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Despite the environmental stresses that mangrove forests experience – including fluctuating salinity, low soil oxygen and buffeting by waves – they can be highly productive. Facilitation, defined here as the benefits to an organism by the minimisation by neighbouring organisms of biotic or physical stress, may help explain this. Theory suggests that facilitation is likely in stressful environments, and trees and shrubs have been found to be particularly likely to exhibit facilitation. Hence, we should find facilitation in mangrove forests, and this chapter summarises new and published evidence for its existence. Facilitation occurs at a wide range of scales and during all different points in a mangrove tree's life. Amelioration of hydrodynamic and dessicative stresses can be important during seedling establishment and early growth. Interactions with fauna, including crabs and ants, can sustain tree production and help defend against herbivores. Ecosystem-scale facilitation helps ensure resilience in the face of changes such as sea-level rise. Hence facilitation is common in mangroves, and the challenge now is to gain a theoretical understanding of when and where to expect it.
The rocky shores of the north-east Atlantic have been long studied. Our focus is from Gibraltar to Norway plus the Azores and Iceland. Phylogeographic processes shape biogeographic patterns of biodiversity. Long-term and broadscale studies have shown the responses of biota to past climate fluctuations and more recent anthropogenic climate change. Inter- and intra-specific species interactions along sharp local environmental gradients shape distributions and community structure and hence ecosystem functioning. Shifts in domination by fucoids in shelter to barnacles/mussels in exposure are mediated by grazing by patellid limpets. Further south fucoids become increasingly rare, with species disappearing or restricted to estuarine refuges, caused by greater desiccation and grazing pressure. Mesoscale processes influence bottom-up nutrient forcing and larval supply, hence affecting species abundance and distribution, and can be proximate factors setting range edges (e.g., the English Channel, the Iberian Peninsula). Impacts of invasive non-native species are reviewed. Knowledge gaps such as the work on rockpools and host–parasite dynamics are also outlined.
Two sites in North Wales, UK, were compared for growth, survival,
immunocompetence and gonad development of Crassostrea gigas. Juvenile C. gigas spat were purchased as
a cohort and placed in bags on trestles at the Menai Strait (MS, two heights
on the shore) and the Inland Sea (IS) in the summer of 2003. Performance was
examined as a function of several environmental parameters; temperature,
coloured dissolved organic material absorption coefficient (cDOM), organic
and inorganic nutrient levels, chlorophyll a and phytoplankton community
Both sites produced variations in growth, as assessed by dry weight indices
and condition index, which were found to be lower at IS, where the animals
were permanently immersed, than at MS, where they were emersed for at least
1 h/tide (at the low shore height) and 4 h/tide (at the high shore height)
during spring tides. Condition index was also significantly higher at MS
high shore than at MS low shore. Mortality was low at all sites, though an
increase at IS at the end of the trial led to a significantly greater final
percentage mortality of 15.6%. Gonad development was limited,
particularly at IS where most animals remained undifferentiated. Gonad
development was significantly higher at MS high shore than at MS low shore.
cDOM, organic and inorganic nutrients were similar at the two areas. At IS
the temperature and chlorophyll a levels were higher than MS. The
phytoplankton communities were significantly different, with a bloom of
Prorocentrum micans dominating at the Inland Sea for much of the experimental period.
Differences in the hydrodynamics, as well as Phytoplankton community
appeared to be the only parameters that might cause a lower growth rate in
the Inland Sea. The possibilities of P. micans having a sub-lethal effect on C. gigas are discussed.
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