Academic literature on the topic 'Otago Harbour'

The horizontal distribution and speciation of iron in the Otago Harbour, New Zealand, a shallow, vertically well mixed estuary, was investigated on six occasions from April to November 1993. Iron speciation was determined by a suite of analytical methods focussing on the chemical reactivity of iron. The dominant source of iron into the water column in these waters was resuspension of bottom sediments, particularly under windy conditions. The only important freshwater source of iron to the harbour, the Water of Leith, appeared to be a major source of iron to Otago Harbour only under conditions of high stream flow. However, the influence of the Water of Leith was often detectable down harbour by the presence of more reactive/labile iron phases. Prolonged periods of strong winds also appeared to supply large concentrations of reactive iron to the water column, possibly by mixing and resuspension of sediment material from below the redox boundary. Experiments on natural samples from Otago Harbour revealed that at pH 4.0 ascorbic acid was able to reduce Fe(III) oxyhydroxides more effectively than was hydroxylamine hydrochloride. This difference may reflect either different mechanisms for the reduction of iron oxyhydroxides or differences in the crystallinity of these oxyhydroxides.

Parasitism is increasingly recognized as an important determinant of population dynamics, productivity and community structure in intertidal ecosystems, and yet there is very little known about the effect of parasites on polychaetes, which represent a major component of the benthic fauna. We surveyed 11 polychaete species from a mudflat in Otago Harbour, New Zealand, and found that seven of these were infected by five parasite species: four trematodes and one apicomplexan gregarine. The gregarine found in Spirobranchus cariniferus and a strigeid trematode using Streblosoma toddae as its first intermediate host are both likely to have negative fitness impacts on their hosts. Other trematodes found were at the metacercarial stage and thus use polychaetes as second intermediate hosts. The most common, an opecoelid, infected the polychaetes Heteromastus filiformis and Abarenicola affinis at relatively high abundance. There was no indication of parasite-induced mortality in these two hosts based on the relationship between host size and infection intensity. However, a comparison of intact H. filiformis individuals with those that fragmented during collection revealed a significantly higher number of opecoelid metacercariae per segment in the fragments than in the complete individuals, suggesting that infection may compromise the structural integrity of the polychaetes. These results suggest that there exists a great diversity of both trematodes and host–trematode associations within the polychaete fauna, whose ecological impact remains to be quantified.

AbstractEvidence is accumulating rapidly showing that temperature and other climatic variables are driving many ecological processes. At the same time, recent research has highlighted the role of parasitism in the dynamics of animal populations and the structure of animal communities. Here, the likely interactions between climate change and parasitism are discussed in the context of intertidal ecosystems. Firstly, using the soft-sediment intertidal communities of Otago Harbour, New Zealand, as a case study, parasites are shown to be ubiquitous components of intertidal communities, found in practically all major animal species in the system. With the help of specific examples from Otago Harbour, it is demonstrated that parasites can regulate host population density, influence the diversity of the entire benthic community, and affect the structure of the intertidal food web. Secondly, we document the extreme sensitivity of cercarial production in parasitic trematodes to increases in temperature, and discuss how global warming could lead to enhanced trematode infections. Thirdly, the results of a simulation model are used to argue that parasite-mediated local extinctions of intertidal animals are a likely outcome of global warming. Specifically, the model predicts that following a temperature increase of less than 4°C, populations of the amphipod Corophium volutator, a hugely abundant tube-building amphipod on the mudflats of the Danish Wadden Sea, are likely to crash repeatedly due to mortality induced by microphallid trematodes. The available evidence indicates that climate-mediated changes in local parasite abundance will have significant repercussions for intertidal ecosystems. On the bright side, the marked effects of even slight increases in temperature on cercarial production in trematodes could form the basis for monitoring programmes, with these sensitive parasites providing early warning signals of the environmental impacts of global warming.

