[Coral-List] Acidification & Boring Erosion

Christine Schoenberg C.Schoenberg at aims.gov.au
Sun Dec 9 03:13:29 EST 2012

Hi all,

thanks for free advertising, Mike! One of our papers was just published in PLoS ONE - more to come. Aline Tribollet has actually done OA work before we did - on microendoliths, with similar results. And lately similar approaches seem to appear everywhere.

Presently available experimental results show that sponges and microendoliths erode more in lower pH. Makes sense when you consider that they erode chemically. Some natural gradients of bioerosion were linked to pH gradients in the field, but this kind of study is very tricky, because often you cannot exclude many of the other gradients that also strongly influence bioerosion. But there is also some ongoing work near CO2 seeps, which may be a bit more conclusive. So, evidence and interest are growing. Already there are strong indicators that at least chemical bioerosion will significantly increase in future and that endolithic organisms are comparatively sheltered against environmental changes that harm reef builders (= double whammy: they survive where reef builders die AND increase their activities). Presently, on some reefs sponge bioerosion alone was estimated to be larger than the local calcification (as shown by Mike himself years ago in the Caribbean and from the Mexican Pacific). We need more budgets to find the patterns.

Andrew aked: >Should this be part of our climate change adaptation planning?

Most certainly, and people like Mike Risk are always urging to pay bioerosion more attention. He already pointed some of the below points out as early as 30+ years ago:

- Many bioeroders are filter feeders or rely on dissolved nutrients, and bioeroder abundances and bioerosion rates increase with decrease in water quality, as was shown numerous times.
- Epilithic bioeroders such as sea urchins have benefited from overfishing.
- Endolithic bioeroders do not appear to suffer as much from heat events such as reef builders do, but it looks as if they can take advantage of recent reef mortality and spread faster.
- Some bioeroders can be spread around by fragmentation, i.e. we may also have to worry about an increase of storm frequencies. My own experience showed that on a storm-trashed reefs bioeroding sponges may do just fine.
- And, chemical bioerosion increases with OA, as shown for microendoliths and sponges.
And all of this interacts as well...

However, bioeroders are understudied, cryptic critters that are often not easy to identify, and conditions are so very different from reef to reef to whatever other habitat, and methods vary all over the field. It would be good if we could share a bit more and standardise some of our approaches to generate more meaningful data faster and over larger scales. And what we desperately need is 'before-after' data or time series.

Cheers, Christine

Dr. Christine Schönberg
Australian Institute of Marine Science
Oceans Institute at The University of Western Australia
39 Fairway
WA 6009
ph +61-8-63694042
From: coral-list-bounces at coral.aoml.noaa.gov [coral-list-bounces at coral.aoml..noaa.gov] On Behalf Of Michael Risk [riskmj at mcmaster.ca]
Sent: Saturday, December 08, 2012 10:39 AM
To: andrew ross
Cc: Coral List (coral-list at coral.aoml.noaa.gov)
Subject: Re: [Coral-List] Acidification & Boring Erosion

Hello Andrew.

Yes, you have hit the nail on the head. Acidification will certainly accelerate bioerosion.

Many of the common bioeroding critters employ chemical dissolution as part of the process. The most common, ubiquitous eroders in photic waters are the boring algae. There is no piece of reef coral that does not contain boring algae. They bore purely by chemical means, seeking out the crystal surfaces with the highest free energy and secreting a variety of organic acids. In sponges, a protoplasmic loop secretes carbonic anhydrase, etching the perimeter of a chip-amoebocytes then rip that chip off the surface. The actual chemical part of the process is only a few %, but will obviously be accelerated.

Sadly, there is still a dearth of research in this field: although bioerosion is a process which is volumetrically more important in reef carbonate budgets than coral growth, the coral reef community continues to pay little attention. Fortunately there is some good work on acidification appearing now-I especially recommend papers by Christine Schoneberg and Max Wisshak.

On 2012-12-07, at 11:21 AM, andrew ross wrote:

> List,
> With discussion about acidification related reef erosion is there an elephant in the room in boring organisms? Admittedly my experience is primarily in very broken systems, but for me it's common to be able to tear chunks of hard reef away with my hands. When I look inside the hole I've made I see little but sponge, plus scrambling cryptic beasties. This has been my observation in obviously "enriched" locations like Montego Bay (Jamaica) and on less obvious sites such as St. Mary to the East, where our recent visitor Hurricane Sandy demonstrated the issue on a much larger and messier scale. I found this condition particularly notable when I could not break bits off at the more remote Pedro Banks this past spring.
> Can we expect that boring erosion be increased under a reduced ocean pH? Can we expect this to occur additively, or might these processes work in synergy?
> Should this be part of our climate change adaptation planning?
> Andrew Ross
> UWI (Mona)
> _______________________________________________
> Coral-List mailing list
> Coral-List at coral.aoml.noaa.gov
> http://coral.aoml.noaa.gov/mailman/listinfo/coral-list

Michael Risk
riskmj at mcmaster.ca

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