No abstract

No abstract

No abstract

Zooplankton samples were collected from 0 to 50 m depth at 2 stations in Jones Sound and 1 in Baffin Bay in August and September of 1983. Levels of chlorophyll and phaeopigment were measured in several stages of Calanus hyperboreus and Calanus glacialis at 4 h intervals, to examine diurnal feeding behavior in copepods which do not vertically migrate on a daily basis. All stages examined for each of the 2 species showed diurnal variations in feeding activity. In addition, different stages and species always started to feed synchronously, although timing of onset of evening feeding was different at each of the 3 stations. On each occasion feeding started when incident light intensity decreased to < 4 W m-2. Cessation of feeding in the morning, however, was not linked to a particular intensity of incident light and may be controlled by satiation of appetite. Levels of 3 digestive enzymes -protease, laminarinase, and amylase -were measured in 2 stages of C. hyperboreus and C. glacialis at 4 h intervals over a 48 h time series at the second of the Jones Sound stations. There were no rhythmic changes in amounts of enzymes in any of the stages. Maximum levels of gut pigment within any 1 stage were not necessarily correlated with ambient chlorophyll concentrations, which varied by a factor of 4 among stations.

The effect of major pigments on the absorption characteristics of phytoplankton were evaluated by comparing the in vjvo absorption spectra of phytoplankton with pigment data obtained using high-performance liqu~d chromatography (HPLC) for samples of phytoplankton collected in the northwestern Atlantic Ocean, during spring. Four groups of spectra having distinct absorption characteristics and well-defined regional distributions were identified. The result of using general parameters to estimate the absorption coefficient of phytoplankton from any region, the 'general approach', was compared with the result of using specific parameters for each region, or the 'regional approach' Two methods of estlrnating the absorption coefficient were tested for each approach. These were: a 'slnglepigment' method (Prieur & Sathyendranath 1981, Limnol Oceanogr 26:671-689), and a 'multi-pigment' method (Hoepffner & Sathyendranath 1991, Mar Ecol Prog Ser 73:ll-23). It was shown that the regional approach performed better (<10% average error) than the general approach (~2 0 % average error). Nevertheless, the results given by the general approach could be acceptable for some applications. The multi-pigment and the single-pigment methods performed equally well in the context of the reglonal approach, whereas in the general approach, the s~ngle-pigment method gave better results than the multi-pigment method. Overall, it appears that part~tioning the oceans into regions according to their absorption characteristics should improve regional models of light transmission and the algorithms for detection of pigments by remote sensing.

Chlorophyll destruction by Calanus spp. grazing on phytoplankton (diatoms and Phaeocystis) was assessed at stations in the Labrador Sea and off Labrador and Newfoundland (Canada). Copepods were fed at natural or diluted food concentrations over several (4 to 8) sequential 12 h feeding periods. Initial chlorophyll concentrations were between 0.2 and 19 pg I -' , and degrees of chlorophyll destruction were between 20 and 100%. For replicate incubations, degrees of chlorophyll destruction were similar. Over all experiments degrees of destruction were generally high and variable at low ingestion rates (<50 ng chl mg-' h-'), decreasing to a limit of about 4 5 % at higher ingestion rates. The relationship between ingestion rate and degree of chlorophyll destruction was not obviously affected by differences in in situ conditions (e.g. stage of the spring bloom). Filtration rates, by contrast, did vary, decreasing in the presence of an apparently noxious food (Phaeocystis) and sometimes increasing during experiments, perhaps in response to increasing hunger. Faecal pellets, collected from copepods fed at natural food concentrations, did not leak pigment over a 4 d period, and neither chlorophyll nor phaeopigment was lost as copepods with food in their guts were alloived to defecate for 3 h in filtered seawater. These results suggest that most chlorophyll destruction occurs at an early stage of feeding, and that phaeopigments are not intermediates. When we assumed in a simple model that the 'bleaching' reaction was enzymatically mediated, we found that enzyme activity varied linearly with initial ingestion rate, with a positive y-intercept. One interpretation of this is that there are 2 pools of enzyme activity: one associated with the copepods and the other with the phytoplankton. The algal enzymes are normally latent, but are activated by the physical break-up of cells during ingestion. At low ingestion rates the copepod enzyme can destroy all, or most, of the ingested chlorophyll, whereas at higher ingestion rates more of the destruction is due to the algal enzymes. The high variability in degrees of chlorophyll destruction reported here and elsewhere can be explained partly by differences between algal foods (e.g. differences in levels of the bleaching enzyme), partly by differences in copepod behaviour (e.g. effects on filtration rates), and partly by differences in experimental conditions, which affect the range of ingestion rates exhibited during an incubation (e.g. density of copepods, duration of incubation).

No abstract

During a period of 8 d in late September and early October 1992, 5 grazing experiments were carried out in an area off the coast of Morocco. Water was collected from the depth of the chlorophyll maximum and fed to copepods of either 500 to 1000 pm or 200 to 500 pm in size. Two chlorophylls and 2 carotenoids dominated the pigment composition of the particulate material: chlorophyll (chl) a; chl c (c, + cz); fucoxanthin and 19-hexanoyloxyfucoxanthin. Initial concentrations of chl a in experiments were between 0.4 and 2.2 pg I-' and those of chl c were between 0.04 and 0.54 pg 1-' Initial concentrations of fucoxanthin were between 0.1 and 1.1 pg I-' and those of 19-hexanoyloxyfucoxanthin between 0.07 and 0.32 pg 1-l. The ratio of fucoxanthin:l9-hexanoyloxyfucoxanthin varied between 0.3 and 15 (w/w). The fucoxanthin was probably associated with diatoms and the 19-hexanoyloxyfucoxanthin w~t h prymnesiophytes. Some chl a-derived fluorescent breakdown products were found in faecal pellets collected after grazing, but neither fucoxanthin nor 19-hexanoyloxyfucoxanthin were present. Hence these carotenoids were destroyed following ingestion by copepods, so that decreases in their concentrations in the incubation medium could be used to measure grazing rates on the different types of phytoplankton independently. In this way it was shown that copepods 500 to 1000 pm in size fed preferentially on diatoms, and that their overall feeding rate was depressed when fucoxanthin: 19-hexanoyloxyfucoxanth~n ratios were relatively low. By contrast, copepods 200 to 500 pm in size fed randomly or preferred the prymnesiophytes. When chl a concentrations were initially < 1 pg I-', then for both size ranges of copepods, only a very small proportion (< 10%) of the ingested chl a was converted into a-type phaeopigments, the rest apparently being destroyed during digestion. In one case, however, when copepods 200 to 500 pm were fed with water in which the initial chl a concentration was > 2 pg I-', about 30% of ingested chl a was recovered in a-type phaeopign~ents.