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Marine ecological communities: coastal and intertidal zones • What key physical factors structure intertidal and coastal communities? • Consist of organisms in a defined area • Who lives in these communities? • What determines the nature of a community? • How do they make a living? • What are the main challenges that organisms face in these communities? Intertidal and coastal communities • • • • • • Ecological communities Rocky intertidal Sandy beaches Estuaries Salt marshes Mangroves Lagoons – E.g. Sonoran desert, coral reef, intertidal – Physical stresses – Organisms’ interactions Characteristic stresses • Physical stresses include – Submersion/exposure – Waves – Temperature extremes • Biological Stresses – Space – Competition – Predation • Chemical stresses – Salinity changes (balance seawater-freshwater inputs; evaporation/precipitation) – Human impacts from pollution, nutrients, runoff changes 1 Limiting factors Zonation • Physical, biological: examples? • Physical stresses vary along vertical gradient • Biological stresses can also be structured vertically • Coastal/intertidal ecosystems are usually vertically zoned stress Optimum stress Low Optimal range intolerance intolerance Temperature (or any physical variable) Rocky Intertidal - British Columbia Exposure to air Always exposed (= most stressful for a marine organism!) 2 Intertidal height (m) Abundance Population size High 1.5 1 0.5 0 0 2000 4000 Hours exposed in 6 months Always submerged 2 Barnacles, mussels, and algae Anemone and mussels Rocky intertidal zonation Rocky intertidal zonation • Organisms live at specific levels in intertidal • Level is determined by how the organism handles physical and biological stresses • Lichens and cyanobacteria • Algae • Mussels and barnacles • Sea stars and anemones 3 How to cope with exposure to air? • Build a tight shell • Live in a tide pool • Be very mobile so you can follow a falling tide Competition between intertidal barnacles Wave stress How to manage this? Hold on tight! Hide in a crevice or behind a rock Competition for space • Anemone Anthopleura elegantissima common on W coast • Massive clonal groupings separated by clear demarcations • Anemones “fight” - sometimes to the death! • Chthamalus tolerates dry conditions better, but can also grow submerged: their potential range overlaps with Balanus. • Balanus can outcompete Chthamalus for space by dislodging them • Result is zonation with C above, B below. -Lower limit of C is set by competition with B. -The upper range of both C and B is set by tolerance for drying. http://life.bio.sunysb.edu/marinebio/rockyshore.html 4 Starfish and mussels • Starfish are predators on mussels, barnacles • Feed at lower edge of mussel beds • Set lower limit of mussels (mussel beds expand when starfish removed) Tidepools in the rocky intertidal • Tide pools: – Oases of water during low tide – Concentrations of food for predators! – Physical conditions can change rapidly (warm/cold, salty/fresh) Algae and anemones Tide pool inhabitants 5 Nudibranch Sea hare Sandy beach - intertidal • Sandy beaches: – High-energy waves – Soft substrate; hard to hold on – Sand in motion: abrasion – Pebbles and cobbles rolling around – Waves deliver constant supply of food particles Octopus in a clam shell Life in the sandy intertidal • Crabs: run away from waves; burrow • Clams: burrow • Worms: burrow 6 Estuaries • Productive but not diverse • Support critical life stages of many mobile organisms – Migratory birds – Young fish (including sharks) Adaptations to counter salinity stresses Estuarine environments have strong salinity gradients associated with fresh and salt water mixing; few organisms can tolerate the full range of salinities • Move to avoid highly variable regions (typically, avoid freshest parts) • Close your shell • Burrow underground • Internal stabilization of water and ionic concentrations – When external salinity low, some orgs can absorb ions from blood and come into osmotic equilibrium that way Salt marsh and mangrove distribution • Mangroves tropical and subtropical (dark blue) • Salt marshes temperate to higher latitude (aquamarine) Salt marshes: vegetated intertidal flats • • • • • Mostly temperate-zone ecosystem Low-energy environments; estuarine Plants are terrestrial - rooted in mud Drained by a meandering network of tidal channels Highly productive 7 Salt marsh zonation Spartina alterniflora adaptations to salty environment • special tissues (aerenchyma) increase oxygen availability to the roots • salt and organic substances to increase the solute concentration in cells http://life.bio.sunysb.edu/marinebio/spartina.html • excretion of excess salt from leaves and stems Spartina alterniflora Spartina patens • likes high marsh but competitively displaced to low marsh by S.p. • can’t live in low marsh due to anoxic soils; displaces S.a. from high marsh Marsh animals - fiddler crabs • Fiddler crabs (Uca pugnax) - burrow to escape most extremes; aerate sediments and help drainage with burrows Marsh animals - Ribbed mussels • Ribbed mussels (Geukensia demissa) cluster at the base of S. alterniflora; attach to each other and the substrate with threads that help stabilize the plants and sediment • Filter feeders; their excretions fertilize the plants. 8 Marsh animals - predators Salt marsh and mangrove distribution • These herons prey on small fish and invertebrates • Predators also include raccoons and other terrestrial mammals • Mangroves tropical and subtropical (dark blue) • Salt marshes temperate to higher latitude (aquamarine) Mangroves Mangrove food web • Detritus of mangrove trees supports diverse aquatic ecosystem • 60% is consumed by detritovores; just 1-2% becomes soil; rest is flushed away • Diverse invertebrate fauna (especially crabs!) • • • • Mangroves are dominant intertidal plants of tropics/subtropics Woody, tree-like plants with exposed roots Grow in soft sediment, low-energy environments Zonation - different species dominate different zones http://www.specola.unifi.it /mangroves/fauna/Inv/inv ertnew.htm 9 Other mangrove fauna www.mykenya.co.uk/ info_htm/funzi.htm Mangroves and fish http://cars.er.usgs.gov/pics/manatee/manatee/ • Reefs adjacent to mangroves had more and larger fish • Mangroves provide refuge from predation for sub-adults • Local extinction of prominent fish species has occurred when mangroves removed http://www.tracc.org.my/Borneo coast/MANGROVES/MANG_FA UNA.html http://www.stockpix.com/stock/animal s/endangeredspecies/indexb.htm www.duke.edu/~cwcook/ pix/panama/birds4.html Mangroves under threat • • • • Deforestation Development Shrimp aquaculture Sea level rise Mangroves and shoreline protection “IPS News Agency 2005-02-14 PENANG, Malaysia, Feb 14 (IPS) - When the Indian Ocean tsunami struck the coastlines of South and South-east Asia, areas with dense mangroves suffered fewer human casualties compared to areas without them.” 10 Lagoons Laguna San Ignacio • Grey whale breeding ground • Desirable salt plant location! (Mitsubishi) • Semi-isolated bodies of shallow water without significant freshwater input (i.e. not an estuary) • Exchange with ocean depends mainly on tides • Salinity brackish to hypersaline – Extreme evaporation can lead to reverse flow: deep water flows out, fresh in on top • Can be populated with mangroves, sea grass, marsh plants, coral reef organisms, or be barren… Coastal ecosystems and “ecosystem services” Human impacts on coastal ecosystems • • • • • • • • Pollution Nutrient overloads Freshwater diversions Development Aquaculture Sedimentation increases Invasive species Sea level rise Over half of all coastal wetlands have been lost. • Ecosystem services = services (not goods, resources) provided by an ecosystem • Can be evaluated in monetary terms • Coastal ecosystems are disproportionately valuable (Costanza et al. 1997) – 6% of world area, 43% of ecosystem value • Services include: – – – – – Nutrient cycling Water storage and purification Recreation Coastal protection Fish nurseries 11