University:
Arizona State University
Course:
ABS 370 | Ecology
Academic year:

2024
Views:

288

Pages:

1
Author:

Patel R.

‭FLOATING AND SPATIAL DISTRIBUTION OF PLANKTON‬ ‭Floating mechanisms of plankton: the greater the density of the body compared to that of the‬ ‭water, the greater the sinking in the water column. Sinking is harmful in the long run for both‬ ‭phytoplankton and zooplankton. In the case of phytoplankton there is a progressive distancing‬ ‭from the light source, in the case of zooplankton there is a distancing from the phytoplankton.‬ ‭Consequently, for all planktons there is a need to resist sinking. Among these adaptations is‬ ‭weight reduction: in many forms‬ ‭planktonic cells equipped with shells and exoskeletons, these structures are reduced and become‬ ‭lighter. This solution is adopted for example by heteropod and pteropod gastropods, foraminifera,‬ ‭crustaceans, which have a much lighter covering, sometimes absent, compared to similar but benthic‬ ‭species. A further method consists in altering the composition of internal liquids to achieve a density‬ ‭similar to or lower than that of sea water. For example, heavy ions are replaced by lighter ions without‬ ‭altering the osmotic values of the internal liquids. In the noctiluca dinoflagellate there are high‬ ‭concentrations of NH4, which is isosmotic with respect to sea water but lighter. The same solution to‬ ‭the flotation problem has also been found in large animals that are part of the nekton, such as squid:‬ ‭they have a flotation chamber, filled with a solution rich in ammonium which can reach up to 2 ⁄ 3 the‬ ‭size of the interior animal.‬ ‭Another strategy is that of salps and ctenophores that eliminate heavier, divalent ions, such as‬ ‭the sulfate ion, replacing them with lighter monovalent ions such as the chloride ion. Another‬ ‭weight reduction mechanism consists in the storage of light material: in particular lipid droplets,‬ ‭which can find localization both at a cellular and extracellular level. In some colonial algae,‬ ‭especially diatoms, lipid reserves are observed which reduce their specific weight. Lipid droplets‬ ‭are also found in pelagic eggs and larvae and in copepods even at the adult stage. These drops‬ ‭therefore have a dual function, that of energy reserve and that of flotation. Structures with a‬ ‭similar function are also gas vacuoles, present in many cyanophyceae, radiolarians and bacteria.‬ ‭In the plankton we saw a strong presence of organisms‬ ‭gelatinous, a further flotation strategy permitted by an increase in water‬ ‭in the tissues. To float better you can then use gas-filled flotation organs,‬ ‭the pneumatophores.‬ ‭Pneumatophores are typical of siphonophores and jellyfish. Among the‬ ‭algae we find floating organs such as the heterocysts of the Sargasso‬ ‭and of many phaeophyta present along the coasts such as‬‭Fucus‬‭. Most‬ ‭teleosts also use the swim bladder, but this strategy is also typical of‬ ‭cephalopods, such as cuttlefish, spirulina and‬‭Nautilus‬‭, which have‬ ‭chambered shells.‬ ‭very slowly, it seems to take them 15 years to reach size and reproductive age and I am among‬ ‭the oldest living beings (500 million years ago like ammonites).‬