Estuaries, formed where rivers enter the ocean and fresh water mixes with the saltwater environment, are among the most productive ecosystems on earth. They develop on deltas, where fine soil materials (sediment), are carried hundreds of miles downstream by the rivers and deposited on gentle shoreline slopes. These materials accumulate faster than they can be carried away by ocean currents, wave, and tidal action. Estuaries are most well developed where they are protected from oceanic forces by offshore islands and spits, or at the end of long fjords. Estuarine plants and animals occupy different zones depending on their ability to tolerate salt concentration (salinity), wave action, river flow,tidal changes, and sedimentation levels.
What is their ecology? Estuary ecology is complex and dynamic because of the interaction of three very different environments – freshwater aquatic, terrestrial, and marine. The unusual conditions create many challenges for estuarine plants and animals, and relatively few species can survive in an estuary. Those that do survive have few competitors and predators, and so are able to grow and re-produce quickly, making estuaries among the most productive ecosystems on earth.
The most distinct feature of an estuary is the rich and vibrant benthic ecosystem. It is home to microorganisms and tiny animals that live between grains of sand, large burrow-ing worms and scavengers such as crabs and snails, and sandy areas with filter-feeders like clams. On harder surfaces, such as rocky headlands or ar-tificial structures, you will find reef-forming shellfish like oysters and mussels, and strange, colourful animals like sponges and feathery hydroids.
Estuary ecology is complex and dynamic because of the interaction ofthree very different environments – freshwater aquatic, terrestrial, andmarine. The unusual conditions create many challenges for estuarine plantsand animals, and relatively few speciescan survive in an estuary. Those that do survivehave few competitorsand predators, and soare able to grow and re-produce quickly, mak-ing estuaries among the most productive ecosystems on earth. There are several reasons for this exceptionally high productivity.
Estuaries are constantly being fertilized by river sediment.
Estuary vegetation, and the barrier islands or sandbars protecting it,combine to trap and hold sediments. The constantly moving tides and currents carry in oxygen, nutrients, and plankton, and take away excess wastes. Plant foods are available in a variety of forms – phytoplankton, algae, sea-grasses, wetland plants – which support a variety of animal consumers. Most importantly, estuaries are extremely efficient at extracting, recycling,and conserving nutrients. Most of this activity takes place in the top 50 centimetres of estuary sediment, where a dense network of micro-organ-isms lives, recycling waste, and regulating or modifying most of the ecological processes in the estuary. This phenomenon is known as the “benthic effect.” Benthic fungi and bacteria consume dead organic material (“detritus”) – most of which comes from intertidal wet land plants – and are in turn consumed by other organisms. Other microbes also convert animal wastes into forms that plankton, eelgrass, and algae can use. What is remarkable is that most of this takes place in the low-oxygen benthic environment. Sub-surface micro-organisms are force d to use sulphur in place of oxygen, which is what gives stirred up estuary sediments their characteristic “rotten egg” smell.
ES students have been studying two estuaries on Saltspring Island between 1996 to 2006. We have two established Shore Keepers plots where the Ganges and Fulford creeks empty into the ocean. Throughout this period we have mapped the changing ecozones associated with these estuaries. Mapping populations conducting benthic analysis and recording impacts on the regions.
What is their ecology? Estuary ecology is complex and dynamic because of the interaction of three very different environments – freshwater aquatic, terrestrial, and marine. The unusual conditions create many challenges for estuarine plants and animals, and relatively few species can survive in an estuary. Those that do survive have few competitors and predators, and so are able to grow and re-produce quickly, making estuaries among the most productive ecosystems on earth.
The most distinct feature of an estuary is the rich and vibrant benthic ecosystem. It is home to microorganisms and tiny animals that live between grains of sand, large burrow-ing worms and scavengers such as crabs and snails, and sandy areas with filter-feeders like clams. On harder surfaces, such as rocky headlands or ar-tificial structures, you will find reef-forming shellfish like oysters and mussels, and strange, colourful animals like sponges and feathery hydroids.
Estuary ecology is complex and dynamic because of the interaction ofthree very different environments – freshwater aquatic, terrestrial, andmarine. The unusual conditions create many challenges for estuarine plantsand animals, and relatively few speciescan survive in an estuary. Those that do survivehave few competitorsand predators, and soare able to grow and re-produce quickly, mak-ing estuaries among the most productive ecosystems on earth. There are several reasons for this exceptionally high productivity.
Estuaries are constantly being fertilized by river sediment.
Estuary vegetation, and the barrier islands or sandbars protecting it,combine to trap and hold sediments. The constantly moving tides and currents carry in oxygen, nutrients, and plankton, and take away excess wastes. Plant foods are available in a variety of forms – phytoplankton, algae, sea-grasses, wetland plants – which support a variety of animal consumers. Most importantly, estuaries are extremely efficient at extracting, recycling,and conserving nutrients. Most of this activity takes place in the top 50 centimetres of estuary sediment, where a dense network of micro-organ-isms lives, recycling waste, and regulating or modifying most of the ecological processes in the estuary. This phenomenon is known as the “benthic effect.” Benthic fungi and bacteria consume dead organic material (“detritus”) – most of which comes from intertidal wet land plants – and are in turn consumed by other organisms. Other microbes also convert animal wastes into forms that plankton, eelgrass, and algae can use. What is remarkable is that most of this takes place in the low-oxygen benthic environment. Sub-surface micro-organisms are force d to use sulphur in place of oxygen, which is what gives stirred up estuary sediments their characteristic “rotten egg” smell.
ES students have been studying two estuaries on Saltspring Island between 1996 to 2006. We have two established Shore Keepers plots where the Ganges and Fulford creeks empty into the ocean. Throughout this period we have mapped the changing ecozones associated with these estuaries. Mapping populations conducting benthic analysis and recording impacts on the regions.
The map of the Ganges intertidal study plot, shows the course of Ganges creek at a .3 m low tide. This estuary had been dredged in the 1970's and still appears to be recovering an ecosystem balance. Substrate sampling show low diversity and low counts of invertebrates within the estuary region. The plot is 100 m wide and about 300 meters into the ocean.
The ES class have conducted 10 surveys at this site since 1996. |