High mangrove density enhances surface accretion, surface elevation change, and tree survival in coastal areas susceptible to sea-level rise.

Survival, growth, aboveground biomass accumulation, sediment surface elevation dynamics and nitrogen accumulation in sediments were studied in experimental treatments planted with four different densities (6.96, 3.26, 1.93 and 0.95 seedlings m(-2)) of the mangrove Rhizophora mucronata in Puttalam Lagoon, Sri Lanka. Measurements were taken over a period of 1,171 days and were compared with those from unplanted controls. Trees at the lowest density showed significantly reduced survival, whilst measures of individual tree growth did not differ among treatments. Rates of surface sediment accretion (means ± SE) were 13.0 (±1.3), 10.5 (±0.9), 8.4 (±0.3), 6.9 (±0.5) and 5.7 (±0.3) mm year(-1) at planting densities of 6.96, 3.26, 1.93, 0.95, and 0 (unplanted control) seedlings m(-2), respectively, showing highly significant differences among treatments. Mean (±SE) rates of surface elevation change were much lower than rates of accretion at 2.8 (±0.2), 1.6 (±0.1), 1.1 (±0.2), 0.6 (±0.2) and -0.3 (±0.1) mm year(-1) for 6.96, 3.26, 1.93, 0.95, and 0 seedlings m(-2), respectively. All planted treatments accumulated greater nitrogen concentrations in the sediment compared to the unplanted control. Sediment %N was significantly different among densities which suggests one potential causal mechanism for the facilitatory effects observed: high densities of plants potentially contribute to the accretion of greater amounts of nutrient rich sediment. While this potential process needs further research, this study demonstrated how higher densities of mangroves enhance rates of sediment accretion and surface elevation processes that may be crucial in mangrove ecosystem adaptation to sea-level rise. There was no evidence that increasing plant density evoked a trade-off with growth and survival of the planted trees. Rather, facilitatory effects enhanced survival at high densities, suggesting that managers may be able to take advantage of high plantation densities to help mitigate sea-level rise effects by encouraging positive sediment surface elevation.

Response of intertidal macrofauna to multiple disturbance types and intensities - an experimental approach.

Two of the best-supported theories which describe the effects of disturbance within marine benthic habitats are the organic enrichment 'Successional Model' and the 'Intermediate Disturbance Hypothesis'. Underlying these models, biological mechanisms thought to drive community change include competition, facilitation, inhibition, tolerance and random colonisation. To further examine the effects of disturbance an experimental test of the effects of different types (burial, raking and organic enrichment) and intensities of disturbance on infaunal intertidal communities at two different sites with similar suites of species was carried out. The same type and frequency of disturbance, applied to the two different sites, produced different responses at the species, community and trophic group level. In models that assume a linear relationship between disturbance intensity and effect, knowledge of the intensity of any novel disturbance, combined with the original disturbance regime experienced by a community (i.e. its 'starting point'), should be sufficient to predict final community characteristics. The current results do not conform to such a linear interpretation, as at both sites the intensity of treatments did not always predict the degree of disturbance. Therefore the response to disturbance may depend on site-specific factors such as the history of prior disturbance and the inherent ecological plasticity exhibited by many benthic species. Whilst current models perform well in predicting benthic responses to gross disturbance, detecting subtler effects requires a recognition that community response may depend on the site, the species and the sources of disturbance.

The use of time-series data in the assessment of macrobenthic community change after the cessation of sewage-sludge disposal in Liverpool Bay (UK).

Sewage sludge was disposed of in Liverpool Bay for over 100 years. Annual amounts increased from 0.5 million tonnes per annum in 1900 to approximately 2 million tonnes per annum by 1995. Macrofauna and a suite of environmental variables were collected at a station adjacent to, and a reference station distant from, the disposal site over 13 years, spanning a pre- (1990-1998) and post- (1999-2003) cessation period. Univariate and multivariate analyses of the time-series data showed significant community differences between reference and disposal site stations and multivariate analyses revealed station-specific community development post-disposal. Temporal variability of communities collected at the disposal station post-cessation was higher than during years of disposal, when temporally stable dominance patterns of disturbance-tolerant species had established. Alterations of community structure post-disturbance reflected successional changes possibly driven by facilitation. Subtle faunistic changes at the Liverpool Bay disposal site indicate that the near-field effects of the disposal of sewage sludge were small and therefore could be considered environmentally acceptable.

Morphological, total nucleic acid and total protein analyses of rat embryos cultured in supplemented and unsupplemented human serum.

Culture of explanted 9 1/2 day rat conceptuses for 48 hours (i.e. until 11 1/2 days) in 100% human serum supplemented only with glucose does not result in growth and development comparable to those conceptuses cultured for the same period in 100% rat serum. Significant differences were observed in the yolk sac diameter, crown-rump length, morphological score and total embryonic nucleic acid content. No difference was observed in the total embryonic protein content. A large proportion of the embryos cultured in glucose-supplemented human serum (100%) exhibited abnormalities of the neural tube. Supplementation of the human serum with glucose and 10% rat serum resulted in embryos showing higher indices of embryonic growth and differentiation (in all criteria of assessment) than those cultured in pure rat serum; no abnormalities were observed. The significance of better growth and differentiation of the conceptuses in human serum supplemented with glucose and 10% rat serum is discussed.