Grazing Rates of Calanus finmarchicus on Thalassiosira weissflogii Cultured under Different Levels of Ultraviolet Radiation

UVB alters photosynthetic rate, fatty acid profiles and morphological characteristics of phytoplankton. Copepods, important grazers of primary production, select algal cells based upon their size, morphological traits, nutritional status, and motility. We investigated the grazing rates of the copepod Calanus finmarchicus on the diatom Thalassiosira weissflogii cultured under 3 levels of ultraviolet radiation (UVR): photosynthetically active radiation (PAR) only (4 kJ-m−2/day), and PAR supplemented with UVR radiation at two intensities (24 kJ-m−2/day and 48 kJ-m−2/day). There was no significant difference in grazing rates between the PAR only treatment and the lower UVR treatment. However, grazing rates were significantly (∼66%) higher for copepods feeding on cells treated with the higher level of UVR. These results suggest that a short-term increase in UVR exposure results in a significant increase in the grazing rate of copepods and, thereby, potentially alters the flow rate of organic matter through this component of the ecosystem

Residency and movement patterns of Cuvier’s beaked whales Ziphius cavirostris off Cape Hatteras, North Carolina, USA

Cuvier’s beaked whales Ziphius cavirostris are wide-ranging, deep-diving cetaceans that are particularly sensitive to anthropogenic noise. Current stock assessments assume a single population in the western North Atlantic Ocean, but knowledge of the residency patterns and distribution of the species is currently lacking in the region. Here we describe the spatial ecology of 20 Cuvier’s beaked whales equipped with satellite-linked tags off Cape Hatteras, North Carolina, USA, between 2014 and 2017. We applied a hierarchical switching state-space model to filter location estimates and define behavioral states of area-restricted search (ARS) and transit. We used kernel density estimation to identify high use areas, and net squared displacement analyses to assess residency. The vast majority (96%) of locations were classified as ARS behavior, suggesting that tagged whales allocated much of their time to foraging. Maximum net displacement had a sample median of 50 km, and 81% of individual whales were classified as demonstrating a resident, or ‘home range,’ movement pattern. Overall, our research indicates a localized population of Cuvier’s beaked whales occupying the area off Cape Hatteras. The tagged animals demonstrated a small, defined core use area and exhibited little displacement from the region. These patterns of movement and spatial use can inform future conservation and management of this species, which is vulnerable to anthropogenic disturbances caused by several sources, including mid-frequency active sonar and seismic exploration.</jats:p