Ecological Effects of Undaria pinnatifida (Harvey) Suringar and Nutrient-Enrichment on Intertidal Assemblages in the Wellington Region of New Zealand

The introduction of non-native species and the alteration of seawater nutrient regimes due to anthropogenic impacts are two important threats to marine environments. Moreover, these disturbances may interact in such a way that promotes the success of invasive species in coastal habitats. This thesis contributes to current gaps in knowledge in these areas for low-intertidal communities. Algal community dynamics and ecological effects of the invasive kelp Undaria pinnatifida on low shores in the Wellington region, New Zealand, were examined, using field surveys and experiments. In addition, the role of variability in nutrient concentrations in coastal waters in mediating algal community structure and diversity, and the success of U. pinnatifida reproduction were investigated. Algal surveys were used in two locations thought to differ in nutrient regimes, the Wellington Harbour and the Wellington south coast, to explore the structure and dynamics of algal assemblages. Results showed high variability of low-intertidal algal communities among sites, but no consistent differences in algal community composition were found between the two locations, despite higher U. pinnatifida cover in the harbour. Over the duration of the study, nutrient regimes did not differ greatly between the locations. The response of rocky intertidal algal assemblages to chronic exposure to high nutrient effluent was investigated using two nearshore sewage outfalls in the Wellington region. The Titahi Bay outfall showed a stronger relationship between nutrients and algal community composition. Variation in algal assemblage structure and diversity was best explained by phosphate concentrations. By contrast, at the more wave-exposed Pencarrow outfall, patterns of change in the algal community were less clear and there was a much weaker relationship with seawater nutrients. Because removal of native algal canopy species may facilitate the establishment of invasive macroalgae, the invasion process of U. pinnatifida in disturbed patches in a rocky low-intertidal habitat was investigated. In a site where U. pinnatifida had not yet established, patches were scraped clear of native algal cover at two different times of year, and recruitment of U. pinnatifida was monitored. While U. pinnatifida invaded the site, it recruited in control plots at a similar rate as cleared plots, suggesting that physical disturbance of the native algal assemblage is not a key requirement for this kelp to invade and establish in new areas in the low intertidal zone. The response of native algal assemblages to removal of U. pinnatifida individuals was investigated at intertidal sites in the Wellington Harbour and on the south coast. No significant effect of U. pinnatifida on community composition, diversity, and species richness was detected. Removal of this invader did not change native intertidal assemblage structure in either harbour or south coast sites. Lastly, effects of different nutrient regimes and light intensities on early development and reproduction of U. pinnatifida were studied using a laboratory experiment. Under low light conditions U. pinnatifida gametophyte growth and reproduction stalled and was not increased by the addition of nutrients. However, at medium and high light levels, gametophyte growth and reproduction, and particularly early stage sporophyte growth rates increased when exposed to higher nutrient concentrations.These effects could have implications for U. pinnatifida population dynamics in intertidal habitats where light is not often a limiting resource. This research contributed to a better understanding of factors that underlie invasion dynamics, distribution, and ecological effects of U. pinnatifida and seawater nutrient regimes on low-intertidal assemblages in the Wellington region. The outcomes can assist in setting up strategic environmental protection and conservation plans

Scour protection of submarine pipelines using rubber plates underneath the pipes

YesThis paper presents the results from laboratory experiments to investigate the protection of scour around submarine pipelines under unidirectional flow using a rubber plate placed underneath the pipes. The pressure difference on the two sides of the pipeline is the driving force to initiate the movement of sediment particles and can be obtained by force balance analysis. Experiments covering a wide range of incoming flow velocity, pipe diameter and plate length show that there exists a critical pressure difference over which the movement of sediment and, thus, scour takes place. Analysis of the experimental results demonstrates that this critical pressure difference is related to the pressure difference of the axial points between upstream and downstream of the pipe, which can be easily determined. This critical pressure difference is used to develop an empirical formula for estimating the critical length of the rubber plate, over which the sediment movement and scour will not take place. Good agreement between the experiments and calculated critical plate length using the proposed formula is obtained.National High-Tech Research and Development program of China (863 Program, Grant No.2008AA09Z309), National Nature Science Fund of China (Grant No.50879084, 51279071 and 51279189), the Open Funding from the State Key Laboratory of Hydraulics and Mountain River Engineering, Sichuan University (SKLH-OF-1306

Ecological Effects of Undaria pinnatifida (Harvey) Suringar and Nutrient-Enrichment on Intertidal Assemblages in the Wellington Region of New Zealand

