Coral Garden by Jan Messersmith

What at first appears to be a blanket of fine snow on the sea bed is actually a patch of bleached coral off the northern shore of Papua New Guinea. As sea temperatures rise, this scene is becoming more and more common in coral reefs around the globe. Rising temperatures make corals expel their zooxanthellae (algae with which corals have a symbiotic relationship), leading to starvation.

This is particularly bad news because once a reef dies, it turns to rubble, making it impossible for new coral to grow on top of it. This essentially turns what was once a flourishing biodiversity mini-hotspot into a sort of ecological deadzone.

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The blue coral snake (Calliophis bivirgata) is sometimes colloquially referred to as the “100-pace snake” because it is said that a human can make it 100 paces away after sustaining a bite from this animal before they die. However, there are not many recorded cases of human fatalities due to this snake, which hints that the snake gets a worse reputation than it deserves. Its typical prey is other snakes.

(Photo © Tom Charlton)

“Reefs in the Caribbean are experiencing a budget crisis: Corals’ production of calcium carbonate — their bony material that creates reefs — is way down, a 16-month-long investigation finds. Shallow-water reefs are in especially bad shape, with growth rates that are 30 to 40 percent of historical values. Many of these shallow sites also lack Acropora species, which are key reef-building corals that typically produce a lot of carbonate. These degraded reefs also have a lot of smothering seaweed and few critters to graze upon it, the study of 19 sites found.

The new analysis, published January 29 in Nature Communications, suggests that when the amount of live coral in a reef drops below about 10 percent, erosion begins to outpace growth of new reef structures. Many Caribbean coral reefs are approaching this tipping point, the team led by Chris Perry of the University of Exeter in England found. Ongoing assaults such as warming waters and ocean acidification may further hinder reefs’ efforts to get their budgets back in the black.”

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The Red Sea contains arguably the richest, most biologically diverse, and most spectacular coral reefs outside Southeast Asia. Live coral cover throughout the Red Sea reefs is generally high, at about 60–70%, as is the diversity of stony and soft corals, fish (including the famous Red Sea lionfish [Pterois miles]), and other reef organisms. More than 260 different species of stony coral have been identified in the central Red Sea.

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Most of the 5000 or more sponge species are marine, although some 150 species life in fresh water. Marine sponges are abundant in all seas and at all depths, and a few even exist in brackish water. Although their embryos are free swimming, adults are always attached, usually to rocks, shells, corals, or other submerged objects.

This orange demosponge, known as the orange icing sponge (Mycale laevis), often grows beneath platelike colonies of stony corals. The large oscula of the sponge are seen at the edges of the plates. Unlike someother sponges, Mycale does not burrow into the coral skeleton and may actually protect the coral from invasion by more destructive species.

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While most corals grow as colonies in tropical waters, the Devonshire cup coral (Caryophyllia smithii) is solitary and lives in temperate parts of the ocean. It grows with its cup-shaped skeleton attached to a rock or even a shipwreck. When the tentacles are expanded, these tiny corals look just like anemones, with each tapering, transparent tentacle ending in a small knob. Devonshire cup coral often occurs in a variety of corals from white or orange.

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Animals in the phylum Cnidaria are often classified into four classes: Hydrozoa, Scyphozoa, Cubozoa, and Anthozoa. “Cnidaria” means “stinging nettle,” and animals are classified in this phylum for possessing stinging cells called nematocysts.

Hydrozoa - Siphonophores and Hydra (3,600 species) (Photo source)
Scyphozoa - Jellyfish (228 species) (Photo source)
Cubozoa - Box Jellies (42 species) (Photo source)
Anthozoa - Sea Anemones, Corals, and Sea Pens (6,100 species) (Photo source)

A nudibranch Pteraeolidia ianthina, common name Blue Dragon, glides across the coral.

Photo © Christopher Bartlett

Dendrophyna soft branching coral and a feather star, a marine animal of the class Crinoidea of the echidnoderms.

Photo © Christopher Bartlett