[Coral-List] pelagic carbon dominant source for reef predatory fish

[David Blakeway]

Thanks for the extra information Tina.
I see your point regarding Science Advances' limit on references (80). I
can't see a strong argument for a limit, seems it will inevitably suppress
citation of older research. But anyway it appears most journals do it...
I was being too self-righteous about the lethal sampling - stems from
myself having killed too many fish for inadequate reasons. Obviously you
thought about the issue and worked out the best practical option.
Here's a possible argument against your conclusions: 1) because the
Maldives atolls are open and deep, conditions are very oceanic, even inside
the lagoons, 2) your sampling sites, including the lagoon sites, are almost
all on the upcurrent edge of the reefs, 3) the sampled predator species are
site-attached diurnal predators of planktivorous fish. So it could be
argued that you're not effectively samping the system, only a short chain:
pelagic plankton to wall-of-mouths to small serranids. Therefore it's not
necessarily valid to conclude that the reefs are 'overwhelmingly reliant on
external sources for maintaining their exceptional productivity.'
This is partly a devil's advocate argument. I recognise that if the pelagic
input is there it will be used. I also recognise it's far easier to
criticise than to do!


Hi David,

Thank you for your interest in our study! I agree that the early work by
Chartock is important and perhaps we should have cited it, but strict
limits on the number of references in Science Advances means we couldn’t
include everything unfortunately.

As for the sampling of the groupers, we deliberately avoided smaller
juvenile groupers and focussed solely on adults/larger individuals on the
reefs. However, I do agree that sampling lethally is not ideal. For other
reef fish predators (snappers, emperors, jacks) that we sampled as part of
a wider project, we were able to use handlines or trolling. Often this
meant we could sample the fish non-lethally using a biopsy punch (e.g.
Skinner et al. 2019, J Anim Ecol). To further reduce our impact, we also
joined tourist resort night fishing activities where guests were fishing
for their dinners and took tissue samples before the fish were taken to the
BBQ! Unfortunately, it’s pretty hard to catch groupers in this way, and
timeframes and logistics meant pole spear was the most effective method for
them. I’m not aware of too much work on CSIA of fish scales, but it’s
definitely necessary to look into non-lethal methods of collecting this
data and it’s an important discussion to have.

Always happy to chat more and thanks again!

Tina Skinner