[i] Estuaries

• Estuaries

  • Inlet of the ocean into a river valley, as far as the upper limit of the tide
  • Areas that can be partially isolated from sea by land, diluted by freshwater
• Label the ff. types of estuaries

  A) Coastal plain

  B) Tectonic

  C) Fjord

  D) Bar-built

  
• Drowned river valleys in more temperate areas, water from melting glaciers

  Coastal plain
• Manila bay is an example of a coastal plain
• Type of estuary caused by movements of tectonic plates, sunken areas become pools of water

  Tectonic
• Estuary in more temperate, polar areas, valleys cut by glaciers eventually filled with water

  Fjord
• Estuary where sediments from river create a geographic barrier, create lagoons

  Bar-built
• Freshwater move at the top, saltwater at the bottom

  Positive estuary
• Reverse flow due to higher temp and evaporation rate, higher salinity as freshwater evaporates, saltwater at the top

  Negative estuary
• Phenomenon where cooler surface sinks, replaced by warmer deeper water at the top; saltwater moves at the bottom

  Winter turnover
• Salt-wedge estuaries involve an angled boundary between downstream freshwater and upstream saltwater
• Well-mixed estuaries involve low river flow, are mainly controlled by tidal currents, and have uniform salinity at all depths
• Partially-mixed estuaries have strong surface flow and a strong influx of seawater, with rapid exchange and higher salinity
• Because estuaries are shallow, changes in air temperature leads to rapid changes in water temperature
• Cool estuaries experience winter turnover, leading to vertical mixing of nutrients
• Estuarine Productivity

  • Freshwater carries detritus and nutrients, seawater carries more phosphorus
  • Support primary production → Support marine communities
  • Allochthonous complementary nutrients
  • Introduced from a different area
  • Detritus - basis of estuarine food webs
• Bivalves produce pseudofeces when there are large amounts of phytoplankton in the environment, which is easily manipulated by organisms
• Since bivalves are selective deposit feeders, they defecate the nutrients they don't need
• Osmoconformers

  • Organisms with cells and tissues that can tolerate dilution
  • Isosmotic with their environment, unable to actively change amount of water in their tissues
  • Tunicates take in more water in their cells
  • Green algae thin cell walls are more flexible
  • Examples:
  • Tunicates, molluscs, jellyfish, sea anemones
• Osmoregulators

  • Able to actively maintain osmotic balance
  • Concentrate salts in less saline environments
  • Excrete salts in hypersaline environments
  • Decreased permeability due to calcified exoskeletons
  • Increased number of mucus glands
• The constant movement makes it difficult for some organisms to feed or do vital functions

  • Therefore, natural selection favors benthic organisms
• Remaining Stationary:

  • Corals encrusting to prevent breakage
  • Attachment to substrate with roots, holdfasts
  • Animals live at the bottom
  • Nonbenthic animals live in the more protected estuary as juveniles
  • Feathered star - makes use of holdfast, uses constant waves to feed themselves
• Estuaries as nurseries

  • Emperor fish juveniles hide in seagrass
  • Seagrass
  • Fulfill growth and development
  • Provides covert
  • Extensive root network of mangroves creates obstacle course
• Many estuarine species are euryhaline, meaning they can tolerate a broad range of salinities
• Oyster reefs:

  • Dead shells as substrate
  • Occur at 90 degree angle, at lower salinities
  • Provide habitats to other animals:
  • Molluscs, anemones, sponges, bivalves
• Mudflats:

  • Occur where land is protected from wave action
  • Allochthonous source of food deposits contribute to rich food reserves
  • Mostly burrowing organisms
  • Primary producers:
  • Photosynthetic bacteria
  • Primary consumers:
  • Also bacteria, feeding on detritus
  • Secondary consumers:
  • Nematodes, polychaetes, gastropods
  • Tertiary:
  • Birds, fishes, carnivores
• Seagrass meadows

  • Highly productive communities
  • Provides place of attachment
  • High biodiversity
  • Types of animals:
  • Infauna - benthic
  • Epifauna - surface
  • Mobile fauna - in water, over canopies
• Common seagrasses:

  • Enhalus acoroides
  • Thin blades, extra long
  • Syringodium isoetifolium
  • Cylindrical leaves
  • Halophila ovalis
  • Round leaf