Abstract:The potential role of the hyporheic zone as a refugium for stream invertebrates during hydrological perturbations was acknowledged more than fi ve decades ago. However, fi eld evidence to support the hyporheic refuge hypothesis during periods of fl ow recession and severe low fl ow remains equivocal. Some studies report fauna using the hyporheic zone during periods of fl ow cessation whilst others have recorded little or no refuge use due to limited habitat availability or harsh abiotic conditions. We assessed aquatic macroinvertebrate community changes associated with severe low fl ow conditions during a severe supra-seasonal drought on the Little Stour River (UK). Paired benthic and hyporheic samples were collected from four sites (two perennial, two intermittent) on the upper reaches of the river. The number of benthic taxa and the proportion of benthos (particularly the amphipod Gammarus pulex) within the hyporheic zone relative to those in the benthic samples increased signifi cantly during the latter stages of the drought at all sites. These changes coincided with elevated benthic and hyporheic water temperatures rather than a reduction in river discharge alone. The abundance of obligate hypogean macroinvertebrates also increased during the latter stages of the event, suggesting that hypogean taxa may also utilise the shallow hyporheic zone during adverse environmental conditions. Our results, based on paired surface-hyporheic fi eld samples at multiple sites, support the hyporheic refuge hypothesis within a temperate groundwater-dominated stream during severe drought.The results also clearly demonstrate the importance of considering surface-subsurface linkages when assessing responses to disturbance in streams.

There is an increasing demand for environmental assessments of the marine environment to include ecosystem function. However, existing schemes are predominantly based on taxonomic (i.e. structural) measures of biodiversity. Biodiversity and Ecosystem Function (BEF) relationships are suggested to provide a mechanism for converting taxonomic information into surrogates of ecosystem function. This review assesses the evidence for marine BEF relationships and their potential to be used in practical monitoring applications (i.e. operationalized).Five key requirements were identified for the practical application of BEF relationships: 1) a complete understanding of strength, direction and prevalence of marine BEF relationships, 2) an understanding of which biological components are influential within specific BEF relationships, 3) the biodiversity of the selected biological components can be measured easily, 4) detail which ecological mechanisms are the most important for generating marine BEF relationships, e.g. identity effects or complementarity, and 5) establish what proportion of the overall functional variance is explained by biodiversity, and hence BEF relationships.Many positive and some negative BEF relationships were found within the literature, although many reproduced poorly the natural species richness, trophic structures or multiple functions of real ecosystems. Null relationships were also reported. The consistency of the positive and negative relationships was often low that compromised the ability to generalize BEF relationships and confident application of BEF within marine monitoring. Equally, some biological components and functions have received little or no investigation.Expert judgement was used to attribute biological components using spatial extent, presence and functional rate criteria. This approach highlighted the main contributing biological components to the ecosystem functions, and that many of the particularly influential components were found to have received the least amount of research attention.The need for biodiversity to be measureable (requirement 3) is possible for most biological components although difficult within the functionally important microbes. 3Identity effects underpinned most marine BEF relationships (requirement 4). As such, processes that translated structural biodiversity measures into functional diversity were found to generate better BEF relationships.The analysis of the contribution made by biodiversity, over abiotic influences, to the total expression of a particular ecosystem function was rarely measured or considered (requirement 5). Hence it is not possible to determine the overall importance of BEF relationships within the total ecosystem functioning observed. In the few studies where abiotic factors had been considered, it was clear that these modified BEF relationships and have their own direct influence on functional rate.Based on the five requirements, the information required for immediate 'operationalization' of BEF relationships within marin...

SUMMARY1. The aquatic invertebrate 'seedbank' comprises life stages that remain viable in the bed sediments of temporary freshwaters during dry phases. This seedbank promotes persistence of temporary-stream macroinvertebrates, but how its inhabitants respond to extended dry phases or repeated transitions between wet and dry phases remains unknown. 2. We rehydrated samples collected from the dry bed of a temperate-zone stream during a supra-seasonal drought, to examine the seedbank assemblage. Samples were first collected in autumn, from 12 sites along the ephemeral (4 sites), intermittent (2) and near-perennial (6) reaches, which had been dry for up to 8 months. Our first hypothesis was that assemblage composition would be related to the dry-phase duration preceding sampling, with longer dry phases reducing abundance and richness. 3. We revisited the same sites in three subsequent seasons, collecting and rehydrating sediments from all dry sites: five sites in early spring, three in late spring and four in late summer. Unpredictable flow resumption and redrying occurred between sampling dates. Our second hypothesis was that repeated wet-dry cycles would not degrade the assemblage because temporary-stream taxa would be adapted to fluctuating hydrological conditions. 4. Multiple individuals of only Chironomidae, Oligochaeta and Pisidium were present at sites that experienced the longest dry phases, providing some support for our first hypothesis. An additional 21 taxa were recorded across the remaining (shorter dry phase) sites in autumn, indicating that such sites act as refuges and potential recolonist sources following flow resumptions. 5. Although several insect orders first recorded in early spring were absent in later seasons, taxon-specific life cycles indicated that these absences were probably seasonal and not due to repeated wet-dry cycles. 6. We recorded 38 taxa in total, highlighting the seedbank as a dry-phase resistance mechanism for many temporary-stream macroinvertebrates. Our results also suggest that seedbank diversity may be threatened by increases in drought extent and duration.

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