Category America South – Atlantic Coast – Tropical

Hard Coral

Mussismilia spp.

Hard corals are also referred to as stony corals, and are members of the order Scleractinia. Hard Corals can be differentiated from other types of corals by their calcium skeleton or base. These corals are often broken down into two groups by their polyp type: small polyp stony corals (SPS) and large polyp stony corals (LPS). Live corals are found throughout the world in tropical waters on coral reefs. Most of these corals are found at depths no greater than 50 metres.

Hard corals are similar to anemones in that both animals use a mechanism called a nematocyst to deliver a sting to ward off predators, or maintain their space on the reef from other species of competing corals. Some species of LPS have sweeper tentacles that can reach several inches long at night...

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Long spined sea urchin

Diadema spp.

Sea urchins are often used as indicator organisms in public aquariums to determine whether the system is functioning properly. These organisms are extremely sensitive to water conditions and are first to show signs of stress, seen when their spines are laid down or are shed.

Warning! Some sea urchins are covered with sharp venom-filled spines that can easily penetrate and break off into the skin – even through a wetsuit. The DAN (Divers Alert Network) website contains useful information on how to handle the unfortunate effects of accidental brushes with these and other poisonous marine organisms. Check out for any information that you need.

Sea urchins (echinoderms) are a group of marine invertebrates that can be found in almost every maj...

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When people talk about coral reefs, fishermen tend to shrug their shoulders and complain about snagged lines and torn nets. But when you talk about groupers, they suddenly sit up and pay attention. Groupers are among the economically most important fishes of the coral reef, because of their popularity as food. Yet without the coral reef there would probably be no groupers. For this reason, groupers are an extremely important indicator species and your record of their existence or non-existence during your dive tells us a lot. Like all indicators, it is valuable if you can record the particular species you sight. However, recording the total number of groupers is just as important...

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Identifying sharks in the wild is a great challenge! While scientists can spend weeks examining every detail of a species, divers may encounter a shark for only a few seconds or minutes. Many species look alike and one individual may not be identical to the next. There are, however, relatively few species in any one specific dive site and with some preparation and a little practice it is possible for all of us to recognise the more common and distinctive species. The key to successful shark identification underwater is a process of elimination, based on a mental checklist of the main features to look for in every animal encountered. One feature alone is rarely enough for a positive identification, so gather as much information as you can before drawing firm conclusions.

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