Gondogeneia Antarctica Research Articles

Age composition and feeding ecology of early juvenile Notothenia rossii (Pisces, Nototheniidae) at Potter Cove, South Shetland Islands, Antarctica

AbstractAge and diet of 140 brown phase early juvenile Notothenia rossii specimens caught at Potter Cove from December 2005–March 2006 were studied. Fish were immature, in the range 8.5–21 cm TL and of age groups 1–2 (otolith/scale readings). The diet (F% and coefficient Q methods) was mainly benthic-demersal organisms with Gammaridean amphipods (primarily Gondogeneia antarctica) as the most frequent (F% = 98) and main prey (Q% = 97). The occurrence of algae, gastropods and harpacticoid copepods was high, but these organisms were secondary or occasional food. The importance of other benthic (bivalves, polychaetes, isopods) and pelagic (ostracods, calanoids, hyperiid amphipods, krill) prey was very low. Preference of larger fish for larger prey was evident. Stomach fullness analysis showed high food availability during the sampling period. Young stages of N. rossii are demersal, preying mainly on gammarideans and other invertebrates of the benthic community associated with macroalgae beds. The almost complete lack of plankton components in the diet of early juvenile fish suggests they do not migrate vertically to feed.

UV-tolerance and instantaneous physiological stress responses of two Antarctic amphipod species Gondogeneia antarctica and Djerboa furcipes during exposure to UV radiation

We investigated the shielding against solar ultraviolet radiation and inducible damage, as well as the short-term response of whole animal metabolic rate in two Antarctic shallow water amphipod species. Light absorbance by the carapace of Gondogeneia antarctica and Djerboa furcipes was higher in the UVR (UVB+UVA) range (42.1% and 54.5% on average respectively) compared to the PAR (photosynthetically active radiation) range (38.1% and 50.1% respectively) of the solar spectrum. Bands of higher absorbance correlated with maximal absorbance ranges of sunscreening compounds indicating mycosporine-like amino acids (MAAs) and carotenoids to be innate compounds of the exoskeleton of these species. Though the antioxidant enzyme catalase was photoinhibited, protein damage products did not accumulate under experimental exposure to a daily dose of 6.84 kJ m(-2) d(-1) UVB, 66.24 kJ m(-2) d(-1) UVA and 103.14 kJ m(-2) d(-1) PAR. Animal oxygen consumption during UV-exposure was measured as an indicator of immediate behavioural and physiological stress response. UVB as well as UVA induced a response with altered and highly variable respiratory intensity. Our findings indicate that sub-lethal UVR exposure causes increased oxygen consumption in polar amphipods due to radiation avoidance, shelter seeking behaviour, and presumably also from cellular repair processes.

Feeding rates of common Antarctic gammarid amphipods on ecologically important sympatric macroalgae

Single species feeding trials employing both fresh algal tissues and alginate food pellets containing dried finely ground algal tissues were conducted to examine the relative palatability of sympatric Antarctic macroalgae (three brown and five red macroalgal species) to three common herbivorous gammarid amphipods ( Prostebbingia gracilis Chevreux, Gondogeneia antarctica (Chevreux) Thurston, and Metaleptamphopus pectinatus Chevreux). In fresh algal tissue bioassays, both the amphipods P. gracilis and G. antarctica consumed significantly greater amounts of the red alga Palmaria decipiens over all other seven species of macroalgae. The amphipod M. pectinatus failed to consume measurable quantities of fresh thalli of any macroalgae and therefore is likely to feed on other resources. In food pellet bioassays, the consumption rates of amphipods fed with eight different species of macroalgae were compared with consumption rates on a highly palatable control green alga. Alginate pellets containing finely ground tissues of P. decipiens were consistently the most palatable of any of the macroalgae to P. gracilis and G. antarctica, while pellets containing the brown algae Desmarestia menziesii, D. anceps and the red alga Plocamium cartilagineum were not consumed by any of the three amphipod species. Regression analysis indicated that feeding rates of the amphipods P. gracilis and G. antarctica on alginate food pellets were not significantly correlated with known species-specific parameters of macroalgal nutritional quality (%N, %C, C:N ratio, soluble protein, soluble carbohydrate, and lipid). Therefore, differences in amphipod macroalgal palatability are most likely related to other factors including physical and/or chemical deterrents.

