The average salinity of seawater in the world's oceans is around 3.5%, which makes it difficult for most freshwater organisms to survive in such an environment.

Additionally, few large trees can adapt to the salinity of seawater because the high salt content leads to dehydration due to excessive osmotic pressure inside and outside the cells.

However, there are exceptions to everything. Along tropical and subtropical coastal beaches, a unique group of plants grows. They rise and fall with the tides, their roots almost interlocked, standing like a wall along the coast. They are mangroves.

For those unfamiliar with mangroves, it's easy to imagine them resembling the autumnal appearance of maple trees, but that would be far from the truth. Mangroves, like other forests, are green in color. They are called "mangroves" because tannins are abundant in the mangrove species. When exposed to air, these tannins rapidly oxidize, forming a reddish-brown color.

In ancient times, the bark of mangroves was used as a dye. It's important to note that mangroves are not a single species of tree but rather a category of trees. Approximately 100 species of mangrove plants worldwide are widely distributed along the coasts of tropical and subtropical regions.

Having lived by the sea for a long time, mangroves have adapted to the ebb and flow of the tides. During high tide, mangrove trunks are submerged in seawater; during low tide, the roots are exposed. Describing them as the "miracle of the sea" with "one forest and two scenes" is not an exaggeration.

Of course, mangroves vary depending on the location: mangrove populations growing inland and in tidal zones are called "semi-mangroves." Those plants growing only along the coast are referred to as true mangroves.

Not all places are suitable for mangrove growth; numerous stringent conditions must be met: Firstly, temperatures must be high, with the coldest time of the year not dropping below 20 degrees Celsius, and the temperature difference must remain within 5 degrees Celsius.

Secondly, the sediment must be relatively soft, preferably in areas where sediment carried by inland rivers impacts the estuary, making it suitable for seedlings to take root. Lastly, the tides cannot be too strong; otherwise, waves will carry away sediment and seedlings, making it difficult for mangroves to form.

This area must also be large enough to allow mangroves to grow freely; otherwise, limited space would restrict their survival.

The Secret of Surviving in Seawater

Even humans, powerful as they are, cannot stay in the sea for extended periods, let alone every day. Mangroves can survive in such harsh environments thanks to their unique regulatory mechanisms.

It's not difficult for plants to survive in seawater as long as they can control the concentration of cell sap and seawater. However, growing on the sea surface is quite challenging. Not only must they overcome the issue of seawater concentration, but they must also consider the threat of direct sunlight.

Growing in seawater, the concentration of seawater remains almost constant. However, in the mangrove growth area, there are tidal phenomena where water may recede. During this time, the sunlight shines directly on the tidal flats, causing water to evaporate and increasing salt content. This is the most challenging aspect of mangroves surviving by the sea.

Additionally, seawater reflects sunlight, causing plant moisture to evaporate.

Underneath is highly saline seawater and oxygen-deficient soil, occasionally being hit by seawater, which is bad news for plant seeds. Thus, mangroves have evolved an exceptional method of reproduction.

Moreover, the cuticle structure of mangroves is thick, containing water storage tissue, which prevents cells from swelling and bursting due to excessive water absorption. The leaves resist sunlight, a prerequisite for mangrove growth and development. The unique structure of the roots is fundamental to mangroves surviving on tidal flats.

Tidal phenomena continuously erode the soil at the roots of mangroves, so a massive root system must be established to avoid being washed away by seawater.

As everyone knows, plant roots also require a certain degree of air permeability; root rot is likely to occur if they stay in water for a long time.

To solve this problem, mangrove lateral roots bulge upward on the side, forming a plate-like prop root structure. Some mangroves grow erect breathing roots, which generally break through the soil and grow above the water surface.

Through these two unique structures of leaves and roots, mangroves achieve their goal of surviving on tidal flats.

Currently, there are 120 million people globally living near mangrove wetland systems, relying on mangroves for their survival. According to statistics, there are over 3,500 species of fish known to inhabit mangrove ecosystems worldwide, serving as the birthplace of 76% of tropical fish and the habitat of 80% of marine economic fish species.

Therefore, humanity needs to continually establish standards and norms for mangrove ecosystems, increase the probability of converting scientific research results, and carry out diverse educational activities about mangroves, creating a good atmosphere of concern for and cherishing mangroves throughout society.