Biosphere II. Fresh water and marine systems

Learning Goals:

* determine the factors that are used to differentiate freshwater systems (velocity, water clarity, depth, temperature)- lotic vs lentic
* determine the factors that are used to differentiate marine systems (depths, proximity to shoreline, tides, biota)- learn the names and characteristics of the zones
* learn the zones associated with different depths of both freshwater and marine systems
* learn what anthropogenic factors are impacting both freswater and marine systems

Large scale biological organization characterized by physical location as well as a combination of the types of organisms, including both plants and animals.

Freshwater systems- lakes and rivers/streams
Biological zones in freshwater systems are associated with the velocity, depth, temperature, clarity, and chemistry of the water
Freshwater streams and lakes are a key connection between terrestrial and marine ecosystems, processing inputs of chemical elements and energy from terrestrial systems and transport them to the oceans.

Streams and rivers are lotic (flowing water) systems.
The smallest streams at high elevation are first-order streams. These converge to form second-order streams. Large rivers (e.g. Mississippi) are sixth-order streams or greater
Stream/ river zonation- channel, bottom (benthic zone),  and subsurface zone influenced by moving water (hyporheic zone)
Human impacts on lotic (flowing water) ecosystems are extensive, and include:
* use for disposal of sewage and industrial wastes
* runoff of agricultural fertilizers, herbicides, and pesticides
*  increase sediment inputs into streams from deforestation and mining, which can reduce water clarity, alter benthic habitat, acidify the water, and inhibit gill function in many aquatic organisms
 * introduction of non-native species

Lakes and still waters (lentic systems) occur where depressions in the landscape fill with water.
Lakes can be formed by glacial processes, from river oxbows, in volcanic craters, in tectonic basins, or by animal activities, including humans and beavers
The depth and area of a lake has important consequences for the composition of its biological communities.  Deep lakes with a relatively small surface area tend to be nutrient-poor compared with shallow lakes with a relatively large surface area.
Lentic biological assemblages are determined by depth and degree of light penetration, and include:
Pelagic zone: Open water; dominated by plankton (small organisms suspended in the water).  Photosynthetic plankton (phytoplankton) are limited to the upper layers through which light penetrates (photic zone).
Littoral zone - near shore where photic zone reaches the bottom; can support macrophytes (rooted aquatic plants)
Benthic zone, detritus derived from the littoral and pelagic zones serves as an energy source for animals, fungi, and bacteria. This zone may be cold and have low oxygen.

Marine biological zones
Ocean is a massive- 71% of Earth surface area, up to 11 km (6.8 miles) deep relatively open system, lacking natural boundaries.  Biodiversity is high, and not fully described
Biological zones determined by ocean depth, light availability, and the stability of the bottom substrate- categorized by depth and relationship to shorelines

Nearshore marine zones- Subject to tidal and wave action- influences salinity, oxygen, and temperature
Estuaries-
* Occur at junctions of rivers and oceans
* Salinity varies as fresh water flows in from the river and salt water flows in from the sea
* Rivers are a source of terrestrial sediments and nutrients, contributing to the productivity of estuaries
* Many fish species spend juvenile stages there, avoiding predators that cannot tolerate salinity change
* Many shellfish and other invertebrates also live in estuaries
* Estuaries are increasingly threatened by pollution carried in rivers.
* Nutrients from agriculture can create local dead zones (anoxia), and loss of biodiversity

Salt marshes are shallow coastal wetlands dominated by emergent plants such as grasses and rushes.
* Terrestrial nutrients brought in by rivers enhance productivity
* Plants occur in zones that reflect salinity gradients that result from periodic flooding at high tide

Mangrove forests —salt-tolerant, evergreen trees and shrubs (many species); found in shorelines in tropics and sub-tropics
* Mangrove roots trap sediments carried by the water, which build up and modify the shoreline (protection from high winds and tsunamis)
* provide habitat for many animals, including manatees, crab-eating monkeys, fishing cats, and monitor lizards
* threatened by human development, particularly shrimp farms, water pollution, diversion of inland freshwater sources, and cutting

Rocky intertidal zones provide a stable substrate for a diverse collection of algae and animals
* The environment alternates between marine and terrestrial with the rise and fall of the tides
* Bands of organisms associated with their tolerance to drying, salinity, temperature, and interactions with other organisms
* Sessile organisms are fixed in place, and must have mechanisms to tolerate the daily changes—barnacles, mussels, seaweeds.
* Mobile animals such as starfish and sea urchins can move to pools to avoid desiccation

Sandy Shores subject to high wave action and an unstable substrate
* low productivity
* organisms live on the surface (e.g. swimming crabs), or burrow into the sand (e.g. clams, sea worms, and mole crabs)
* Large number of smaller organisms, such as polychaete worms, hydroids, and copepods live on or among the grains of sand

Shallow ocean zones allow light to penetrate to the bottom and support photosynthetic organisms, which provide energy and substrate for a diverse community of organisms
Coral reefs are restricted to warm, shallow water
* Corals are related to jellyfish, form large colonies, and have associated algal partners
* Many corals extract calcium carbonate from seawater to build a skeleton-like structure that over time, forms large reefs
* Coral reefs develop a structurally complex habitat that supports a huge diversity of marine life, up to a million species of organisms, the highest diversity on Earth
* Many economically important fishes rely on coral reefs for habitat, and reef fishes provide a source of food for fishes of the open ocean, such as jacks and tuna
Many human activities threaten coral reefs, including:
* Sediments carried by rivers that can cover and kill the corals.
* Excess nutrients that increase the growth of algae on the surface of the corals, increasing mortality
* Climate change and change in ocean acidity due to higher atmospheric CO₂

Kelp beds or forests are composed of several genera of large brown algae
* have leaf-like fronds, stems, and holdfasts which anchor to solid substrates.
* support a diverse marine community, including sea urchins, lobsters, mussels, abalones, many other seaweeds, and sea otters

Seagrass beds are submerged flowering plants in subtidal marine sediments of mud or fine sand
* plants have roots, stems and flowers like land plants
* larval stages of some organisms, such as mussels, depend on them for habitat.
* nutrients from upstream agricultural activities can increase the algal growth in seagrass beds

The pelagic zone - the open ocean beyond the continental shelves
* The photic zone, which supports the highest densities of organisms, extends to about 200 m depth.
* Below the photic zone, energy is supplied by falling detritus
Organisms in the pelagic zone include:
* Nekton (swimming organisms capable of overcoming ocean currents)—fish, mammals, sea turtles, squid, octopus.
* Phytoplankton- green algae, diatoms, dinoflagellates, and cyanobacteria.
* Zooplankton—protists (e.g., ciliates), crustaceans (e.g., copepods and krill), and jellyfish
All require some mechanism to stay in the photic zone

Life below the photic zone in the ocean is sparse, and dependent on the “rain” of energy from above
environmental conditions include low temperature, high water pressure, low light
organisms include detritus feeders (e.g. crustaceans and copepods) and predators (e.g. squid, fish)
Deep sea hydrothermal vent communities have high abundance of life, despite extremely high pressures, high sulfide and metal concentrations- energy derived from chemosynthesis

examples of questions to address from the reading/ lecture notes:
What are the similarities and differences between salt marshes and mangroves?

What is causing the “dead zones” in some estuaries (e.g. Mississippi River)?

What creates the zonation of communities in the rocky intertidal?

Why is diversity of organisms in coral reefs so high?

What are the challenges of organisms living on or near the bottom of the ocean (pelagic zone)?