## 7 Algal Primary Production
### Macroalgae  
Mangrove macroalgae are dominated by the rhodophytes, _Bostrychia_, _Stictisolphonia_, _Hypnea_, and _Calgossa_, the chlorophyte, _Chaetomorpha_, and the phaeophyte, _Dictyota_[192]. In some forests, species of _Bostrychia_ grow as turf algae on trees along with other associated red macroalgae, such as _Calgossa_ and _Catenella_, forming an intertidal plant association termed _'Bostrychietum'_[193; 194; 195]. In the Americas, 55% of red macroalgae colonizes pneumatophores, prop roots, downed wood, and trunks and 19% may be entangled with or epiphy on other macrophytes, while 28% and 20% grow in hard surfaces and on mangrove sediments, respectively [196]. Mangrove macroalgae are highly tolerant to temperature and salinity variations, but sensitive to desiccation. The sample size of the macroalgal NPP in mangroves is considerably greater (\(n\) = 102) than for microthytobenthos, averaging 17.4 \(\pm\) 14.2 (1 SD) g C m\({}^{-2}\) d\({}^{-1}\) with a range of 0.0-51.5 g C m\({}^{-2}\) d\({}^{-1}\) and a median of 17.4 g C m\({}^{-2}\) d\({}^{-1}\)[8; 192; 193; 194; 195; 196; 197; 198; 199; 200; 201; 202; 203; 204; 205; 206], assuming weight-specific and oxygen data conversions to g C m\({}^{-2}\) d\({}^{-1}\) and a wet weight (WW)/dry weight (DW) conversion factor of 15 [196], a photosynthetic quotient (PQ) of 1.2, and a g DW: m\({}^{2}\) conversion factor of 27.5 [197]. The macroalgal production correlated positively with temperature ([PERSON]'s r = 0.63; \(p\) < 0.001) but inversely with photon flux density ([PERSON]'s r = 0.73: \(p\) < 0.001). The macroalgal NPP is thus nearly 4.5 times greater than the mangrove ANPP on a unit area basis, suggesting that they play a highly significant role in the carbon flow in mangrove ecosystems, but only if they carpet a sufficiently large area of forest. Most photosynthesis measurements have been performed in the Caribbean, including in Florida waters where the work of [PERSON] and his colleagues established that the mangrove macroalgae were both abundant and productive [197; 199; 203]. The peak rates of red macroalgal photosynthesis measured in Florida mangroves with _Bostrychia binderi_ showed an unusual tolerance to desiccation and equally high rates of photosynthesis both in air and while submerged [199]. The photosynthetic quotients for _B. binderi_ and _Gracilaria verrucosa_ were 1.2 with diel fluctuations in photosynthesis and pronounced mid-morning peaks [197]. In the Belize Barrier Reef-magnrove ecosystem, the production of the fondose algae, _Dictyota divariata_ and _Acanthophora spicifera_, was high in the mangroves with higher N and P concentrations than in the same species at a barrier reef site. This finding suggests that macroalgae in fringinging mangroves may not be as severely nutrient-limited as they are in adjacent reef habitats [201]. Submerged macroalgae were similarly productive, and this was attributed to greater nutrient availability near the mangroves and to reduced levels of herbivory [200]. Macroalgae are conspicuous in Latin American and South African mangroves. The red algae, _Bostrychia radicans_ and _Calgossa leprieuvii_, are common on _A. marina_ pneumatophores with peak photosynthetic rates measured between 25% and 58% desiccation and with increases in the photosynthetic and respiratory rates with increasing temperatures, peaking at 32-37 \({}^{\circ}\)C, low light intensities, and a wide range of salinity [202]. However, some species, such as _B. binderi_, do not show a sensitivity to high-light conditions while other species show a wide tolerance to a range of light intensities [196]. Both the _Calgossa_ and _Bostrychia_ species acclimate to harsh environmental conditions by synthesizing and accumulating high concentrations of the osmotic osmolytes D-mannitol, D-mannitol, and D-dulcitol which are involved in osmotic acclimation [192; 203]. For _Bostrychia calliptera_ and _C. leprieuvii_ living as epiphytes on the prop roots of _R.