JanDajka
commented
6 years ago Predictors: In general, there are three 'stages' in the breakdown of a reef that Shaun and I agreed on while on fieldwork. One example scenario to make the distinction: dead corals are still structurally intact and once physically broken become rubble and that gets eroded over time to sand. All three would have different theoretical effects on herbivores.
Dead corals still provide structure to fish, so it's unlikely to have a alternate effect on herbivores than our measure of hard coral would.
Rubble can move with wave energy and crush whatever settles on it, including corals and algae. Perhaps herbivores make us of it as protection though (e.g. by hiding in between / actively move it to create shelter and dig for plant matter).
Sand by itself doesn't provide protection anymore, unless a fish buries (short of cyptic gobies and blennies that aren't included in the UVCs, I don't know of a herbivore that buries). Sand is sometimes ingested by fish to "clean" their stomachs or because the sand is somewhat covered in algae matter that they ingest but those aren't very promising links.
Sand + turf: If sand becomes trapped in the turf algae, it deters grazers, protecting the turf algae and allowing them to grow more or less undisturbed. This often happens on patch reefs with low wave energy. But I've seen the opposite on reefs with high wave energy (e.g. granitic headlands), where the sand doesn't get trapped in the EAM and the turf algae lay bare, ready to be munched.
Soooo, depending on what type of reef we have, it will determine whether a turf + sand combo will make sense. Seeing as sand itself might not yield in anything, perhaps a combo and turf by itself if we can be sure about that distinction? Definitely should consult Nick about this.
Seychelles: Turf - you're right, no turf measure. I checked the data from our fieldtrip again, seems like Shaun didn't record it. Would be with a good reason though. Rubble - should be rubble by itself.
Maldives: EAM + sand depends on whether we can infer about the hydrodynamics somehow, I'd say. Talking with Nick should clear this up though. Rubble is rubblerubble, yes.
Chagos: Also no turf recorded, it seems. Rubble is rubblerubble, yes.
GBR: Turf is 'turf' + 'turfs' + 'EAM'. Maybe Nick changed his labels over the years. Would again wait to see what Nick says. Rubble is rubblerubble, yes.
jpwrobinson
samanthajh
Jeneen
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@JanDajka the benthic man. Can you help me identify which categories should be included in our new rubble and turf regime covariates? The benthic taxa vary between regions, with some surveys including dead coral (this should be included as rubble, right?) and turf recorded under different names (EAM, turf).
If we're thinking about alternate regimes that are neither hard coral or macroalgal, should we also include sand in the turf regime? This was one of 3 Pacific regimes identified by JB Jouffray et al. (2015, Proc B).
We should run our selections by Nick at some point, but we can select the groups here and start incorporating into models straightaway.
Seychelles
Maldives
Chagos
GBR