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.
"Author(s) agree that this article remain permanently open access under the terms of the Creative Commons Attribution License 4.0 International License 2014; McClanahan et al., 2012; Palumbi et al., 2014) and anthropogenic disturbances, especially increases in human activities and associated development (West and Woesik, 2001; Wolanski et al., 2009; Hughes et al., 2010). In many cases, these declines have been linked to human induced perturbations that influence gradients of water quality and levels of exploitation that lead to increased sea surface temperature (SST) and atmospheric CO 2 (Fabricius, 2005; Pandolfi et al., 2005; Fabricius and McCorry, 2006; Richmond et al., 2007; Doropoulos et al., 2012; Logan et al., 2014). Recently, local and regional risk assessments have ranked the degree of vulnerability of reefs to anthropogenic stressors based primarily on potential landbased sources of disturbances (Burke and Maidens, 2004; Nyström et al., 2000; Wolanski et al., 2009). "
[Show description][Hide description] DESCRIPTION: The effects of sediment concentration and season on coral recruitment algal abundance and benthic community structure were studied in Kenyan coral reef lagoons to determine their potential influence on coral recovery. Nutrient levels and recruit numbers were higher during the southeast monsoon (SEM) than during the northeast monsoon (NEM) season and in sediment-exposed compared to nonsediment exposed reefs. Mean algal biomass also exhibited the same seasonal trend (except at one site), but was higher in the non-sediment exposed reef compared to the other reefs. Corals in the sediment exposed reef exhibited morphological differences relative to the other reefs: fewer corymbose
and plate-like but more branching, massive and solitary forms and increased colony and corallite sizes. However, sediments did not suppress coral recruitment rates. These morphological changes coupled with the interaction between biological and physico-chemical characteristics have important ecological and geological implications: by potentially modifying calcium carbonate production and ameliorating the adverse effects of climate induced stress events, this may minimize coral mortality and enhance reef recovery.
[Show abstract][Hide abstract] ABSTRACT: We investigated habitat use by juvenile Chinook salmon (Oncorhynchus tshawytscha) and coho salmon (O. kisutch) to identify environmental characteristics that may define their optimal marine habitat. We utilized physical and biological
data from four cruises in the northern California Current system from Newport, Oregon, to Crescent City, California, in June
and August 2000 and 2002. A non-parametric statistical method was used to analyze and select environmental parameters that
best defined ocean habitat for each species. Regression trees were generated for all cruises combined to select the most important
habitat variables. Chlorophyll a concentration best defined habitat of yearling Chinook salmon, while decapod larvae, salinity, and neuston biovolume defined
habitat of yearling coho salmon. Using criteria from the regression tree analysis, GIS maps were produced to show that the
habitat of yearling Chinook salmon was widespread over the continental shelf and the habitat of yearling coho salmon was variable
and mainly north of Cape Blanco.
KeywordsRegression trees–GIS–Coho salmon–Chinook salmon–California Current–Habitat
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