Stephen D. A. Smith

The effects of dredge-spoil dumping on a shallow water soft-sediment community in the Solitary Islands Marine Park, NSW, Australia

In December 1999, 28,000 m3 of sediment was dredged from two sites within the harbour at Coffs Harbour, NSW. Dredging was carried out using a trailing suction hopper-dredge which transported the spoil to a shallow (6 m) site within the adjacent Solitary Islands Marine Park for disposal. Evaluation of the effects of the dredge-spoil dumping at the receiving site was conducted by taking replicated van Veen grab samples at the disposal site and at two control sites, before, immediately after, and three months after dumping. The results indicated that dredge-spoil dumping had no detectable effect on either the structure of the invertebrate community or the physical characteristics of sediment at the receiving site. Although there were some significant faunistic differences between samples from the disposal site and the control sites immediately following dumping, these were related to pre-existing differences between sites rather than to the effects of dredge-spoil disposal. Four principal factors are likely to have contributed to the lack of impact: (i) dredged material had similar sedimentary characteristics to those at the receiving site; (ii) dredged material was free from contaminants; (iii) the disposal method systematically distributed a number of shallow layers of sediment over the disposal site and thus motile macrofauna had the opportunity to migrate upwards between passes of the barge; and (iv) the disposal site was in a high energy environment where the resident biota are likely to be adapted to dynamic sedimentary conditions. The lack of detectable effects suggests that the disposal strategy was one which minimized impacts within an area which has high conservation value and should thus be adopted as a model for future works within the region.

Artificial substrata in a shallow sublittoral habitat: do they adequately represent natural habitats or the local species pool?

Artificial substrata have been advocated as tools which have considerable potential for monitoring both natural and anthropogenic effects on invertebrate communities of shallow coastal environments. In this experiment, community structure was compared between two dominant natural algal habitats (kelp holdfasts and algal turf) and artificial substratum units (ASUs; nests of pan scourers) deployed in close contact with, and 20 cm above the substratum. Univariate and multivariate statistical analyses were applied to the data to determine the similarity of community structure between the four different habitats. In addition, recently developed measures of taxonomic distinctness were applied to the data from both sets of artificial substrata to determine if they provided a representative sample of the local epifaunal species pool and thus have the potential to be used as surrogate samples for this important faunal group. There were marked differences between community structure in each of the habitats. Both sets of artificial substrata were dominated by tubicolous polychaetes with abundances that were more than an order of magnitude greater than in the holdfast and turf samples. The fauna recruiting to the artificial substrata deployed above the substratum showed the lowest values in the univariate summaries of diversity and evenness and were unrepresentative of the local species pool. Artificial samples deployed in contact with the substratum showed greater diversity and evenness but were still mostly unrepresentative of the local species pool. The tendency for both sets of artificial substrata to under-sample amphipods and to be dominated by suspension-feeding polychaetes suggests that methods using these units may be relatively insensitive to the effects of anthropogenic impacts (e.g. sewage outfalls) where shifts in community structure including increased dominance of suspension-feeders and polychaetes and a reduced dominance of amphipods have been observed. Further studies, including the evaluation of temporal variation in community structure related to the time at which the ASUs are deployed and duration of deployment, are needed to test the wider utility of artificial substrata as tools for monitoring shallow, sublittoral, epifaunal communities.

The effects of domestic sewage effluent on marine communities at Coffs Harbour, New South Wales, Australia

Abstract Studies of the impact of secondary treated domestic effluent have been conducted at Coffs Harbour, NSW, Australia for the last 8 years. During that time, monitoring has shown that impacts are restricted to within approximately 300 m of the outfall for most variables (e.g. algal species richness, changes to the structure of invertebrate communities living in kelp holdfasts) but that the ephemeral green alga Ulva lactuca has significantly greater cover than at reference sites for a distance of 500 m from the point of discharge. Based on the results of this study, a new outfall proposed for the northern area of Coffs Harbour was predicted to have effects over a much smaller spatial scale. It is suggested, therefore, that the recent decision to abandon the plans for the new outfall reflects growing public concern over issues other than cost minimization and biological impact in the use of ocean disposal as an option for the management of human sewage waste.

