The nutritional eco-physiology of Chaetomorpha linum and Ulva rigida in Peel Inlet, Western Australia

The uptake rates and critical tissue concentrations of nitrogen and phosphorus were determined for Chaetomorpha linum and Ulva rigida , the dominant algae in Peel Inlet, Western Australia. Both species had rate-saturating mechanisms of phosphate uptake described by Michaelis-menten type functions; C. linum had the faster uptake rate (667 c.f. 272 mu g P g/dwt/h) although U. rigida had a lower half-saturation value. Both species displayed linear relationships between ammonium uptake rates and substrate concentrations with C. linum having the greater slope (4.4 c.f. 1.7). Chaetomorpha linum also had a linear increase in uptake rate with increasing concentration of nitrate, but U. rigida showed rate-saturating kinetics; below 750 mu g/L, U. rigida had the higher rate of uptake. Ulva rigida had critical tissue nitrogen and phosphorus concentrations of 20 and 0.25 mg g/dwt respectively. Corresponding concentrations for C. linum were 12 and 0.5 mg g/dwt. Ulva is frequently nitrogen limited during spring in Peel Inlet, reflecting the high nitrogen requirements of this plant compared to Chaetomorpha as well as the reduced ability of Ulva to store nutrients over winter

Role of carbonate burial in Blue Carbon budgets

Calcium carbonates (CaCO 3 ) often accumulate in mangrove and seagrass sediments. As CaCO 3 production emits CO 2 , there is concern that this may partially offset the role of Blue Carbon ecosystems as CO 2 sinks through the burial of organic carbon (C org ). A global collection of data on inorganic carbon burial rates (C inorg , 12% of CaCO 3 mass) revealed global rates of 0.8 TgC inorg yr −1 and 15–62 TgC inorg yr −1 in mangrove and seagrass ecosystems, respectively. In seagrass, CaCO 3 burial may correspond to an offset of 30% of the net CO 2 sequestration. However, a mass balance assessment highlights that the C inorg burial is mainly supported by inputs from adjacent ecosystems rather than by local calcification, and that Blue Carbon ecosystems are sites of net CaCO 3 dissolution. Hence, CaCO 3 burial in Blue Carbon ecosystems contribute to seabed elevation and therefore buffers sea-level rise, without undermining their role as CO 2 sinks. © 2019, The Author(s)

Macrophyte abundance in Waquoit Bay : effects of land-derived nitrogen loads on seasonal and multi-year biomass patterns

Author Posting. © The Author(s), 2008. This is the author's version of the work. It is posted here by permission of Springer for personal use, not for redistribution. The definitive version was published in Estuaries and Coasts 31 (2008): 532-541, doi:10.1007/s12237-008-9039-6.Anthropogenic inputs of nutrients to coastal waters have rapidly restructured coastal ecosystems. To examine the response of macrophyte communities to land-derived nitrogen loading, we measured macrophyte biomass monthly for six years in three estuaries subject to different nitrogen loads owing to different land uses on the watersheds. The set of estuaries sampled had nitrogen loads over the broad range of 12 to 601 kg N ha-1 y-1. Macrophyte biomass increased as nitrogen loads increased, but the response of individual taxa varied. Specifically, biomass of Cladophora vagabunda and Gracilaria tikvahiae increased significantly as nitrogen loads increased. The biomass of other macroalgal taxa tended to decrease with increasing load, and the relative proportion of these taxa to total macrophyte biomass also decreased. The seagrass, Zostera marina, disappeared from the higher loaded estuaries, but remained abundant in the estuary with the lowest load. Seasonal changes in macroalgal standing stock were also affected by nitrogen load, with larger fluctuations in biomass across the year and higher minimum biomass of macroalgae in the higher loaded estuaries. There were no significant changes in macrophyte biomass over the six years of this study, but there was a slight trend of increasing macroalgal biomass in the latter years. Macroalgal biomass was not related to irradiance or temperature, but Z. marina biomass was highest during the summer months when light and temperatures peak. Irradiance might, however, be a secondary limiting factor controlling macroalgal biomass in the higher loaded estuaries by restricting the depth of the macroalgal canopy. The relationship between the bloom-forming macroalgal species, C. vagabunda and G. tikvahiae, and nitrogen loads suggested a strong connection between development on watersheds and macroalgal blooms and loss of seagrasses. The influence of watershed land uses largely overwhelmed seasonal and inter-annual differences in standing stock of macrophytes in these temperate estuaries.This research was supported by the National Oceanic and Atmospheric Administration (NOAA), Cooperative Institute for Coastal and Estuarine Environmental Technologies (CICEET-UNH#99-304, NOAA NA87OR512), NOAA National Estuarine Research Reserve Graduate Research Fellowship NERRS GRF, #NA77OR0228), and an Environmental Protection Agency (EPA) STAR Fellowship for Graduate Environmental Study (U-915335-01-0) awarded to J. Hauxwell. S. Fox was supported by a NOAA NERRS GRF (#NA03NOS4200132) and an EPA STAR Graduate Research Fellowship. We also thank the Quebec-Labrador Foundation Atlantic Center for the Environment's Sounds Conservancy Program and the Boston University Ablon/Bay Committee for their awarding research funds

