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Seamounts are underwater mountains rising over 1000 metres from the ocean floor. They do not reach the water's surface. They are formed by extinct volcanoes whose lava piles suddenly rise to form peaks. They are important manne ecosistems that support a wide variety of oceanic wildlife, from corals to sharks . Seamounts and guyots are most abundant in the North Pacific Ocean, and follow a distinctive evolutionary pattern of eruption, build-up, subsidence and erosion. In recent years, several active seamounts have been observed, for example Loihi in the Hawaiian Islands.

Because of their abundance, seamounts are one of the most common marine ecosystems in the world. Interactions between seamounts and underwater currents, as well as their elevated position in the water, attract plankton, corals, fish, and marine mammals alike. Their aggregational effect has been noted by the commercial fishing industry, and many seamounts support extensive fisheries. There are ongoing concerns on the negative impact of fishing on seamount ecosystems, and well-documented cases of stock decline, for example with the orange roughy (Hoplostethus atlanticus). 95% of ecological damage is done by bottom trawling, which scrapes whole ecosystems off seamounts.

Because of their large numbers, many seamounts remain to be properly studied, and even mapped. Bathymetry and satellite altimetry are two technologies working to close the gap. There have been instances where naval vessels have collided with uncharted seamounts; for example, Muirfield Seamount is named after the ship that struck it in 1973. However, the greatest danger from seamounts are flank collapses; as they get older, extrusions seeping in the seamounts put pressure on their sides, causing landslides that have the potential to generate massive tsunamis.

Credit : Wikipedia 

Picture Credit : Google

An organism's appearance and body colour serve various purposes and they are strongly linked to the environment. In the marine environment, colouration is tied to how light penetrates ocean water and an animal's ability to blend in with its surroundings. A new study has found that fish communities on the Great Barrier Reef in Australia may become less colourful as corals bleach. The researchers studied the reef health, coral types, and resident fish over three decades.

The Great Barrier Reef, the largest coral reef system on Earth, has been subject to frequent bleaching events due to global warming in the past few decades. Coral bleaching events profoundly change the make-up of the ecosystem. Researchers say the loss of corals is a likely factor in the disappearance of brightly-coloured fish in the GBR.

The study looked at the diversity of colours found in communities of reef fishes and related that to the types of habitats where those fishes live.

 Fish communities in healthy parts of the reef with plentiful complex corals were compared to other areas where bleached corals dominate in the wake of major disturbances, such as heatwaves. The researchers found that as the cover of structurally complex corals increases on a reef, the range of colours present on fishes living and around them also increases. The diversity of fish colours declines in areas covered in dead, damaged corals. The bleached and dead corals probably provide less protection from predators for brightly-coloured fishes.

The researchers also found that the eye-catching yellow and green fishes, such as the lemon damselfish and green coral goby, have declined by about two-thirds, since the first recorded mass bleaching event of the reefs around Orpheus Island in 1998.

Picture Credit : Google