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Lobsters, like shrimps and crabs, are decapods – literally meaning 10 legs – and can be found in all of the world’s tropical and subtropical seas as well as more temperate waters. They are predatory, nocturnal animals with a vividly decorated coat. They are often numerous locally; they linger in crevices (with their long antennae sticking out) during the day and hunt small benthic organisms at night, but they also feed on organic detritus whenever they happen across it. As with all crustaceans, the lobster moults or sheds its shell to grow.

Lobsters have recently suffered a dramatic demographic decline; intensive fishing has annihilated entire populations, especially where tourism abounds.

The lobster families that you may encounter are the spiny rock lobsters, Palinuridae, ...

Serranidae

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 economicallymost important fishes of the coral reef, because of their popularity as food. Yetwithout the coral reef there would probably be no groupers. For this reason, groupers are an extremely important indicator species and your record of theirexistence or non-existence during your dive tells us a lot.

The Dusky Grouper (Epinephelus marginatus) feeds on octopi, crustaceans (crabs) and fishes. It lives on rocky bottoms very close to the coasts. Because of its enormous final size (1,5 meters of length) it is the most impressive coastal fish...

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.

earthdive wants you...

Diplodus sargus capensis

Seabream or porgies are members of the Sparidae family of carnivorous bony fishes. Porgies are carnivores of hard-shelled benthic (bottom dwelling) invertebrates. Many species have been found to be hermaphroditic; some have male and female gonads simultaneously. Others change gender as they get larger.

The structure of the fins of Porgies is essentially the same as in the family Serranidae of seabasses with which they can be confused. There are important anatomical differences, however, most obvious of which are that the edge of the gill cover does not end with a sharp spine in the porgies but is rounded or at most bluntly angular; and that the maxillary bone (the bone forming the margin of the upper jaw) is sheathed and hidden when the mouth is closed.

Lo...

of the families Blennidae & Clinidae

The family of combtooth blennies, Blenniidae is primarily marine, although they are occasionally found in brackish and freshwater. Blennies are diurnal, shallow-water species, and are for the most part found in the tropical and subtropical seas, distributed worldwide, being found in the Pacific, Atlantic, and Indian Oceans, in the Red and Mediterranean Seas, and in the Caribbean. This preference for warmer waters means that of well over 300 species worldwide, only a few will be found in the cooler waters of the Benguela Current.

Blenniids are small, naked-bodied (scaleless) fishes, usually with blunt heads. The pelvic fins are before the pectoral fins and have one short embedded spine and between two and four soft rays...

Parechinus angulosus

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. Sea urchins are highly sensitive to air and direct sunlight, and often use bits of shell and pebbles as sunshade ‘umbrellas’. Sea urchins (echinoderms) are a group of marine invertebrates that can be found in almost every major marine habitat from the poles to the equator and from the inter-tidal zone to depths of more than 5,000 metres. There are around 800 extant species and the group has a long and detailed fossil record stretching back many millions of years.

All echinoderms have ...

Mytilus galloprovincialis, Perna perna and Semimytilus algosus

Mussels are fast becoming South Africa’s biggest source of income from marine products and the industry is gaining a considerable export market. Mussels are marine molluscs of the class Pelecypoda, which means hatchet-foot. They are bivalves, having a shell consisting of two valves, or movable pieces, hinged by an elastic ligament.

Within the shell there is a fleshy layer of tissue called the mantle with a cavity (the mantle cavity) between the mantle and the body wall proper. The mantle secretes the layers of the shell, including the inner nacreous, or pearly, layer. Nacreous layers can also be formed around a foreign body in reaction to irritation...

Mytilus galloprovincialis, Perna perna and Semimytilus algosus

Mussels are fast becoming South Africa’s biggest source of income from marine products and the industry is gaining a considerable export market. Mussels are marine molluscs of the class Pelecypoda, which means hatchet-foot. They are bivalves, having a shell consisting of two valves, or movable pieces, hinged by an elastic ligament.

Within the shell there is a fleshy layer of tissue called the mantle with a cavity (the mantle cavity) between the mantle and the body wall proper. The mantle secretes the layers of the shell, including the inner nacreous, or pearly, layer. Nacreous layers can also be formed around a foreign body in reaction to irritation...

Epinephulus spp.

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 economicallymost important fishes of the coral reef, because of their popularity as food. Yetwithout the coral reef there would probably be no groupers. For this reason, groupers are an extremely important indicator species and your record of theirexistence or non-existence during your dive tells us a lot.

The Goliath Grouper (Epinephelus itajara), sometimes called the jewfish, is classified as critically endangered on the IUCN Red List. Found in shallow, inshore waters to depths of 45m, this indicator prefers areas of rock, coral, and mud bottoms...

of the species Polysteganus undulosus, Petrus rupestris, Chrysoblephus cristicepsand C. gibbiceps

Seabream or porgies are members of the Sparidae family of carnivorous bony fishes. Porgies are carnivores of hard-shelled benthic (bottom dwelling) invertebrates. Many species have been found to be hermaphroditic; some have male and female gonads simultaneously. Others change gender as they get larger.

The structure of the fins of Porgies is essentially the same as in the family Serranidae of seabasses with which they can be confused...