In nature, everything is interconnected and life doesn’t exist in isolation. On our wonderful planet there are more than 10 millions different species of animals. They share the same habitats and the same resources. In order to survive, or sometimes just for convenience, many creatures establish lifelong relationships with a completely different organism. A bond that will last forever, in biology this is called symbiosis. This comes from the Greek word Symbiosis: Syn “living together with another” and Biosis “life”.

Symbiotic relationships are an important component of life in the Ocean, and we can divide them in three different groups:

1. Mutualistic symbiosis
2. Commensalistic symbiosis
3. Parasitic symbiosis

Mutualistic Symbiosis

This is the life long bond between two organisms of different species and both of them are benefitting from the relationship. Mutualism can be obligate and facultative:

Obligate mutualism means that neither organism can live without one another.

Facultative mutualism means that the relationship is not essential for their survival.

An example of obligate mutualism is the specific relationship between coral and the algae (Zooxanthellae).

Zooxanthellae are microscopic and photosynthetic algae that live inside the corals. The coral provides housing and protection. With photosynthesis the zooxanthellae give the nutrients to their coral host, providing them energy and their beautiful colors. Without the algae, coral would starve to death (coral bleaching), so without this symbiosis coral reefs would not even exist.

An example of facultative symbiosis is the relationship between clownfish and anemone.

Sea anemones are predators with poisonous tentacles, that they use to paralyze their prey and bring it to their mouth to digest it. Clownfish, unlike other fish, have a special mucus layer that allows them to live within the anemone’s tentacles. While protecting themselves from other predators, clownfish help feeding the anemone.

Commensalistic Symbiosis

In the commensalistic symbiosis, one organism benefits from the relationship and the other doesn’t experience any significant positive or negative effects. Many coral reef shrimp species are in commensal relationships with their coral host. They use the coral structure as a safe place to live, and consume some of the coral’s detritus or waste products.

Parasitism

The last symbiosis in the ocean is the parasitism: one organism, the parasite, benefits by living on another organism, the host, causing harm and potentially leading to the death of the host.

And example are the isopods, crustacean parasites. Isopods are divided in 95 different families. There are several hundreds of species distributed worldwide in many different habitats. Isopods will attach themselves to the body of fish and they can act in different ways: some feed on blood and tissues, others even attach themselves to the fish’s tongue causing the tongue to disappear. After that, they will effectively take the tongues place. They can alter the fish behaviour, bring infections, increase stress hormone levels and impair the senses of the hosts.

It may be brutal, but parasites help maintain a healthy balance within the ecosystem, regulating the populations of various marine organisms. It is crucial to respect all living creatures on earth and in the ocean, in order to maintain the delicate ecological balance and preserve the diversity and the beauty of our planet.