Tag Archives: seagrass

Australia suffers not only the loss of coral reefs.

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Research just in reveals that extreme events from climate change (2011-2017) have damaged 45% of Australia’s coastal habitats, including coral reefs, mangroves, kelp forests and seagrass.  These habitats provide food and shelter for a huge range of marine and estuarine species, including large fish, turtles and dugongs.  Vital for fisheries, these key habitats are also used and much loved by local and international visitors. 

The rate of their loss is extremely worrying, especially given that these changes have essentially occurred during an increase in global temperature of 1°C above the preindustrial era. As we go towards warming of 1.5oC, these serious impacts are more than likely to be amplified.

Extreme weather likely behind worst recorded mangrove dieback in northern Australia (Photo: Norm Duke)

Much of the damage has been driven by unusually long and hot underwater heat waves.  Other changes have been due to knock-on effects.  For example, large amounts of kelp forests have disappeared from the south-east coast of Australia due to the spread of sea urchins and tropical grazing fish species as higher latitudes warm.

The future is of concern.  The authors used ecosystem models to evaluate long-term outcomes from changing extreme events, which are predicted to become more frequent and intense with return times diminishing rapidly.  In the latter case, this means that many ecosystems are failing to recover in time prior to the next extreme event.

Check out the peer-reviewed study here.

 

 

Whales Store Some Carbon, Oceans Store Loads of It

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The is quite a bit of buzz today about recent research that quantifies how much whaling has – and is – contributing to atmospheric carbon. It appears that whales store significant amounts of carbon. I doubt, however, we will ever have a global breeding program to increase our whale populations, thereby offsetting our own carbon emissions. It’s just not feasible. (Besides, encouraging more people-whale interactions isn’t a popular idea at the moment.)

The focus needs to be broadened beyond whales. Ocean habitats are continually overlooked by the global community as viable sites of carbon sequestration. Blue carbon – as some call it – is a new concept being researched by the NGO community and receiving blog hits. The New York Times has even taken notice. Three months ago, Dan Laffoley of IUCN wrote a wonderful NYT op-ed entitled, To Save the Planet, Save the Seas. Read it.

In short, blue carbon emphasizes the key role of marine and coastal ecosystems. It places value on carbon-rich marine vegetation such as mangrove forests, seagrass, brackish marshes and salt marshes. Coastal and marine ecosystems are believed to be able to complement the role of forests  in taking up carbon emissions through sequestration.

See our related posts on this here, here and here.

This is a management area that was greatly overlooked in Copenhagen. It’s a concept to which the UN and coastal nations ought to give more attention. Island nations rich in blue carbon, like Indonesia, could benefit similarly to the way Brazil is predicted to benefit from “green carbon” sequestration programs, like REDD.

In my opinion, blue carbon sequestration programs will need new research, the right political advocates, and better governance. The question I pose to you marine scientists/environmental managers/policy makers: Where to start?

Could coral reefs close to seagrass be buffered from ocean acidification?

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coral1Seagrass meadows have long been known to be highly productive habitats, and as a result producing oodles of oxygen in the midday sun. Anyone who’s ever snorkelled over a seagrass meadow on a sunny day will have seen seagrass leaves furiously bubbling away. This photosynthetic productivity can result in an increase in the pH of the water column (becoming less acidic). This is primarily because CO2 and, thus, its form when dissolved in seawater, carbonic acid, are withdrawn from the water as a substrate for photosynthesis. This results in the production of the bubbling O2. But what are the consequences of such a pH change?

Recent research by the Universities of Dar es Salaam, Tel Aviv and Stockholm published in the Marine Ecology Progress Series (volume 382) and conducted in tropical seagrass meadows of East Africa have investigated the impact of such pH changes.  Semasi et al. revealed that this change in pH can cause localised increases in the rates of calcification and growth of calcareous algae such as Hydrolithon sp., Mesophyllum sp., and Halimeda sp., hence seagrass buffers high acidity (low pH).

As has been debated by ClimateShifts previously, there is increasing evidence that oceans have become more acidic since the start of the industrial era. Recent predictions suggest that oceans could become much more acidic over the next 100 years as a result of increasing CO2 emissions. Current predictions suggest that this will result in (amongst other things) declining reef calcification rates.

Although this study by Semesi et al. shows the effects of seagrass upon algae, the questions on the lips of many reef conservationists will be whether such findings are cross transferable to the calcification of corals. These studies in Zanzibar were small scale, carried out in seagrass mesocosms, and currently only reflect small scale patterns. Whether seagrass productivity can result in larger spatial scale changes that could buffer pH changes on nearby reefs remains to be seen. Maybe the World should be looking at seagrass meadows with greater attention?