precipitates, that of the daytime correlation is >4 times as steep. We attribute these differences to the role of photosynthesis in calcification and conclude that bulk SffCa is related principally to daytime calcification rate rather than directly to SST. More reliable estimates of past SST may be arrived at through selective analysis of nighttime skeleton.

SynopsisHerbivorous fishes and invertebrates are conspicious elements of coral reef communities where they predominate both in numbers and biomass. Herbivores and the coral reef algae on which they feed represent a co-evolved system of defense and counter-defense. Algal species have developed toxic, structural, spatial and temporal defense or escape mechanisms, while the herbivores employ strategies that involve anatomical, physiological and behavioral adaptations. Current research demonstrates that many reef fishes are highly selective in the algae they consume. Food selection in these fishes may be correlated with their morphological and digestive capabilities to rupture algal cell walls. Sea urchins select more in accordance with relative abundance, although certain algal species are clearly avoided.The determinants of community structure on coral reefs have yet to be established but evidence indicates a strong influence by herbivores. Reef herbivores may reduce the abundance of certain competitively superior algae, thus allowing corals and cementing coralline algae to survive. We discuss how the foraging activities of tropical marine herbivores affect the distribution and abundance of algae and how these activities contribute to the development of coral reef structure and the fish assemblages which are intimately associated with reef structure.

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Certain herbivorous fishes are well known for morphological specializations enabling trituration; such as scarids with a pharyngeal mill and mullets with a gizzard-like stomach. However, utilization of plant foods by fishes is limited by these animal's digestive capabilities, most notably the apparent lack of cellulose digesting enzymes. Fishes possessing a grinding mechanism are able to break open plant cells for digestion. But how fishes without grinding mechanisms make plant cell contents accessible to digestion is unknown. These fishes include many acanthurid and pomacentrid species which are among the most abundant on reefs.Another mechanism for rupturing plant cell walls has been recently proposed, namely lysis by gastric acidity. This study surveyed stomach and intestinal pH for 17 herbivorous species at Fanning Atoll, Central Pacific and two species from St Croix, Caribbean with additional data for seven selected carnivorous species. The herbivorous fishes included acanthurids (surgeonfishes), mugilids (mullets), pomacanthids (angelfishes), pomacentrids (damselfishes) and a scarid (parrotfish). The effect of different pH concentrations and trituration was examined experimentally for eight common Pacific marine algae including two reds, two blue-greens, two greens, one brown, and the algal mat complex from inside damsel fish territories.Fishes, possessing morphological adaptations for trituration, ingested quantities of calcium carbonate material and did not contain gastric acidity low enough to lyse algal cell wells. However, fishes without grinding mechanisms but with defined stomachs have gastric pH values from 2.4 to 4.25 which can be as effective as trituration in releasing algal cell contents of certain algae. These results are considered in a review of previous studies of herbivory in fishes. The trophic relationship between fishes and algae of specified morphologies are predicted by extrapolation from the experimental results on algae vulnerable to acid lysis or trituration.

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