AbstractMarine limpets, Notoacmea scapha, were collected from an intertidal mud flat in Otago Harbour, New Zealand, and examined for infection with larval trematodes. Three separate species of trematode (opecoelid sp. A, Acanthoparyphium sp. A and Curtuteria australis) were identified from the limpets, based on molecular evidence. This is the first report of these three trematodes in limpets, indicating that the latter are physiologically suitable second-intermediate hosts. However, based on ecological information on the diet of the parasites' definitive hosts, we conclude that the limpet N. scapha does not contribute to the transmission of any of the trematodes. Instead, it acts as a sink for cercariae that fail to locate appropriate second-intermediate hosts.

Pseudochromadora reathae n. sp. is described from intertidal sand in Otago Harbour (southern New Zealand), and Pseudodesmodora lacrima n. sp. is described from subtidal sediment in the Firth of Thames (northern New Zealand). Pseudochromadora reathae n. sp. differs from other species of the genus through the combination of the following characters: sexual dimorphism in the shape of the apertura amphidialis, no interdigitation of body annuli at level of lateral alae, presence of eight longitudinal rows of somatic setae, and conspicuous pre-cloacal supplements consisting of star-shaped projections flanked by two cuticularised pieces. Pseudodesmodora lacrima n. sp. is characterised by the presence of large unispiral amphids on amphidial plates, conspicuous ducts in the head region, low a values, and short cephalic setae.

Studies were conducted to broadly describe and understand the sediment benthos of a shallow-water coastal area (Aramoana Beach - Heyward Point - Blueskin Bay) near the entrance to Otago Harbour, a system largely representative for southeastern New Zealand. Benthic assemblages were examined in relation to gradients of wave exposure and disturbance, sediment type and bathymetry, and dredge-spoil disposal. Sediment and macrofaunal surveys in autumn and spring 2003 found little change in sediment texture gradients from historical studies and a lack of vertical stratification. Macrobenthic samples from spring produced significantly higher abundances of three numerically dominant phyla (Arthropoda, Annelida, and Mollusca) and higher taxon richness compared to autumn. Within water depths of 6-30 m, abundance, richness, and diversity increased with depth. Multivariate analyses identified similar assemblages among deeper sites, despite sediment textural differences, whereas distinct assemblages were found in the shallow portions of the three areas. Meiofaunal abundance patterns did not reflect those of macrofauna, possibly indicating greater vertical penetration of sediments in these hydrodynamic environments. Several new kinorhynch taxa were found. In a field manipulation, part of the Aramoana dredge-spoil dumpground was protected from spoil disposal for an extended period followed by experimental dumping of sandy and muddy spoil. Macrofaunal samples were collected before dumping and at nine sites < 119 d after disposal. Water velocities at the sediment-water interface were compared to a local sediment disturbance model. Dumpground samples were depauperate in individuals and taxa compared to an area protected from dumping for > 180 d. A drop in abundance and a dissimilar community coincided with muddy spoil, but fine sediments were dispersed within 26 d and macrofaunal assemblages recovered to the pre-existing state. Sandy spoil, while not altering native sediment textures, had a more prolonged impact due to transplantation of macrofauna from the dredged area that persisted for < 41 d after disposal. Side-scan sonar mapping indicated that the disposal footprint model used approximated the extent of sandy spoil impacts well, while local conditions spread muddy sediments beyond the initial impact site. A novel sediment profile imaging device was constructed that has many advantages over existing devices for spoil mound studies and habitat mapping: it is smaller, can be manually deployed from small boats, is cheaper, and can be modified to work in almost any soft sediment. Studies of one dominant taxon, the gastropod Zethalia zelandica, showed it was better able to survive sand burial than mud burial, did not vary in overall activity through a range of 5-14� C, and contributed a large proportion of biomass of its community. The spoil disposal strategy used does not appear as environmentally neutral as originally thought. Only muds are effectively dispersed whereas coarser sediments accumulate, affecting physical and biological benthic processes of a wider area. Two mitigation strategies were evaluated using a heuristic model. Reducing the disposal area and spreading mud disposal events over a longer time span may be an effective interim strategy. Overall, the studies will help guide management of the area.