Epiphytes of seagrasses

In all aquatic environments, available surfaces are rapidly colonized by a variety of organisms. If these organisms grow on plants they are called epiphytes. Seagrasses provide an excellent substratum for epiphytic organisms and these organisms are an integral component of seagrass ecosystems. The ecology and physiology of seagrass epiphytes have been reviewed previously (Harlin, 1980; Borowitzka and Lethbridge, 1989) and this chapter focuses primarily on new developments in our understanding of seagrass epiphyte biology and ecology that have occurred since then

Macroalgal-sediment nutrient interactions and their importance to macroalgal nutrition in a eutrophic estuary

The potential for algal banks to influence water quality and sediment nutrient flux was examined through laboratory experiments and in situ monitoring of algal banks. Loose macroalgal banks displayed seasonal changes in tissue nutrient concentrations suggesting a strong dependence on water column nutrients. These banks fail to generate conditions suitable to sediment nutrient release. Dense banks generated low oxygen conditions in the inter-algal water (0–1 mg l−1), corresponding to zones of high, and relatively stable, phosphate and ammonium concentrations (up to 96 μg l−1 PO4P and 166 μg l−1 NH4N). Laboratory experiments confirmed that macroalgal banks can generate reducing conditions at the sediment surface, regardless of the aeration regime, through the decomposition of macroalgal tissue. Platinum electrode potentials as low as −200 mV were recorded in the inter-algal water. In such banks, redox-dependent sediment nutrient release and anaerobic accumulation of nitrogen accounted for inter-algal nutrient concentrations of over 60 μg l−1 phosphate and 800 μg l−1 ammonium. The generation of reducing conditions in inter-algal water required 7 days of still conditions and so this mechanism of nutrient generation is unlikely to be important in winter, when strong winds frequently shift the algal banks. It is suggested that in summer this mechanism may provide a source of nutrients to dense algal banks, supplementing reserves stored in winter

Changes in the biomass and species composition of macroalgae in a eutrophic estuary

More than 20 years of data are presented on the macroalgal biomass, species composition and water quality of Peel-Harvey estuary in south-western Australia. The occurrence of macroalgal blooms was a sudden event in the late 1960s, and appears to have resulted from nutrient availability surpassing a threshold of some kind. Cladophora dominated the system until 1979 and appears to have had a competitive advantage in deep-water areas because of its morphology. A catastrophic event compounded by a series of unfavourable conditions resulted in the loss of Cladophora from the deep areas and its estuary-wide replacement by Chaetomorpha, which was more competitive in the shallows. Since 1979, changes in water quality have been reflected in changes in biomass and species composition in the system. Average annual biomass is linearly related to average light attenuation over the summer growth period. Periods of high nutrient concentrations favour Ulva and Enteromorpha, while Chaetomorpha resumes dominance during periods of lower mean nutrient concentrations. Nutrient concentrations appear to be more influential on an inter-annual than seasonal scale, except in the case of Ulva which, on the basis of tissue N and P concentrations, is seasonally nitrogen-limited. Light attenuation appears to have seasonal and long-term effects. The data support the hypothesis of other workers that inter-annual differences in hydrographic events and phytoplankton dynamics influence macroalgal dynamics. The concept is examined further in light of this extensive database

Nitrate reductase activity in macroalgae and its vertical distribution in macroalgal epiphytes of seagrasses.