The introduction of non-native species and the alteration of seawater nutrient regimes due to anthropogenic impacts are two important threats to marine environments. Moreover, these disturbances may interact in such a way that promotes the success of invasive species in coastal habitats. This thesis contributes to current gaps in knowledge in these areas for low-intertidal communities. Algal community dynamics and ecological effects of the invasive kelp Undaria pinnatifida on low shores in the Wellington region, New Zealand, were examined, using field surveys and experiments. In addition, the role of variability in nutrient concentrations in coastal waters in mediating algal community structure and diversity, and the success of U. pinnatifida reproduction were investigated. Algal surveys were used in two locations thought to differ in nutrient regimes, the Wellington Harbour and the Wellington south coast, to explore the structure and dynamics of algal assemblages. Results showed high variability of low-intertidal algal communities among sites, but no consistent differences in algal community composition were found between the two locations, despite higher U. pinnatifida cover in the harbour. Over the duration of the study, nutrient regimes did not differ greatly between the locations. The response of rocky intertidal algal assemblages to chronic exposure to high nutrient effluent was investigated using two nearshore sewage outfalls in the Wellington region. The Titahi Bay outfall showed a stronger relationship between nutrients and algal community composition. Variation in algal assemblage structure and diversity was best explained by phosphate concentrations. By contrast, at the more wave-exposed Pencarrow outfall, patterns of change in the algal community were less clear and there was a much weaker relationship with seawater nutrients. Because removal of native algal canopy species may facilitate the establishment of invasive macroalgae, the invasion process of U. pinnatifida in disturbed patches in a rocky low-intertidal habitat was investigated. In a site where U. pinnatifida had not yet established, patches were scraped clear of native algal cover at two different times of year, and recruitment of U. pinnatifida was monitored. While U. pinnatifida invaded the site, it recruited in control plots at a similar rate as cleared plots, suggesting that physical disturbance of the native algal assemblage is not a key requirement for this kelp to invade and establish in new areas in the low intertidal zone. The response of native algal assemblages to removal of U. pinnatifida individuals was investigated at intertidal sites in the Wellington Harbour and on the south coast. No significant effect of U. pinnatifida on community composition, diversity, and species richness was detected. Removal of this invader did not change native intertidal assemblage structure in either harbour or south coast sites. Lastly, effects of different nutrient regimes and light intensities on early development and reproduction of U. pinnatifida were studied using a laboratory experiment. Under low light conditions U. pinnatifida gametophyte growth and reproduction stalled and was not increased by the addition of nutrients. However, at medium and high light levels, gametophyte growth and reproduction, and particularly early stage sporophyte growth rates increased when exposed to higher nutrient concentrations.These effects could have implications for U. pinnatifida population dynamics in intertidal habitats where light is not often a limiting resource. This research contributed to a better understanding of factors that underlie invasion dynamics, distribution, and ecological effects of U. pinnatifida and seawater nutrient regimes on low-intertidal assemblages in the Wellington region. The outcomes can assist in setting up strategic environmental protection and conservation plans

The effects of temperature on producers, consumers, and plant-herbivore interactions in an intertidal community

Although global warming is acknowledged as a primary threat to populations and communities, the impact of rising temperature on community structure remains poorly understood. In this study, we investigated the direct and indirect effects of temperature on epilithic primary producers (micro- and macroalgae) and an abundant consumer, the rough limpet Lottia scabra, in the rocky intertidal zone in central and northern California, USA. We factorially manipulated temperature and limpet abundance in the field to determine the effects of temperature on herbivore growth and mortality, algal abundance, and the strength of plant¿herbivore interactions. Microalgal growth was positively affected by shading at both locations, and negatively affected by limpet grazing at Pacific Grove but not at Bodega Bay. Macroalgae were only abundant at Bodega Bay, where changes in abundance were negatively related to grazing and independent of temperature. Despite temperature-related changes in microalgal food supply, there were no direct or indirect effects of temperature manipulation on L. scabra growth or mortality. Furthermore, temperature did not alter the importance of herbivory at either site. These results indicate that the influence of increasing temperature, as is predicted with climate change, will have differential effects on producers and consumers. However, thermal effects at one trophic level do not necessarily propagate through the food web to other trophic levels

Automated mapping of the intertidal beach from video images

This paper presents a fully automated procedure to derive the intertidal beach bathymetry on a daily basis from video images of low-sloping beaches that are characterised by the intermittent emergence of intertidal bars. Bathymetry data are obtained by automated and repeated mapping of shorelines from video time exposure images for different (tidal) water levels (Aarninkhof, S.G.J., Turner, I.L., Dronkers, T.D.T., Caljouw, M., Nipius, L., 2003. A video-based technique for mapping intertidal beach bathymetry. Coastal Engineering 49, 275–289; Plant, N.G. and Holman, R.A., 1997. Intertidal beach profile estimation using video images. Marine Geology 140, 1–24.). The developed procedure handles intelligent selection of a shoreline search area and unsupervised quality control of the obtained bathymetry data. The automatically retrieved beach bathymetries compare very well to bathymetries derived from the original manual mapping procedure and to ground truth data points (DGPS)

Automated mapping of the intertidal beach bathymetry from video images

This paper presents a fully automated procedure to derive the intertidal beach bathymetry on a daily basis from video images of low-sloping beaches that are characterised by the intermittent emergence of intertidal bars. Bathymetry data are obtained by automated and repeated mapping of shorelines from video time exposure images for different (tidal) water levels (Aarninkhof, S.G.J., Turner, I.L., Dronkers, T.D.T., Caljouw, M., Nipius, L., 2003. A video-based technique for mapping intertidal beach bathymetry. Coastal Engineering 49, 275–289; Plant, N.G. and Holman, R.A., 1997. Intertidal beach profile estimation using video images. Marine Geology 140, 1–24.). The developed procedure handles intelligent selection of a shoreline search area and unsupervised quality control of the obtained bathymetry data. The automatically retrieved beach bathymetries compare very well to bathymetries derived from the original manual mapping procedure and to ground truth data points (DGPS)