Arxiu d'etiquetes: dam

Carnivorous plants

The carnivorism is a nutrition style associated to animals, to the world of heterotrophs. But it has been seen that there are plants that are also able to feed on other organisms. They are called carnivorous plants and their strategies to capture dams are very different and curious.


A carnivorous plants , even being autotroph, get part of their nutritional supplement by feeding on animals, especially insects.

There are three basic requirements that  carnivorous plants must comply:

  • they must be able to attract, capture and kill the preys. To get their attention, they usually show reddish coloration and secrete nectar. Morphological and anatomical adaptations for retaining and killing the preys such as traps are used.
  • Digestion and absorbance of the nutrients releasedby the damn .
  • And finally, it has to draw significant benefit from the process.
Dionaea muscipula
Venus flytrap (Dionaea muscipula) (Author: Jason).


Carnivorous plants are  not competitive in normal environments and tend to have a small root system, they need this specialization to allow them to grow faster. They are usually found in low mineralization soils, but with a high concentration of organic matter, sunny areas (as they still perform photosynthesis) and with  a high humidity.

Normally they are also calcifuges, i.e., they are not well adapted to alkaline soils and prefer acidic environments, where the source of calcium comes from the prey. They tend to inhabit soils with low oxygen and  saturated in water in a reducing environment. Some are aquatic and live either floating or submerged, but always near the surface.


The capture system is quite diverse, but can be classified according to whether there is movement or not. We consider active strategies for those plants having mechanical or suction movements. Semi-active strategies which present mucilaginous glands and have movement and finally, passive ones, with no motion for prey capture. They can present mucilaginous glands or pitfall traps. Somes amples are given below.


Venus flytrap

In the case of this plant, the traps are mechanical and they are formed by two valves joined by a central axis. These valves are the result of non photosynthetic leave transformations. The stem acts as a petiole and performs photosynthesis, for this reason, it is thickened, increasing its surface and facilitating the process. Furthermore, the valves have nectar glands to attract preys and its perimeter is surrounded by teeth which help the capture, as when the trap is closed, the teeth overlay perfectly avoiding the animal’s escape..

But, what mechanism drives the closing? There’s a gigh number of triggers hairs inside the valves. When the dam is located on the trap and makes the trigger hairs move twice or more in less than 20 seconds, the valves close immediately.

In this vídeos From the BBC one (Youtube Channel: BBC) we can observe the whole process.

Utricularia, the bladderwort

This plant lives submerged near the surface and is known as the bladderwort, because it has bladder-like traps. The bladders are characterized for having sensitive hairs that activate the suction mechanism of the dam. Then, the bladder generates a very strong internal pressure that sucks water in, dragging the animal to the trap. It’s volume can increase up to 40% when water enters.

In the following video we can see the bladderwort trapping a tadpole of cane toad (Youtube Channel: Philip Stoddard):


When I caught you, you won’t be able to escape

The presence of stalked mucilaginous glands is not unique in the carnivorous plant world, many plants use them as a defence or to prevent water loss. But, some carnivorous plants they are used to capture animals, as the sundews (Drosera) does.

The glands presents on the leaves of the sundews are formed by a stalk and an apical cell that releases mucilage. This substance attracts preys by its smell and taste. When the dam is located on the leaves, some drops of mucilage join each other to form a viscous mass that will cover all the prey, preventing its escape. We note that the glands have some mobility and move themselves to get in contact with the prey. Also, as a result, the leaf wrappes, facilitating the subsequent digestion.

The following video shows the operation of this mechanism (Youtube Channel: TheShopofHorrors):


Don’t get to sticky! 

The Drosophyllum‘s case is very similar to the previous one, but this time the stalked mucilaginous glands don’t have mobility and, therefore, the leaf doesn’t have either. The insect gets caught just because it is hooked on it’s sticky trap and cannot escape.

Insects trapped by Drosophyllum‘s stalked mucilaginous glands  (Author: incidencematrix).

Carefull not to fall!

Finally, we see the passive pitfall traps. They sometimes have a lid that protects them from an excess wàter getting in, even though it isn’t a part of the trap mechanism. The pitfall traps can be formed by the leaf itself or by an additional structure that is originated from an extension of the midrib (the tendril). The tendril lowers to ground level and then forms the trap.

Nepenthes (Author: Nico Nelson).

Dams are attracted to these traps due to nectar glands located inside. Once inside, going out is very complicated!  Walls may be viscous,  have downwardly inclined hairs that hinder to escape or present translucent spots that suggest the prey that there’s an exit, acting like windows , confusing and exhausting the prey, making it fall to the bottom, where it will drown. Other species also release substances that stun the preys, preventing them from running away.

Heliamphora (Author: Brian Gratwicke).

In some cases, large animals have fallen into these traps, though it is considered more as an effect of “bad-luck” than the plants supposed diet, though some traps measure up to 20cm long.



Why are beaches disappearing?

