Reproduction and respiration of a climate change indicator species: effect of temperature and variable food in the copepod Centropages chierchiae

The abundance of the calanoid copepod Centropages chierchiae has increased at the northern limits of its distribution in recent decades, mainly due to oceanic climate forcing, suggesting this as a key species in monitoring climate change. Laboratory experiments were conducted to study the combined effect of temperature, food type and concentration on the egg production rate (EPR) and hatching success (HS) of C. chierchiae. Females were fed on two monoalgal diets (Gymnodinium sp. and Phaeodactylum tricornutum) at two food concentrations and at three different temperatures (13, 19, 24C). Respiration rates of both genders were measured at four different temperatures (8, 13, 19, 24C). EPR was significantly different between temperatures and food concentrations, the maximum EPR being attained when the copepods were exposed to high food levels and at 19C. Prey type significantly influenced EPR; feeding on P. tricornutum resulted in higher egg production than Gymnodinium sp. HS was significantly lower at 13C than at 19 and 24C and higher with Gymnodinium sp. Respiration rates were sex independent and increased exponentially with temperature. To maintain basal metabolism, the minimum food intake of P. tricornutum ranged between 0.4 and 1.8 g C and for Gymnodinium sp. between 0.03 and 0.13 g C. Food intake was always higher than the metabolic demands, except for the highest temperature tested (24C). The present results confirm the sensitivity of C. chierchiae to temperature variations and may help in understanding the successful expansion of its distribution towards northern latitudes.Portuguese Science and Technology Foundation (FCT) [PTDC/MAR/098643/2008, PTDC/MAR/111304/2009, PTDC/MAR/0908066/2008]; FCT [SFRH/BD/28198/2006]; [SFRH/BPD/38332/2007

Hydrocarbon Contamination Decreases Mating Success in a Marine Planktonic Copepod

The mating behavior and the mating success of copepods rely on chemoreception to locate and track a sexual partner. However, the potential impact of the water-soluble fraction of hydrocarbons on these aspects of copepod reproduction has never been tested despite the widely acknowledged acute chemosensory abilities of copepods. I examined whether three concentrations of the water-soluble fraction of diesel oil (0.01%, 0.1% and 1%) impacts (i) the swimming behavior of both adult males and females of the widespread calanoid copepod Temora longcornis, and (ii) the ability of males to locate, track and mate with females. The three concentrations of the water-soluble fraction of diesel oil (WSF) significantly and non-significantly affect female and male swimming velocities, respectively. In contrast, both the complexity of male and female swimming paths significantly decreased with increasing WSF concentrations, hence suggesting a sex-specific sensitivity to WSF contaminated seawater. In addition, the three WSF concentrations impacted both T. longicornis mating behavior and mating success. Specifically, the ability of males to detect female pheromone trails, to accurately follow trails and to successfully track a female significantly decreased with increasing WSF concentrations. This led to a significant decrease in contact and capture rates from control to WSF contaminated seawater. These results indicate that hydrocarbon contamination of seawater decreases the ability of male copepods to detect and track a female, hence suggest an overall impact on population fitness and dynamics

Molecular Systematic of Three Species of Oithona (Copepoda, Cyclopoida) from the Atlantic Ocean: Comparative Analysis Using 28S rDNA

Species of Oithona (Copepoda, Cyclopoida) are highly abundant, ecologically important, and widely distributed throughout the world oceans. Although there are valid and detailed descriptions of the species, routine species identifications remain challenging due to their small size, subtle morphological diagnostic traits, and the description of geographic forms or varieties. This study examined three species of Oithona (O. similis, O. atlantica and O. nana) occurring in the Argentine sector of the South Atlantic Ocean based on DNA sequence variation of a 575 base-pair region of 28S rDNA, with comparative analysis of these species from other North and South Atlantic regions. DNA sequence variation clearly resolved and discriminated the species, and revealed low levels of intraspecific variation among North and South Atlantic populations of each species. The 28S rDNA region was thus shown to provide an accurate and reliable means of identifying the species throughout the sampled domain. Analysis of 28S rDNA variation for additional species collected throughout the global ocean will be useful to accurately characterize biogeographical distributions of the species and to examine phylogenetic relationships among them

Seasonal abundance of copepod assemblages and grazing pressure in the Kerguelen Island area (Southern Ocean)

A long-term survey of the monthly variations of the copepod assemblages was carried out off Kerguelen Island (Kerfix Station) from February 1992 through to January 1995. Copepods were clearly dominant in the mesozooplankton (>90% of the total), with population abundances ranging from <100 individuals m(-3) in winter to 700 individuals m(-3) in summer. Calanus simillimus, Rhincalanus gigas, Metridia lucens, Oithona frigida, Oithona similis and Calanoides acutus were the most abundant species. From mid-1993, incubation experiments were performed with copepods in order to estimate the grazing pressure on the phytoplankton standing stock. In addition, estimations of their metabolic cost (oxygen comsumption) were also made. All experimental measurements were made using four size groups (Gr) defined by the cephalothorax length of the copepods. These are: Gr I, 0.2-1.1 mm; Gr II, 1.2-2.5 mm; Gr III, 2.6-3.3 mm; Gr IV, 3.7-6.5 mm. The average grazing rates ranged between 0.7 and 2.2 ng of chlorophyll (Chl) a copepod(-1) day(-1), according to the size class of the individuals. For the whole copepod assemblage, seasonal changes in the estimated grazing rate (27-1299 ng of Chi a m(-3) day(-1)) were due to changes in the abundance of the copepod species, not to apparent intrinsic seasonal trends in their physiological rates. The average ingestion reached a maximum level of 356 ng Chi a day-(1) m(-3) (or 38 mu g C day(-1) m(-3)), representing 0.12% of the mean phytoplankton standing stock. In the summer period, up to 2% of the primary production was consumed, but the carbon needs, expressed by the respiratory metabolism, showed a slight discrepancy with the contribution of phytoplankton: the carbon required for the resting metabolism alone (94 mu g C day(-1) m(-3)) representing similar to 0.31% of the algal standing stock. In summer, this metabolism could have been equivalent to 13% of the primary production. These results strongly suggest that the food of the mesozooplanktonic copepods off the Kerguelen Islands must include a large proportion of non-phytoplankton material