Bathymetric barriers promoting genetic structure in the deepwater demersal fish tusk (Brosme brosme)

Population structuring in the North Atlantic deepwater demersal fish tusk ( Brosme brosme ) was studied with microsatellite DNA analyses. Screening eight samples from across the range of the species for seven loci revealed low but significant genetic heterogeneity ( F _ST = 0.0014). Spatial genetic variability was only weakly related to geographical (Euclidean) distance between study sites or separation of study sites along the path of major ocean currents. Instead, we found a significant effect of habitat, indicated by significant differentiation between relatively closely spaced sites: Rockall, which is surrounded by very deep water (>1000 m), and the Mid-Atlantic Ridge, which is separated from the European slope by a deep ocean basin, were differentiated from relatively homogeneous sites across the Nordic Seas. Limited adult migration across bathymetric barriers in combination with limited intersite exchange of pelagic eggs and larvae due to site-specific circulatory retention or poor survival during drift phases across deep basins may be reducing gene flow. We regard these limitations to gene flow as the most likely mechanisms for the observed population structure in this demersal species. The results underscore the importance of habitat boundaries in marine species.     

A System for Continuous Measurement of Photosynthetic Rate and Dark Respiration at Constant CO2-Level

A system for maintaining a constant CO₂-level during photosynthesis and dark respiration in an assimilation chamber is described. The assimilation chamber has two loops for control of the CO₂-level. If the CO₂-concentration is increased over a preset value, CO₂ is removed by passing the gas flow over a lime filter. If CO₂ is consumed, concentrated CO₂ is added to the system. The system is operated through the computer in the Phytotron and has been constructed mainly for studies of dusk and dawn effects on photosynthesis where a high degree of control of the CO₂-level in the system is of the utmost importance.     

Multivariate analysis of morphometric differentiation within the Laonice cirrata-group (Polychaeta, Spionidae)

Principal component, and canonical variate analysis based on six characters show that there are morphological differences between three Laonice forms (L. bahusiensis, L. sarsi, and Laonice sp.). This supports Söderström's division of L. cirrata into four species; a decision often questioned by other taxonomists. We cannot exclude the possibility that the morphological differences are caused by polymorphism or seasonal variation within a single species. There is, however, no information to vindicate this and we conclude that the three forms should be regarded as separate species until this hypothesis can be rejected.