Enzyme activity, body measures and heart mass of Sepia officinalis sampled in the English Channel and Adriatic Sea

In the eurythermal cuttlefish Sepia officinalis, performance depends on hearts that ensure systemic oxygen supply over a broad range of temperatures. We therefore aimed to identify adjustments in energetic cardiac capacity and underlying mitochondrial function supporting thermal acclimation and adaptation that could be crucial for the cuttlefish's competitive success in variable environments. Two genetically distinct cuttlefish populations were acclimated to 11, 16 and 21°C. Subsequently, skinned and permeabilised heart fibres were used to assess mitochondrial functioning by means of high-resolution respirometry and a substrate-inhibitor protocol, followed by measurements of cardiac citrate synthase and cytosolic enzyme activities. Temperate English Channel cuttlefish had lower mitochondrial capacities but larger hearts than subtropical Adriatic cuttlefish. Warm acclimation to 21°C decreased mitochondrial complex I activity in Adriatic cuttlefish and increased complex IV activity in English Channel cuttlefish. However, compensation of mitochondrial capacities did not occur during cold acclimation to 11°C. In systemic hearts, the thermal sensitivity of mitochondrial substrate oxidation was high for proline and pyruvate but low for succinate. Oxygen efficiency of catabolism rose as temperature changed from 11 to 21°C via shifts to oxygen-conserving oxidation of proline and pyruvate and via reduced relative proton leak. The changes observed for substrate oxidation, mitochondrial complexes, relative proton leak and heart mass improve energetic efficiency and essentially seem to extend tolerance to high temperatures and reduce associated tissue hypoxia. We conclude that cuttlefish sustain cardiac performance and, thus, systemic oxygen delivery over short- and long-term changes of temperature and environmental conditions by multiple adjustments in cellular and mitochondrial energetics.

Fecal pellet ingestion rate and feeding behavior of Oithona similis, Calanus helgolandicus and Pseudocalanus elongatus from the North Sea

Studies of fecal pellet flux show that a large percentage of pellets produced in the upper ocean is degraded within the surface waters. It is therefore important to investigate these degradation mechanisms to understand the role of fecal pellets in the oceanic carbon cycle. Degradation of pellets is mainly thought to be caused by coprophagy (ingestion of fecal pellets) by copepods, and especially by the ubiquitous copepods Oithona spp. We examined fecal pellet ingestion rate and feeding behavior of O. similis and 2 other dominant copepod species from the North Sea (Calanus helgolandicus and Pseudocalanus elongatus). All investigations were done with fecal pellets as the sole food source and with fecal pellets offered together with an alternative suitable food source. The ingestion of fecal pellets by all 3 copepod species was highest when offered together with an alternative food source. No feeding behavior was determined for O. similis due to the lack of pellet capture in those experiments. Fecal pellets offered together with an alternative food source increased the filtration activity by C. helgolandicus and P. elongatus and thereby the number of pellets caught in their feeding current. However, most pellets were rejected immediately after capture and were often fragmented during rejection. Actual ingestion of captured pellets was rare (<37% for C. helgolandicus and <24% for P. elongatus), and only small pellet fragments were ingested unintentionally along with alternative food. We therefore suggest coprorhexy (fragmentation of pellets) to be the main effect of copepods on the vertical flux of fecal pellets. Coprorhexy turns the pellets into smaller, slower-sinking particles that can then be degraded by other organisms such as bacteria and protozooplankton.

Water chemistry, and body temperature, swimming depth and stomach contents of Arctic char (Salvelinus alpinus) in inner Frobisher Bay, Canada

The influence of salinity, temperature and prey availability on the marine migration of anadromous fishes was determined by describing the movements, habitat use and feeding behaviours of Arctic char (Salvelinus alpinus). The objectives were to determine whether char are restricted to the upper water column of the inter-/subtidal zones due to warmer temperatures. Twenty-seven char were tracked with acoustic temperature/pressure (depth) transmitters from June to September, 2008/2009, in inner Frobisher Bay, Canada. Most detections were in surface waters (0-3 m). Inter-/subtidal movements and consecutive repetitive dives (maximum 52.8 m) resulted in extreme body temperature shifts (-0.2-18.1 °C). Approximately half of intertidal and subtidal detections were between 9-13 °C and 1-3 °C, respectively. Stomach contents and deep diving suggested feeding in both inter-/subtidal zones. We suggest that char tolerate cold water at depth to capture prey in the subtidal zone, then seek warmer water to enhance feeding/digestion physiology.