4.3 Flashcards
Marine ecosystems
Marine ecosystems include oceans, estuaries, saltmarshes, mangroves and coral reefs. They cover more than 70% of Earth’s surface. They are made of saline water
Oceanic Zones (know 2-3)
Epipelagic zone (depth of 0 to 200m): into which light penetrates allowing primary produces to grow. It is the most productive zone, with little photosynthesis occurring outside this area.
Mesopelagic zone (depth of 200m to 1,000m): where there is insufficient light penetration to allow for plant growth. This zone contains a diverse range of organisms.
Bathypelagic zone (depth of 1,000m to 4,000m): is also known as the dark zone due to the absence of light apart from that produced by any bioluminescent organisms present.
Abyssalpelagic zone (depth of 4,000m to 6,000m): is dark and the water temperature is just above freezing. Few organisms can withstand the high pressure in this zone.
Hadalpelagic zone (depth of more than 6,000m): usually includes trenches and canyons. The water again is very cold and life here needs to be adapted to extremely high pressure.
Marine Trophic Levels
Primary producers form the base of the food web and include phytoplankton and seaweeds.
Primary consumers include the zooplankton, small floating animals in the sea that graze on the phytoplankton.
Secondary consumers are small predators such as some fish (e.g. sardines, menhaden and herring)
Tertiary consumers include top predators such as large fish (eg sharks, tuna and mackerel), marine mammals (e.g dolphins, seals and walruses) and birds (e.g penguins and albatross).
What is thermal stratification
Sunlight heats the upper layer of water and surface movements create a layer with a fairly consistent temperature.
Water movement below the surface mixed layer is reduced due to the calm weather and the sun continues to warm the water. Sunlight penetration declines with depth resulting in a temperature variation from the top to the bottom of the thermocline.
Aquatic ecosystems - freshwater zones (know 2)
Lake zones
Lake ecosystems include the following zones:
Littoral zone: the shallow area of the lake that goes up to the shore area. This is where large freshwater plants called macrophytes occur.
Limnetic zone: covers the open water in the lake where there is enough light for phytoplankton to photosynthesize.
Euphotic zone: includes both the littoral and limnetic zone where there is sufficient light for photosynthesis to occur.
Profundal zone: the deep water where there is no light penetration.
Benthic zone: the lake bottom, where organisms live within the sediments or on the surface of the lake sediments.
Name Freshwater trophic levels
Primary producers: phytoplankton and macrophytes. Phytoplankton includes freshwater varieties of diatoms, dinoflagellates, and cyanobacteria.
Primary consumers: zooplankton (e.g. waterfleas, copepods and rotifers) and water snails.
Secondary consumers: fish (e.g. perch, smelt, minnows), birds (e.g. ducks) and frogs.
Tertiary consumers: large fish (e.g. trout, charr and piranhas), large birds (e.g. kingfisher) and mammals (e.g. otters and humans).
Food products from aquatic ecosystems
Green algae: such as sea lettuce (Ulva sp.).
Brown algae: such as Japanese kelp (Laminaria japonica) and Bladdewrack (Fucus vesiculosus).
Red algae: Laver, known as Nori in Japan (Porphyra spp.) and Irish moss (Chrondus crispuscrispus).
Human consumption has changed in what way over the years?
Global production of fish has more than doubled since 1960 and continues to rise. Consider the significance of the following two annual growth rates?
Annual growth rate of global fish supply is 3.2%.
Annual growth rates of global population of 1.6%.
Factors contributing to the increase in demand include:
Growth in human population.
Promotion of health benefits of consuming fish
Growth of a more affluent global population which can afford to import fish. Instead of availability of fish being confined to local and seasonal produce, the importation of fish has allowed for a diverse range of fish being available throughout the year in many places around the world.
Use of nets
Trawler nets used to catch demersal fish by dragging a funnel shaped net along the seabed.
Drift nets hung vertically in the water are used to catch pelagic schools of fish such as sardines, swordfish and tuna.
Aquaculture
“Aquaculture is the farming of aquatic organisms: fish, molluscs, crustaceans, aquatic plants, crocodiles, alligators, turtles, and amphibians. Farming implies some form of intervention in the rearing process to enhance production, such as regular stocking, feeding, protection from predators, etc…”.
Open vs semi-closed aquaculture systems
Open based systems are the most popular and involve farming the organisms within a natural aquatic ecosystem such as the sea or a lake.
Semi-closed systems involve the abstraction and use of water from the sea or lakes within tanks or ponds situated on land. This allows for greater control over environmental conditions such as temperature and water velocity. If required the water can be filtered to remove any predators or pathogens. Semi-closed systems tend to be more expensive than open-based systems.
Environmental impacts of aquaculture
Increase in organic sediments
Over time, the organic material is broken down initially by aerobic bacteria to form carbon dioxide, water, nitrates, phosphates and sulphates.
Increase in available nutrients
Soluble nutrients released from the uneaten fish food and fish faeces increase the overall dissolved levels of nutrients in the water.
Spread of disease
Within intensely stocked cages, disease can easily spread from one fish to another and even potentially to other fish outside the cages.
Attracted predators
Predators attracted by the farmed fish can become entangled and caught within the nets of the fish cages.
Use of medicines and hormones
Medicines such as antibiotics and hormones used to treat the farmed fish can contaminate
the water and affect other aquatic life.
Managing environmental impacts
Action to reduce some of the environmental impacts of fish farming includes:
Reducing the waste from uneaten feed by careful selection of appropriate feed and not overfeeding.
More effective application of any medicines to reduce losses to the environment.
Regular removal of any dead fish from the cages.
Moving the cages at regular intervals to prevent build-up of organic sediments and give the area time to recover.
Reduce nutrient levels in the water.
Reduce phytoplankton levels in the water and disperse any blooms.
Reduce build-up of waste by dispersing it.
Aerate the water to prevent anoxic conditions.
