Barrie M. Forrest

The role of natural dispersal mechanisms in the spread of Undaria pinnatifida (Laminariales, Phaeophyceae)

Abstract The Asian kelp Undaria pinnatifida (Laminariales, Phaeophyceae) was first recorded in New Zealand in 1987 and has since spread via shipping traffic and other vectors to a number of ports and harbours. Here we report the results of laboratory and fieldstudies devised to assess the potential for natural dispersal of Undaria from a founding population. Under laboratory conditions, > 90% of Undaria spores were viable in seawater for at least 5 days, with some viable after 14 days. Spores artificially released into a tidal current resulted later in sporophytes appearing on artificial surfaces positioned 10 m down-current of the release point. Field monitoring of a founding population within the Marlborough Sounds, New Zealand, suggested that natural populations spread at least 100 m yr−1. Reasons for the differences between the dispersal distances of the artificially released spores (10 m) and natural populations (100 m) are discussed. We propose that spore dispersal from fixed stands of Undaria results primarily in short-range spread (metres to hundreds of metres), with dispersal of fragments or whole sporophytes facilitating spread at scales of hundreds of metres to kilometres.

Assessing Invasion Impact: Survey Design Considerations and Implications for Management of An Invasive Marine Plant

We use a three-year study of sheltered low shore assemblages colonised by the non-indigenous Asian kelp Undariapinnatifida to explore survey design issues for assessing the ecological impacts of invasive species. The weight of evidence overall suggested little impact from Undaria on low shore assemblages, with control–impact contrasts that could plausibly be interpreted as impacts probably reflecting natural causes. We demonstrate that the potential for reaching incorrect conclusions regarding the impacts of invasive species using control–impact designs is greater than when such designs are used to assess traditional forms of anthropogenic impact. We suggest that a before–after control–impact framework is essential, but recognise that such an approach has a number of limitations. In particular, there is no assurance that the before–after impact site will be invaded at all, or to the extent that provides worst-case impact information for coastal managers. We discuss possible ways of assessing invasive species impacts, but suggest that the uncertainty inherent in extrapolating impact information to other places and times means that the precautionary principle should be applied, and ‘worst-case’ impacts assumed, until the level of scientific uncertainty is reduced. Such an approach should only be applied, however, after an evaluation of the feasibility, costs and benefits of managing a particular pest in relation to other priorities for invasive species.

Assessing the efficacy of spray-delivered ‘eco-friendly’ chemicals for the control and eradication of marine fouling pests

Despite its frequent use in terrestrial and freshwater systems, there is a lack of published experimental research examining the effectiveness of spray-delivered chemicals for the management of non-indigenous and/or unwanted pests in marine habitats. This study tested the efficacy of spraying acetic acid, hydrated lime and sodium hypochlorite for the control of marine fouling assemblages. The chemicals are considered relatively ‘eco-friendly’ due to their low toxicity and reduced environmental persistence compared to synthetic biocides, and they were effective in controlling a wide range of organisms. Pilot trials highlighted acetic acid as the most effective chemical at removing fouling cover, therefore it was selected for more comprehensive full-scale trials. A single spray of 5% acetic acid with an exposure time of 1 min effectively removed up to 55% of the invertebrate species present and 65% of the cover on fouled experimental plates, while one application of 10% acetic acid over 30 min removed up to 78% of species present and 95% of cover. Single-spray treatments of 5% acetic acid reduced cover of the tunicate pest species Didemnum vexillum by up to 100% depending on the exposure duration, while repeat-spraying ensured that even short exposure times (1 min) achieved ∼99% mortality. Both 5 and 10% acetic acid solutions appeared equally effective at removing the majority of algal species. This technique could be used for controlling the introduction of unwanted species or preventing the spread of pests, and is applicable to use on a variety of natural and artificial substrata, or for the treatment of structures that can be removed from the water.

A preliminary assessment of biofouling and non-indigenous marine species associated with commercial slow-moving vessels arriving in New Zealand.

