[Coral-List] Mixed Messages; Barbados vs. Cuba's Garden: it's nutrients, but not sewage.

[tomascik at novuscom.net]

Hi Joe,
For those not familiar with Barbados I would like to point out that there
are two types of coral reefs surrounding the island, the fringing reefs
and an offshore submerged barrier reef that we used to call the Bank Reef.
The reef that you are showing in the video is the Bank Reef located
anywhere from 0.5 to 1.0 km offshore.  Because of its location the Bank
Reef is well flushed and does not suffer from land-based stressors ‘as
much as’ the fringing reefs that line the shoreline, especially on the
west coast of the island. I would love to see some videos of these
fringing reefs. Have you folks done any quantitative studies on the
offshore Bank Reef to compare their status the study done by Bruce Ott in
1975?:

https://onlinelibrary.wiley.com/doi/abs/10.1002/iroh.19750600601

Tomas

> Mike,
>
> As a reminder of the "purpose of this post", you referenced SW Barbados as
> "..an outhouse built on a karst outcrop" to make a point about sewage
> destroying coral reefs.
> I provided recent video from the same location you referenced to indicate
> that those reefs look pretty good.
>
> As Yogi Berra may have said "You can see a lot by looking!"
>
> With that in mind, I ask coral-listers to compare two videos of reefs,
> taken less than a year apart (March 2018, Jan 2019):
> Cuba's Garden of the Queen, considered by many as "pristine" as a coral
> reef can be in the Caribbean:
> https://youtu.be/KZWeYIeHTyk
> And the reefs of SW Barbados, directly offshore from an island heavily
> populated for hundreds of years and very close to Bridgetown (see Mike
> Risk's summary at the bottom of this email):
> https://youtu.be/pFA5pw5FMVE
>
> Which reefs looks "better" to you??
>
> To my eye, coral cover is similar, but there's a lot more seaweed on
> Cuba's reefs.
> And, Mike, Cliona delitrix has higher cover in Cuba - see large patches at
> time points 5:31 and 6:56.
> Why the difference in seaweed cover?  Because Diadema populations are
> higher on reefs off SW Barbados, unlike Cuba (even though Cuba has lots of
> big fishes, including large parrots, while Barbados is heavily
> overfished).  Notice the pink coralline crusts in the Barbados video that
> you don't see in the Cuba video - too much seaweed there.
>
> Again, please notice the high biomass of barrel sponges in both locations,
> and lots of sponges in general.
>
> While in Barbados, I met a local who started diving there in the 1960s,
> and I asked him what the biggest changes he'd seen to the reef - he said
> the two most obvious things were the loss of Acropora corals and the
> increase in giant barrel sponges.
>
> This is about nutrients, but not about sewage (at least not at broad
> geographic scales) -- the nutrients (and DOC) are tightly cycled in the
> ecosystem.
>
> In Cuba, all those sponges are making nutrients (from eating algal DOC and
> phytoplankton) as they disrupt the boundary layer and churn the water
> column, which fertilizes the seaweeds. All those fishes also make
> nutrients, and fish herbivory can't keep up with seaweed growth. The
> ecosystem was altered when coral and urchin diseases went through in the
> 1970s and 1980s, freeing real estate, removing a critical herbivore
> (urchins), and allowing seaweeds to take-over quickly, followed by
> sponges. This is the vicious circle (see ref below).
> In Barbados, the returning urchin populations seem to be controlling the
> seaweed, despite sponges already having taken significant real estate.
> Interestingly, this is in the absence of strong fish herbivory.
>
> And correlations of boring sponge abundance (cover) with "pollution" are
> confounded by coral loss and increases in boring sponge habitat.
>
> The vicious circle and the relationship between sponge cover and
> "pollution" are topics covered here:
> Pawlik, J.R., McMurray, S.E. 2020. The emerging ecological and
> biogeochemical importance of sponges on coral reefs. Annual Review of
> Marine Science, 12: 3.1-3.23
>
> You can find a copy at the PDF site below.
>
> Regards,
>
> Joe
> **************************************************************
> Joseph R. Pawlik
> UNCW Center for Marine Science
> PDFs: http://people.uncw.edu/pawlikj/pubs2.html
> Video Channel: https://www.youtube.com/user/skndiver011
> **************************************************************