Peter Tiselius

The nearshore zone during coastal upwelling: daily variability and coupling between primary and secondary production off Central Chile

The nearshore region of central Chile is important for spawning of sardine (Sardinops sagax) anchovy (Engraulis ringens) and jack mackerel (Trachurus murphyii) and the importance of fisheries for these species has led to an interest in factors controlling the areas productivity. We studied daily variations in productivity at a nearshore station (25m depth) off Dichato, Chile (36°30′S) during January 1986 to understand how wind-driven variability in the hydrography is translated into pulses of primary and secondary production of the plankton. During the study period, we observed three complete cycles of upwelling favourable/unfavourable winds. Water column destratification, as indicated by the surface-to-bottom gradient of sigma-t, lagged the wind by about one day. During active upwelling, cold water (<11.5°C) of high nitrate and low oxygen concentration (20–25μM and 1–2ml 1−1 respectively) was found near the surface. During subsequent relaxation of upwelling, the water column became stratified as temperature, oxygen and chlorophyll increased. The size and taxonomic composition of the phytoplankton varied from one event to the next. Over the course of the study, from 15–100% of the chlorophyll could pass a 20μm mesh screen. Chain-forming diatoms, microflagellates, and the autotrophic ciliate Mesodinium rubrum dominated the first, second and third events, respectively. In rank order of abundance, Paracalanus parvus, Centropages brachiatus, Oithona spp., Acartia tonsa, Oncaea spp., Calanoides patagoniensis and Calanus chilensis dominated the copepod community. Changes in abundance of most species did not closely follow the upwelling cycle. Possibly, vertical movements or other behavioural responses caused zooplankton distributions to be uncorrelated with movements of the surface Ekman layer. Fecundity of several of the important copepod species was measured using the egg ratio and bottle incubation techniques. Compared to values reported in the literature, egg production was usually suboptimal, despite high nutritional quality of the phytoplankton, as indicated by protein/carbohydrate ratios. Food availability, due to either small phytoplankton size or spatial and temporal uncoupling of phyto- and zooplankton populations, was probably most important in limiting copepod production. Event-scale advection, both zonal and alongshore, can be important in uncoupling primary and secondary production and probably determines the degree to which upwelling-generated pulses of phytoplankton production are utilized by herbivorous plankton in the nearshore zone.

Propagation of planktonic copepods: production and mortality of eggs

Data on fecundity and egg mortality of neritic copepods were collected in various seasons, areas and under various hydrographical conditions. On a seasonal basis variations in fecundity (F) were related to temperature rather than to the abundance of phytoplankton (P). However, a strong correlation between F and P was evident when water column stability varied horisontally or temporally (i.e. at a tidal front or subsequent to a storm). Estimated specific egg-mortalities were variable and occasionally very severe, up to 9.1 d−1, implying that down to 10−4% of the eggs survive to hatching. The implications for phenology and distribution of copepods are discussed.

The importance of uptake from food for the bioaccumulation of PCB and PBDE in the marine planktonic copepod Acartia clausi

The accumulation of (14)C-labelled PCB 31, PCB 101, PCB 153 and PBDE 99 was investigated at the two lowest trophic levels of the pelagic food web. Accumulation was measured in the small phytoplankter Thalassiosira weissflogii (Coscinodiscophyceae: Thalassiosirales) and in the neritic zooplankter Acartia clausi (Copepoda: Calanoida) exposed to the substance either only via water or through ingestion of contaminated T. weissflogii. Bioaccumulation factors (BAFs) for all four compounds were significantly higher in A. clausi feeding on contaminated phytoplankton than in animals exposed only via water. The logBAF for the PCBs increased linearly with the octanol-water partitioning coefficients (logK(OW)) in both the algae and the copepods, but with steeper slopes for feeding than non-feeding animals. Reported values for K(OW) for PBDEs vary by almost an order of magnitude and it was therefore not meaningful to calculate a logBAF-logK(OW) ratio for PBDE 99. It is clear that the nutritional status of the zooplankton affects the uptake of the compounds and that the bioaccumulation cannot be modelled as a passive partitioning between the organisms and the surrounding water. Small copepods are typical of coastal waters and point sources (both temporal and spatial) may be the rule for HOC releases into the sea. Thus, the pathways shown in this study are important and realistic.

