Other Potential Climate Change Effects in the Oceans

Apart from temperature and pH, oceans are expected to alter in several other ways due to the current global climate change. Climate change is predicted to influence oceanographic patterns and conditions such as current direction and velocity, depth of stratification, salinity (fresher in the higher latitudes and more salty in the subtropics), and the oxygen concentration of the ventilated thermocline (IPCC, 2007). Climate change, for instance, is predicted to modify coastal upwelling either by intensifying (Bakun, 1990) or weakening it (Vecchi et al., 2006), depending on the model used. These changes are predicted to affect, for example, survivorship and delivery of propagules to the shore as well as food supply in coastal ecosystems. On rocky shores for instance, increasing upwelling intensity and duration in intermittent upwelling regions such as the Oregon coast during the summer will reduce sessile invertebrate larval recruitment (by moving the larval pool further offshore) lowering abundances of sessile invertebrates and through higher nutrient fluxes increase macrophytes, thus making rocky intertidal habitats in Oregon more similar to those in California (Menge et al., 2004). Alternatively, if upwelling is reduced, the structure of the seaweed assemblages will change, with decreases in Laminarians and likely some red algae, and enhanced abundances of sessile invertebrates (due to higher recruitment, see Connolly and Roughgarden, 1999).

Increasing sea levels will permanently submerge some intertidal areas while others might be created changing the mosaic of communities along the shore. In areas where tidal amplitudes are small, such as the Mediterranean Sea, sea-level rise can change the structure of communities because the ratio of vertical versus horizontal surfaces will probably change and communities on different rock aspects are different (Vaselli et al., 2008). In regions where most of the rocky shore is horizontal and at mean sea level, for example where vermetid platforms are found (warm temperate seas such as the eastern Mediterranean, Bermuda, Safriel, 1974), a rapid sea-level rise would cause an inundation of most of the intertidal zone by seawater, effectively turning the platforms into subtidal reefs. Based on measurements of sea-level rise for the eastern Mediterranean (~8.5 cm between 1992 and 2008) and projections for the next 100 years of up to a meter or more (Rosen, 2008), most of the Israeli rocky shore will be underwater and that unique ecosystem will be mostly lost.

Increasing storm intensity, including tropical storms (hurricanes, cyclones), will increase the frequency and severity of disturbance inflicted on coastal communities such as mangroves, coral reefs, and rocky shores. There is already evidence that a progressive decadal increase in deep-water wave heights and periods have increased breaker heights and elevated storm wave run-up levels on beaches in the US Pacific Northwest (Allan and Komar, 2006). This of course can have substantial effects on disturbance regimes on the shore that surely will affect the structure of coastal ecological communities (Dayton and Tegner, 1984; Underwood, 1998). Larger, stronger storms are also expected to increase beach erosion. The resultant increased erosion of the shore can also affect coastal geomorphology, increase sedimentation, and therefore affect the ecology of the shore. A study on the Oregon shore that looked at effects of a cliff collapse (and with it highway 101) and reconstruction showed how rocky intertidal communities have been altered due to change in small-scale geomorphology and possibly sediment accumulation on the shore (Rilov, unpublished data).

The rate at which physical changes caused by global climate change might unfold could be slow, but they could also be fast and therefore their manifestation in the structure of communities and in biodiversity could be strong and immediate. For example, the onset of hypoxia on the shelf of Oregon coast in 2002 was relatively sudden and unprecedented (Grantham et al., 2004; Chan et al., 2008). Hypoxic conditions have since re-occurred each summer, and greatly intensified such that conditions were anoxic in 2006 (Chan et al., 2008). This resulted in massive die-offs of benthic invertebrates (e.g., crabs, sea stars) and the dwindling of reef fishes on subtidal reefs (Service, 2004). The delayed upwelling observed in 2005 on the Oregon coast (Barth et al., 2007) had not been observed in at least the previous 20 years, and had immediate consequences for concentrations of phyto-plankton and larvae of sessile invertebrates. These intense coastal events seem to correspond with larger-scale oceanographic and atmospheric changes in the North Pacific that are consistent with global climate-change scenarios (e.g., Hooff and Peterson, 2006; Barth et al., 2007) and may linger and therefore have profound ecological effects on regional and potentially global scales.

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