Within-thallus variation in chemical and physical defences in two species of ecologically dominant brown macroalgae from the Antarctic Peninsula

Macroalgae along the Antarctic Peninsula are generally unpalatable to sympatric herbivores. This is particularly true of the large, brown macroalgae that dominate the communities in terms of cover and biomass. Variation within and between individuals of the ecologically dominant genus Desmarestia has also been detected. In the present study, we examined within thallus variation of both chemical (palatability) and physical (toughness) defences in Desmarestia anceps and Desmarestia menziesii. Each species was divided into the holdfast, the primary stem, and the lateral branches, with tissue fitness values assigned to each component. Lipophilic and hydrophilic extracts were obtained from each thallus component and incorporated into artificial alginate foods. A series of bioassays tested the palatability of these foods to the sympatric, herbivorous amphipod Gondogeneia antarctica. Toughness measurements were also performed on each thallus component. Results from D. anceps, a highly differentiated species, were consistent with the Optimal Defence Theory (ODT) in that the most valuable tissue component (the primary stem) was the most strongly chemically and physically defended. The holdfast, also with a high tissue fitness value, was strongly physically defended. Laterals, which are replaceable and assigned a lower fitness value, were moderately chemically defended. No significant differences were detected in the palatability of the differing thallus parts in D. menziesii, although the holdfast and primary stem were tougher than the lateral branches. These results remain consistent with the ODT as D. menziesii displays less differentiation between the primary stem and the lateral branches and were assigned a similar fitness value.

PRELIMINARY RESULTS ON SECONDARY METABOLITES FROM ANTARCTIC BROWN ALGAE AND THEIR ECOLOGICAL RELEVANCE

Iken, K. 1, Amsler, C. D.1, Hubbard, J. M.2, McClintock, J. B.1, Baker, B. J.3 1University of Alabama at Birmingham, Dept. of Biology, Birmingham, AL 35294‐1170 USA 2Hanshew Middle School, 10121 Lake Otis Pkwy., Anchorage, AK 99507 USA; 3Dept. of Chemistry, Florida Institute of Technology, Melbourne, FL 32901 USABrown algae (Phaeophyceae) are often dominant members in abundance and biomass of Antarctic macroalgal communities. They are ecologically important in providing habitat structure and shelter to many invertebrates and fish. However, as live algae they often appear to be of little importance as food for herbivores. Palatability of thalli of eight abundant Antarctic brown algae was tested against two sympatric algal grazers, the fish Notothenia coriiceps and the sea star Odontaster validus. Polar and non‐polar organic extracts of six brown algae were also tested against these grazers and against the omnivorous amphipod Gondogeneia antarctica. Almost all thalli and at least one of the extract types per algal species were unpalatable to the grazers, suggesting that chemical defenses are probably present in Antarctic brown algae. We further tested biological activity of brown algal extracts in antimicrobial assays as well as antifouling assays with sympatric bacteria and diatoms, respectively. We chemically screened organic brown algal extracts for the occurrence of secondary metabolites. Acetogeno‐terpenes were detected in Desmarestia menziesii and D. anceps. Phlorotannins were present in all brown algal species analyzed, but at different concentrations between species as well as between different thallus parts within individuals. Phlorotannin extracts were size fractionated to examine distribution and abundance of various size classes between species as well as between different thallus parts within individuals.

The specialized diet of Harpagifer bispinis:

The diet of Harpagifer bispinis (Pisces: Nototheniidae) from two localities of the South Shetland Archipelago was studied. Simultaneous to the capture of H. bispinis and at the same sites the availability of food was considered, and amphipod diversity was compared with the density of Harpagifer. It was found that three quarters of the fish fed only on amphipods (mainly Gondogeneia antarctica) and for the rest amphipods were also the main component, even when other prey species were available. The high selectivity of G. antarctica is due to its high mobility and to the fact that Harpagifer is an ambush feeder. At different predator densities the amphipod fraction of the community appears to be highly modified by the predator both numerically and in species evenness. We postulate that Harpagifer can be a key species in structuring the mobile epibenthic community, even when this environment is subject to strong physical stress.