Arsenic distribution and species in two Zostera capricorni seagrass ecosystems, New South Wales, Australia

Environmental context Arsenic concentrations and species were determined in seagrass ecosystems where the food web was established using carbon and nitrogen isotopes. There was a clear increase in the proportion of arsenobetaine in tissues of higher trophic level organisms, which is attributed to an increasing arsenobetaine content of the diet and the more efficient assimilation and retention of arsenobetaine over other arsenic species. The results provide an explanation for the prominence of arsenobetaine in higher marine animals. Abstract Arsenic concentrations and species were compared in biota from two Zostera capricorni ecosystems. Mean arsenic concentrations were not significantly different for non‐vegetative sediment, rhizosphere sediment, Z. capricorni blades, roots, rhizomes, epiphytes, amphipods, polychaetes, molluscs, crustaceans and fish, but were significantly different in detritus. Sediments and plant tissues contained mostly inorganic arsenic and PO4–arsenoriboside. Detritus contained mostly PO4–arsenoriboside. Fish tissues contained predominately arsenobetaine. Other animals had lower proportions of arsenobetaine and variable quantities of minor arsenic species. Bioconcentration but not biomagnification of arsenic is occurring with no evidence of arsenic hyper accumulation. The proportion of arsenobetaine increases through the food web and is attributed to a shift from a mixed diet at lower trophic levels to animals containing mostly arsenobetaine at higher trophic levels and the more efficient retention of arsenobetaine, compared to other arsenic species.

A COMPARISON OF THE EFFECTS OF TAPIS CRUDE OIL AND DISPERSED CRUDE OIL ON SUBTIDAL ZOSTERA CAPRICORNI

ABSTRACT Oil spill mitigation managers need to know the effects of chemical dispersants on subtidal seagrass in order to determine the least net environmental impact of their actions. The decision-making process for chemical dispersant use in Australia, known as Net Environmental Benefit Analysis, is compromised in near shore areas due to a lack of information on dispersed oil impacts on subtidal seagrasses. This study aimed to determine the toxic effects of crude oil, dispersed and non-dispersed, on subtidal seagrass and to quantify the exposure amount. Zostera capricorni plants were exposed to a range of concentrations of different oil and dispersant combinations in the field. ?hotosynthetic health was measured using Pulse Amplitude Modulated (PAM) fluorometry and chlorophyll pigment analysis. Oil concentration was calculated in relative oil units using Ultraviolet Fluoresence (UVF) spectrophotometry. Limited photo synthetic impact was detected in Z. capricorni exposed to the water soluble fraction of the non-dispersed Tapis crude oil treatments. No significant photo synthetic impact was evident in the dispersed Tapis crude oil treatment even though the Total Petroleum Hydrocarbon (TPH) concentration in these treatments was higher than in the non-dispersed Tapis crude oil treatments. Plants from both treatments recovered following replenishment from the surrounding seawater. A substantial reduction of the total petroleum hydrocarbons within the mesoscosms over the 10 hour exposure period was evident and would likely suggest a rapid loss of the toxic mixture to the sediments rather than assimilation by the seagrass.

Patterns of small fish distributions in seagrass beds in a temperate Australian estuary

Beds of the seagrass Zostera capricorni are an integral part of the estuarine landscape along the east coast of Australia, forming an important habitat for juvenile fish. Seagrass beds can vary in their size, shape and patchiness of seagrass cover as well as their distance from the estuary mouth. We tested for a correlation between these features and small fish assemblages in seagrass. Fifteen beds were selected from three size-categories (small, 980 to 2300 m2; medium, 3375 to 4090 m2; and large, 5335 to 6630 m2). We found that the size of beds, the patchiness of seagrass cover and location within the estuary (distance from estuary mouth) were all related to differences in fish assemblages. There were greater densities of fish species in small (10.3 ±0.79 species .net-1) compared to medium (7.6 ±0.6) and large (8.2 ±0.5) beds. This occurred regardless of bed placement within the estuary, its patchiness or time of sampling (day and night). The fish assemblages within seagrass beds also changed as bed distance to estuary mouth increased. Six species had greater densities in beds closer to the estuary mouth, while only two species were in greater densities far from the mouth. Fish assemblages were different between beds with patchy and continuous cover, although total densities of all fish species combined were similar. There were greater densities of four species in continuous beds compared to two species that were greater in patchy beds. Overall, an important finding was that even small patchy seagrass beds contain greater densities of small fish species than larger beds with continuous seagrass cover.