Human Impacts and an Estuary's unique characteristic (Moon)

     As has been mentioned before, humans have a heavy impact on estuaries. Currently, estuaries are under threat from human activities such as pollution and overfishing. They are also threatened by sewage, coastal settlement, land clearance and much more. Estuaries are affected by events far upstream, and concentrate materials such as pollutants and sediments. Land run-off and industrial, agricultural, and domestic waste enter rivers and are discharged into estuaries. Contaminants can be introduced which do not disintegrate rapidly in the marine environment, such as plastics, pesticides, and heavy metals.

     Such toxins can accumulate in the tissues of many species of aquatic life in a process called bioaccumulation. They also accumulate in benthic environments, such as estuaries and bay muds: a geological record of human activities of the last century.

     For example, Chinese and Russian industrial pollution, such as phenols and heavy metals, in the Amur River have devastated fish stocks and damaged its estuary soil.


     Estuaries tend to be naturally eutrophic because land runoff discharges nutrients into estuaries. With human activities, land run-off also now includes the many chemicals used as fertilizers in agriculture as well as waste from livestock and humans. Excess oxygen depleting chemicals in the water can lead to hypoxia and the creation of dead zones. It can result in reductions in water quality, fish, and other animal populations.

     As mentioned previously, overfishing also occurs. Chesapeake Bay once had a flourishing oyster population which has been almost wiped out by overfishing. Historically the oysters filtered the estuary's entire water volume of excess nutrients every three or four days. Today that process takes almost a year, and sediment, nutrients, and algae can cause problems in local waters. Oysters filter these pollutants, and either eat them or shape them into small packets that are deposited on the bottom where they are harmless. Without oysters, humans would be in a crisis in the future.

Estuaries are unique in many ways: The Indians called the estuary "Between-Land", and the mixture of fresh and saline water is a unique combination. However, what I feel makes an estuary special is its resistance to change. Estuaries are constantly evolving environments. This constant change means that the entire estuary ecosystem must maintain a dynamic, rather than static, equilibrium. It is this ability to handle change that makes estuaries unique. A hurricane has devastating consequences for coastal ecosystems such as estuaries as well as for residents of coastal areas. But like people, the estuary ecosystem rebuilds itself; plants establish new territory, mud dwelling creatures move to accommodate new sediments or longer periods of overlying fresh water, and fish swim further downstream to spawn.

 This is what makes an estuary beautiful, and necessary to protect. If even the hardy estuary is at risk from human impacts, than maybe we should all think about how to protect the environment. From the colorful coast of the Amazon, to the cold beauty of the Gulf of St. Lawrence, and the quiet grace of Chesapeake Bay, estuaries are truly wonderful places.

 89°19'33.16"S

 60° 5'44.22"W

(Moon)

Estuarine succession and Eco-tourism (Thames Estuary)

It is difficult to say estuaries experience succession, since they are an aquatic biome. However, if, for example, vegetation disappears from the ocean floor or riverbed due to herbivory, a form of succession occurs. In this case, the process of regrowth is essentially considered succession.

Eco-tourism is rather common these days. I would like to recommend that any eco-tourists touring an estuary remember the five most important things:


1. Estuaries are some of the most nutrient-rich biomes on the planet.

2. Estuaries have some characteristics of salt water and some of fresh water.

3. The key food source in estuaries is sedimentary detritus.

4. Estuaries have some of the greatest natural fish nurseries in the world.

5. Estuaries are one of the most at-risk biomes in the world.

51°28'7.68"N
0°50'3.97"E

Biogeochemical Cycles in an Estuary (Rio de la Plata)

Estuaries follow the natural biogeochemical cycles of all biomes: the water cycle, the carbon cycle, the nitrogen cycle, and the phosphorus cycle.

The Water Cycle

The Carbon Cycle

The Nitrogen Cycle

The Phosphorus Cycle

The only differences between estuarine and regular cycles in this case is that all cycles are generally aquatic.

35° 7'29.26"S
56°45'36.24"W

Limiting Factors in an Estuary (Long Island Sound)

 There are many limiting factors in an estuarine environment. Here are a few applicable to the Long Island Sound estuary:
Density-Independent:

1. Overfishing: In the Long Island Sound, overfishing of clams is especially prevalent.

 2. Habitat Destruction: There are many examples of habitat destruction in the Long Island Sound. Coastal land cleared for development destroys coastal ecosystems, increases runoff, and reduces filtration into the Sound. Trash and toxic waste also contribute to the destruction of estuarine habitats.

Density-Dependent:

1. Disease: Long Island Sound has had many aquatic diseases affect its non-human residents. One recent example is the current lobster epidemic. This disease attacks the shell of the lobster without harming the rest with what is likely a bacterial infection.

