Deep-sea life in the fiords: Part 1When people visit Fiordland, New Zealand, they are awed by the ma

Deep-sea life in the fiords: Part 1When people visit Fiordland, New Zealand, they are awed by the majesty of its natural landscapes, and rightly so. The place has a kind of fantastic, rugged, natural beauty - the likes of which is rarely found elsewhere. But below the veiled peaks, vast forests, and innumerable waterfalls for which it is famed, lies a unique underwater world. This is due to dynamics caused by the high level of rainfall in the area. Fiordland is one of the wettest places in the country, subject to an average of 7.5 metres (about 25ft) of rainfall each year. On its journey down the towering peaks, the rainwater picks up compounds (called tannins) from the organic plant material in the forest leaf litter. These tannins stain the water so that it becomes the colour of strong tea. It then enters the sea below, providing an essential source of nutrients for the rich marine ecosystem.Because seawater is denser than freshwater, and because there is little to no wave or tidal action within the fiords, the rainwater and the seawater do not mix. Instead, the freshwater sits as a permanent layer atop the seawater. This layer is usually about 4 metres (13ft) deep, but it can vary between 1 and 12 metres (3ft - 43ft) depending on the amount of rainfall at a given time.The existence of this freshwater band is what makes Fiordland’s marine environment so special. The stained freshwater acts like a screen, limiting the amount of light that is able to penetrate the depths to create an unusually dark marine environment at relatively shallow depths. Constrained by low salinity at the surface and limited light in the depths, marine life is concentrated within a band between 5 and 40 metres (16ft - 131ft) deep (also variable depending on the volume of rainfall). This band is characterised by calm, clear, and relatively warm water, which allows a diverse assortment of creatures - from carpet sharks to cup corals - to thrive here: collectively forming rich marine communities. More on this in the next post.VPReferences: http://bit.ly/1RIiEEQImage credit: Florian Rohart (https://flic.kr/p/rmccRh) -- source link
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