Marine Biodiversity of Antarctic Hard Rock Communities: Species Biomass and Energy Use

• Main Author: Souster, Terri A.
• Format: Thesis
• Language: unknown
• Published: The Open University 2018
• Subjects: Adelaide Island; Antarctic; Austral; Nacella; Rothera; Rothera Point; The Antarctic; Antarc*
• Online Access: https://dx.doi.org/10.21954/ou.ro.0000d2c7; http://oro.open.ac.uk/id/eprint/53959

This thesis presents the first seasonal study in the Antarctic of shallow water hard rock communities, including surveys to quantify biodiversity and biomass (Ash Free Dry Mass, AFDM). In addition temporal changes in biodiversity since 1998 were evaluated in the same location. To do this all benthic organisms greater than 3mm in size were collected at 6m, 12m and 20m depth from three transects near Rothera Point, Adelaide Island (67° 34’ S, 68° 07’ W) in the summer and winter of 2015. Organisms were identified and their wet, dry and ash free dry masses obtained. Benthic community structure did not vary seasonally, low metabolic costs due to slowed growth rates, reproduction, development with the ability to cease feeding for the winter months may explain the lack of change between season. Community structure did, however, vary with depth, which agrees with previous studies of shallow water Antarctic hard substratum communities. Comparisons between the 2015 and 1998 survey showed reductions of both biodiversity and organic biomass at all three depths over the intervening 17 years. The greatest change was at 12m where faunal density, diversity, richness and biomass all declined significantly between 1998 and 2015. Ice scour is thought to be the main driver of this change as previous studies have shown an increase in ice scour frequency around 10m depth. The effects of seasonality on metabolism were also investigated using the five most common marine invertebrates and significant energy transformers Odontaster validus, Sterechinus neumayeri, Nacella concinna, Heterocucumis steineni and Ophionotus victoriae. Measurements of metabolic rates using closed circuit respirometry were carried out across a size range (juveniles to fully reproductive adults), to represent the population of five locally abundant species during the austral summer and winter. Oxygen consumption of Sterechinus neumayeri and Odontaster validus was significantly higher (by 39% & 44% respectively) in summer than winter. However, metabolic rates showed no consistent seasonal trends in Nacella concinna, and in Ophionotus victoriae and Heterocucumis IV steineni were higher in summer than winter, but only in large individuals which could be due to feeding and reproducing during the summer months. Seasonal metabolic changes were in line with previous studies on Antarctic marine invertebrates. Having established the metabolic rates of these species, identifying how much organic carbon there is in each and what they eat (diet), it is possible to estimate the energy required within the ecosystem to meet their metabolic demands long term. Molecular methods were employed to advance our understanding of diet. Gut contents from the same five species were analysed using DNA extraction and molecular techniques. This project forms a baseline to understand future changes in Antarctic benthic biodiversity and to analyse energy flows in these communities.