Commercial fishing is one of the most important human impacts on the marine benthic environment. One such impact is through disturbance to benthic habitats as fishing gear (trawls and dredges) are dragged across the seafloor. While the direct effects of such an impact on benthic communities appear obvious, the magnitude of the effects has been very difficult to evaluate. Experimental fishing‐disturbance studies have demonstrated changes in small areas; however, the broader scale implications attributing these changes to fishing impacts are based on long‐term data and have been considered equivocal. By testing a series of a priori predictions derived from the literature (mainly results of small‐scale experiments), we attempted to identify changes in benthic communities at the regional scale that could be attributed to commercial fishing. Samples along a putative gradient of fishing pressure were collected from 18 sites in the Hauraki Gulf, New Zealand. These sites varied in water depth from ∼17 to 35 m and in sediment characteristics from ∼1 to 48% mud and from 3 to 8.5 μg chlorophyll a/cm3. Video transects were used for counting large epifauna and grab/suction dredge and core sampling were used for collecting macrofauna. After accounting for the effects of location and sediment characteristics, 15–20% of the variability in the macrofauna community composition sampled in the cores and grab/suction dredge samples was attributed to fishing. With decreasing fishing pressure we observed increases in the density of echinoderms, long‐lived surface dwellers, total number of species and individuals, and the Shannon‐Weiner diversity index. In addition, there were decreases in the density of deposit feeders, small opportunists, and the ratio of small to large individuals of the infaunal heart urchin, Echinocardium australe. The effects of fishing on the larger macrofauna collected from the grab/suction dredge samples were not as clear. However, changes in the predicted direction in epifaunal density and the total number of individuals were demonstrated. As predicted, decreased fishing pressure significantly increased the density of large epifauna observed in video transects. Our data provide evidence of broad‐scale changes in benthic communities that can be directly related to fishing. As these changes were identifiable over broad spatial scales they are likely to have important ramifications for ecosystem management and the development of sustainable fisheries.

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Contrasting environments for phytoplankton growth are found in Manukau Harbour. Nutrient levels are higher in parts of the inner harbour than elsewhere; and cells spend less time in aphotic waters there than in the outer harbour. Phytoplankton photosynthesis and growth in these regions were determined during 1991-92. Average levels of biomass in the inner regions were 2-4 times those in the outer regions, where chlorophyll a averaged 2-3 mg m 3 . However, the euphotic zones were about twice as deep in the outer regions, so average rates of gross photosynthesis were reasonably similar overall (344-557 mg C m -2 d -1 ). Respiration losses were greatest in the outer harbour, so net photosynthesis was lower there. During a late-summer diatom bloom in the inner harbour, peak values of chlorophyll a and gross photosynthesis were 66 mg m -3 and 4100 mg C m -2 d -1 , respectively. A simple equation involving biomass, euphotic depth, and incident light accounted for most of the variability in euphotic zone photosynthesis. Average growth rates varied across the harbour: from about 0.4 d -1 in the inner harbour, to less than half this in the outer regions where the aphotic zone was deeper.

Elevated atmospheric CO 2 concentrations are contributing to ocean acidification (reduced seawater pH and carbonate concentrations), with potentially major ramifications for marine ecosystems and their functioning. Using a novel in situ experiment we examined impacts of reduced seawater pH on Antarctic sea ice-associated microalgal communities, key primary producers and contributors to food webs. pH levels projected for the following decades-to-end of century (7.86, 7.75, 7.61), and ambient levels (7.99), were maintained for 15 d in under-ice incubation chambers. Light, temperature and dissolved oxygen within the chambers were logged to track diurnal variation, with pH, O 2 , salinity and nutrients assessed daily. Uptake of CO 2 occurred in all treatments, with pH levels significantly elevated in the two extreme treatments. At the lowest pH, despite the utilisation of CO 2 by the productive microalgae, pH did not return to ambient levels and carbonate saturation states remained low; a potential concern for organisms utilising this under-ice habitat. However, microalgal community biomass and composition were not significantly affected and only modest productivity increases were noted, suggesting subtle or slightly positive effects on under-ice algae. This in situ information enables assessment of the influence of future ocean acidification on under-ice community characteristics in a key coastal Antarctic habitat.

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