Aquatic Biomes Notes

Aquatic Biomes

Learning Outcomes

• Describe the effects of abiotic factors on the composition of plant and animal communities in aquatic biomes.

• Summarize the characteristics of lentic and lotic freshwater biomes.

• Compare and contrast the characteristics of the ocean zones.

Introduction

The presentation provides an overview of aquatic biomes, spanning across various geographical locations including North America, Europe, Africa, South America, Antarctica, Asia, and Australia, highlighting the presence of Arctic, Atlantic, Pacific, Southern, and Indian Oceans.

Factors Affecting Aquatic Ecosystems

• Water Depth

• Temperature

• Current

• Nutrient Availability

• pH, Salinity, and Dissolved Oxygen

1. Water Depth

• Photic Zone: The sunlit region near the surface where photosynthesis can occur. Photosynthetic organisms reside here.

• Aphotic Zone: Depths greater than 200m where light cannot penetrate. Larger animals like sharks and squids inhabit this zone.

• Benthic Zone: The bottom zone, such as the ocean floor or lake bottom. Organisms living in this zone are called benthos.

Depth Water Zones

• Intertidal Zone

• Neritic Zone

• Oceanic Zone

• Pelagic Realm

  • Photic

  • Aphotic

• Abyssal Zone

• Benthic Realm

Ocean Zones Based on Depth and Light Level

The ocean is divided into three zones based on depth and light level: Photic Zone (0-200m), Mid-Water Zone (200-1000m), and Aphotic Zone (1000+m). The maximum ocean depth is the Mariana Trench at 10,911m.

• Euphotic Zone: The sunlit zone where algae and phytoplankton are abundant. Most marine life is concentrated here due to the plentiful food source.

• Disphotic Zone: A barely-lit ocean layer (twilight zone) receiving faint, filtered sunlight, insufficient for photosynthesis. Food is not abundant in this zone.

• Aphotic Zone: The deepest layer, also known as the midnight zone, characterized by low temperature and high pressure. Bioluminescent organisms thrive in this zone.

2. Temperature and Currents

• Temperature: Varies with depth in aquatic habitats. The deepest parts of lakes and oceans are often colder than surface waters.

• Currents: Can significantly affect water temperature by carrying water that is warmer or cooler than typical for a given latitude, depth, or distance from shore.

3. Nutrient Availability

Organisms require substances like oxygen, nitrogen, potassium, and phosphorus to survive. The type and availability of these dissolved substances vary within and between bodies of water, significantly influencing the types of organisms that can thrive.

4. pH, Salinity, and Dissolved Oxygen

• pH: Lower pH levels are detrimental to corals, reducing their ability to form structures.

• Salinity: Freshwater intrusion in clam beds can stress organisms, leading to disease and mortality.

• Dissolved Oxygen (DO): Low DO levels, influenced by eutrophication and low flushing rates, can cause massive fish kills.

Ocean Acidification

$CO_2$: Atmospheric carbon dioxide. Increase leads to more acidic conditions. Could lead to an irreversible decline in coral reefs by 2040.

$H^+$: Hydrogen ions

$CO_3^{2-}$: Carbonate ions

Eutrophication

An enrichment of an ecosystem with chemical nutrients, typically compounds containing nitrogen, phosphorus, or both. It can result in excessive plant growth and decay, leading to oxygen depletion.

Intertidal Flooding/Evaporation

Highlights the impact of salinity changes on organisms, illustrating the processes of osmosis, water loss through the skin, and active ion transport. It also touches on oxidative stress and distress, as well as physiological and pathophysiological responses to environmental changes.

Aquatic Ecosystems

• Freshwater

• Marine

Freshwater Ecosystems

Ice caps glaciers bogs Ponds Lakes Rivers Streams Groundwater (aquifer and underground streams).

Marine Ecosystems

Coral reefs, Open ocean, Estuaries,Seagrass meadows, Mangrove Swamps

Types of Freshwater Habitat

• Lentic Habitat: Calm freshwater habitat or standing water.

• Lotic Habitat: Washed or running water.

Freshwater Ecosystems: Lakes and Ponds

Water flows in and out of lakes and ponds, circulating between the surface and the benthos, distributing heat, oxygen, and nutrients.

• Lakes: Large and open, deeper with photic and aphotic zones. Sunlight doesn't reach the bottom; temperature is not uniform.

• Ponds: Small and enclosed, shallow with only a photic zone. Sunlight reaches the bottom; temperature is uniform.

Lake Zones

• Littoral Zone

• Limnetic Zone

• Temperature Zones:

  • Euphotic/Photic

  • Aphotic

• Light Zones

  • Epilimnion

  • Thermocline

  • Hypolimnion

• Profundal/Benthic Zone

Thermal Stratification

Thermal stratification occurs in temperate regions from late spring to late fall. It involves the formation of distinct layers based on temperature:

• Epilimnion: The surface layer, mixed by wind and warmed by the sun.