2. Predation and Competition: See earlier post.

41° 6'40.95"N
72°48'29.68"W

Coevolution in Estuaries (Puget Sound)



Aquatic Fungi



Secondary Compounds - Many secondary metabolites are found in aquatic microorganisms such as algae and the aquatic fungi Cephalosporium acremonium. It is the latter that we will discuss here. Cephalosporium acremonium produces a group of antibiotics called cephalosporins. They fight invader bacteria from attacking the fungus, but have no metabolic function. This is a common example of the use of secondary compounds in estuarine environments.

Camouflage - Octopi have built-in camouflage in their skin.


Octopus in Camouflage



An octopus's camouflage is aided by certain specialized skin cells which can change the apparent color, opacity, and reflectiveness of the epidermis. Chromatophores contain yellow, orange, red, brown, or black pigments; most species have three of these colors, while some have two or four. Other color-changing cells are reflective iridophores, and leucophores (white). This color-changing ability can also be used to communicate with or warn other octopuses. The very venomous blue-ringed octopus becomes bright yellow with blue rings when it is provoked. Octopi can use muscles in the skin to change the texture of their mantle to achieve a greater camouflage. In some species the mantle can take on the spiky appearance of seaweed, or the scraggly, bumpy texture of a rock, among other disguises. However in some species skin anatomy is limited to relatively patternless shades of one color, and limited skin texture. It is thought that octopuses that are day-active and/or live in complex habitats such as coral reefs have evolved more complex skin than their nocturnal and/or sand-dwelling relatives.





Aposematic Coloration - Cuttlefish display aposematic coloration. Their bright coloring hints of their toxicity to other organisms. Pfeffer's Flamboyant Cuttlefish in particular has neurotoxins in its saliva and shows that with its bright red coloration.

Mimicry - Cleaner fish are the allies of many other species, which allow them to eat their parasites and dead skin. Some allow the cleaner to venture inside their body to hunt these parasites. However, one species of cleaner, the Bluestreak cleaner wrasse (Labroides dimidiatus), is the unknowing model of a mimetic species, the Sabre-toothed blenny (Aspidontus taeniatus). This wrasse resides in coral reefs in the Indian and the Pacific Oceans, and is recognized by other fishes who then allow it to clean them. Its imposter, a species of blenny, lives in the Indian Ocean and not only looks like it in terms of size and coloration, but even mimics the cleaner's 'dance'. Having fooled its prey into letting its guard down, it then bites it, tearing off a piece of its fin before fleeing the scene.

Pollination in an estuary is commonly a form of hydrophily, which is pollination by the flow of water. Therefore no primary pollinators exist.




47°56'49.54"N
122°33'58.32"W

Mutualism, Commensalism, Parasitism, and Competition in the Chesapeake Bay



Oyster



Boring Sponge

Parasitism- The boring sponge bores through the bay's oysters' shells and may kill the oyster.

Mutualism- The clownfish and the sea anenome benefit eachother.  It has been suggested that the activity of the clownfish results in greater water circulation around the sea anemone. In addition to providing food for the clownfish, the sea anemone also provides safety due to its poison. The clownfish is dependent on the sea anemone for its daily bread. After the anemone paralyzes and eats a fish, the clownfish will polish off the remaining uneaten bits and pieces. In return, the clownfish helps to keep the anemone free of dead tentacles by eating these. The clown fish also helps the anemone get food by using its bright coloration to lure unsuspecting fish into the vicinity of the anemone.


Clownfish and Sea Anemone



Competition- The oyster and the slipper lampet (a type of snail) have a competitive relationship. They compete for space. When oysters began to die off from overfishing, the slipper lampet invaded the oyster beds and began to grow like crazy.

Slipper Lampet

Commensalism- Barnacles are a well-documented example of commensalism. They hook themselves to another organism such as a whale, and while they don't really harm it, they do get some benefit by having a place to stay. It also helps that this means they are dragged through the water quickly, since they are filter feeders.

Barnacles

38°34'36.56"N
 76°27'22.92"W

Predation and Food Webs in an Estuary (Chesapeake Bay)

Many symbiotic and predatory relationships are relevant to the estuary biome. Here is an example of a common food chain in an estuary:

Phytoplankton(producer)-Zooplankton(primary consumer)-Crab (Secondary consumer)-Fish(Tertiary consumer)-Human (Quaternary consumer). In the Chesapeake Bay estuary discussed before this chain is prevalent. On the left is a Chesapeake Bay food chain illustrating this. Above is a Chesapeake Bay food web.

These food webs and food chains illustrate common predator-prey relationships in estuaries. Several of these include:

The Blue crab (Callinectes sapidus) and the infaunal clam prey (Mya arenaria).

 

Also, the pennate freshwater diatom(Asterionella formosa) and the estuarine copepod zooplanktonn (Acartia hudsonica).

And finally, Rockfish (Morone saxatilis) larvae feed on various types of nauplii, including krill (Euphausia pacifica).

 38°32'25.18"N

 76°26'21.51"W