Grazing impact of Oikopleura dioica and copepods on an autumn plankton community Published in collaboration with the University of Bergen and the Institute of Marine Research, Norway, and the Marine Biological Laboratory, University of Copenhagen, Denmark

Abstract Copepods and appendicularians are major grazers in the pelagic environment. They have different retention efficiencies for prey and may therefore exert a variable grazing pressure on the spectrum of pico- to micro-plankton. We determined clearance rates of both groups at one station during 24 h in the Gullmar fjord, west Sweden, in autumn 1999. Total potential prey biomass ranged from 75 µg C l−1 at the surface to 14 µg C l−1 at 30 m with a dominance of larger dinoflagellates (10–25 µm athecate species and Gymnodinium /Gyrodinium sp.) and the pennate diatom Pseudo-nitzschia sp. Grazer biomass was dominated by copepods (Acartia clausi, Paracalanus parvus) and appendicularians (Oikopleura dioica). O. dioica showed non-selective clearance rates of 0.7–1.8 ml µg C−1 h−1 on most diatoms, flagellates and ciliates, whereas Pseudo-nitzschia sp. and dinoflagellates and ciliates >25 µm were not removed by O. dioica. Appendicularian grazing impact was 0.06% d−1 on the phytoplankton and 0.4% d−1 on bacterial biomass. Despite a seven-fold higher biomass, the grazing impact of copepods on phytoplankton biomass was only 0.28% d−1 indicating that O. dioica had a proportionally greater impact and, in contrast to copepods, also utilised bacteria. The low observed grazing impact was due to a low grazer biomass and a prey community largely unavailable to the investigated grazers.

Solid phase extraction and metabolic profiling of exudates from living copepods

Copepods are ubiquitous in aquatic habitats. They exude bioactive compounds that mediate mate finding or induce defensive traits in prey organisms. However, little is known about the chemical nature of the copepod exometabolome that contributes to the chemical landscape in pelagic habitats. Here we describe the development of a closed loop solid phase extraction setup that allows for extraction of exuded metabolites from live copepods. We captured exudates from male and female Temora longicornis and analyzed the content with high resolution LC-MS. Chemometric methods revealed 87 compounds that constitute a specific chemical pattern either qualitatively or quantitatively indicating copepod presence. The majority of the compounds were present in both female and male exudates, but nine compounds were mainly or exclusively present in female exudates and hence potential pheromone candidates. Copepodamide G, known to induce defensive responses in phytoplankton, was among the ten compounds of highest relative abundance in both male and female extracts. The presence of copepodamide G shows that the method can be used to capture and analyze chemical signals from living source organisms. We conclude that solid phase extraction in combination with metabolic profiling of exudates is a useful tool to develop our understanding of the chemical interplay between pelagic organisms.

Community cascades in a marine pelagic food web controlled by the non-visual apex predator Mnemiopsis leidyi

Trophic cascades are a ubiquitous feature of many terrestrial and fresh-water food webs, but have been difficult to demonstrate in marine systems with multispecies trophic levels. Here we describe significant trophic cascades in an open coastal planktonic ecosystem exposed to an introduced top predator. The ctenophore Mnemiopsis leidyi was monitored for an 8-year period concurrent with measures of the food web structure of the plankton and strong trophic cascades were evident. In the 5 years when M. leidyi were found, their target prey (grazing copepods) were reduced 5-fold and the primary producers doubled their biomass when released from the grazing pressure. The increased phytoplankton biomass could unequivocally be assigned to grazing release since concurrent measurements of primary production did not differ between years with or without M. leidyi. Copepod biomass prior to the mass occurrence of the ctenophore was important. The years without M. leidyi had significantly higher biomass of copepods in July, the month preceding the outburst of the ctenophore. The profound changes of the pelagic ecosystem faced with a non-selective apex predator shows that marine communities are not exceptions from trophic cascade mechanisms.

Evidence of diel vertical migration in Mnemiopsis leidyi.

