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Unformatted text preview: KELP FORESTS
Lecture adapted from Dr. Katrina Mangin (University of Arizona) What Charles Darwin said...
"I can only compare these great aquatic forests...with the terrestrial ones in the intertropical region. Yet if in any country a forest was destroyed, I do not believe nearly so many species of animals would perish as would here, from the destruction of the kelp. Amidst the leaves of this plant numerous species of fish live, which nowhere else could find food or shelter..."
Charles Darwin, 1 June 1834, Tierra del Fuego, Chile Kelp (Brown Algae)
Brown Algae (Phaeophyta) 1000 species, almost all marine Includes Sargassum, Pelvetia, and kelps Most common in cold, temperate seas Three pigments for photosynthesis: 1) Chlorophyll a (like all plants) 2) Chlorophyll c 3) Fucoxanthin (brown color) Parts of a kelp Gasfilled pneumatocysts Holdfast to attach to substrate Long stipe Leaflike blades Kelp: Division Phaeophyta (Brown Algae) FUNCTION AND FORM Giant Kelps largest of all algae
Kelp Forests One plant can grow 2530 m in one season Can reach 45 m long Among most productive of all plant communities Subtidal to 20 meters Kelps like cold water Kelp diversity
Low taxonomic diversity (few species of kelp) High structural and functional diversity (many shapes and creates many different architectural habitats that promote diversity of associated organisms) Kelp forest zonation Cold, temperate water Kelp forests Where do they occur? Kelp forests are more common off West Coast of N. America than E. Coast Why? Giant kelp forests Kelp forests Where do they occur? More common off West Coasts of N. America than E. Coast because of cool California current off Ca coast vs.warm Gulf Stream on East Coast Kelp forests occur in cool water The ecological role of kelp Dave Witting/NOAA The ecological role of kelp
Dampen wave action Reduce coastal erosion Enhance recruitment of fish and invertebrates High productivity and turnover of plant matter puts many nutrients into system High structural diversity (like a forest on land) provides shelter and habitat for many species Habitat complexity created: understory with filtered light canopy at surface Kelp forests vs terrestrial forests Similarities and differences to terrestrial forests
Both forest types:
Recruitment and growth depends upon canopy breaks for available light Form foundation for large diversity of animals and plants Both are primary producers, get their energy from the sun Kelp forests have shorter life spans, shorter heights, but are faster growing:
Few kelp species last more than 25 years Terrestrial forest trees can live for thousands of years Kelp forests are more diverse in terms of number of animal phyla, less in terms of animal species:
Terrestrial forests are habitat for roughly 3 phyla Kelp forests are habitat for 10 or more phyla Animals of the kelp forest Kelp forests come and go... Salinity, temperature change, storms, seasons Can recover fairly quickly under natural conditions Kelp forests are deforested by natural causes Sea urchins (Strongylocentrotus) graze on kelp Sea otters (Enhydra lutris) control urchin populations by eating them CALIFORNIA CA kelp forests considered most diverse in world Exploited for past 12 13,000 yrs Shell middens from aboriginal people show decrease in animal size with hunting White sea bass landings Animals begin to disappear from kelp forests
Otters functionally gone by early 1800s Kelp forest ecosystem persisted for next 150 years Probably because other predators, like fish, compensated by increasing in numbers and eating urchins CA kelp begins to change CA kelp forest so diverse, other predators keep urchins in check even with few otters Continues to persevere for another 150 years Now in trouble not so diverse Kelp conservation status Climate change (global temp. increase), human pop. growth, coastal development, oil spills, overfishing impacts, nonnative sp. invasions all predicted to increase over next 25 years Currently, in some areas fisheries for urchins coincide with fisheries for urchin predators a delicate balance Not all areas will be affected in future by temperature changes, but mean annual global temperature predicted to increase (last century 1 degree C increase in global air temp) A sign of things to come NORTH PACIFIC/ALASKA
Sea otters, sea cows, sea urchins and humans History of fishing in N. Pacific Colonization 30,000 years ago, boats used off Japan coast for past 25,000 years Steller's sea cow hunted to extinction (35 feet long, several tons) due to the demand for its meat "As good as the best cuts of beef..." History of fishing in Alaska
Humans in Alaska for 900010,000 years. Indigenous tribes began to hunt otters ~ 2500 years ago. Otter hunting intensified with European arrival in 1700s. Ecosystem changed to urchin dominated. Otters and urchins A new threat emerges In 1991, first killer whale attack on Alaskan otter is witnessed Killer whales may have switched to otters because their normal food (whales and seals) has become rare. Sequential overharvesting of marine mammals NORTH ATLANTIC Sea urchins and kelp, but no sea otters, but very large predatory fish! Cod fishery intense for centuries Urchins rise again Fishing technology decreases cod pop. by 1930s CONCLUSION Kelp forests are home and nurseries for much marine life Kelp forests could disappear or become functionally extinct within decades in absence of effective management that takes complex ecosystem into effect, including direct and indirect effects (eg, overhunting of whales leads to killer whale predation on sea otters, leads to rise of urchins and death of kelp) References Dayton, PK, Tegner MJ, Edwards PB, et al Sliding baselines, ghosts, and reduced expectations in kelp forest communities ECOL APPL 8 (2): 309-322 MAY 1998 Estes, JA, Duggins, DO, Rathbun, GB. The ecology of extinctions in kelp forest communities. CONSERV BIOL 3 (3): 252264 SEP 1989 Jackson, JBC, Sala E Unnatural oceans SCI MAR 65: 273-281 Suppl. 2 SEP 2001 Jackson, JBC, Kirby, MX, Berger, WH, et al. Historical overfishing and the recent collapse of coastal ecosystems SCIENCE 293 (5530): 629-638 JUL 27 2001 Jackson, JBC What was natural in the coastal oceans? P NATL ACAD SCI USA 98 (10): 5411-5418 MAY 8 2001 Simenstad CA, Estes JA, Kenyon KW. Aleuts, sea Otters, and alternate stable-state communities SCIENCE 200 (4340): 403411 1978 Steneck RS, Graham MH, Bourque BJ, et al. Kelp forest ecosystems: biodiversity, stability, resilience and future ENVIRON CONSERV 29 (4): 436-459 DEC 2002 Tegner, MJ, Dayton, PK Sea-urchins, El-Ninos, and the long-term stability of southern California kelp forest communities MAR ECOL-PROG SER 77 (1): 49-63 OCT 1991 ...
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- Winter '08