The paper presents a relationship between climate change, ocean acidification and corals' condition.

Trends in the percentage cover of macroalgae are generally used as an important indicator of the health of coral reefs. While considerable data exist on patterns of macroalgal cover, the underlying patch dynamics of macroalgae are poorly understood. It is important to appreciate the dynamical processes of algae because they determine the frequency and duration of competitive interaction with other taxa, such as corals, and thereby contribute to our understanding of competitive interactions. We used transition matrices to quantify and describe the patch dynamics of 2 common macroalgae in the Caribbean, Dictyota pulchella and Lobophora variegata, over a 9 mo period. Size-based matrices were constructed for both species from forereef habitats subjected to contrasting levels of wave exposure. The dynamics of D. pulchella are highly sensitive to the physical environment, whilst those of L. variegata are far less sensitive. The patch dynamics of D. pulchella showed a higher temporal variation than L. variegata, but only on the exposed forereef. D. pulchella virtually disappeared in January at both the exposed and sheltered sites, whereas L. variegata exhibited a continuing increase in patch size irrespective of exposure. D. pulchella formed larger, more dynamic patches under high exposure. This implies that contact interactions with coral colonies and space pre-emption for settling planulae will occur more frequently than in sheltered environments. Our results demonstrate the need to investigate patch dynamics of macroalgae at the individual species level, whilst taking into account environmental conditions.

Territorial behaviour is a conspicuous determinant of social organisation in many reef fishes including parrotfishes. Most parrotfish studies in the Caribbean have focused on the species Scarus iserti and Sparisoma viride over limited ranges of reef habitat. By contrast, our study has included all common parrotfishes in Belize (Sc. iserti, Sp. viride, Sparisoma aurofrenatum, Sparisoma chrysopterum, and Sparisoma rubripinne) at three sites with different physical and biotic conditions and a wide range of fish densities. Density in Sc. iserti was strongly positively correlated to substrate rugosity. In contrast, densities of Sp. chrysopterum and Sp. rubripinne were unrelated to rugosity and territories were large. Territory size was smallest in Sc. iserti (mean areas at the three sites ranged from 41 to 120?m2) and largest in Sp. rubripinne (ranged from 168 to 1400?m2). All species except Sp. chrysopterum exhibited significantly larger territories where density was low as suggested by territory theory. Territory size decreased rapidly with increasing density of competitors. Patterns of harem size differed between two groups of parrotfishes. (1) Sc. iserti, Sp. viride, and Sp. aurofrenatum exhibited an expected positive correlation with territory size. (2) Harem size was smaller in Sp. rubripinne and Sp. chrysopterum, and showed no spatial pattern. Aggression in Sp. viride and Sc. iserti was directed entirely towards intraspecifics and positively density dependent. Interspecific interactions accounted for only 10% of observations and were recorded exclusively whilst following Sp. chrysopterum, Sp. rubripinne, and, to a lesser extent, Sp. aurofrenatum. A meta analysis of species interactions suggested that intraspecific interactions were most common where overall fish density was greatest and conversely, interspecific interactions occurred more often at lower densities. This may suggest that the economic defensibility of territories is largely confined to intraspecifics where density is greatest. Most (62%) of the interspecific interactions comprised Sp. rubripinne chasing the smaller species Sp. chrysopterum, suggesting that territorial behaviour has at least some non-reproductive origin and may therefore be associated with either food or shelter. It is feasible that at such low population densities, it is economically feasible for Sp. rubripinne to defend against intraspecifics and Sp. chrysopterum. Social behaviour in Sp. chrysopterum and Sp. rubripinne, and to a lesser extent Sp. aurofrenatum, differs to that of Sc. iserti and Sp. viride which conform to existing theories of social behaviour in reef fish.