The algae resource pool represents a combination of algae turf mats, macroalgae, and the epilithic algae matrix (not including detritus). It is not size structured to reflect the fact that herbivorous fish feed on algae regardless of their body size.
Details
A low standing biomass relative to production is ecologically expected on
a grazed reef: algal turfs are highly productive but are cropped down by
herbivores, keeping standing biomass low even though production is high
(see getAlgaeProduction()). This is well documented empirically – for
example Carpenter, R.C. (1990). Mass mortality of Diadema antillarum:
I. Long-term effects on sea urchin population dynamics and coral reef
algal communities. Marine Biology, 104, 67-77, which found that algal
cover roughly doubled within months once a dominant grazer's population
collapsed, with grazing pressure otherwise removed. Note that this
ecological expectation is about the low value being relative to a
realistic absolute scale (the literature range is roughly 10-100 g dry
weight/m^2, see setAlgaeParams()'s algae_growth_initial docs) – it
does not by itself explain the much smaller absolute values
(~1e-9 g/m^2) currently reported for the bundled models, which is a
separate, known calibration-scale issue (see
inst/to-do-list.txt's "FUTURE WORK PLAN" entry).