• Metalimnion: The middle layer, characterized by a steep temperature gradient.

• Hypolimnion: The deepest layer of uniformly cold water with low circulation reaching max density at $4^\circ C$.

Lake Trophic Classification

• Oligotrophic Lakes: Generally deep and clear with little aquatic plant growth. They maintain sufficient dissolved oxygen to support cold-water fish.

• Mesotrophic Lakes: Lakes that fall between oligotrophic and eutrophic extremes.

• Eutrophic Lakes: Have poor clarity and support abundant aquatic plant growth. Cool bottom waters usually contain little or no dissolved oxygen, supporting only warm-water fish.

Rivers and Streams

• Streams: Small channels of freshwater containing flowing water; can be natural or artificial.

• Rivers: A ribbon-like body of water that flows downhill due to gravity and is larger than a stream.

Stream Types

• Perennial Streams: Flow all year long.

• Seasonal Streams: Seen only at certain times of the year, usually in wet seasons or due to snow/ice melting.

• Continuous Streams: Flow without stopping until reaching an endpoint or another body of water.

• Interrupted Streams: May have breaks or different reaches depending on seasonality, barriers, and other factors.

River Zones

Rivers transition from:

• Mountain headwater streams, flowing swiftly down steep slopes cutting a deep V-shaped valley with rapids and waterfalls,

• To low elevation streams that merge and flow down gentler slopes where the valley broadens and the river begins to meander,

• And finally to even lower elevation where a river wanders and meanders slowly across a broad, nearly flat valley, dividing into many separate channels as it flows across a delta into the sea.

Stream Dynamics

Illustrates the changes in stream width and ecological characteristics along a river's course, describing how microbial activity, organic matter, and the composition of organisms change from headwaters to larger streams. It also highlights the shift from shredders and grazers in narrower streams to collectors and a greater diversity of organisms in wider streams.

Stream Organism Size

Illustrates the categorization of stream organisms with different size: Trout, bass, perch, and catfish.

Wetlands

An area of land covered by water or saturated with water, entirely or partially throughout the year; considered a transition zone.

• Three major kinds of wetlands: swamps, marshes, and bogs.

  • Freshwater swamps form on flat land around lakes or streams with high water tables and slow runoff.

  • Freshwater marshes are dominated by grasses and aquatic plants, often developing around lakes and streams. Swamps and marshes are commonly found in warm climates.

  • Bogs develop in areas with high water tables, often in glacial depressions called kettle lakes, commonly found in cold or Arctic areas.

Estuaries

An area where freshwater rivers or streams meet the ocean, resulting in brackish water (a mix of salty ocean water and freshwater).

Estuaries are among the most productive ecosystems globally, serving as critical habitats for breeding, feeding, and migration.

Estuary Types Classified by Geology

• Drowned river valley

• Bar-built

• Tectonic

• Fjords

Zones of Estuaries

• Upper or Fluvial Estuary

  • Freshwater

  • Only tidal influence

• Middle Estuary

  • Fresh and salt water mixing zone

  • Reversing currents

• Lower or Marine Estuary

  • Ocean dominance

  • Mainly salt water

  • Sediment transport

Marine Ecosystems

Coral Reefs

Ocean ridges formed by marine invertebrates living in warm, shallow waters within the photic zone. They are among the most biologically diverse and economically important ecosystems, providing the foundation for many marine species and growing in shallow, clear water.

Corals and their Diets.

Illustrates an overview of what different corals consume, such as mucus, eggs and larvae, coral and zooplankton.

Coral Types

• Hermatypic Corals:

  • Possess zooxanthellae

  • Reef builders

  • Require clear water and warm temperatures 18-32^\,\circ C

  • Thrive in low nutrient conditions

• Ahermatypic Corals:

  • No zooxanthellae

  • Rely on tentacular feeding

  • Can live in the aphotic zone

Hermatypic vs. Non-Hermatypic Corals

• Brain Coral (Diploria)

• Mushroom Coral (Fungia)

Distribution of Coral Reef Communities

Coral reefs are predominately located between the 30° latitudes, prefer warmer temperatures, and are often near warm currents.

Coral Reefs Conditions

Different light waves, and wave energy:

• High: Cauliflower coral (Pocillopora meandrina) (6 m)

• Moderate: Lobe coral (Porites lobata) (0 m)

• Low: Finger coral (Porites compressa) (25 m)

• Very Low: Plate coral (Porites rus) (13 m)

Types of Coral Reefs

Fringing, Barrier, Atoll, and Drowned.

Reef Structures

• Fringing Reef: Beach, Reef flat, Reef slope, Mangroves, Rocky shore, Sediment and rubble, Reef crest.