Probably you have listened that our beaches are disappearing. Why do beaches disappear during storms? Why do beaches not regenerate naturally? There are several causes that explain the regression of line coast, having all of them a human origin. In this article, I want to explain which are the reasons of the regression of beaches and which are the possible solutions to this problem. 


Beaches are zones placed between land and sea where sediments accumulates. Not only are they a place where people can enjoy, but also a habitat for many animal and plant species and with a defensive function.


On beaches, there is a sediment accumulation from fluvial flows. Swell, on the one hand, causes a displacement of these sediments through the coast (with more or less intensity), what is known as longitudinal littoral transport. To maintain a beach, the amount of sediments that disappear from a beach have to be the same that those that are added. On the contrary, the beach reduces (prevails the erosion) or increase. It has to be added the transversal littoral transport, which consists on the swell moving sediments from emerged beach to underwater beach, or backwards. Wind, at the same time, can produce an accumulation of sediments in the more interior part of the beach, creating dunes.

Funcionament dinàmic de la costa (Imatge: Directrices sobre Actuaciones en Playas)
Dinamic functioning of coast  (Picture: Directrices sobre Actuaciones en Playas)

So, a beach is working correctly if:

  • There is a stable source that contribute with the necessary sediments to make a beach.
  • There is a free movement of the sediments through the coast and in the transversal way.

Therefore, the main problems of regression of beaches are due to a modification of one or both factors.


Now, it’s time to talk about the reasons why beaches in our littoral are being reduced or in regression. As mentioned above, these can be classified in two types: causes that reduce the source of sediments and causes that impede their movement.


Construction of dams, with the aim of regulating the flow of rivers, is one of the main causes of the regression of beaches. The construction of dams produce a retention of sediments in the reservoir of water, what impedes their movement river downhill and, for this reason, their arrival in coast. It is this accumulation that explain that the useful life of dams is just 55-60 years. To give an example, in the Ebro Delta (Catalonia) arrives every year 200,000 tonnes of sediments, 10 times less than what is necessary to maintain the delta constant and 100 times less than what arrived in 20th Century.

Les preses produeixen l'acumulació de sediments i, per tant, la regressió de les platges (Foto extreta de Adasa).
Dams produce an accumulation of sediments and, for this reason, the regression of beaches (Picture from Adasa).

The urbanization of littoral zone close to beaches impedes the mobilization of sediments. Without going any further, due to the increase of the interest in the last decades of the population to coast, there have been a massive construction of promenades behind beaches, followed by important flat blocks. This has supposed the destruction of dunes and their plants mostly in all the littoral. Dunes are important zones of accumulation of sediments, so they constitute a sediment reservoir, it is that after a storm, wind can sweep along sand form this ecosystem and, thus, it can naturally regenerate the beach. Moreover, dune’s vegetation give stability to the beach since it affixes the sand and impede its erosion.

La construcció de passeigs marítims sovint va acompanyada de la destrucció de les dunes, el que té un efecte negatiu sobre les platges (Foto de
Construction of promenades is usually accompanied by the destruction of dunes, that has a negative effect on beaches (Picture from

There are other explanations, like the occupation of the surface of rivers by urbanizations or the removal of sand and gravel, among others.

As we have seen with dunes, these could be a source of natural regeneration of beaches. We have to had also in consideration that the destruction of seagrasses (like Posidonia) due to the urban development, bottom trawling, construction of harbours, piping and sewage pipes and the increase of anchors helps that the transported sand during a storm isn’t retained in the zone close to the beach, so this sand don’t naturally return by swell to the original position.

La destrucció de la Posidonia afavoreix l'erosió de la costa (Foto de Periodico de Ibiza).
Destruction of Posidonia contributes to the erosion of coast (Picture from Periodico de Ibiza).


Again, the occupation of beaches by buildings and other infrastructures explains why sediments can’t be spread through coast with freedom. Anyway, it is important to mention the construction of maritime structures. Effectively, we are referring to the construction of dikes, breakwaters and harbours, that constitute a barrier that produce the accumulation of sediments in the opposite side of the current direction, while it produce erosion downhill.

Les obres marítimes alteren la dinàmica del transport de sediments (Foto de Cyes).
Maritime constructions modify the dynamics of sediment transportation (Picture from Cyes).

To all this causes, we have to add the global change that, due to the rise in the sea level, is producing the disappearance of the littoral because it is sinking.


There are several possible solutions to face beach regression, but all of them have their problems:

  • Artificial regeneration of beaches with marine or terrestrial sediments. The dredging of sea floor has a negative impact on plants and animals of the zone, specially if these areas have seagrasses like Posidonia. When the origin is terrestrial, it usually come from quarries (with the posterior crushing), so its touch is not pleasant and it produces the destruction of mountains.
  • Construction of maritime structures like dikes and walls. These are not free from problems because they produce the erosion downhill.
  • Elimination of obstacles that stop the sediments or the free circulation.

Sometimes, the most prudent solution, in the case of not being any interest for population, is to leave the beach to its luck. It means to leave the natural evolution of the beach happen.