Crabs, coral, and climate change: Why crustaceans matter, for all of us

From boxing crabs with sea anemones to those hitching rides on turtles, decapod crustaceans are among the most fascinating creatures on Earth. Yet many of us know very little about them. Today, on Crustacean Compassion Day 2025, we take a moment, not to focus solely on welfare or industry, but to celebrate the remarkable role these animals play in shaping our world. 

Decapod crustaceans belong to a group of animals known as invertebrates, which includes everything from insects, arachnids, crustaceans, corals, jellyfish, and sponges - right to the humble garden snail.  Numbering in their trillions, they are perhaps among the least understood animals on Earth.  Yet they play a central and often invisible role in shaping our world.  Invertebrates structure vital global ecosystems.  

Their roles are often invisible but essential: structuring habitats, recycling nutrients, and supporting biodiversity. Without them, many ecosystems, especially marine ones, would collapse. 

Nature’s recyclers: crustaceans and ecosystem health Without crustaceans like lobsters, crabs, and shrimp vast amounts of organic matter would simply not break down and the nutrients would fail to be recycled through ecosystems. It would pile up on the seafloor. The seas would become a soup of materials reducing oxygen levels, the ability to absorb carbon dioxide, and impacting life cycles from seaweeds and seagrasses right up to apex predators and the largest species alive on planet earth today. 

And it’s not just the sea. Coral reefs, crucial to over a billion people globally, depend on invertebrates. It is estimated that 1 in 6 people depend on coral reefs around the world for food, protection, and their livelihoods. In the UK, deep-sea cold-water corals are natural storm buffers, erosion shields, and nurseries for thousands of fish and other species - creating a biodiverse system vital for life.  

Corals themselves are invertebrates, but decapods play a critical role in their upkeep: cleaning algae, deterring predators, and enabling coralline seaweed to thrive, which locks away carbon as calcium carbonate.  Without crustaceans, coral reef – and they life they support - would falter.   

From larva to lifeline: A food web foundation 

Every single decapod crustacean goes through a planktonic larval stage as meroplankton to adults.  As part of the planktonic group they are food to a multitude of species (many fish species including salmon, rockfish, and herring have been found with bellies full of crab larvae) right up to apex ocean predators (whales, seal, otter, polar bear) and also land  species like sea birds, otters and yes, even humans.   

Their very existence as a planktonic form means they are a readily available food source, and their loss would not just mean no crabs or lobsters but would see entire ecosystems collapsing right up to the largest mammals on earth. 

Crustaceans are sentinels of change  We have all heard of the ongoing climate changes as a result of anthropogenic (human led) impact.  And the impacts of climate change are already visible. Major international industries such as the Alaskan crab fleet closed due to there being fewer and fewer crabs. This isn’t a minor dip in numbers; it’s a loss of millions of animals, linked to rising sea temperatures, acidification, deoxygenation, and unsustainable fishing. It's a reminder that decapods are sentinels of change, and that our choices are reshaping the oceans, often faster than these species can adapt. 

Evolution’s favourite shape: the crab  

Decapod crustaceans are a uniquely fascinating group of animals.  They are part of a delicate and dynamic series of interlocking ecosystems, vital to plant, animal, and human health.  Our influence over this group of animals either in direct contact or through wider population actions is increasingly damaging and we must be acutely aware of the long-term effects.  Without understanding these wonderful animals, the issues they face, and the potential measures needed to aid recovery we will witness an ongoing loss of diversity vital to all species on the planet.  Let’s get together and celebrate this truly remarkable group of animals. 

There are over 7,600 known crab species. What’s amazing is that crabs have evolved to live on land independently 7 to 17 times, and in some cases, they've re-evolved to return to the sea. Most animals make this leap once - if at all. This repeated pattern is so striking that biologists have a term for it: carcinisation, the tendency of evolution to produce crab-like forms. 

Some even jokingly say we’re destined to become crabs, because this body plan is so evolutionarily successful. For comparison: wings have evolved four times. Crab-like bodies? At least six. 

Crabs with character

People often ask me what my favourite decapod is. It’s hard to choose, but crabs absolutely fascinate me. Not only for their incredible evolutionary story, but for their feisty behaviours and clever adaptations. 

My favourite things are quite simple, I love the variety of ways they live – from Pom Pom crabs who carry tiny sea anemones in and on its claws which it uses for food gathering, defence and fighting – just like a boxer. Bromeliad crabs who live inland living  water filled plants, only have a few young and will actively catch insects to feed to the young; our common European Green crab who has been demonstrated to have maze solving capabilities similar to a mouse,  the Mandarin crab who completely bucks the aquatic trend of having millions of eggs in favour of only having 8-12 which she carries on her back and ultimately protects her brood. And lastly... the Flotsam crab who has a cushy life hitching free rides on sea turtles – basically hiding next to the turtles bottom where it’s safe from predators.  Typically, it is a male / female pair who ride along together – what a way to see the world! 

Take a moment

Next time you're at the beach, look down. That tiny crab you see has been on a longer evolutionary journey than the human species. It may seem simple, but it’s not: they can regrow limbs, climb trees, breathe air, and water, raise young, and even form symbiotic relationships.  In our quest to understand life on Earth, and beyond, perhaps the most fascinating creatures are already right here with us. 

Celebrate, learn, protect

On this Crustacean Compassion Day, let’s do more than just observe. 

• Learn something new about decapods. 

• Share a fun fact with someone. 

• Support marine conservation. 

• Pause and marvel at the life beneath the waves. 

Because if we lose them, we lose far more than just a species, we lose the systems that sustain life itself. 

Take action to protect crustaceans