Spatial variation in the community structure of intertidal habitats at Macquarie Island (sub-Antarctic)

The shore environments of most sub-Antarctic islands have been described in a number of previous studies. However, there have been few attempts to quantify the variation in population and community patterns over different spatial scales. The objectives of this study were to provide an analysis of differences in the community structure of the biota of three exposed shore zones and of the macrofauna inhabiting holdfasts of the kelp Durvillaea antarctica across spatial scales of hundreds of metres, kilometres, and between a sheltered and exposed coast. Data were collected using a combination of quadrat, transect and direct sampling methods over the 1994–95 summer season. The results indicated that there were significant differences between coasts for some of the biotic variables in most of the habitats examined but that differences at the smaller spatial scales were more often significant. Thus, although wave exposure exerts an obvious effect on the shore biota of Macquarie Island, these effects are modified by other factors operating at smaller spatial scales. For the holdfast macrofauna, the overall patterns of community structure are likely to be due to the differential response of the component taxa to variation in holdfast volume and holdfast sediment content as well as other, currently undetermined factors.

Monitoring the shallow sublittoral using the fauna of kelp (Ecklonia radiata) holdfasts

Abstract The macrofaunal community inhabiting the holdfast of the kelp, Ecklonia radiata, was assessed for changes along a putative gradient resulting from an outfall of low volume domestic effluent. Multi-dimensional scaling (MDS) revealed a consistent separation of treatment sites from controls at each of the three sample periods. Changes in trophic structure were dectected as well as shifts in relative abundances of amphipods and polychaetes as measured by the amphipod to polychaete ratio. Data were further analysed using the Ewens-Caswell neutral model which proved a useful tool for detecting differences between samples from control and treatment locations.

Evaluating stress in rocky shore and shallow reef habitats using the macrofauna of kelp holdfasts

Kelp often dominates hard rocky substrata in the coastal watersof temperate, boreal and subantarctic regions of the worlds oceans. The habitat providedby kelp holdfasts supports high species richness and high abundance of a range of invertebratetaxa. Studies conducted on the effects of stress on these communities have indicated that theyare sensitive to stressors and that the response is often predictable. With the growing body ofliterature on natural variation in holdfast community structure, studies of the impacts of stressare becoming more readily interpretable making the macrofauna of this habitat a potentiallyimportant tool for evaluating anthropogenic effects on hard substrata in coastal environments. Limitations of the use of holdfast fauna in studies of stress include the fact that brownseaweeds may disappear from polluted areas of reef, and where they persist, holdfaststructure may be altered directly by the stressor. An additional problem is that manipulative,experimental studies are difficult. Artificial holdfasts may provide a means by which thedemonstrated sensitivity of the holdfast community can be combined with a manipulative approach to testspecific hypotheses related to effects of stress in shallow coastal environments.

The effects of a spillage of diesel fuel on a rocky shore in the sub-Antarctic region (Macquarie Island)

Abstract On 3 December 1987, the supply ship Nella Dan ran aground at Macquarie Island (54°29′S, 158°58′E) releasing about 270 000 I of oil, mostly light marine diesel, into the sea. At the time of the incident, many marine invertebrates were washed up dead along 2 km of shoreline. Twelve months later, the shore community was investigated using 1. algal and invertebrate populations of the littoral and sublittoral rocky shore, and 2. the invertebrate communities living in the holdfasts of the giant kelp Durvillaea antarctica, which were collected for later examination. Investigations were undertaken at both affected and control locations. Analyses of differences in community structure involved nested ANOVA and multidimensional scaling techniques. On the rocky substrate, the effect of the spill was restricted to some biota of the lower littoral and sublittoral zones—particularly echinoderms and the patellid limpet Nacella macquariensis. There were differences in cover for some algal species between locations. Within the kelp holdfasts, communities were dominated by peracarid crustaceans at control locations and by polychaetes (particularly the opportunistic groups—capitellids, cirratulids and spionids) at oil-affected locations. The communities have recently been re-surveyed (in the summer of 1994–1995) to assist in the interpretation of the results and to gauge the extent of recovery of the affected biota.

The effects of a small sewage outfall on an algal epifaunal community at Macquarie Island (sub-Antarctic) : A drop in the Southern Ocean?

Macquarie Island, in the sub-Antarctic, is the location of one of four permanently staffed bases operated by the Australian Antarctic Division. As part of a wider programme investigating the effects of human presence on Antarctic and sub-Antarctic ecosystems, this study evaluated the impact of the small sewage outfall at Macquarie Island on the epifauna living within turfs of the intertidal red alga Chaetangium fastigiatum. Sampling was conducted during early December (austral summer) in both 1996 and 1997 at six sites, two sites within each of three adjacent bays. The site closest to the outfall was 3 m from the point of discharge. Data analyses at the population and community levels failed to demonstrate a significant effect of the outfall. Small scale spatial patterns, probably related to wave exposure, and inter-annual variation in recruitment, are suggested as the main causes of variation in patterns of epifaunal dominance during the study.