Ecological Succession and Dredging

ecological succession – the replacement of one community with another over time

pioneer species – first organisms to come into a new area

• change ecosystem slightly• can then be outcompeted by another species

• next species replaces pioneer species

• climax species/community – dominant organisms or community in a mature stable area – outcompete others

pioneer species

climax species

typical ecological successionon land:

disturbance - any kind of disruption to community that sends it back to an earlier successional stage

disturbances to forest ecosystem:

forest fire volcano

land slide

disturbances to forest ecosystem:

farmer plowing field – if the farmerlets the field lie fallow, ecologicalsuccession will occur

• ecological succession also occurs in the ocean

• usually changes in animal community, not plant community

• ecological succession affects biodiversity

benthic communities includemany types of organisms

• Over time, one community changes the environment slightly and is outcompeted by members of another community.

• The dominant community has changed – ecological succession is occurring.

• The community will remain until it is outcompeted or there is a disturbance.

example of organismschanging the sediments:

some amphipods and worms (deposit feeders) build tubes in sediments

• tubes stabilize sediments• makes it easier for other

organisms (suspension feeders) to survive

• suspension feeders outcompete original deposit feeders

example of organisms changing the sediments:

• some organismsbuild burrows inanoxic (no oxygen)sediments

• pump oxygen-rich water throughburrows

• brings oxygen into sediments• aerobic bacteria can now survive• changes and increases nutrient

cycling

• dredging disturbs benthic habitat- when sediments are dredged up- when dredge spoils are deposited

Human Disturbance – Dredging:underwater excavation of bottom sediments

dredging is often for navigation – sediments settle andbuild up on bottom

> 500 million cubic yards per year in U.S

• ecological succession may start over after dredging occurs

• sediment types may change from original• therefore species may change from what

was originally there

Dredge Disposal• Dredged material must be disposed

somewhere – LIS, ocean, on land?• Disposal site depends on level of toxic

contamination of sediments• Uncontaminated

dredged material may be used forbeach nourishment, fill, construction, cap landfills

• dredging may also occur to removecontaminated sediment

• ecological succession may also occurafter dredge spoils are dumped

• may change sediment grain size

• can smother existing organisms• can impact species that

reproduce when dredging is occurring

• sediments often contain toxic

contaminants • sediments can harm eggs and larvae

sediments can harm coral reefs:• clog feeding apparatus• block sunlight for photosynthesis• make it hard for new larvae to

settle and attach

Dredge Disposal - OPTIONS

• Cap disposal sites to prevent leaching of contaminants to water and isolate contaminants from organisms

• Dredge from inner harbor (more polluted) to outer harbor (less polluted) – less polluted covers more polluted sediments

• Locate dump sites in deeper water

Dredge Disposal - OPTIONS

• Restrict dredging and disposal to fall and winter (less biological activity)

• Can use on-land sites or containment islands instead

• Put dump sites in areas with high natural rate of deposition – less likely to erode