The Coastal Challenge: Quiz Answers!

How well did you do, explorer? Check your answers below and discover some extra fascinating facts from the guide!

Finding your sea legs! (Easier round)

The Answer: Moon Jellyfish (Aurelia aurita). Did You Know? Moon jellyfish are bioluminescent, meaning they can produce a gentle glow, especially when disturbed at night. They have a very mild sting that most humans can’t even feel!
The Answer: ~1000 cm. Did You Know? Despite their enormous size, basking sharks are gentle giants. Their huge mouths can be over a metre wide, but they use them to filter tiny plankton from the water, not to bite.
The Answer: Velvet swimming crab (Necora puber). Did You Know? Its nickname isn’t just for show! This crab is famously aggressive and will often raise its claws and track your movements if you get too close. Its back legs are flattened like paddles, making it a surprisingly fast swimmer.
The Answer: Plaice (Pleuronectes platessa). Did You Know? Plaice are masters of disguise. They can change their skin colour and pattern in minutes to perfectly match the sand or gravel they are lying on, making them nearly invisible to predators and prey.
The Answer: Blue.Did You Know? The Portuguese man o’ war isn’t a single jellyfish but a ‘siphonophore’—a floating colony of individual organisms working together. The gas-filled float acts as a sail, catching the wind to travel across the ocean.
The Answer: W-shaped. Did You Know? Cuttlefish have three hearts! Two are used to pump blood to their gills, while the third circulates blood to the rest of the body. Their blood is blue-green because it uses a copper-containing protein to transport oxygen.
The Answer: It expels its internal organs. Did You Know? This dramatic defence is called ‘evisceration’. The sticky, toxic organs entangle and deter predators, giving the sea cucumber a chance to escape. It can then regrow all of its lost organs within a few weeks!
The Answer: John Dory (Zeus faber). Did You Know? Its body is incredibly thin when viewed head-on, allowing it to sneak up on prey without being seen. When it’s ready to strike, it shoots its tube-like mouth forward to vacuum up small fish and crustaceans.
The Answer: Garfish (Belone belone). Did You Know? The green colour in a garfish’s bones comes from a harmless iron phosphate called ‘biliverdin’. This is the same pigment that can cause a green colour in bruises!
The Answer: Over 40 miles per hour. Did You Know? Bluefin tuna are ‘endothermic’, meaning they can keep their body temperature warmer than the surrounding water. This allows their muscles to work more efficiently, giving them the power for incredible bursts of speed.
The Answer: Thresher shark (Alopias vulpinus).Did You Know? The thresher shark’s tail slap is so fast and powerful that it can create an underwater shockwave, stunning or killing multiple fish at once.
The Answer: Sandeel (Ammodytes tobianus). Did You Know? Sandeels aren’t true eels but a type of fish. They are a vital keystone species; the breeding success of many seabirds, including puffins, directly depends on a healthy sandeel population.
The Answer: Langoustine (Nephrops norvegicus).Did You Know? Langoustines spend most of their lives in intricate burrows they dig in the muddy seabed. They only emerge at night to feed, using their sensitive antennae to search for food in the dark.
The Answer: A “home scar”. Did You Know? A limpet’s shell is shaped to fit its unique home scar perfectly, creating a tight seal that protects it from predators and stops it from drying out at low tide. They use a tough, tooth-covered tongue called a radula to scrape algae from the rocks.
The Answer: Brown crab (Cancer pagurus).Did You Know? The guide mentions its pie-crust shell edge. Fishermen often call this crab the “pasty crab” in Cornwall because its crimped shell looks just like the edge of a Cornish pasty!
The Answer: By-the-wind sailor (Velella velella). Did You Know? The tiny sail is made of chitin (the same material as an insect’s exoskeleton) and is set at an angle to the float. This means the colony sails at an angle to the wind, not straight downwind, helping to spread them across the ocean.
The Answer: It drills holes into their shells. Did You Know? This drilling process can take several days! The whelk uses its radula to physically scrape away at the shell while also secreting a chemical that helps to soften it.
The Answer: By rubbing its antennae to make rasping sounds. Did You Know? The sound they create is surprisingly loud and is thought to be used to startle and deter predators like octopuses.
The Answer: Porbeagle (Lamna nasus) Did You Know? Like its relative the bluefin tuna, the porbeagle shark is also warm-blooded, which allows it to be a fast and powerful hunter in the cool waters of the UK. The Tope (Galeorhinus galeus) is also critically endangered.
The Answer: Cornish sucker / Clingfish (Lepadogaster purpurea). Did You Know? The suction disc of a clingfish is so powerful it can hold a weight of up to 150 times its own body weight.

