Estimates of Heterozostera tasmanica, Zostera muelleri and Ruppia megacarpa distribution and biomass in the Hopkins Estuary, western Victoria, by GIS

Knowledge of the spatial arrangement of the seagrass distribution and biomass within the Hopkins Estuary is an essential step towards gaining an understanding of the functioning of the estuarine ecosystem. This study marks the first attempt to map seagrass distribution and model seagrass biomass and epiphyte biomass along depth gradients by the use of global positioning system (GPS) and geographical information system (GIS) technologies in the estuary. For mapping seagrass in small estuaries, ground-surveying the entire system is feasible. Three species of seagrasses, Heterozostera tasmanica (Martens ex Aschers), Zostera muelleri (Irmisch ex Aschers) and Ruppia megacarpa (Mason), were identified in the Hopkins Estuary. All beds investigated contained a mixed species relationship. Three harvest techniques were trialed in a pilot study, with the 25 × 25-cm quadrat statistically most appropriate. Biomass of seagrasses and epiphytes was found to vary significantly with depth, but not between sites. The average estimate of biomass for total seagrasses and their epiphytes in the estuary in January 2000 was 222.7 g m^–2 (dry weight). Of the total biomass, 50.6% or 112.7 g m^–2 (dry weight) was contributed by seagrasses and 49.4% of the biomass (110.0 g m^–2) were epiphytes. Of the 50.6% of the total biomass represented by seagrasses, 39.3% (87.5 g m^–2) were leaves and 11.3% (25.2 g m^–2) were rhizomes. The total area of seagrasses present in the Hopkins Estuary was estimated to be 0.4 ± 0.005 km², with the total area of the estuary estimated to be 1.6 ± 0.02 km² (25% cover). The total standing crop of seagrasses and epiphytes in the Hopkins Estuary in January 2000 was estimated to be 102.3 ± 57 t in dry weight, 56% (56.9 ± 17 t, dry weight) seagrasses and 44% (45.4 ± 19 t, dry weight) epiphytes. Of the seagrass biomass, 39% (39.7 ± 13 t, dry weight) was contributed by leaves and 17% (17.3 ± 7 t, dry weight) by rhizomes.

Study of the physiology and biochemistry of chlorophyllase in Zostera muelleri

Examines the biochemistry and physiology of chlorophyllase in the marine angiosperm Zostera muelleri. Enzyme activity was found to be highly correlated with chlorophyll synthesis in developing leaf tissue. This study provides evidence for the physiological role of chlorophyllase in chlorophyll degradation and provides insights into the senescence process in seagrass.

Development of twenty-three novel microsatellite markers for the seagrass, Zostera muelleri from Australia

Seagrasses are one of the most productive and economically important habitats in the coastal zone, but they are disappearing at an alarming rate, with more than half the world’s seagrass area lost since the 1990s. They now face serious threat from climate change, and there is much current speculation over whether they will survive the coming decades. The future of seagrasses depends on their ability to recover and adapt to environmental change—i.e. their ‘resilience’. Key to this, is understanding the role that genetic diversity plays in the resilience of this highly clonal group of species. To investigate population structure, genetic diversity, mating system (sexual versus asexual reproduction) and patterns of connectivity, we isolated and characterised 23 microsatellite loci using next generation sequencing for the Australian seagrass species, Zostera muelleri (syn. Z. capricorni), which is regarded as a globally significant congeneric species. Loci were tested for levels of variation based on eight individuals sampled from Lake Macquarie, New South Wales, Australia. We detected high to moderate levels of genetic variation across most loci with a mean allelic richness of 3.64 and unbiased expected hetrozygosity of 0.562. We found no evidence for linkage disequilibrium between any loci and only three loci (ZosNSW25, ZosNSW2, and ZosNSW47) showed significant deviations from Hardy–Weinberg expectations. All individuals displayed a unique multi-locus genotype and the combined probability of identity across all loci was low (P _ID = 1.87 × 10⁻¹²) indicating a high level of power in detecting unique genotypes. These 23 markers will provide an important tool for future population genetic assessments in this important keystone species.

Physiological and morphological responses of the temperate seagrass Zostera muelleri to multiple stressors: investigating the interactive effects of light and temperature

Understanding how multiple environmental stressors interact to affect seagrass health (measured as morphological and physiological responses) is important for responding to global declines in seagrass populations. We investigated the interactive effects of temperature stress (24, 27, 30 and 32°C) and shading stress (75, 50, 25 and 0% shade treatments) on the seagrass Zostera muelleri over a 3-month period in laboratory mesocosms. Z. muelleri is widely distributed throughout the temperate and tropical waters of south and east coasts of Australia, and is regarded as a regionally significant species. Optimal growth was observed at 27°C, whereas rapid loss of living shoots and leaf mass occurred at 32°C. We found no difference in the concentration of photosynthetic pigments among temperature treatments by the end of the experiment; however, up-regulation of photoprotective pigments was observed at 30°C. Greater levels of shade resulting in high photochemical efficiencies, while elevated irradiance suppressed effective quantum yield (ΔF/FM'). Chlorophyll fluorescence fast induction curves (FIC) revealed that the J step amplitude was significantly higher in the 0% shade treatment after 8 weeks, indicating a closure of PSII reaction centres, which likely contributed to the decline in ΔF/FM' and photoinhibition under higher irradiance. Effective quantum yield of PSII (ΔF/FM') declined steadily in 32°C treatments, indicating thermal damage. Higher temperatures (30°C) resulted in reduced above-ground biomass ratio and smaller leaves, while reduced light led to a reduction in leaf and shoot density, above-ground biomass ratio, shoot biomass and an increase in leaf senescence. Surprisingly, light and temperature had few interactive effects on seagrass health, even though these two stressors had strong effects on seagrass health when tested in isolation. In summary, these results demonstrate that populations of Z. muelleri in south-eastern Australia are sensitive to small chronic temperature increases and light decreases that are predicted under future climate change scenarios.

Zostera nigricaulis seed germination experiment

Data from seed germination experiment to determine the impact of temperature, salinity, sediment type and sediment depth on seed germination.

Description of new species of Setosabatieria and Desmolaimus (Nematoda: Monhysterida) and a checklist of New Zealand free-living marine nematode species

Two new marine nematode species are described from intertidal sediments in southern New Zealand. Setosabatieria australis sp. nov. is characterised by an amphideal fovea with 3.5 turns, 7–9 small pre-cloacal supplements, and 2–5 sub-cephalic setae per file. Setosabatieria australis sp. nov. differs from all known species of the genus in having L-shaped spicules with a hollow median region, in contrast to the typical curved shape. Desmolaimus courti sp. nov. is characterised by the presence of four long (15 µm) cephalic setae, two cuticularised rings in the buccal cavity, and a lightly cuticularised pharyngeal lumen. It differs from other species of the genus by having eight sub-cephalic setae. A total of 116 marine species are included in the checklist of New Zealand free-living nematodes, with the majority of records from the coast of Campbell and Auckland islands from the early part of the 20th century. Most records were from habitats such as seaweed or sponge, which may explain the high proportion (>50%) of cosmopolitan species recorded in New Zealand to date. Little is known about the sediment nematode fauna, particularly in deeper waters (>120 m), from where there are no records to date.