A biochemical investigation of a Phaeocystis sp. bloom in the Irish Sea

132

ABSTRACT-Colonies of the prymnesiophyte marine microalga Phaeocystis globosa were tested for mechanical properties, permeability and biochemical composition using the rnicropipette aspiration technique. We found that the Phaeocystis colony is enclosed by a thin, yet very strong, semi-permeable skin (pore size between 1 and 4.4 nm diameter) with plastic and to a limited extent also elastic properties. Qualitative staining of single colonies with selective fluorescent dyes indicated absence of lipophilic compounds and chitin but presence of amino groups in the colony skin. Individual cells in the colony appear to be weakly connected with one another and attached to a very dilute, peripheral gel. Suction apphed to the colony resulted in volume loss due to expulsion of water and squeezing together of the cells within the skin into a tight pouch; the presence of any firm gelatinous matter within the colony was not discernible. On increasing suction pressure, the skin eventually ruptured and the cells were sucked out of the hole leaving the empty skin behind. We propose that the skin effectively protects the colony cells from grazing and infection by viruses and other pathogens. The unsuspected presence of a skin is probably the main reason why Phaeocystis colonies have reduced mortality relative to solitary cells and form large blooms in many regions of the world's ocean. Our findings indicate that the colonies should be viewed as 'bags of water' rather than 'balls of jelly'

Section: The Colony Skin As a Grazer Deterrentmentioning

confidence: 71%

Colonies of Phaeocystis globosa are protected by a thin but tough skin

Hamm¹,

Simson²,

Merkel³

et al. 1999

132

“…However, during the Phaeocystis dominated period a bloom of ciliates was present exceeding copepod biomass (R. Bak unpubl.). Protozoa are judged to be high-quality food for zooplankton (see review by Stoecker & Capuzzo 1990), in contrast to Phaeocystis for which a biochemical investigation reports a low nutritional value (Claustre et al 1990). If copepod grazing on Phaeocystis is affected by the availability and quality of alternative food sources, this might explain why most laboratory studies indicate that Phaeocystis, when offered alone or in mixture with other phytoplankton, is appropnate food, whereas field studies indicate grazing to be depressed dunng Phaeocystis blooms (Daro 1986, van Rijswijk et al 1989).…”

Section: Discussionmentioning

confidence: 99%

Grazing pressure of the calanoid copepod Temora longicornis on a Phaeocystis dominated spring bloom in a Dutch tidal inlet

Hansen¹,

Boekel

1991

Between 30 March and 1 1 May 1990, total copepod abundance and the abundance. b~o m a s s and gut fluorescence of Temora longlcornls were determined and related to the abundance and succession of phytoplankton development in a Dutch tidal inlet Gut plgment values were h~g h e s t In females and lowest In young copepodites, but weight-spec~f~c pigment concentrations were about slrnilar Pigment levels measured In the guts were relatively high at the beginning and end of the penod of investigation when diatoms d o m~n a t e d the phytoplankton community, dnd low d u n n g the Phaeocystls d o m~n a t e d period, when ambient chlorophyll concentrations were h~g h e s t For the latter period, calculated ingestion rates In T longlcornls were low and estimated dally consumption amounted to less than 1 % of the phytoplankton standing stock, s u g g e s w g a negl~gible grazlng Impact on the development of the Phaeoc)/stls bloom In splte of the low grazrng on phytoplankton. T long]-corms biomass increased by one older of magnitude The discrepancy between low giazlng pressuie and copepod development is explained by assumlng that T long~cornls scvltched to heterotrophic food a bloom of ciliates present during the Phaeocystls dominated period

“…Sterility imparted to the guts of these animals was demonstrated to be a function of acrylic acid produced by P. pouchetu colonies ). An inhibitory effect of P. pouchetii colonies upon zooplankton predation has also been suggested (Martens 1980, 1981, Daro 1985, Schnack et al 1985, Claustre et al 1990). However, the inhibitory effect of P. pouchetii has recently been called into question by field and laboratory experiments showing active predation by copepods upon colonies and single cells of P. pouchetii (Eilertsen et al 1989, Tande & BAmstedt 1987.…”

Section: Introductionmentioning

confidence: 87%

Predation by copepods upon natural populations of Phaeocystis pouchetii as a function of the physiological state of the prey

Estep¹,

Nejstgaard²,

Skjoldal³

et al. 1990

117

Confl~chng data have been previously presented on the ablllty of copepods to prey upon the prymneslophyte Phaeocystls pouchetu Whde some have suggested that gelatinous colonies of thls species c o n t a n blochemlcal substances that prevent t h e~r consumption others have shown that both slngle cells and colon~es of P pouchetu can serve as an excellent food source The present study presents data from feedlng expenments uslng 4 specles of copepods and natural samples of phytoplankton prey from a south-north transect dunng May 1989 in the Barents Sea Natural phytoplankton contalned P pouchefn colonies m assoclatlon w t h varylng amounts of diatoms Along the transect these colonies vaned from h~g h l y fluorescent and healthy In the north to weakly fluorescent In the south Results of expenments uslng both image analysis and radiotracer techniques indicate that diatoms were actlvely preyed upon In all expenments w t h long-chain-formlng species as the preferred food Predahon upon P pouchefn colon~es was dependent upon the physiological condition of the colonies Healthy colonies were not consumed, while suscephble colon~es were consumed at rates 2 to 10 tlmes those for chain-forrmng dlatoms The selective predalon descnbed here has important impl~cations for specles composition in Archc waters