A pinboard by
Kaitlyn O'Mara

PhD candidate, Australian Rivers Institute, Griffith University


Natural vs. pollution effects of terrestrial sediment delivery to estuarine fisheries

Floods are facilitators for sediment delivery from catchment areas to estuaries and coastal bays. Sediment particles have a chemical affinity for nutrients and trace metals and estuarine sediment deposits can act as a source and sink for these substances to become available to inhabiting biota. Floods can be large disturbance events and short-term effects are driven by water quality changes, however longer-term effects are less well known. In natural, unmodified areas it is likely that floods bring nutrients and trace metals to fuel food webs and increase productivity. However, in modified catchments, especially those with cleared riparian vegetation, accelerated erosion causes more rapid infilling of estuaries and pollution from agriculture, industry and residential areas enter waterways in excess. Understanding how organisms in receiving waters respond to these increased substances is important for developing better management strategies to deal with catchment erosion and stormwater contamination.

My research incorporates several aspects of environmental science, including biology, chemistry and geology. Firstly, it involves looking at the processes of nutrient release from soils during flooding, to determine if different soil types supply different nutrients to estuaries and if they have to potential for longer-term nutrient supply after flooding. I am also studying differences in food web dynamics and condition of fish, prawns and other common species in two large coastal bays before and after flooding, and tracing connections between organisms and the sediments on which they live. These sediment will then be traced to it's terrestrial origin using known catchment sediment geology. In addition, to better understand trace metal movement through food webs, I performed an experiment using radiotracers to determine the sources for accumulation and sensitivity of common estuarine organisms occupying several trophic levels (cockles, prawns, fish).

Together, these studies will help to improve understanding of the importance and longer-term effects of floods on estuarine fisheries and food webs in both natural and disturbed areas.


Growth of estuarine fish is associated with the combined concentration of sediment contaminants and shows no adaptation or acclimation to past conditions.

Abstract: We tested whether the growth rates of small benthic fish (Gillichthys mirabilis) in three southern California estuaries corresponded with the local concentrations of contaminants. Fish originating from each estuary were transplanted to cages in each estuary in two reciprocal transplant experiments. The growth rates of caged fish, and the size-distribution of natural populations, showed the same pattern of difference among estuaries. Twelve metals and organic contaminants occurred in bulk sediments at concentrations close to their individual ERL values, and a simple index of their combined concentration (the mean ERL quotient) was inversely correlated to the growth of caged fish. Metals in the water column occurred at lower concentrations, relative to toxicity thresholds, than those in sediments and were unrelated to fish growth. Fish used in the field caging experiments, and other fish held in the laboratory under constant conditions, showed no difference in growth according to their estuary of origin. Fish originating from different estuaries also showed no consistent differences in their tissue burden of organic contaminants. Our results thus suggested no genetic adaptation or physiological acclimation to the past contaminant regime, but revealed a possible association between fish growth rates and the combined concentration of multiple sediment contaminants.

Pub.: 10 May '03, Pinned: 27 Jul '17

Fluctuations of macrobenthic populations: a link between climate-driven river run-off and sole fishery yields in the Gulf of Lions

Abstract: The Rhone river is the most important input to the Mediterranean Sea, responsible for 50% of the primary productivity of the Gulf of Lions. A highly variable amount of 1–23×106 t year–1 of terrestrial material is exported to the sea by the Rhone and stocked on the continental shelf for the most part. Soft-bottom communities off the Rhone delta were dominated by polychaetes both in species richness and abundance, and exhibited strong temporal fluctuations mainly related to flooding events. Floods caused pulses of organic matter followed, with different time lags, by peaks of polychaetes. Opportunistic, short-lived species, such as Mediomastus sp. and Aricideaclaudiae, exhibited high short-term peaks in density and biomass a few months after flooding events. Conversely, long-lived species, such as Laonicecirrata and Sternaspisscutata, peaked in density and biomass with a time lag of 1–3 years, and their population increase lasted for a few years. The common sole, Soleasolea, is a voracious predator of polychaetes which represent >80% of its prey. A positive correlation was found between the mean annual discharge of the Rhone river and the annual commercial landings of S.solea with a time lag of 5 years in the two fishing harbours (Sete and Martigues) located close to the Rhone delta. The long-term increase in food (i.e. polychaete density and biomass) after flooding events might favour the different stages of the sole life cycle, enhancing its population size for several years. Fluctuations of sole fishery yields in the Gulf of Lions could be influenced by climate, as the Rhone river flow is related to the North Atlantic Oscillation that drives precipitation over Western Europe.

Pub.: 01 Nov '02, Pinned: 27 Jul '17