and
New Caledonia, SW Pacific Ocean. s (C-I) that react with the dust particles in the colony core and generate dissolved Fe (C-II). This dissolved Fe, complexed by siderophores, is then acquired by both
Trichodesmium and its resident bacteria (C-III), resulting in a mutual benefit to both partners of the
consortium.
Trichodesmium is found in oligotrophic waters, often when waters are calm and the
mixed layer depth is shallow (around 100 m).
Trichodesmium is found primarily in water between 20 and 34 °C and is frequently encountered in tropical and sub-tropical oceans in western boundary currents. As a
diazotroph,
Trichodesmium contributes a large portion of the
marine ecosystem's new nitrogen, estimated to produce between 60 and 80 Tg of nitrogen per year.
Sociality Trichodesmium are able to transfer between living as a single filament and as a colony. These different morphologies impact the way that the
Trichodesmium interact with the environment. Switching between morphologies shows that there are different benefits and costs of existing in each form, and helps scientists understand why transferring from one form to another is necessary. Trichomes, or free-floating single filaments, have higher rates of nitrogen fixation as opposed to colonies. When iron and phosphorus are limiting in the environment, the filamentous
Trichodesmium are stimulated to aggregate together to form colonies. Colonies can outcompete trichomes when environmental factors such as predation and rate of respiration for nutrient fixing are at play. The size of the colonies are also linked with the environmental oxygen content, due to the influence of oxygen in the process of photosynthesis.
Trichodesmium colonies are microbially diverse and are considered to be a holobiont, where multiple epibiont bacteria form a singular colony. In these holobionts,
Trichodesmium is the core host, but the microbial diversity of the holobiont colony is an essential part of its ecological interactions. Some examples of the
Trichodesmium microbiome’s epibiont bacteria include diazotrophs and several cyanobacteria species such as
Richelia.
Trichodesmium and the epibiont bacteria within the holobiont colonies may perform mutualistic interactions where limiting nutrients such as iron can be mobilized from dust. Other interactions with organisms arise when trichomes start to accumulate together. When colonies of
Trichodesmium aggregate in large numbers, it is possible for them to produce a phycotoxin that can affect the growth other microorganisms in the local space of the ocean.
Blooms Trichodesmium forms large, visible blooms in the surface waters. Blooms have been described in the Baltic Sea, the Red Sea, the Caribbean Sea, the Indian Ocean, the North and South Atlantic and the North Pacific, and off the coast of Australia. One of the earliest blooms was described by E. Dupont in the Red Sea, noticed for turning the surface of the water a reddish color. This bloom was said to extend about 256 nautical miles. Most blooms are several kilometers long and last one to several months. Blooms can form in coastal or oceanic waters, most frequently when the water has been still for some time and surface temperatures exceed 27 °C.
Trichodesmium blooms release carbon, nitrogen and other nutrients into the environment. Some species of
Trichodesmium have been shown to release toxins which cause mortalities in some copepods, fish, and oysters. Blooms have also been credited with releasing the toxin which causes clupeotoxism in humans after ingesting fish which have bioaccumulated the toxin during
Trichodesmium blooms. The larger impact of these blooms is likely important to the oceanic ecosystem and is the source of many studies. It is expected that blooms may increase due to
anthropogenic effects in the coming years. Phosphate loading of the environment (through fertilizer pollution, waste disposal, and mariculture) will reduce the growth constraints associated with limited phosphate and likely increase bloom occurrences. Likewise, global warming is projected to increase stratification and cause a shallowing of the mixed layer depth. Both of these factors are associated with
Trichodesmium blooms and may also cause an increase in the occurrence of blooms in the future. ==References==