BIOL3301 Marine Biology: Estuaries PDF

BIOL3301 Marine Biology Estuaries Pedro J Jimenez [email protected]  Physical characteristics Estuaries body of salt/fresh water mixing – unique niche space dynamic over geological time – low relat...

BIOL3301 Marine Biology Estuaries Pedro J Jimenez [email protected]  Physical characteristics Estuaries body of salt/fresh water mixing – unique niche space dynamic over geological time – low relative biodiversity energy source/sink – high productivity intimate land-water interface – sensitive to global change  Physical characteristics Salinity zonation in an estuary brackish  Physical characteristics fresh Estuarine! marine Coastal plain Tectonic Pearl River Delta?? Coastal plain Lagoon Fjord  Physical characteristics Estuary Types: by Geomorphology Coastal Plain (Chesapeake Bay, Delaware Bay) Tectonic (via subduction; San Francisco Bay) Lagoon (semi-enclosed; North Carolina Coast) Fjord (glacially formed valley; Alaska, Scandinavia, New Zealand)  Hydrology Estuary Types: by Hydrology Positive: “Salt wedge”, River dominated, stratified – River discharge > tidal intrusion (common!) the SALT WEDGE  Salinity Salinity Positive estuary salt wedge https://www.youtube.com/watch?v=SLFp_XKlAao Positive estuary tidal cycle https://www.youtube.com/watch?v=feBHj0HAZLI  Hydrology Estuary Types: by Hydrology Negative (evaporation): Freshwater input is limited; evaporation maintains high salinity (hypersaline waters) – More saline in headwaters (i.e. inverse estuary)  Hydrology Estuary Types: by Hydrology Homogenous (neutral): Marine dominated, well-mixed – Water mixing and evaporation rate equals freshwater discharges. – Similar salinities from surface to bottom. Homogenous estuaries are rare Encyclopædia Britannica  Hydrology Estuary Types: by Hydrology Seasonal: Temporal variation in salinity; Formed in areas with mediterranean climate: – Wet/dry periods cause variation - positive to negative or dry; – During rainy season there is freshwater input and it is open to the ocean (“Positive”); – During dry season, no freshwater and may become dry or stagnated.  Characteristics Estuaries: as a Habitat Salinity Substrate Temperature Waves & Currents Turbidity Oxygen ALL HIGHLY VARIABLE, RELATED & DEFINE BIOLOGY!  Substrates Substrates In Fjords: – Some have bedrocks with sediment cover arriving from adjacent watershed; – Glaciers may leave cobble deposits, leaving estuary with cobble substrate covered by sediments. Most other estuaries have soft, muddy substrates: – River bring smaller particles, such as silt; – Winds may transport large sand particles, particularly in coastal lagoons behind barrier beaches.  Substrates Substrates Large (heavy) particles sink first – upper river reaches – Finer sediment/silts carried by downstream currents – end up in lower reaches where velocity is lower. Flocculation: salts increase particle binding: –  salinity  sedimentation  turbidity. Results in expansive deltas of fine sediment: – Rich in organics, great for plants, deposit feeders!.  Substrates Flocculation Increasing SALINITY  Substrates Sediments – buffer salinity  Temperature Temperature marine ΔT fresh ΔT ΔT ΔT ΔT = relative change in temperature  Waves and currents Waves & Currents Dynamic engineering of the ecosystem! Estuaries tend to be calm – low fetch: – Fetch: length over water which wind has blown. Calm waters facilitate sedimentation; Sediments facilitate submerged aquatic vegetation (SAV).  Waves and currents Waves & Currents Hurricane Irene cut two inlets in the Pea Island National Wildlife Refuge on Hatteras Island. Photo: U.S. Fish & Wildlife Service  Waves and currents Currents define habitats  Oxygen Oxygen Ample supply of oxygen from – Freshwater and sea water input; – Shallowness coupled with turbulence by wind bring supply of oxygen. In deeper estuaries during summer, thermocline may develop; Stratification impedes exchange of oxygen between shallow and deeper waters; This can cause oxygen depletion in bottom waters and sediments.  Oxygen Factors related to dissolved oxygen Temperature - T = [O2] Salinity - Salinity = [O2] * Both due to gas solubility in water.  sediment organic matter Fine particle sizes  respiration (bacteria) limit interchange of interstitial water – –  [O2] anoxic layer below  biological oxygen demand first few centimeters.  Oxygen Factors related to dissolved oxygen Thus, almost any environmental gradient can influence available oxygen; Biological activity can help oxygenate deeper sediment layers. Quintana et al. (2011) Marenzelleria viridis Callianassa sp.  Fauna Fauna in estuaries  Fauna Number of species in estuaries is significantly lower than in the nearby marine or freshwater: – Most true estuarine species derive from marine stocks; – Small number of true estuarine species: Possible reason: fluctuating environment and/or short geological history. Callinectes sapidus Crassostrea virginica Nereis diversicolor  Fauna - Salinity Species & salinity Steno = narrow; Eury = broad; haline = salt – Stenohaline: >25 ppt; mostly marine species – Euryhaline: >5 – 18 ppt; truly estuarine Transitional: species that can transit a large range of salinities to feed/reproduce – Ana- = UP ; Cata- = DOWN; -dromus = running – Anadromous: moves from marine to fresh (e.g. salmon) – Catadromous: moves from fresh to marine (e.g. eels)  Fauna - Salinity Species & salinity  Fauna - Osmoregulation Strategies of common estuarine fauna to cope with salinity Poor osmoregulators Protective shells Good osmoregulator Impermeable shell Intracellular osmotic balance using amino acids Good osmoregulator v. Tolerant (conforms) Kidneys  Fauna - Osmoregulation When the salinity drops…  Fauna - Osmoregulation osmoregulation  Fauna - behavior behavior  Flora Common estuarine flora: microalgae and macroalgae > Abundant diatoms. Many motile, Don’t survive well in muddy, turbid moving up and down into the mud, conditions. Not very significant in depending on the illumination. estuaries. Sometimes seasonal. Microalgae will provides abundant organic matter that is subject to decomposition by rich bacteria community in the mud  Flora Common estuarine flora: vascular plants Saltmarshes, mangroves, seagrasses.  Flora Plant adaptation Anoxic sediments High salinity Cross-section of Spartina below Spartina leaves exhibiting salt gas sediment - note excretion by salt glands. aerenchymal tissue - allows exchange  Food web Food web  Eutrophication Estuaries are prone to eutrophication Eutrophication: an ecosystem state following nutrient over- enrichment Characterized by: – High water column production – Increased turbidity – Benthic hypoxia Made worse by: – High temperature – Low water flow Leads to: – Loss of ecosystem services & biodiversity  Eutrophication eutrophication Breitburg et al 2018 Policy Brief  Eutrophication eutrophication  Hypoxia and anoxia eutrophication, anoxic dead zones Breitburg et al 2018 Science  Hypoxia and anoxia Hypoxia and anoxia in Kong Kong μmol dissolved O2 Kg-1 Qian et al. 2018  Summary Summary Estuaries – General characteristics: Types by geomorphology and hydrology; Salinity, oxygen, temperature, substrate, waves and currents. – Fauna and its adaptations; – Flora; – Eutrophication.