Tuesday, 29 October 2013

The bigger picture

Our next leg from Bermuda will be about 900 miles and that could take us 9 days.  We carry only enough fuel for about 3 days.   So studying the wind becomes central to our travel plans.  We’ve been doing this and today looks like our day to move to St. Maarten.

While I do not expect anyone to be waiting for the next installment of my blog, I thought I’d take this opportunity to describe a bit of the bigger picture…..

So Why Do This Research?

Science requires you attend to details but sometimes it is good to step back and consider the bigger picture.  In case the science interests you, read on….

Science of the bigger picture
We live in the Anthropocene.  This is the most recent period of significant biological change.  Paleontologists have names for each period when life on Earth changes. Animals with shells and hard parts appeared over 500 million years ago during a period called the Cambrian.  Dinosaurs ruled land during the Triassic, Jurassic and Cretaceous periods of the Mesozoic Era.  More recently, in the Cenozoic Era of the Eocene period, modern reef fishes evolved.  During the Pleistocene glaciers covered the poles and during the Holocene, humans evolved.  The Anthropocene describes the period when the biosphere was clearly affected by human activity.

There is no place on Earth where human presence cannot be detected.  Some impacts are conspicuous such as forest clear-cutting but others are subtle such as global warming and ocean acidification of our world.  The scale of the climate and atmospheric effects is huge – in some ways it is global.  This can have profound effects on lots of critters but none are more affected than coral reefs.  For example, when ocean temperatures coral reef exceeds its average summer temperature by more than about 2 degrees C, corals bleach.  Coral bleaching occurs when tiny, but useful, algae that live within the corals are expelled and corals bleach white.

Bleached brain corals (right side of left photo is not bleached). Bonaire 
Bleached star coral in Bonaire 2010
Another bleached brain coral from Bonaire 2010
Most climate scientists have concluded that the burning of fossil fuels creates a greenhouse condition in which sunlight turned into heat when it strikes Earth, becomes trapped in this greenhouse.  Carbon dioxide also readily reacts with water creating carbonic acid.  This resulted in the acidification of the world’s oceans.

Plants and animals that create limestone skeletons such as lobsters, sea urchins and coral, invest metabolic energy to calcify.  With ocean acidification, the cost of doing the business of calcification has gone up.  Many reef scientists fear that thermal-stress of global warming and ocean acidification have created a ‘double whammy’ that may have serious synergistically negative impacts on coral reefs.

Getting from what we know, to what we don’t know
Reef corals have declined in abundance over the past half-century (at least).  Coral reefs as with most ecosystems are named for their dominant organism, reef corals.  Since reef corals are declining in abundance, coral reef ecosystems are threatened.  On many reefs, as corals decline, seaweed increases in abundance.  Given that in the 1970s seaweed was rare throughout the Caribbean, the trend is clear but what drives this trend is hotly debated. 

Coral reefs in Jamaica (Discovery Bay) shifting to seaweed reefs between 1978 and 1988
Top two and bottom two photos were taken at exactly the same locations.

Could climate change and ocean acidification have caused the decline in coral reefs?  Perhaps.... but there are other, non-mutually exclusive ideas as well.  Some scientists argue instead that the increase in seaweed is due to nutrient increases that stimulate their growth.  Seaweed can smother and even poison coral so that’s a plausible explanation.  Others argue that over fishing coral reef fishes – especially those that graze down seaweed resulted in the blooms of algae.  Still others wonder if fish are important at all perhaps it was the decline in grazing long-spined sea urchins that resulted in the seaweed bloom.

The fact is, not all coral reef ecosystems have declined. The coral reefs in Bonaire remain relatively healthy with a high coral cover.  So, why have some (perhaps most) coral reefs declined but others remain healthy? 

Healthy coral reefs of Bonaire (note high coral cover, little seaweed)

Looking for the perfect laboratory
With this background, I sought to find the best place to explore the question of what’s plaguing the health of Caribbean coral reefs.  I focused on the low islands of the eastern Caribbean because they are dry and have little runoff, the Trade Winds and the north equatorial current bathes them in clear tropical seawater with a minimum of upstream pollution.  Since all of the eastern Caribbean islands are in a relatively small north to south archipelago, it is reasonable that global warming and ocean acidification will affect the reefs in similar ways.  So, by studying similar reef zones from island to island we can see if the reefs differ.  If they do, it likely the result of local factors such as the fish fauna rather than pollution, climate or atmospheric stresses.  This is not to say the other factors are unimportant but that they may not be the sole drivers of the health of coral reefs. 

The Caribbean.  Note the small dot to the north is Bermuda (image: Google Earth)

The Antilles of the eastern Caribbean.  My study sites for this expedition (image Google Earth)

How do you find the ‘pulse’ of a coral reef?  
For the last 20 years, several colleagues and I have worked to develop rapid assessment protocols for Caribbean coral reefs.  The gold standard for such assessments is the Atlantic and Gulf Rapid Reef Assessment known as “AGRRA” (http://www.agrra.org/index.html).  Over the years, research my students and I have conducted rapid assessments to characterize all the important reef organisms (especially coral, algae and fishes) with only a few dives per reef.  Since 1997 I’ve conducted AGRRA-like surveys in the Bahamas, St. Croix, St. John, Bonaire, Mexico, Belize, Honduras and Guatemala.  My work in Mexico along with AGRRA surveys at 38 other sites conducted by over 100 scientists was published in July 2003 in Atoll Research Bulletin (free to download at the AGRRA site). 

So by conducting rapid assessments on similar reef-types at the same depth allows us to determine if significant differences exist among reefs.  I'll get into the details of the differences we are looking for a bit later.  Nevertheless, if differences are found among islands, an excellent question would be, why are they different?  It is a bit premature for me to speculate on this but suffice to say, I do have a plan on how to proceed. 

No comments:

Post a Comment