The importance of the shells
By Elisa Aliberti and Nadja Gunzinger

Monday, 21st October 2024

The importance of marine shells in coastal ecosystems

Aliberti Elisa, Gunzinger Nadja (visiting student and volunteer project on a non-sea day)

The importance of shells starts from the principle of their creation by marine organisms that use them for protection and home. In fact, shells are an interesting fusion of biology and chemistry because they constitute the exoskeleton of molluscs such as gastropods, bivalves and scaphopods, necessary to protect the internal organs of their body.

So firstly the shells that settle on the seabed and beaches are important as they contribute to the release of calcium carbonate into the ocean, contributing to the marine cycle. In fact, calcium carbonate is an essential component of the biogeochemical carbon cycle in the oceans, playing a fundamental role in the sequestration of atmospheric carbon. So the shells, once the organisms die and are deposited, can be subject to dissolution, releasing inorganic carbon into the water. The pH of the ocean varies with depth: at the surface, it is higher due to photosynthesis which consumes CO2, while at depth it decreases due to the respiration and decomposition of organic matter which produces CO2. Above 1000 metres, the pH tends to increase slightly due to lower biological activity and increased dissolution of calcium carbonate, which acts as a buffer against acidity.

Furthermore, shells can serve as new homes for other animals such as hermit crabs, as well as providing shelter for other marine organisms such as algae, marine plants, sponges and crustaceans, they can provide nest-building material for various types of seabirds.

Lastly, shells are also fundamental for science, as they are true geochemical records, in fact they preserve information on the marine environment in which they are found, such as light, temperature and the composition of the water useful for studies on changes environmental.

The problem of collecting shells

Shells are fascinating structures sometimes thought of as just a harmless souvenir.

But shell-building marine animals are suffering a decline due to intensive fishing, rising temperatures and acidification of the waters.

The shells already present on the beaches suffer damage from erosion, the construction of new structures, as well as from mass tourism which causes uncontrolled collection of them from the beaches. Furthermore, some machinery such as tractors used for beach cleaning, in addition to removing rubbish, also remove part of the shells and cause them to break.

In fact, some states limit the use of such machinery in certain periods of the year such as during the nesting of some marine species of birds or turtles.

But marine molluscs and other invertebrates do not receive the same attention or funding that animals like sea turtles receive. Ecologists have found that the International Union for Conservation of Nature's Red List, the official tool for assessing the severe decline of animals underway around the world, severely underestimates the loss of invertebrates, which alone make up roughly the 68.7% of all creatures.

Therefore, to protect the environment and marine animals, various states implement laws that prohibit the collection of shells from beaches in protected areas or which could suffer risks due to their lack.

The South African government, for example, does not allow collection in protected areas and nature reserves, furthermore there are regulations based on the species that is collected in the areas where collection is permitted, this is because a species of shell could be more at risk of disappearing of another. But in general, in areas where harvesting is permitted, it is possible to harvest up to 1 kg of shells without any permit. Permission must be requested when the withdrawal exceeds this threshold. As can be seen from this, it is impossible to truly protect a marine area when the withdrawal is granted in such large quantities, which is why greater restrictions are needed for the future protection of marine areas. It is high time for this law to be revised.