The sea urchin is nocturnal, hiding in crevasses during the day and emerging at night to feed. Sea urchins can be found in both warm and cold water.
No one in his right mind would get close to anything as spiny as a sea urchin, but walking in the water makes it easier for people to step on them. Sea Urchins have long sharp spines that penetrate very deep and sometimes break, causing severe pain and infection. In most sting cases, the spines have to be removed surgically. But sometimes it is a better idea to leave the spines alone if it isnt a severe penetration,being organic ,it will eventually dissolve into the bloodstream.
Not all Sea Urchins are venomous like the very common black spined urchins in the picture but one of the most dangerous, the Flower urchins can be deadly. It looks like its body is covered by flowers instead of thorns, but they are in fact venomous and can cause paralysis or, even worse, death. There have been several reports of people killed by Flower Urchins around Japan.
Lionfish..like the scorpion fish and stone fish cousins , if accidentally stepped on ,have venom in their spines that can be excrutiatingly painful,and in extreme envenomation be fatal. Lion fish is pretty to look at but be careful approaching them.
Many unwary snorkellers or barefoot walker on the shallows of the shore may unintentionally step on a stone fish,or if not looking at where you grab onto while snorkelling or scuba diving , may just as likely grab on to a scorpionfish. They are masters of camouflage,so well blended into their surroundings ,you wont even know its there.
Fire coral mishaps are among the most common among snorkellers who just dont know any better and breath hold dive down to have a closer look at, and then grab on to the fire coral for stability.
Divers who touch or even accidentally brush against fire coral, experience a painful sting that burns like acid on the skin -- thus the name fire coral.
Conversely, fresh water and soapy solutions actually aggravate the nematocysts. The last thing you want to do if you are stung by hydroids or fire coral is to rinse the skin with fresh water. It actually prompts any remaining nematocysts to fire.
If you are ever stung by hydroids or fire coral, you won't forget it. Usually a welt or rash arises immediately and stays for a week or more, burning again every time you take a shower or bath.
Hydroids look like delicate seaweeds, but they are actually animals, closely related to corals, jellyfish, sea anemones and Portuguese man-of-war.
At least 28 species of hydroids, most standing only a few inches tall, inhabit the shallow waters of the main Hawaiian Islands. They are also common along coastlines nearly everywhere else in the world. Rocks, boat bottoms, and piers often bear colonies of these delicate creatures.
The dainty appearance of these animals is deceiving. Hydroids are carnivores, using their nematocyst-laden feeding tentacles, positioned along their "branches", to sting and catch passing shrimp, worms and animal plankton.
These stinging nematocysts also discharge venom into human skin upon contact. Hydroid stings are fairly common among people who clean fouled boat bottoms. Also, scuba divers sometimes get hydroid stings by accidentally brushing up against a colony, like I did during the a diving incident.
Hydroids can cause other trouble. In 1955, pieces of hydroid colonies were dislodged from rocks during construction of a pier in a Harbor. Project workers, who often were standing in the water, were plagued by these drifting remnants that got caught under their clothing,resulting in stings that felt like fire ants.
Most hydroid stings almost immediately produce small red bumps that remain itchy and painful for hours. Sometime victims feel a prickly stinging sensation. This rash can last up to 10 days. Skin with hair on it usually has less reaction than bare skin. More-severe sting reactions are blisters, swelling and hives.
No cure exists. Rinse the sting with water, preferably hot, to wash away any adhering nematocysts, then apply ice for pain. For persistent itching or skin rash, try 1 percent hydrocortisone ointment four times a day, and one or two 25 milligram diphenhydramine (Benadryl) tablets every six hours. Diphenhydramine may cause drowsiness so don't drive, swim or surf after taking this medication. Both these drugs are sold without prescription.
If you encounter anything that resembles a fern like plant,dont touch it.Its actually an animal,A coral.
Sometimes the hydroids are so filament like thin you cannot see it,Very common in rocky crevasses or on the side of old wrecks or inside swim throughs and underwater caves,Just takes a tiny graze with your bare flesh and the stinging pain will be felt instantly.
Crown of thorns
This predator starfish feeds mainly on corals,like the urchin it belongs to the starfish family,but the thorns have venom that is even though not fatal when spiked but the pain is excrutiatingly hard to bear.They like to hide away in daytime in coral nooks and crannies.