Description: We describe two applications of a recently introduced system for very precise, continuous measurement of water oxygen saturation. Oxygen microoptodes (based on the dynamic fluorescence quenching principle) with a tip diameter of ~50µm, an 8-channel optode array, an intermittent flow system, and online data registration were used to perform two types of experiments. The metabolic activity of Antarctic invertebrates (sponges and scallops) was estimated in respiration experiments and, secondly, oxygen saturation inside living sponge tissue was determined in different flow regimes. Even in long-term experiments (several days) no drift was detectable in between calibrations. Data obtained were in excellent correspondence with control measurements performed with a modified Winkler method. Antarctic invertebrates in our study showed low oxygen consumption rates ranging from 0.03 - 0.19 cm3O2oh-1oind-1. Oxygen saturation inside living sponge specimens was affected by flow regime and culturing conditions of sponges. Our results suggest that oxygen optodes are a reliable tool for oxygen measurements beyond the methodological limits of traditional methods.

Description: Population structure, growth and production of the surf clam Donax serra (Bivalvia, Donacidae) inhabiting highly exposed sandy beaches of Namibia, were investigated between November 1997 and December 1999. From length-frequency distribution and tagging-recapture data a von Bertalanffy growth function with an asymptotic length (L*) of 82 mm and a growth constant (K) of 0.274 y-1 was established. Regarding growth performance of Donacidae, D. serra fits in a group of species inhabiting cold-temperate and upwelling regions. The intertidal biomass of the studied population ranged between 141 g ash free dry mass (AFDM) m-2 y-1 and 546 g AFDM m-2 y-1. Individual production was maximal at 56.5 mm shell length (0.83 g AFDM ind.1 y1) and annual production ranged between 167 g AFDM m-2 y-1 and 637 g AFDM m-2 y-1, resulting in productivity values (P/B) between 1.167 y-1 and 1.589 y-1. This data underlines the importance of D. serra for the beach/surf ecosystem. Further the findings of this study are crucial to support future aquaculture or exploitation activities and management.

Description: The lack of reliable methods for age determination often complicates the determination of individual age which is a fundamental parameter for estimating growth in population dynamics. In crustaceans, the quantification of the autofluorescent age pigment lipofuscin has recently revealed more promising results in boreal and tropical species than traditional methods. The presence of morphological lipofuscin and its possible application as an age marker in polar species was assessed in brain sections of five Arctic and five Antarctic species comprising decapods, amphipods and a euphausiid. Lipofuscin granules were located using confocal fluorescence microscopy and quantified (as % lipofuscin area fraction) from digital images. The pigment was found in 94 of 100 individuals and in all ten species, and granules occurred in easily detectable amounts in five species. Two scavenging amphipod species, the Antarctic Waldeckia obesa and the Arctic Eurythenes gryllus, revealed the most conspicuous and numerous granules. There was a broad, though weak, correlation with individual body size within a species, but not with absolute body size of one species compared to another. In larvae of the decapod Chorismus antarcticus, lipofuscin accumulation was quantified over the first four months after larval release. Factors potentially influencing lipofuscin formation and their relevance for polar species are discussed. Factors explaining the pronounced differences in lipofuscin content between species for the moment remain unknown. The possibility for application of morphological lipofuscin as an index of age is encouraging for those investigated species with a sufficient accumulation rate of the pigment, and further studies will therefore be conducted.

Description: The surf clam Donax serra (Bivalvia, Donacidae) dominates sandy beach communities of two southern African biogeographical regions, a cold (Benguela current) and warm province (Agulhas current). Morphometric and behavioural differences led to a controversial discussion of whether or not populations from the two provinces belong to the same species. Shell size measurements confirmed morphological differences: clams from the cold province were significantly rounder, flatter and less wedge-shaped than clams from the warm province. In this study a genetic approach was used to relate phenotypic differences to genetic variability of four populations of D. serra separated by up to 2 500 km of shoreline. Genetic analysis of twenty-two protein-coding loci was carried out by starch-gel electrophoresis. Populations studied are conspecific (genetic distances range from 0.003 to 0.044) and possess genetic variation (alleles per locus: 1.73 - 1.91; mean heterozygosity: 18 - 22%; percentage polymorphism: 45.5 - 59.1%) in the range of most other marine bivalves, which allows for potential adaptation to environmental changes. Wrights fixation indices show little to moderate genetic divergence among the subpopulations relative to the limiting amount under complete fixation (FST = 0.016 - 0.089), moderate divergence of individuals relative to the total population (FIS = 0.265 - 0.452), and comparably high divergence of individuals relative to the compound population (FIT = 0.300 - 0.473). The effective number of individuals exchanged between populations in each generation is high enough (1.44 - 8.65) to counteract genetic drift. We propose that the observed differences represent phenotypic plasticity enabling this species to inhabit different biogeographic regions. Gene flow, balanced selective pressure and evolutionary inertia are discussed as explanations for similarities of the two outlying populations. The substantial subdivision of the two Namibian populations indicates a potential biotic barrier and requires separate studies of the population dynamics.

Description: In the hard clam Eurhomalea exalbida autofluorescent granules were detected in high concentrations in the connective tissue around the intestine and in other tissues. Autofluorescence combined with Sudan Black B and PAS positive reactions suggested that these granules were lipofuscin-like. The concentration of this material in the connective tissue (CT) around the intestine was quantified by image analysis and expressed as total area fraction occupied by lipofuscin granules. Lipofuscin concentration was distinctly better related with individual age as determined from stable isotope validated shell growth bands, than with any morphometric parameter. This relationship was described best by a Gompertz model: Lipofuscint = 24.79 * e -e 0.029 * (Age t 58.578) (N = 38; r2nl = 0.882). Age was predicted from lipofuscinCT concentration by a von Bertalanffy model: Age t = 68.00 * (1 - e -0.146 * (Lipofuscint + 0.028))0.664 (N = 38; r2nl = 0.933). Our findings suggest that lipofuscinCT concentration in E. exalbida is a function of individual age. If this holds true for bivalves in general, lipofuscin may be a suitable proxy for age in species with less clear shell growth band patterns.