So Sea Level Rise (SLR) (or as those fine republican members like to say "recurrent flooding") is another anthropogenic impact that is giving our coral reefs a real test.
This short video below, gives you an idea of the projections for SLR, what has happened so far and how this relates to the projection. It highlights that we are on course for an 80cm rise by 2100. This is concerning and indicates that the projections may be underestimating what will most likely happen.
There are two ways that SLR has and will continue to have an impact on coral reef communities. But first (oh the suspense...), a paper by Nybakken (1993) sets out the basic needs for a coral reef to remain active. Naturally, the most essential requirement is LIGHT. The ability of coral to capture light is dependent on the turbidity of the water column and water depth. If corals cannot harness enough light then their growth ceases with the end result being death. This would be due to reduced photosynthesis by the zooxanthallae, and reduced oxygen production which impedes the coral metabolism thereby limiting calcium carbonate deposition and therefore growth. Nybakken (1993) highlights that corals at a particular water depth need a light intensity that is at least 1-2% of the intensity at the ocean surface. With SLR occurring, the light intensities are being weakened, and as such, reefs cannot and will not be able to keep up with rates of SLR, especially those coral species that exist at the water depth limit of coral growth (70m bsl).
The two ways:
1) SLR in isolation
Hoegh-Guldberg (1999) critically highlights that deep water species under dramatically reduced light intensities at their physiological depth limit will no longer be able to maintain growth and it is projected that they will become extinct. Further, slow growing corals are becoming increasingly vulnerable as they will be out run by SLR, leading to their demise. Grigg et al. (2002) corroborates these former consequences and brings your attention to the fact that coral species are will be significantly impacted under a moderate SLR projection.
However, I have found one source that states that SLR in isolation will have little, if no impact whatsoever. This information is from the Great Barrier Reef Marine Park Authority (GBRMPA). The GBRMPA states that the coral species there can acclimatise to SLR of 3mm per year as coral growth is two fold. For the GBR, this is likely to be true as the majority of reefs are extremely shallow and so the projected increase of +0.68 to 0.9m by 2100 would have little impact on reducing light intensities. Therefore, the impact of SLR in isolation is wholly dependent on the initial depth of the coral species. For species in shallower waters, other factors play a major part.
2) SLR in tandem with other environmental stresses.
Hoegh-Guldberg (1999) states that other stresses such as OA and coral bleaching will exacerbate the impact of SLR, making coral species that were previously unlikely to be effected, effected. The ability of the reefs to keep up with SLR will be drastically reduced. In a paper by Graus (1998), the model simulation illustrated that under a combination of stresses, coral reefs in the Caribbean will be unable to keep pace with projected SLR rates.
It seems that the stress of SLR is more specific than general whereas other stresses are the opposite...
Stay tuned,
Seb
References:
Graus, R.R. and Macintyre I.G., 1998, Global warming and the future of Caribbean coral reefs: Carbonates and Evaporites, vol. 13, no. 1, p. 43-47.
No comments:
Post a Comment