Innocent And Under Threat

A new report has stated that 17% of America's threatened and endangered species are at risk from rising sea levels. This is a shocking amount of species put in danger because of humanity and our hunger for power, so I thought i'd have a little look at the 5 species currently at most risk from sea levels in America.

Key deer - A deer species that only lives in Florida endangered due to the inundation of the island that they are found on.
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Loggerhead sea turtle suffering due to the disappearance of beaches where they lay their eggs.
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Delmarva Fox Squirrel endangered due to the inundation from Chesapeake Bay.
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Western Piping Plover due to the inundation of beaches where they feed and nest.
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Hawaiian Monk Seal put at risk due to the reduction of beaches through rising seas.
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Poor little things! But is it too late to save them?

Saving Nemo

Vibrant Coral Reef
Source: Guardian, Photography: Mark Conlin/Alamy 

Coral reefs are beautiful and dynamic ecosystems that provide critical resources for marine diversity as well as a source of recreational activities, making them vital to the viability of coastal communities. As well as economic and aesthetic services they also provide protection from storm waves, act as habitats and nurseries for fish species and produce sand for the development of beaches.



To create a global view of coral reefs, over 1700 images (red boxes) from the Landsat 7 spacecraft were collected for the Millennium Coral Reef Mapping Project.
Source: NASA

Coral reef development is a very long process and can take thousands of years. As marine organisms with calcium carbonate skeletons die their skeletons break down and become calcium carbonate sediments. These sediments fill in the framework of the reef and cement together constructing a foundation upon which the reef grows upwards and outwards.

Formation of the 3D structure of coral reefs

Source: USGS

Due to their selective environmental requirements these reefs are at risk during periods of changing ocean conditions, such as the present. The number of threats to these coral reefs has increased substantially in the past few decades due to the increasing levels of atmospheric carbon dioxide and the onset of anthropogenic climate change, leading to changes in marine environments (Kleypas, 1999). The most important of these in regards to coral reefs are ocean acidification, increasing sea surface temperature AND sea level rise.

It was first thought that sea level rise wouldn't pose that great of a threat to coral reef communities, at least in the shorter term. This was because the rate of modern sea level rise was previously slower than coral reef growth rates, and that they could therefore 'keep up' with increasing sea levels. This rate of sea level rise has increased substantially in recent years due to increasing inputs from continental ice sheets (Milne, 2009) and our improving understanding of ice sheet dynamics.

However it has been said that healthy shallow water corals may still be able to grow at rates such that they manage to keep up with modern sea level rise and colonise new areas. The key word here is 'healthy', whilst coral reefs under no other major stresses may be able to grow fast enough to escape the oncoming tides, reefs already suffering and dwindling due to increased acid levels, temperature and anthropogenic influences are far from at their optimum conditions and their growth may be inhibited well below natural levels.

If the rate of sea level rise does exceed coral growth rate then they, specifically those with large terrestrial sediment sources in close proximity, will be put at greater risk from enhanced sedimentation rates and turbidity, both being major stresses to coral reefs (Pandolfi et.al, 2003; Fabricius, 2005). A rise in sea level of just 0.2 meters (at the lower end of predictions for this century) has the potential to increase turbidity through two mechanisms:

• Increased resuspension of fine sediment.
• Increased coastal erosion and subsequent input of sediment able to be transported to the reef flats. (Field et.al, 2011)

Effects of projected sea level rise on coral reefs
Source: SPC

Deeper bottom dwelling reefs will be especially affected as the level of sunlight penetration to such depths is reduced. Corals rely on a symbiotic relationship with algae as their main food source, as the light levels drop in deeper water, this symbiotic algae cannot produce enough food for themselves and the coral. As a result the coral is supplied less food, and is therefore less able to catch enough nutrients (phosphates, nitrates and proteins) from other sources to keep the algae properly fed. The symbiotic relationship therefore fails as they can no longer sustain each other.

All may not be lost however, as sea levels rise so does the area of habitats available for branching coral reefs. Coral reef growth itself is inhibited by declining or static sea levels, so as long as these levels don't rise too quickly it could be seen as a positive thing for the future of corals.

Looking at it from another point of view, rising sea levels are not the major threat to coral reefs at present. The other consequences of climate change such as the warming of sea surface temperatures and anthropological interferences can be thought of being the more pressing issues to be addressed when thinking about the future of corals.

Mangroovy

With sea level rise comes the inevitable change in environmental conditions and pressures, with shores and coastlines at the forefront of the threat and therefore likely to be most affected. One such ecosystem selective to coastlines is those of Mangrove Forests. Mangals (Mangrove Forests) are extremely selective in the sense that they are highly adapted to saline conditions and thus can only form around coastlines in intertidal environments.

The distribution of mangroves globally is controlled by the 20° isotherm with mangrove forests found extensively around tropical coastlines, extending into subtropical areas as far north as st. Georges Parish  (32° 23’N) in Bermuda and as far south as Corner Inlet (38° 45’S) in Australia (Woodrolfe, 1990). Whilst abundant along shorelines they are particularly well developed in muddy and well sheltered areas of coast with a large supply of fine grained, silty sediment. They can however also form on peat, sand and coral substrates.

Map Showing World Distribution of Mangrove Forests
Source: (Giri, et.al, 2011)

As sea levels rise mangrove forests are being placed under increasing stress. This is due to the numerous negative effects seawater can have on coastal areas, including; sediment erosion, the inundation of habitats by seawater and increasing salinity levels in landward zones (Ellison, 1994). These effects put these ecosystems and the services they provide under threat. Services such as;

• Trapping sediment, therefore sustaining offshore water quality for coral reefs,
• Providing nursery habitats for fish and invertebrates that spent maturity in coral reef environments,
• Acting as flood and surge protection for inland areas.

Mangrove forests can also be used as building materials, traditional medicines, firewood and as sources of food (Ellison, 1994).

Mangrove Forests as seen from below
Source: BBC Nature

It has been predicted that these coastal ecosystems are therefore likely to migrate landward as their former habitats become increasingly marine, this process will occur through the vertical accretion of sediments held by the extensive mangrove roots. 

However this retreating movement is hindered by an effect coined ' coastal squeeze', which means that their landward migration is becoming increasingly restricted by topography or human developments. (Ellison, 1991). With these woodlands now no longer able to shift inland as outer pressures increase, the question is where can/will they go?

Mangrove destruction on Bimi
Source: Kristine Stump

On another note however it must be said that currently the biggest threat to these diverse ecosystems is not sea level rise but human destruction of these coastal ecosystems to make room for our ever expanding populations (Luther, 2009).