The Advanced Explorer Questions (Harder round)

The Answer: Sunfish (Mola mola). Did You Know? A female sunfish can produce up to 300 million eggs at once—more than any other known vertebrate!
The Answer: Sessile. Did You Know? Many sessile animals, like mussels, have a free-swimming larval stage. This allows them to travel and find a new, suitable place to settle down for their adult lives.
The Answer: Lining up and swapping shells when a larger one becomes available. Did You Know? This orderly process prevents fights. The crabs often arrange themselves from biggest to smallest, and when the largest crab moves into a new, bigger shell, it sets off a chain reaction down the line!
The Answer: Dead organic material (detritus). Did You Know? Detritivores are the ocean’s clean-up crew. They break down dead plants and animals, returning vital nutrients to the ecosystem that fuel the growth of plankton and algae.
The Answer: Pelagic. Did You Know? The pelagic zone is divided into layers based on depth and light penetration, from the sunlit ‘epipelagic’ zone at the surface to the dark ‘hadopelagic’ zone in the deepest ocean trenches.
The Answer: European flat oyster (Ostrea edulis). Did You Know? Oysters are “ecosystem engineers.” A single adult oyster can filter up to 50 gallons of water a day, cleaning the water and creating healthier habitats for other species.
The Answer: Well-camouflaged or an expert at hiding. Did You Know? Many cryptic fish, like scorpionfish, have venomous spines as a last line of defence in case their excellent camouflage fails them.
The Answer: It’s the same across the globe, avoiding confusion from different local or regional names. Did You Know? This system, called ‘binomial nomenclature’, was popularised by Swedish botanist Carl Linnaeus in the 18th century and is still used today.
The Answer: Gephyrocapsa huxleyi (also known as Emiliania huxleyi). Did You Know? These blooms can be so bright that they cause ‘white water’ events, where the sea appears milky-white due to the reflection of sunlight off the tiny plates.
The Answer: Anadromous. Did You Know? Salmon use the Earth’s magnetic field to navigate the vast open ocean and have an incredible sense of smell that helps them find the exact river where they were born.
The Answer: Mackerel (Scomber scombrus). Did You Know? Because they lack a swim bladder for buoyancy control, mackerel would sink if they stopped swimming. They must constantly move forward to generate lift with their fins, much like an aeroplane.
The Answer: Spectacular spring migrations. Did You Know? These crabs migrate from deeper water into the shallows to moult and mate. After moulting, their new shells are soft, so they gather in huge numbers for protection from predators until their armour hardens.
The Answer: Comber (Serranus cabrilla). Did You Know? Being a simultaneous hermaphrodite means a comber can act as a male or female at any given time, and they sometimes even switch roles during a single spawning event!
The Answer: The specific species. Did You Know? Its scientific name, Patella vulgata, is quite descriptive. The Genus name, Patella, is Latin for “little dish” or “kneecap,” which perfectly describes the shape of its protective shell. Vulgata simply means “common” or “general”
The Answer: The male Seahorse broods eggs in a pouch, while the male Snake Pipefish broods them under his tail. Did You Know? Seahorse pregnancy is very active. The male provides the eggs with oxygen and nutrients through the pouch lining and even experiences muscular contractions to ‘give birth’ to the tiny, fully-formed baby seahorses.
The Answer: Grey triggerfish (Balistes capriscus). Did You Know? To eat a sea urchin, a triggerfish will often blow a jet of water at it to flip it over, exposing the urchin’s less-spiny underside and its vulnerable mouth.
The Answer: 10 limbs. Did You Know? For crabs, lobsters and other decapods, this includes their eight walking legs and their two large claws (chelae).
The Answer: Herring (Clupea harengus). Did You Know? Scientists call this unique communication method ‘Fast Repetitive Ticks’ or FRTs. It’s believed to help the shoal stay together in the dark.

During the height of the Cold War, the Swedish Navy repeatedly detected strange underwater sounds on its advanced sonar systems in the Baltic Sea. The sounds were described as ticks, clicks, and fizzing noises, almost like bacon frying.
Given the extreme political tension and previous confirmed incursions by Soviet submarines into their waters, the Swedish military suspected they were hearing a new form of secret, hi-tech propulsion from Soviet mini-subs or underwater drones. This led to massive, expensive, and ultimately fruitless submarine hunts that lasted for years and became a major international incident.

The Surprising Culprit: Herring
The mystery wasn’t solved by military intelligence, but by a marine biologist. In the mid-1990s, Professor Magnus Wahlberg and his team finally proved that the “hi-tech submarines” were, in fact, enormous shoals of herring.
They discovered that herring release air from their swim bladders through their anal duct, creating a high-frequency sound. This unique communication method is now known as FRTs (Fast Repetitive Ticks). The sound is produced when the fish are startled or when they gather in dense shoals at night, exactly when the mysterious sonar contacts were most common.
Essentially, a major Cold War submarine scare, which had baffled an entire navy for over a decade, was caused by the collective sound of fish flatulence!
The Answer: Ling (Molva molva). Did You Know? Ling is a predatory fish that often hides in wrecks and rocky crevices, waiting to ambush other fish and crustaceans that swim past.
The Answer: Sturgeon (Acipenser sturio). Did You Know? Sturgeon have sensitive barbels (whiskers) under their snouts which they drag along the seabed to detect food like worms and crustaceans hidden in the mud.