Vessel traffic is the primary pathway for non-indigenous marine species introductions to New Zealand, with hull fouling recognised as being an important mechanism. This article describes hull fouling on seven slow-moving commercial vessels sampled over a 1 year period. Sampling involved the collection of images and fouling specimens from different hull locations using a standardised protocol developed to assess vessel biofouling in New Zealand. A total of 29 taxa was identified by expert taxonomists, of which 24% were indigenous to New Zealand and 17% non-indigenous. No first records to New Zealand were reported, however 59% of species were classified as ‘unknown’ due to insufficient taxonomic resolution. The extent of fouling was low compared to that described for other slow-movers. Fouling cover, biomass and richness were on average 17.1% (SE = 1.8%), 5.2 g (SE = 1.1 g) and 0.8 (SE = 0.07) per photoquadrat (200 × 200 mm), respectively. The fouling extent was lowest on the main hull areas where the antifouling paint was in good condition. In contrast, highest levels of fouling were associated with dry-docking support strips and other niche areas of the hull where the paint condition was poor. Future studies should target vessels from a broader range of bioregions, including vessels that remain idle for extended periods (ie months) between voyages, to increase understanding of the biosecurity risks posed by international commercial slow-movers.

Minimal impact from long‐term dredge spoil disposal at a dispersive site in Tasman Bay, New Zealand

Abstract The effects of dredge spoil disposal on contaminant concentrations and benthic macrofauna were examined at a shallow marine disposal site used for c. 20 years. The site had received c. 50 000 m3 yr‐1 of maintenance dredgings annually, from the Port of Nelson. Port sediments were contaminated to varying degrees with some trace metals, organo‐chlorine pesticides, polychlorinated biphenyls, and polycyclic aromatic hydrocarbons. They showed mildly elevated toxicity in laboratory bioassays, and their macrofauna was dominated by small‐bodied polychaetes. Despite this, there was very little indication of impact in the spoil disposal area. The disposal area, spoil spreading zone and control sites were all similar in terms of sediment contaminants, sediment toxicity, neogastropod imposex, and macrofauna. The lack of discernible impact is probably because of the dynamic sedimentary environment in the disposal area, which disperses dumped dredgings and mixes them with ambient sediment.

Predation limits spread of Didemnum vexillum into natural habitats from refuges on anthropogenic structures.

Non-indigenous species can dominate fouling assemblages on artificial structures in marine environments; however, the extent to which infected structures act as reservoirs for subsequent spread to natural habitats is poorly understood. Didemnum vexillum is one of few colonial ascidian species that is widely reported to be highly invasive in natural ecosystems, but which in New Zealand proliferates only on suspended structures. Experimental work revealed that D. vexillum established equally well on suspended artificial and natural substrata, and was able to overgrow suspended settlement plates that were completely covered in other cosmopolitan fouling species. Fragmentation led to a level of D. vexillum cover that was significantly greater than was achieved as a result of ambient larval recruitment. The species failed to establish following fragment transplants onto seabed cobbles and into beds of macroalgae. The establishment success of D. vexillum was greatest in summer compared with autumn, and on the underside of experimental settlement plates that were suspended off the seabed to avoid benthic predators. Where benthic predation pressure was reduced by caging, D. vexillum establishment success was broadly comparable to suspended treatments; by contrast, the species did not establish on the face-up aspect of uncaged plates. This study provides compelling evidence that benthic predation was a key mechanism that prevented D. vexillum’s establishment in the cobble habitats of the study region. The widespread occurrence of D. vexillum on suspended anthropogenic structures is consistent with evidence for other sessile invertebrates that such habitats provide a refuge from benthic predation. For invasive species generally, anthropogenic structures are likely to be most important as propagule reservoirs for spread to natural habitats in situations where predation and other mechanisms do not limit their subsequent proliferation.

