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IC19_NZ

The use of GIS as a tool to integrate services of coastal environments in spatial planning

State of the Art
The presence of unusually large amounts of benthic macroalgae in coastal and estuarine habitats, usually occurring seasonally, is often referred to as a "green tide" (Fletcher, 1996). Such events are drawing increasing attention both from the scientific community as well as the general public. The accumulation and subsequent decomposition of macroalgae on the shoreline is a particularly conspicuous symptom of the problem. Green tides are now widespread, occurring regularly in several dozen countries around the world (Schramm & Nienhuis, 1996), and in extreme cases, can lead to densities of accumulated biomass of up to 400 kg wet weight per square meter (Morand & Briand, 1996). This is not only a recent phenomenon. In 1911, Otton reported "On the growth of Ulva latissima in excessive quantity with special reference to the Ulva nuisance in Belfast Lough'' (Otton, 1911) to the United Kingdom's "Royal Commission on Sewage disposal". This shows that even more than a century ago, excessive growth of benthic macroalgae, such as Ulva spp. (sea lettuce) was an issue of public concern. Local residents as well as other recreational and commercial users of the affected areas often perceive green tides as a "nuisance''. The reasons for this are numerous and include macroalgae clogging boat motors, becoming entangled in fishing lines and nets, accumulating and decomposing on the shoreline (leading to unpleasant or even harmful concentrations of hydrogen sulphide in the air), or suppressing the desired growth of edible benthic fauna.
The different macroalgae species that contribute to nuisance blooms are not necessarily closely-related. For example, both the phylum Chlorophyta (green algae), as well as Rhodophyta (red algae) include species involved in such blooms (Fletcher, 1996; Raven & Taylor, 2003). Nonetheless, most do share common characteristics, including a high ratio of surface area to volume and high growth rates (Raven & Taylor, 2003), as well as broad physiological tolerance (Fletcher, 1996). These are characteristics often co-occurring with "ephemeral" population dynamics; in other words, blooms that usually include both an initial fast increase in population biomass, as well as a similar magnitude of decrease at the end of the season, year, or event (Raven & Taylor, 2003. In a list of world-wide reports of green tides compiled by Fletcher (1996), the majority of cases involve species of the genera Ulva or Enteromorpha (both Chlorophyta); the latter of which has since been reduced to synonymy with Ulva (Hayden et al., 2003).
Ephemeral species of Ulva and other genera of the family Ulvaceae have been introduced to a number of non-native habitats by human activities. Due to undesired ecological or economic impacts of their presence, they are then often referred to as "invasive" (in contrast to the less judgmental "introduced") species (Williams & Smith, 2007). In a global review of introduced seaweeds, Molnar et al. (2008) found the number of invasive species from the family Ulvaceae to be significantly higher than expected by chance. In contrast to species which grow excessively only in their role as an introduced species (usually due to the absence of predators or competitors in the new habitat), many Ulvaceae show this behaviour in their native habitat and are therefore sometimes also referred to as "proliferating" algae (Morand & Briand, 1996). In New Zealand, at least 19 distinct taxa of Ulva have been identified, including both native and introduced taxa (Heesch et al., 2007).
The proposed research is centered around the documented high interannual variability of Ulva abundance in Tauranga Harbour, an estuary on the east coast of the North Island of New Zealand. It seems unclear exactly which species of Ulva are involved in these blooms. Park (1996) found and identified U. laetevirens, U. lactuca, and U. rigida based on morphological features, while Heesch et al. (2007) found and identified only U. pertusa and the unnamed "U. species 1" based on molecular sequencing data. Anecdotal reports of Ulva blooms in Tauranga Harbour can be traced back to around 1950, with the first newspaper reports in 1988 (Park, 1996). During seasons of particularly strong blooms (for example 1992), accumulations of up to 20 kg wet weight per square meter have been documented at individual sites (Park, 1996). In response to public concerns, especially "about accumulations of algae on beaches" (Bioresearches, 1989), both the communal (Tauranga City Council, TCC), as well as regional administration (Bay of Plenty Regional Council, BOPRC) have undertaken or commissioned a number of studies in this context (including: Bioresearches, 1989; Bioresearches, 1991; deWinton et al., 1996; deWinton et al., 1998, Park, 2007; Park, 2011).
Currently, the factors that predominantly control or trigger blooms of Ulva in Tauranga Harbour are unknown. Past and current hypotheses include the sporadic input of nutrients from coastal upwelling events (Park, 2007) as well as terrestrial, catchment-derived inputs (Bay of Plenty Polytechnic, 2010).

Project description
The aim of this project is to identify the role and relatiortance of fave impctors contributing to Ulva abundance in Tauranga Harbour. The analysis will be based on both observation, as well as numerical simulation data. Both the ongoing theoretical and practical work, as well as the PhD thesis itself is structured along three main topics:
  1. the analysis of existing observation data of Ulva abundance and related environmental variables (weather, freshwater inputs, water column nutrient concentration and others) from the early 1990s until today;
  2. the development, implementation and application of a mathematical model describing seasonal Ulva growth, well-suited to the local conditions; and
  3. the integration of this growth model with both an existing hydrodynamic, as well as water quality model to examine the relative importance of factors contributing to Ulva abundance in the range of environmental conditions described by the observation data collected by the BOPRC.

Members

Proponents:Dr. Lars BrabynUniversity of Waikato
Prof. Dr. Chris Battershill
:Prof. Dr. Katrin HuhnUniversity of Bremen
Prof. Dr. Michael Flitner
PhD Candidate:Alicia Ferrer-CostaUniversity of Waikato

Publications

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Miscellaneous

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