature.

The competitive exclusion principle tells us that in a stable ecosystem, no two species are in direct competition with each other. So what happens when two or more species whose fundamental niches overlap occupy the same ecosystem? They work out an arrangement which we call “resource partitioning.” This means that they jostle around until each species has reduced its niche size until there is no competition. The result is that, in a real ecosystem, a population is almost always utilizing only a part of the niche (the realized niche) they could have used if they were the only species in the ecosystem — so they are using only part of their fundamental niche. An example of this can be seen below in the work of Joseph Connell with two species of barnacle.

Symbiotic Relationships

Not all relationships in an ecosystem are competitive. Symbiosis is a close relationship between two species in which at least one species benefits. For the other species, the relationship may be positive, negative, or neutral. There are three basic types of symbiosis: mutualism, commensalism, and parasitism.

  • Mutualism is a symbiotic relationship in which both species benefit. An example of mutualism involves goby fish and shrimp. The nearly blind shrimp and the fish spend most of their time together. The shrimp maintains a burrow in the sand in which both the fish and shrimp live. When a predator comes near, the fish touches the shrimp with its tail as a warning. Then, both fish and shrimp retreat to the burrow until the predator is gone. From their relationship, the shrimp gets a warning of approaching danger. The fish gets a safe retreat and a place to lay its eggs.
  • Commensalism is a symbiotic relationship in which one species benefits while the other species is not affected. One species typically uses the other for a purpose other than food. For example, hermit crabs use the shells of dead snails for homes. At no cost to the snail, the hermit crab has obtained a free house.
  • Parasitism is a symbiotic relationship in which one species (the parasite) benefits, while the other species (the host) is harmed. Most marine species are hosts to one or more parasites. Some parasites live on the surface of their host. Others live inside their host. They may enter the host through a break in the skin or in food or water. For example, tapeworms are parasites of many fish species, including wild Alaskan salmon. If you like salmon sushi, be sure its been well frozen before you eat it.

Questions to Research:

  1. Click on the link for “Life in the intertidal zone.”  Follow the directions and record answers for each of the four questions.
  2. Based on the work you did in question 1, consider the life of the common mussel. Identify the following as an abiotic or biotic influence affecting life in the intertidal zone (a. heavy wave action from a storm, b. predation by a common whelk,  c. exposure to the hot sun during a low tide, d. the availability of plankton for them to eat.)
  3. Life is controlled by limiting nutrients. Read the blog post and describe what nutrient limits life for most of the ocean?  Despite this limitation, too many of these nutrients can cause problems.  Describe what I mean.
  4. Read the section from the reading above labeled “The Niche.” Examine the picture (and the caption that goes with it) in that section. Describe what you think would happen if he had instead removed the chthamalus barnacles?  What does this say about Balanus barnacles?
  5. Click on the link “Marine Food Webs” .  The four dominant primary producers in the ocean are diatoms, dinoflagellates, Coccolithophores, and photosynthetic bacteria.  How are these organisms different from the plants that are primary producers on land?
  6. Photosynthesizing phytoplankton are the base of most marine food webs, but how is it that food web exist in the deepest and coldest parts of the ocean far below where the sun can reach.  Read this short article and tell me what you learn.
  7. Consider the call of the Toadfish and the Black Drum.  Are these examples of “intra” or “inter” specific competition?  Please explain your answer (you will need to read my text above.)
  8. Read the section above on symbiosis or the attached link on “Marine Symbiosis,”  then provide one example for each type of symbiotic relationship.
  9. In the carbon cycle, how does the burning of fossil fuels contribute to global warming?  How does it also contribute to ocean acidification (think back a few weeks)?
  10. What is a keystone species? Look up the sea otter and describe how they fit the definition as a keystone species.