Abstract
Investigating how environmental variation influences population, food web, and community dynamics is important for predicting the influence of climate change on ice covered ecosystems. The sea ice gradient that runs from north to south in McMurdo Sound presents a unique opportunity to study how locations with contrasting physical and biological properties influence the structure of marine food webs. Accordingly we have studied the ecological position of four ice fish species, at sites across the sea ice gradient, that occupy contrasting habitats in the Antarctic marine environment. These ice fish act as important sentinel species to better understand how environmental changes may impact food web diversity and stability in the region.
The primary objective of the present study was to determine how changing resource availability, relating to the composition of primary producers, across the sea ice gradient, influences the trophic ecology of ice fish with pelagic and benthic habits. We also aimed to determine if resource availability effected aspects of growth and reproduction in the different ice fishes. Finally we aimed to see if chemical and chronological properties of ice fish otoliths could be used as environmental recorders, for conditions in the seasonal sea ice.
Ice fish were collected from a range of sites across McMurdo Sound using the conventional hook and line method, as well as with hand nets used by divers. Dietary, stable isotope, age and growth, microscopic gonadal, and otolith trace element analyses were conducted on each of the ice fish collected.
As a result of the analyses conducted, we concluded that the trophic dynamics of ice fish differ among species and among sites distributed along the sea ice gradient in McMurdo Sound. Benthic species located at the inner sites in McMurdo Sound derived the highest proportion of diet from food webs supported by the sea ice microbial community, indicating benthic communities at these sites may be more susceptible to changes in sea ice conditions.
Age and growth trajectories, and reproductive strategies were found to differ between pelagic and benthic species. Benthic species were characterised as slower growing, summer spawners, while pelagic species displayed faster growth and are thought to spawn in winter. Our results also indicated that position along the sea ice gradient may affect aspects of growth and reproduction for ice fish.
Lastly we identified ice fish otoliths as potential recorders of, the life history of ice fish species; and the physical and chemical conditions of contrasting habitats, linked with dynamics of sea ice conditions in Antarctica.
From the present study we can conclude that climate related changes to sea ice conditions in Antarctica will effect populations of ice fish differently depending on their species, habitat, location, and sex ratios. The susceptibility of ice fish populations to environmental changes acts as an indicator for how other species connected to the same food webs will be effected by changes to sea persistence in Antarctica. The microchemistry of ice fish otoliths may offer a repeatable way to study the environmental history of ice covered habitats in Antarctica. This would allow environmental variation to be linked to the chemical, physical, and ecological changes occurring at a location.