Alan G. Lewis

Mesozooplankton community characteristics in the NE subarctic Pacific

Mesozooplankton biomass, species composition, abundance, and vertical distribution were determined along a transect from the continental slope off the west coast of Canada to Ocean Station Papa (OSP) in the open-ocean waters of the NE subarctic Pacific as part of the Canadian Joint Global Ocean Flux Study of this area. All of these measurements had distinct seasonal patterns. At OSP biomass peaked in spring, coincident with the annual biomass maximum of large copepods of the genus Neocalanus. Early copepodites of these copepods were present in surface waters at all stations along the transect in winter, but N. plumchrus and N. flemingeri copepodites were only at the offshore stations in spring. This indicated that these large copepods had completed the growth phase of their life cycle slower in the open ocean than closer to shore where they had already descended to deep water by May or June. Summer biomass was low compared to the spring peak. The summer mesozooplankton abundance was similar to the springtime abundance, but the composition had changed from large-bodied copepods in the spring to small copepods and fewer non-copepod taxa in the summer, which accounts for the reduction in total biomass. Winter biomass was the lowest of the year. Winter species composition was similar to summer except for the appearance of juvenile stages of the genera Neocalanus and Calanus. Diel changes in biomass in the upper 150 m were found in summer but not in winter or spring. Vertical distributions of copepods were often distinct, with closely related species occupying different depth strata. Measurements of wet weight at OSP were higher than the long-term mean wet weight during winter and spring, and lower during summer.

The Sternal Furca of Caligoid Copepods

Die Caligoiden Brustgabel liegt etwas caudalwarts zwischen den Maxillipeden der Trebiiden, Euryphoriden und Caligiden. Der Ursprung dieses Gebildes wird vermutet entweder in der Zwischenfussplatte der einfachen Maxillipeden, in der Cuticula der Brustregion des Cephalothorax oder in einem Paar zusammengewachsener Anhange. Funf Arten der Caligoiden, die auf Hawaiischen Fischen gesammelt wurden, bringen etwas Licht in zwei von den drei angenommenen Entstehungsarten. Die Diskussion uber die Entstehung der Brustgabel oder gabelahnlicher Strukturen dieser funf Arten ergibt keine klare Antwort; sie macht aber an Hand weiterer Informationen von anderen Copepoden-gruppen wahrscheinlich, dass die Brustgabel ursprunglich den Zwischenteil der cuticularen Platte, die an das Vorderende des ersten pedigorosen Abschnittes angehangt ist, dargestellt hat.

The effect of manganese-copper interactions on growth of a diatom in water from a manganese-rich British Columbia fjord

Abstract A competitive interaction between manganese and copper has previously been reported for the growth of marine phytoplankton. This was confirmed in an artificial medium with the marine diatom Thalassiosira pseudonana . The reduction in cell division rate produced by excess copper was alleviated by increasing the concentration of manganese. This relationship was also found to exist in natural water from a silled British Columbia fjord; the reduction in cell division rate with added copper was less in manganese-rich deep water than in manganese-poor shallow water. In coastal waters, elevated concentrations of manganese occur under certain hydrographic conditions and have the potential to reduce the detrimental effects of excess biologically available copper. At lower levels of copper, high concentrations of manganese may reduce uptake and produce a copper deficiency.

Lepeophtheirus salmonis (Krøyer, 1837): second nauplius and copepodid locomotor appendages, surface areas and possible appendage functions

Locomotor appendage-body relationships were used to examine whether swimming or reduction in sinking rate is the more important function in the second nauplius and copepodid stages of Lepeophtheirus salmonis (Kroyer, 1837). Except for the similarity in swimming appendage surface areas without setae, the appendages of the two stages are morphologically distinct. Although the nauplius is smaller than the copepodid it has long slender appendages that, with setae, provide greater total surface area than the paddle-shaped copepodid thoracic legs. Copepodid thoracic legs are more similar to those used for swimming by planktonic copepods although with more limited propulsion capability. Naupliar appendages project from the body while copepodid appendages can be folded against the ventral surface, improving hydrodynamic flow as well as body position after attachment to a host. Both copepodid and naupliar appendages are of sufficient size that they should provide escape velocities of more than 100 mm ⋅ s−1. The nature and display of the naupliar appendages suggest they could be used to reduce sinking rate by as much as 64%, reducing the need to swim to maintain a suitable location in the water. Although copepodid thoracic legs could reduce sinking rate by over 40%, their position on the ventral surface and the nature of other appendages suggests a more important use, for orientation and attachment once a host is located.

A comparison of the labrum-paragnath complex in five species of calanoid copepods

Although some information is available on how calanoid copepods collect and handle food, there is very little information on the labrum and paragnaths, structures that are the last to receive food before trituration and ingestion. Five species were used to examine the nature of and differences between the labrum-paragnath complex, species with a variety of feeding modes ranging from detritivore to carnivore. The nature of the complex ranged from very simple in Eucalanus bungii bungii Johnson, 1938, to the heavily sclerotized labrum and paragnaths of the carnivore Paraeuchaeta elongata (Esterly, 1913) with its specialized anterior labral lobe. The labrum, which provides a semi-enclosed space for trituration by the mandible gnathobases, is hood shape while the columnar-shaped paragnaths, which hold and help move food towards the mandible gnathobases, contain setule and spicule armature elements. Not only the shape of the complex, but also its orientation are suggested to play roles in dictating dietary choices. The range of structures, from the simple complex of Eucalanus bungii bungii to the beak like complex of Heterorhabdus tanneri (Claus, 1863), along with its claw-like gnathobase armature, provide an indication of the morphological diversity found in the labrum-paragnath complex of calanoid copepods. For supplementary material, please go here: http://dx.doi.org/10.6084/m9.figshare.1276298 .