The vertical distribution and migration of plankton organisms may have a large impact on their horizontal dispersal and distribution, and consequently on trophic interactions. In this study we used video-net profiling to describe the fine scale vertical distribution of Mnemiopsis leidyi in the Kattegat and Baltic Proper. Potential diel vertical migration was also investigated by frequent filming during a 24-hour cycle at two contrasting locations with respect to salinity stratification. The video profiles revealed a pronounced diel vertical migration at one of the locations. However, only the small and medium size classes migrated, on average 0.85 m h−1, corresponding to a total migration distance of 10 m during 12 h. Larger individuals (with well developed lobes, approx. >27 mm) stay on average in the same depth interval at all times. Biophysical data suggest that migrating individuals likely responded to light, and avoided irradiance levels higher than approx. 10 µmol quanta m−2 s−1. We suggest that strong stratification caused by low surface salinity seemed to prohibit vertical migration.

Vertical distribution, grazing and egg production of calanoid copepods during winter–spring in Gullmarsfjorden

The vertical distribution of copepods in relation to their potential food was examined in Gullmarsfjorden, Sweden (58°15.6′ N, 11°27.2′ E). Plankton distributions were determined from bottle samples at 5 m intervals on four occasions; 30 January, 28 February, 7 March and 10 April 1996. Potential food was crudely divided into chlorophyll containing protists (generally phytoplankton) and ciliates. Weak correlations between copepods and phytoplankton were found in January and April, while there were no correlations during the diatom spring bloom (February-March) when phytoplankton were superfluous throughout the water column. Copepods and ciliates were never correlated. Ingestion as determined from gut fluorescence and egg production analyses suggested a higher degree of herbivory during the spring bloom than before and after. There was potential for copepod predation control of ciliate biomass throughout the study. Due to low copepod abundance in January through March estimated grazing pressure was not sufficient to control phytoplankton biomass until after the diatom spring bloom. Egg production rates were constant for Centropages hamatus (~ 20 eggs female−1 day−1) on all dates but more variable (1–26 eggs female−1 day−1) for the other species. Temora longicornis and Acartia sp. both revealed their lowest fecundity during the bloom.

Toxicity of treated bilge water: The need for revised regulatory control

Water accumulating in the bottom of ships (bilge water), contains a mixture of oil, detergents and other compounds from on board activities. To evaluate ecological effects of released bilge water the chemical composition and toxicity of treated bilge water from seven passenger ships was analysed. The oil content was below 15mgL-1, the threshold for legal discharge, in all but one ship. Still, significant reductions in feeding and reproduction of Acartia tonsa were found after 48h exposure in dilutions with 2.5-5% of bilge water. Mortality was significant at dilutions of 5-10% in 4 of the 5 bilge water samples. Surfactants were the most significant contributor to the toxicity on copepod vital rates and survival. Toxicity was also tested with Microtox where an EC50 was found at dilutions between 4.3% and 52%. The results show that ecological effects might occur also in diluted suspensions of bilge water.

Functional response of Sagitta setosa (Chaetognatha) and Mnemiopsis leidyi (Ctenophora) under variable food concentration in the Gullmar fjord, Sweden

Los organismos gelatinosos carnivoros son importantes componentes del ecosistema pelagico y potencialmente organismos claves en las tramas troficas pelagicas, depredando sobre varios grupos. En el fiordo Gullmar, muchas especies de gelatinosos han sido encontradas ejerciendo un gran impacto depredador sobre A. clausi, un abundante copepodo del mesozooplancton de este ecosistema. El proposito de este trabajo fue evaluar el impacto depredador de M. leydi y S. setosa sobre la comunidad de copepodos del fiordo Gullmar. Los experimentos fueron de respuesta funcional. Ademas, regresiones de longitud- peso seco fueron estimadas para determinar la biomasa del depredador. Sagitta setosa exhibio una respuesta funcional tipo II. Mnemiopsis leidyi mostro una respuesta funcional lineal (Tipo I) con tasas de ingestion maximas (Imax) de 7 copepodos ind-1 h-1 para individuos cuyo tamano oscilo entre 7-15 mm. Sagitta setosa exhibio un Imax de 3,96 (copepodos pred-1 h-1) en individuos de tamanos de 6 y 7 mm. El impacto depredador de ambas especies fue alto, por esto se sugiere que ambas pueden ejercer un fuerte impacto sobre la comunidad del fiordo Gullmar.