River and stream rehabilitation projects are increasing in number, but the success or failure of these projects has rarely been evaluated, and the extent to which buffers can restore riparian and stream function and species composition is not well understood. In New Zealand the widespread conversion of forest to agricultural land has caused degradation of streams and riparian ecosystems. We assessed nine riparian buffer zone schemes in North Island, New Zealand that had been fenced and planted (age range from 2 to 24 years) and compared them with unbuffered control reaches upstream or nearby. Macroinvertebrate community composition was our prime indicator of water and habitat quality and ecological functioning, but we also assessed a range of physical and water quality variables within the stream and in the riparian zone. Generally, streams within buffer zones showed rapid improvements in visual water clarity and channel stability, but nutrient and fecal contamination responses were variable. Significant changes in macroinvertebrate communities toward “clean water” or native forest communities did not occur at most of the study sites. Improvement in invertebrate communities appeared to be most strongly linked to decreases in water temperature, suggesting that restoration of in‐stream communities would only be achieved after canopy closure, with long buffer lengths, and protection of headwater tributaries. Expectations of riparian restoration efforts should be tempered by (1) time scales and (2) spatial arrangement of planted reaches, either within a catchment or with consideration of their proximity to source areas of recolonists.

Marine soft sediments are often considered to be vast, homogeneous expanses of mud or sand; however, most exhibit small‐scale biogenic structures. Generally such structures result from short‐term processes, but mollusk shell debris can last for centuries, providing a settlement surface for plants and animals, which in turn stabilize the debris. This study sampled patches of shell debris and the surrounding sediment at increasing distances from the patches to determine the role of the patches in driving beta biodiversity. Sampling was conducted at three similar sites within 1 km in a marine reserve in New Zealand. The shell debris significantly affected beta diversity at all sites, although the magnitude of the effect was dependent on patch size, density, and debris particle size. These results have important implications for estimating and mapping biodiversity. They also have implications for marine conservation. The role of shell debris, suggested by this study, in increasing and maintaining biodiversity, emphasizes a need for reducing disturbance regimes and actively managing seafloor habitats in areas not previously considered for such.

Ocean acidification is a well recognised threat to marine ecosystems. High latitude regions are predicted to be particularly affected due to cold waters and naturally low carbonate saturation levels. This is of concern for organisms utilising calcium carbonate (CaCO3) to generate shells or skeletons. Studies of potential effects of future levels of pCO2 on high latitude calcifiers are at present limited, and there is little understanding of their potential to acclimate to these changes. We describe a laboratory experiment to compare physiological and metabolic responses of a key benthic bivalve, Laternula elliptica, at pCO2 levels of their natural environment (430 µatm, pH 7.99; based on field measurements) with those predicted for 2100 (735 µatm, pH 7.78) and glacial levels (187 µatm, pH 8.32). Adult L. elliptica basal metabolism (oxygen consumption rates) and heat shock protein HSP70 gene expression levels increased in response both to lowering and elevation of pH. Expression of chitin synthase (CHS), a key enzyme involved in synthesis of bivalve shells, was significantly up-regulated in individuals at pH 7.78, indicating L. elliptica were working harder to calcify in seawater undersaturated in aragonite (ΩAr = 0.71), the CaCO3 polymorph of which their shells are comprised. The different response variables were influenced by pH in differing ways, highlighting the importance of assessing a variety of factors to determine the likely impact of pH change. In combination, the results indicate a negative effect of ocean acidification on whole-organism functioning of L. elliptica over relatively short terms (weeks-months) that may be energetically difficult to maintain over longer time periods. Importantly, however, the observed changes in L. elliptica CHS gene expression provides evidence for biological control over the shell formation process, which may enable some degree of adaptation or acclimation to future ocean acidification scenarios.

When changes in the frequency and extent of disturbance outstrip the recovery potential of resident communities, the selective removal of species contributes to habitat loss and fragmentation across landscapes. The degree to which habitat change is likely to influence community resilience will depend on metacommunity structure and connectivity. Thus ecological connectivity is central to understanding the potential for cumulative effects to impact upon diversity. The importance of these issues to coastal marine communities, where the prevailing concept of open communities composed of highly dispersive species is being challenged, indicates that these systems may be more sensitive to cumulative impacts than previously thought. We conducted a disturbance-recovery experiment across gradients of community type and environmental conditions to assess the roles of ecological connectivity and regional variations in community structure on the recovery of species richness, total abundance, and community composition in Mahurangi Harbour, New Zealand. After 394 days, significant differences in recovery between sites were apparent. Statistical models explaining a high proportion of the variability (R2 > 0.92) suggested that community recovery rates were controlled by a combination of physical and ecological features operating across spatial scales, affecting successional processes. The dynamic and complex interplay of ecological and environmental processes we observed driving patch recovery across the estuarine landscape are integral to recovery from disturbances in heterogeneous environments. This link between succession/recovery, disturbance, and heterogeneity confirms the utility of disturbance-recovery experiments as assays for cumulative change due to fragmentation and habitat change in estuaries.

Three first-order, hill country, pasture streams in Waikato, New Zealand, were chosen to investigate the effects of patches of late-succession indigenous riparian forest on water quality, epilithon, stream morphology, and aquatic macro-invertebrates. Sites were situated in open pasture and at two distances (c. 50 and 300 m) into a forest remnant on each stream. Shade, channel width, and epilithon biomass were restored to conditions similar to a native forest control site within 300 m of the streams entering the native forest remnants, whereas water chemistry and levels of surficial fine sediment changed more slowly. Invertebrate community composition showed shifts towards the native forest condition just 50 m into the forest remnants, and full recovery had occurred within 300 m. Results from this study suggest that discontinuous restoration of riparian margins could mitigate some changes associated with pastoral land use, but sediment and water quality problems may not be solved. Keywords stream habitat; forest remnants; channel morphology; water quality; benthic macroinvertebrates; riparian restoration; New Zealand M98038