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Previous studies of marine soft-bottom communities have shown (1) that natural disturbances (especially biologically-mediated disturbances, which are usually localized and recur reasonably frequently) help maintain spatio-temporal heterogeneity of communities, and (2) that biogenic modification of sediment can affect sediment stability with respect to fluid forces and geotechnical properties and that this is an important factor in community organization, particularly in the trophic structure of the macrofauna. It is argued in this paper that natural disturbances, and the ensuing biogenic alterations to sediment stability, may be important in maintaining trophically-mixed communities where deposit feeders do not have an overriding influence on sedimentary properties. The hypothesis is presented that an initial post-disturbance response by micro-and meiobenthos leads to an increase in sediment stability as a result of mucous-binding of sediment, and that this stage may be of critical significance to potential suspension-feeding colonists if they are competing with deposit feeders for space. It is suggested, partly as a corollary to this hypothesis, that there may be marked differences in the structure and function of meiofaunal communities co-occurring with deposit-feeding and suspension-feeding macrofaunas. Implications for macrofaunal trophic structure of seasonal changes in sediment stability are also examined. Several areas for future research are recommended.

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ABSTRACT1. Invertebrates inhabiting marine and freshwater ecosystems make important contributions to global biodiversity and provide significant services that have cascading effects across ecosystems. However, this group is grossly under-represented in assessments of conservation status and often neglected in targeted aquatic conservation efforts.2. In global assessments of 7857 freshwater invertebrates and 2864 marine invertebrates, 30-34% were considered Data Deficient highlighting the paucity of information for making such assessments. Of the invertebrate groups that could be assessed, those with poor dispersal abilities and high local endemism, such as many gastropods, crayfish and mussels, are the most threatened.3. Springs and subterranean hydrological systems support the highest proportions of threatened freshwater species, while in marine environments coral reefs, lagoons and anchialine systems are particularly vulnerable.4. Key agents of biodiversity decline in aquatic ecosystems are water pollution, overexploitation and harvesting, habitat degradation and destruction, alien invasive species, and climate change. Effects of dams and water management along with pollution from urban, agricultural and forestry sources are the main threats in freshwater ecosystems, whereas a broad range of factors have impacts on marine invertebrates, including biological resource use.5. Significant impediments facing conservation of aquatic invertebrates are limited knowledge of their diversity, the need for broadscale actions to account for connectivity within and across ecosystems, lack of political will and investment, and the prospect that conditions may get worse before they improve, possibly not in time to save some already highly imperilled invertebrate species from extinction.

1. Habitat-forming bryozoans are here defined as extant, heavily-calcified species which regularly attain sizes over 50 mm in three-dimensions and which contribute significantly to benthic habitat structure as living colonies.2. Records of habitat-forming bryozoans were collated and mapped, together with information about the location, environment, habitat-forming species, the nature and size of the habitat formed, any associated fauna, and relevant threats and/or conservation measures.3. Records collated here indicated that habitat-forming bryozoans occurred from~59 N to 77 S, but that they did not occur frequently in the tropics, being found most commonly in temperate continental shelf environments, on stable substrata in places where water movement was relatively fast and consistent.4. Habitat-forming bryozoans are particularly abundant and diverse in New Zealand, where 27 species, a quarter of which are cyclostomes, provide habitat over hundreds of square kilometres of sea floor. Other areas where they are particularly rich and/or abundant include Antarctica (Weddell, Lazarev and Ross Seas), the North Pacific around Japan, the northern Mediterranean and Adriatic, and along the southern edge of the North Sea, through the English Channel and around the United Kingdom.5. Large bryozoans provide habitat for diverse associated assemblages, particularly for other bryozoans, molluscs, annelids, arthropods, cnidarians, sponges, echinoderms and macroalgae.6. Protected areas which include habitat-forming bryozoans occur throughout the distribution of this frequently unrecognized habitat type, but despite this they are prone to damage by anthropogenic impacts including pollution and bottom fishing.

In October 2001, we observed a deep-ocean phytodetritus deposition event on Chatham Rise beneath the Subtropical Front (STF). The origin of this phytodetritus was probably an extensive phytoplankton bloom that occurred in the STF in the preceding weeks. We assessed the spatial distribution of the deposition event using video images from benthic lander and epibenthic trawl deployments and sediment pigment analyses at six sites on a north-south transect across Chatham Rise. High surficial sediment chlorophyll a concentrations were restricted spatially to the southern flank of Chatham Rise (350-1,200-m depth) with the highest values centered at ,750-m water depth (750 S). This southern 750 S site was also the only site where macroscopic phytodetritus was observed, coincident with elevated benthic biomass and sediment community respiration rates. At 750 S, phytodetritus resuspension was observed on video and corroborated by current meter, sediment trap, and optical 1 Corresponding author (s.nodder@niwa.co.nz). AcknowledgementsWe thank the officers and crew of RV Tangaroa, and numerous scientific personnel at NIOZ and NIWA, especially Henk Franken and Eilke Berghuis for lander support. Figures were drafted by Erika Mackay (NIWA). We appreciate the provision of unpublished organic carbon accumulation rates for Chatham Rise by Elisabeth Sikes (Rutgers University). We thank the SeaWiFS Project (Code 970.2) and the Distributed Active Archive Center (Code 902) at the Goddard Space Flight Center, Greenbelt, Maryland, for the production and distribution of the remotely sensed ocean color data, respectively. Thanks also to the two anonymous reviewers for their constructive comments.

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