Changes in octocoral communities and benthic cover along a water quality gradient in the reefs of Hong Kong
ABSTRACT Cover of the main reef benthic groups, and abundances and taxonomic richness of octocorals were surveyed in the reefs of Hong Kong, and related to spatial and water quality gradients. Nutrient and particle concentrations are high throughout the area, with concentrations declining from the south towards the north-eastern region. Regression tree analyses showed that hard coral cover was most strongly related to water clarity, that macroalgal cover was highest in areas with high wave action and high water clarity, and that crustose coralline algae were negatively related to sedimentation. Octocoral communities (42 species in 23 genera) were dominated by zooxanthellae-free taxa; those few species with zooxanthellae were restricted to reefs with low wave action and high water clarity in the north-eastern region. The water quality gradient spans from conditions that are marginal for zooxanthellate octocorals while still supporting diverse scleractinian communities, towards an estuarine endpoint where zooxanthellate octocorals cease to exist and hard coral communities are reduced to a few resilient colonies. The data suggest that the types, abundances and richness of zooxanthellate octocorals, and the shift from zooxanthellate to azooxanthellate octocoral communities, may act as useful indicators of water clarity in regions where long-term water quality data are unavailable.
SourceAvailable from: Pedro M. Alcolado
Article: Variación de la talla de Eunicea flexuosa y Plexaura kuekenthali(Cnidaria: Octocorallia) en arrecifes coralinos cercanos a fuentes contaminantes en La Habana, Cuba Size variation of Eunicea flexuosaand Plexaura kuekenthali(Cnidaria: Octocorallia) in coralreefs close to pollution sources in Havana, Cuba[Show abstract] [Hide abstract]
ABSTRACT: Variation in size of octocorals Eunicea flexuosaand Plexaura kuekenthali was determined in coral reefs with different levels of urban pollution facing Havana city, Cuba. T heheight of the colonies found along a belt transect (100 x 1 m) was measured. Size distribution of both species showed a tendency of colonies to reach a higher relative frequency in the lower size ranges at sites near river basins with the highest pollutant load (measured by the number of pollution sources and disposed load, BOD). The average size of E. flexuosawas significantly smaller in the two sites near the river basin with the highest pollutant load. Its bigger effect sizes (difference between pairs of average height in Monte Carlo analysis) were detected between sites near basins with lower (SA and CH) and higher (AM and ES) pollutant load. The average size of P. kuekenthaliwas significantly bigger in the site near the basin with lower pollutant load. However, the second biggest average size was unexpectedly found at the site near the basin with the highest pollutant load, which is probably due to heterotrophic and/or phototropic mechanisms in the growth, fact that requires future research. Urban pollution seems to affect height growth of E. flexuosaand P. kuekenthali. However, in spite that urban pollution affects size distribution of P. kuekenthali, it is unclear whether it affects its average height.
[Show abstract] [Hide abstract]
ABSTRACT: Southern China hosts coral communities in marginal environments that are characterized by low linear extension rates, low coral cover and/or no reef formation, thus providing natural laboratories to study coral communities with below average growth rates. Here we compare the annual linear extension rates over 10 years (range 1.2 to 11.4 mm yr-1) of six Porites sp. coral cores collected from Hong Kong with monthly hydrographic data from the Hong Kong Environmental Protection Department. At all sites, low-density, dry season extension were more variable than high-density, wet season extension and on average, was lower at two of the three sites. We applied multi-variate linear regressions that revealed high-density, wet season band extension to inversely correlate most significantly to temperature (r = -0.39, p<0.01). In contrast, low-density, dry season band extension was more variable and correlated most significantly with dry season chlorophyll-a (Chl-a) (r = 0.64, p<0.001). Additionally, we find that corals at the site with highest dry season Chl-a have the highest dry season extension lengths. Our findings indicate that relative mixing of fresh and salt water in the wet season and primary productivity in the dry season, and their influences on aragonite saturation, are likely to impact interannual coral extension variability in marginal environments.PLoS ONE 06/2014; 9(6):e99088. DOI:10.1371/journal.pone.0099088 · 3.53 Impact Factor
[Show abstract] [Hide abstract]
ABSTRACT: The Saudi Arabian Red Sea coast is characterized by a strong environmental gradient from north (28.5°N) to south (16.5°N) with challenging conditions for coral growth particularly in the south (high temperature and nutrient input). We investigated whether assemblies of reef-building corals and the distribution of functional groups follow a latitudinal pattern in the Red Sea, and whether these changes affect the assembly structure of coral associated organisms (e.g. fishes). Functional groups were defined based on life-history traits and functional role. 13 reefs along the north-south gradient, including 5 potentially polluted reefs were investigated. Results showed a substantially weaker latitudinal shift in the assembly structure of coral communities than of fishes communities and of other benthic reef taxa. Competitive fast growing branching and tabular species (mainly Acropora), as well as rather stresstolerant slow growing bulky species (e.g. Porites, Goniastrea, Favites, Favia) were fairly evenly distributed along the north-south axis despite strong changes of environmental conditions. This seems on the one hand attributable to the high species richness within a given functional group (functional redundancy) and on the other hand to a high acclimatization / adaptation potential of some Red Sea coral species. The prime ecosystem service of the coral community, the provision of a habitat complex, is thereby maintained throughout the gradient. In contrast to the coral community, the assembly of the fish community shifts along the environmental gradient with higher abundances of small wrasses and butterfly fishes in the north, and overall higher abundance of fishes including large fishes in the south. This shift seems linked to higher food availability in the south. Altered assembly structures of coral communities were found in reefs close to a source of pollution with either an increased relative abundance of stresstolerant species or a general decrease of coral abundance, latter case accompanied by a substantial reduction in fish abundance.