Novel observations of benthic enrichment in contrasting flow regimes with implications for marine farm monitoring and management

We examine macrofaunal and physico-chemical responses to organic enrichment beneath salmon farms in contrasting flow environments, and reveal pronounced flow-related differences in the magnitude and spatial extent of effects. Total macrofaunal abundances at high flow sites were nearly an order of magnitude greater than at comparable low flow sites, representing a significant benthic biomass. These very high abundances occurred in conjunction with moderate-to-high species richness, and were evident in the absence of appreciable organic matter accumulation. Biological responses to increasing sulfide were variable; however a significant biological threshold was evident at 1500 μM. Macrofaunal responses at high flow sites differed substantially from the Pearson-Rosenberg model. The atypical ecological conditions were attributed to (i) limited accumulation of fine sediments, (ii) maintenance of aerobic conditions in near-surface sediments, and (iii) an abundant food supply. Thus, enhanced resilience to organic waste at well-flushed sites appears related to both biological and physical processes.

Multiple indicators reveal river plume influence on sediments and benthos in a New Zealand coastal embayment

Abstract Multiple physico‐chemical and biological indicators were used to delineate the spatial influence of the Motueka River plume on coastal surface sediments and associated biota in Tasman Bay, New Zealand. Sediments were primarily muds at nearshore sites on all transects and comprised coarser sediments at the most seaward sites in Tasman Bay. Organic carbon/nitrogen ratios, stable carbon and nitrogen isotope signatures, and certain lipid biomarkers and trace metals provided suitable indicators of terrestrial and riverine influence on subtidal sediments. Analysis of these parameters revealed a discernible catchment influence extending at least 6 km offshore in the river outwelling plume, with a pronounced signature evident at two sampling stations within approximately 2km of the Motueka River mouth. At these two nearshore sites, nickel and chromium from natural upper‐catchment sources were present at concentrations greatly exceeding sediment quality thresholds for probable ecological effects. The infaunal assemblage at these sites comprised low densities of a few opportunistic taxa, with the spatial distribution of organisms strongly correlated with trace metal concentrations. Although a causal relationship with trace metals is possible, other unmeasured influences such as gradients of salinity, depth and physical disturbance could conceivably be the primary drivers of the biological pattern. By contrast with the effects on infauna, analyses of stable carbon and nitrogen isotopes and trace metals in epibenthic shellfish did not reveal any evidence of a direct terrestrial or riverine influence. Overall, the results from this work indicate a relatively localised river plume effect on subtidal sediments and the associated infaunal assemblage. However, because previous work has shown that the river plume can extend tens of kilometres offshore during flood flows, further investigation is required to understand changes in seabed parameters within the context of spatio‐temporal variation in catchment inputs and river plume discharge.

Evaluation of the sea anemone Anthothoe albocincta as an augmentative biocontrol agent for biofouling on artificial structures

Augmentative biocontrol, defined as the use of indigenous natural enemies to control pest populations, has not been explored extensively in marine systems. This study tested the potential of the anemone Anthothoe albocincta as a biocontrol agent for biofouling on submerged artificial structures. Biofouling biomass was negatively related to anemone cover. Treatments with high anemone cover (>35%) led to significant changes in biofouling assemblages compared to controls. Taxa that contributed to these changes differed among sites, but included reductions in cover of problematic fouling organisms, such as solitary ascidians and bryozoans. In laboratory trials, A. albocincta substantially prevented the settlement of larvae of the bryozoan Bugula neritina when exposed to three levels of larval dose, suggesting predation as an important biocontrol mechanism, in addition to space pre-emption. This study demonstrated that augmentative biocontrol using anemones has the potential to reduce biofouling on marine artificial structures, although considerable further work is required to refine this tool before its application.

Challenges associated with pre-border management of biofouling on oil rigs

The potential for oil rigs to transport diverse, reef-like communities around the globe makes them high risk vectors for the inadvertent spread of non-indigenous species (NIS). This paper describes two case studies where a suite of pre-border management approaches was applied to semi-submersible drilling rigs. In the first case study, a drilling rig was defouled in-water prior to departure from New Zealand to Australia. Risk mitigation measures were successful in reducing biosecurity risks to the recipient region, but they resulted in the unintentional introduction of the non-indigenous brown mussel (Perna perna) to New Zealand when the rig was defouled in-water by divers. In the second case study, lessons learned from this high-profile incursion resulted in a more structured approach to pre-border management, and this serves as a useful template for future rig transfers.