• Barrier Reefs: Lagoon, Patch reefs, Spur and groove, Back-reef flat, Reef crest, Fore-reef slope, Sand cay.
  The Great Barrier Reef is a prime example of a barrier reef.

• Atoll Reefs: Ring-shaped reef structures encircling a lagoon, often formed around a sinking volcano: Lagoon, Fore-reef (outer) slope, Back-reef (inner) slope, Pinnacle, Algal ridge, Sand cay, Reef flat, Wind, Spur and groove.

Environmental Factors Affecting Corals

• Water Motion

• Depth: photic vs aphotic zone & water motion

• Sedimentation

• Salinity: 32-35 ppt

• Temperature: 18-32 °C

• Tidal fluctuations

• Nutrients: Eutrophic vs oligotrophic

Open Ocean

The largest marine biome with a relatively uniform chemical composition. The physical diversity significantly influences marine life.

The ocean is categorized into different zones based on the reach of light into the water, with each zone hosting a distinct group of species adapted to its specific biotic and abiotic conditions.

Ocean Zones Based on Depth and Light Availability.

Major Life Zones and Vertical Zones

Coastal zone, Estuarine Zone, Continental shelf, Open Sea

• Sunlight to Euphotic Zone (0-200 m)

• Then Bathyal Zone

• Abyssal Zone (Darkness)

Ocean Zones and Continental Margins

• Continental Margin: Submerged area of continents.

  • Continental Shelf: Flat gradually sloping seafloor from shoreline to ~200m; End of Shelf is called the Shelf Break.

  • Continental Slope: Steeply sloping seafloor seaward of shelf break.

  • Continental Rise: Moderately sloping seafloor seaward of slope.

Pelagic and Benthic Zones

• Pelagic Zone: The water column. Organisms that swim through it are known as nekton.

• Benthic Zone: The ocean floor. Organisms that live here are benthic organisms or benthos.

Pelagic and Benthic Zone Divisions

Different Species in Ocean Zones

Here is an overview of where different species are located in the different ocean zones:

EPIPELAGIC (0-400m):
Whales, Epipelagic fish, Copepods, Sharks, Dolphins/porpoises, Jellyfish

MESOPELAGIC (400-1,000m):
Starfish, Salps, Ctenophores, Squid, Tomopteris worm, Mysid shrimp

BATHYPELAGIC (1,000-4,000m):
Bathypelagic octopus, Sea cucumbers, Urchin Amphipods, Angler Fish, Deep sea octopus

ABYSSOPELAGIC (4,000-6,000m):
Abyssal bryozoan, Stalked ascidians, Hydrothermal vents, Deep sea coral, Brittle stars, Deep sea shrimp, Giant tube worms, Clams, Galatheid crabs

HADALPELAGIC:
Greenland shark, Rattail fish, Brotulid fish deepest living fish, Deep sea worms, Mussels

Saltwater Wetland

• Saltwater Swamps: Regions dominated by trees.

• Saltwater Marshes: Coastal wetlands flooded and drained by saltwater brought in by the tides. Marshy due to deep mud and peat (decomposing plant matter).

Mangroves

A group of trees and shrubs that live in the coastal intertidal zone. Mangrove forests stabilize coastlines, reducing erosion from storm surges, currents, waves, and tides. The intricate root system provides food and shelter for fish and other organisms.

Ecological Impact

Details the causes and impacts of human activities on lake ecosystems, including pollution, habitat modification, and species introduction. The activities increase sediment and nutrient levels, leading to eutrophication, anoxia, and ecological shifts. It emphasizes how these changes in lake environments affect various organisms and ecosystem functions, such as algal blooms, food web shifts, and the spread of invasive species.

Freshwater Ecosystems in Crisis

Highlights the severe decline in freshwater species populations (84% since 1970) and the loss of wetland ecosystems due to human activities. It also addresses the growing demand for freshwater, the pollution of freshwater systems, and the vulnerability of these ecosystems and communities to climate change impacts.

Identifies key threats to freshwater and marine water quality, including the presence of microplastics from various sources like fishing gear, road markings, and consumer products. It's impact sedimentation and the fragmentation and degradation of water quality.

Threats to Marine Environments

1. Climate Change and Ocean Acidification

2. Overfishing and Bycatch

3. Pollution and Plastic Waste

4. Habitat Destruction

5. Tourism and Recreational Activities

6. Global Trade and Shipping

7. Noise Pollution

8. Illegal and Unregulated Fishing

9. Invasive Species

State of Marine Ecosystems

Climate change continues to affect the marine environment, with oceans acidifying, sea levels rising, and sea-surface temperatures increasing. These changes impact marine species, habitats, ecosystems, and people, affecting coastal infrastructure and communities. Excess sediment, nutrients, plastics, and non-indigenous species can pose risks to marine ecosystems, influencing biodiversity and ecosystem connections.