Effects of Epiphytes and Depth on Seagrass Spectral Profiles: Case Study of Gulf St. Vincent, South Australia.

Seagrasses are a crucial indicator species of coastal marine ecosystems that provide substratum, shelter, and food for epiphytic algae, invertebrates, and fishes. More accurate mapping of seagrasses is essential for their survival as a long-lasting natural resource. Before reflectance spectra could properly be used as remote sensing endmembers, factors that may obscure the detection of reflectance signals must be assessed. The objectives in this study are to determine the influence of (1) epiphytes, (2) water depth, and (3) seagrass genus on the detection of reflectance spectral signals. The results show that epiphytes significantly dampen bottom-type reflectance throughout most of the visible light spectrum, excluding 670-679 nm; the depth does influence reflectance, with the detection of deeper seagrasses being easier, and as the depth increases, only Heterozostera increase in the exact "red edge" wavelength at which there is a rapid change in the near-infrared (NIR) spectrum. These findings helped improve the detection of seagrass endmembers during remote sensing, thereby helping protect the natural resource of seagrasses.

The distribution of triclosan and methyl-triclosan in marine sediments of Barker Inlet, South Australia.

In this work, we investigated the transport and burial of triclosan and its methylated derivative, in surface sediments near the mouth of Barker Inlet in South Australia. The most likely source of this commonly used bactericide to the area is a wastewater outfall discharging at the confluence of the inlet with marine waters. Triclosan was detected in all samples, at concentrations (5-27 µg kg(-1)) comparable to values found in other surface sediments under the influence of marine wastewater outfalls. Its dispersal was closely associated with fine and organic-rich fractions of the sediments. Methyl-triclosan was detected in approximately half of the samples at concentrations <11 µg kg(-1). The occurrence of this compound was linked to both wastewater discharges and biological methylation of the parent compound. Wastewater-borne methyl-triclosan had a smaller spatial footprint than triclosan and was mostly deposited in close proximity to the outfall. In situ methylation of triclosan likely occurs at deeper depositional sites, whereas the absence of methyl-triclosan from shallower sediments was potentially explained by photodegradation of the parent compound. Based on partition equilibrium, a concentration of triclosan in the order of 1 µg L(-1) was estimated in sediment porewaters, a value lower than the threshold reported for harmful effects to occur in the couple of species of marine phytoplankton investigated to date. Methyl-triclosan presents a greater potential for bioaccumulation than triclosan, but the implications of its occurrence to aquatic ecosystem health are difficult to predict given the lack of ecotoxicological data in the current literature.

PHOTOPHYSIOLOGY OF A TURF ALGAL COMMUNITY: INTEGRATED RESPONSES TO AMBIENT LIGHT AND STANDING BIOMASS(1).

This study investigated the variation in the relationship between photosynthesis and ambient light (P-E curves) for turf algal communities on a temperate reef off the coast of South Australia, analyzing the integrated effects of ambient light and standing biomass. The photophysiology of turfs was studied in situ on a seasonal basis, examining algal communities growing on artificial substrate (plates) at depths of 4 m and 10 m. P-E curves and estimates for the photokinetic parameters (Pm , Rd , α, Ek , and Ec ) were obtained through oxygen evolution methods, using an automated underwater respirometer. Photoacclimation responses to changes in ambient light were strongly affected by the biomass of the community. Pm showed an inverse relationship to standing biomass, irrespective of depth and season, which was considered to be a response to self-shading and boundary layer effects. Biomass effects imposed a high variance on estimates for all photosynthetic parameters, overshadowing differences observed for season and depth. Biomass also affected photoinhibition on turf communities, where significant afternoon depression of photosynthesis was observed in sparse turf patches when compared to denser patches. High areal productivity rates were maintained across all seasons with a significant decrease only being observed during winter.

An in situ study of photosynthetic oxygen exchange and electron transport rate in the marine macroalga Ulva lactuca (Chlorophyta).

Direct comparisons between photosynthetic O(2) evolution rate and electron transport rate (ETR) were made in situ over 24 h using the benthic macroalga Ulva lactuca (Chlorophyta), growing and measured at a depth of 1.8 m, where the midday irradiance rose to 400-600 mumol photons m(-2) s(-1). O(2) exchange was measured with a 5-chamber data-logging apparatus and ETR with a submersible pulse amplitude modulated (PAM) fluorometer (Diving-PAM). Steady-state quantum yield ((F(m)'-F(t))/F(m)') decreased from 0.7 during the morning to 0.45 at midday, followed by some recovery in the late afternoon. At low to medium irradiances (0-300 mumol photons m(-2) s(-1)), there was a significant correlation between O(2) evolution and ETR, but at higher irradiances, ETR continued to increase steadily, while O(2) evolution tended towards an asymptote. However at high irradiance levels (600-1200 mumol photons m(-2) s(-1)) ETR was significantly lowered. Two methods of measuring ETR, based on either diel ambient light levels and fluorescence yields or rapid light curves, gave similar results at low to moderate irradiance levels. Nutrient enrichment (increases in [NO(3) (-)], [NH(4) (+)] and [HPO(4) (2-)] of 5- to 15-fold over ambient concentrations) resulted in an increase, within hours, in photosynthetic rates measured by both ETR and O(2) evolution techniques. At low irradiances, approximately 6.5 to 8.2 electrons passed through PS II during the evolution of one molecule of O(2), i.e., up to twice the theoretical minimum number of four. However, in nutrient-enriched treatments this ratio dropped to 5.1. The results indicate that PAM fluorescence can be used as a good indication of the photosynthetic rate only at low to medium irradiances.