Macroalgal epiphytes within seagrass meadows make a significant contribution to total primary production by assimilating water column N and transferring organic N to sediments. Assimilation of NO3 – requires nitrate reductase (NR, EC 1.6.6.1); NR activity represents the capacity for NO3 – assimilation. An optimised in vitro assay for determining NR activity in algal extracts was applied to a wide range of macroalgae and detected NR activity in all 22 species tested with activity 2 to 290 nmolNO3 – min–1 g–1 frozen thallus. With liquid-N2 freezing immediately after sample collection, this method was practical for estimating NR activity in field samples. Vertical distribution of NR activity in macroalgal epiphytes was compared in contrasting Posidonia sinuosa and Amphibolis antarctica seagrass meadows. Epiphytes on P. sinuosa had higher mass-specific NR activity than those on A. antarctica. In P. sinuosa canopies, NR activity increased with distance from the sediment surface and was negatively correlated with [NH4 +] in the water but uncorrelated with [NO3 –]. This supported the hypothesis that NH4 + released from the sediment suppresses NR in epiphytic algae. In contrast, the vertical variation in NR activity in macroalgae on A. antarctica was not statistically significant although there was a weak correlation with [NO3 –], which increased with distance from the sediment. Estimated capacities for NO3 – assimilation in macroalgae epiphytic on seagrasses during summer (24 and 46 mmolN m–2 d–1 for P. sinuosa and A. antarctica, respectively) were more than twice the estimated N assimilation rates in similar seagrasses. When the estimates were based on annual average epiphyte loads for seagrass meadows in other locations, they were comparable to those of seagrasses. We conclude that epiphytic algae represent a potentially important sink for water-column nitrate within seagrass meadows

Effects of dredging on critical ecological processes for marine invertebrates, seagrasses and macroalgae, and the potential for management with environmental windows using Western Australia as a case study

Dredging can have significant impacts on benthic marine organisms through mechanisms such as sedimentation and reduction in light availability as a result of increased suspension of sediments. Phototrophic marine organisms and those with limited mobility are particularly at risk from the effects of dredging. The potential impacts of dredging on benthic species depend on biological processes including feeding mechanism, mobility, life history characteristics (LHCs), stage of development and environmental conditions. Environmental windows (EWs) are a management technique in which dredging activities are permitted during specific periods throughout the year; avoiding periods of increased vulnerability for particular organisms in specific locations. In this review we identify these critical ecological processes for temperate and tropical marine benthic organisms; and examine if EWs could be used to mitigate dredging impacts using Western Australia (WA) as a case study. We examined LHCs for a range of marine taxa and identified, where possible, their vulnerability to dredging. Large gaps in knowledge exist for the timing of LHCs for major species of marine invertebrates, seagrasses and macroalgae, increasing uncertainty around their vulnerability to an increase in suspended sediments or light attenuation. We conclude that there is currently insufficient scientific basis to justify the adoption of generic EWs for dredging operations in WA for any group of organisms other than corals and possibly for temperate seagrasses. This is due to; 1) the temporal and spatial variation in the timing of known critical life history stages of different species; and 2) our current level of knowledge and understanding of the critical life history stages and characteristics for most taxa and for most areas being largely inadequate to justify any meaningful EW selection. As such, we suggest that EWs are only considered on a case-by-case basis to protect ecologically or economically important species for which sufficient location-specific information is available, with consideration of probable exposures associated with a given mode of dredging