Lecture 17: Estuatries

• An estuary is a partially enclosed and diluted marine environment. They have fluctuating salinity and temperatures. They are highly productive with reduced waves which allows for lots of nutrients and detritus communites.
• Types of estuaries: coastal plain, tectonic, fjord, bar-built
• Coastal edge estuaries formed at the last ice age with rising sea levels.
• Tectonic estuaries formed as the earth sinks along a geological fault and is flooeded.
• Fjords forms when a valley has been carved by glacial action and invaded by the sea.
• Bar-built estuaries formed when sandbars build up parallel to the coastline and partially cut off waters behind them from the sea.
• Salinity in estuaries: salt wedge, well mixed, partially mixed, restricted (fjord)
• Salt wedge: substantial freshwater output and reduced evaporation to allow for reduced salinity in surface waters and higher salinities in deeper waters.
• Well mixed salinity: low river flow; tide, wind, wave action; uniform salinity with depth.
• Partially mixed salinity: high river flow, wedge more prominent.
• Restricted salinity: bottom obstruction limits flow, dense water stays in place, freshwater streams over the sea.
• Salinity in estuaries fluctuates.
• Fluctuation in salinity of estuaries due to the point source gradient (salinity decreases up the estuary), tidal change, runoff variation, degree of mixing.
• Other factors of estuaries: temperature, wave action and currents, turbidity (decreases light penetration), oxygen (can be reduced when mixing is low).
• Eutrophication can affect estuaries.
• Adaptations in estuaries from osmoconformers and osmoregulators.

  Osmoconfromer's blood salinity increases with increasing salinity.
• Diversity in estuaries with more freshwater species in lower salinities and marine species in higher salinities.
• High productivity is based on detritus (particulate organic matter).
• Detritus/bacteria consumed either from the water column by suspension feeding benthic invertebrates or by direct consumption of deposit feeders.
• 5 Tributaries (Rivers) That Drain into the Chesapeake Bay:

  1. James River
  2. York River
  3. Susquehanna River
  4. Potomac River
  5. Rappahannock River
• The Chesapeake Bay system is a partially mixed estuary with the majority of the bay shallow to allow for sunlight penetration.
• As in all estuaries, some species are completely estuarine and some only use the estuary for a portion of their life history.
• Blue crabs live in the estuary and mate in the upper Chesapeake

  After mating, females seek higher salinity before releasing larvae

  Larval development continues in coastal waters
• Oyster life cycle within oyster reefs that support algae, sponges, bryozoans, polychaetes, mollusks

  Oysters are broadcast spawners (release of eggs and sperm into the water) and spend their entire life in the Chesapeake
• Two major diseases that wiped out oysters:

  1. MSX
  2. Dermo
• Oyster restoration has 4 challenges:

  1. Recruitment is variable and infrequent
  2. Diseases
  3. Habitat degradation
  4. Low extant spawning stocks
• Outcomes of eutrophication:

  1. Hypoxic and anoxic waters
  2. Reduction in abundance and diversity of benthic animals
  3. Decline in submerged aquatic vegetation
  4. Loss of habitat for juvenile fish and crustaceans
  5. Altered trophic networks by shortening food chains
  6. Fish disease (Pfiesteria)
• Menhaden as a type of suspension feeder that helps filter the waters
• Salt marshes in temperate climates supply food to estuaries and are dominated by halophytes.

  Zonation due to differences in physiological tolerances and competition.
• Salt marsh communities have high detrital primary production food chains.
• Mangroves serve as biochemical filters for terrestrial run-off and a buffer from erosion.
• Mangrove forest species:

  Red: first mangroves to colonize and have the highest salt tolerance

  Black: as substrate builds, red is replaced by black

  White: replace black mangroves with the most substrate and least tolerant to salt