Light-absorbing capacity of phytoplankton in the Gulf of Gdańsk in May, 1987

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Light-absorbing capacity of phytoplankton in the Gulf of Gdańsk in May, 1987 O C E A N O L O G IA, 28, 1990 P L ISSN 0078-3234 P h y to p lan k to n C hlorophyll L ight-absorbing capacity Pigm ent

1 Light-absorbing capacity of phytoplankton in the Gulf of Gdańsk in May, 1987 O C E A N O L O G IA, 28, 1990 P L ISSN P h y to p lan k to n C hlorophyll L ight-absorbing capacity Pigm ent index B. V. K o n o v a l o v, G. A. B e l y a y e v a P. P. Shirshov Institute of O ceanology, A cadem y of Sciences of the USSR, M oscow O. D. B e k a s o v a A. N. Bach Institute of Biochem istry, Academ y of Sciences of the USSR, M oscow A. K o s a k o w s k a Institute of O ceanology, Polish A cadem y of Sciences, Sopot M anuscript received June 24, 1988, in final form July 25, Abstract In o rd er to estim ate the efficiency of m arine p h y to p lankto n photosynthesis by a direct m ethod, a n atu ral variability of p h y to p lankto n characteristics reflecting its light abso rp tio n capacity was studied. Thus, the absolute and specific p h y to p lankto n spectral abso rp tio n coefficients and their m ean values for the PA R range, as well as the pigm ent index / 441/675 were studied. Light abso rp tio n was m easured on n a tu ra l m arine p h y to p lankto n from the G u lf o f G dansk. T w o hundred an d thirty sam ples draw n Irom ten depths betw een 0 and 30 m every six hours during several days were analyzed. T he absolute values of the a b so rp tio n coefficient were observed to vary by a factor of alm ost 15 from m " 1 to 0.85 m - 1 (at 441 nm ) and from m _1 to 0.55 m _1 (at 675 nm). P h y to p lan k to n a b so rp tio n coefficients, norm alized by the chlorophyll concentration, were equal to m 2 (mg C hi a )- 1 a t 675 nm and m 2 (mg C hi a ) 1 at 441 nm. At 675 nm the value o f the abso rp tio n coefficient exceeded its m ean value w ithin the PA R range tim es on average. A negative linear correlation was found betw een the specific abso rp tio n coefficients at 675 nm and the C hi a concentration, the slope of the regression line increasing with depth. T he pigm ent index / 44i /675 varied from 1.29 to T he value of / 441/675 averaged for each depth increased steadily with depth, starting from 5 m. 1. Introduction In the studies of ecology of m arine p h y toplankton photosynthesis it is necessary to estim ate the ability of algae to absorb solar energy, ie their light absorption capacity (LAC). Using LAC d ata and the results of optical m easure-

2 m ents of the underw ater radiation, the am o u n t of energy absorbed by algae under n atu ral conditions m ay be calculated. The results of such calculations can be utilized for the determ ination of the balance of energy of solar radiation reaching the w ater deep. They also allow to establish the real energy efficiency and quan tu m yield of the prim ary production process in the sea (K oblentz-m ishke et al, 1985). Light absorption capacity of p h y toplankton is also very im portant in the determ ination of phyto p lan k to n content and production by m eans of m ethods of passive rem ote sensing (on the basis of d ata on a colour of the sea), since light absorption by algae pigm ents significantly influences the spectrum of radiation ascending from the sea (Yentsch, 1960; P rieur, S ath y en d ran ath, 1981). In o rder to estim ate the light absorption capacity of phytoplankton, the follow ing absolute a n d specific characteristics are used: (i) spectral absorption coefficient (ak) within a range of photosynthetically active ra d ia tio n (PAR), ie nm. W ithin this spectral range, the w avelengths aro u n d 440 nm and 675 nm are the m ost inform ative, since at these wavelengths a m axim um absorption of phytoplankton pigm ents occurs in vivo. T he values of absorption at spectral m axim a of pigm ents are used prim arily for the determ ination of pigm ent content of seaw ater by m ethods which do not com prise pigm ent extraction, rem ote m ethods included; (ii) the average absorption coefficient in the PA R region (âà), characterizing a m ean level of the potential capacity of p h y toplankton to absorb light; (iii) the sam e characteristics as in items 1 and 2, norm alized with respect to the chlorophyll concentration (Ba) (M orel and Prieur, 1977). U sing this characteristics, the ratio of the to tal pigm ent content to a content of chlorophyll a m ay be determ ined. This index is less suitable th an I /for the estim ation of biochem ical com position and species diversity of p h y to p lan k ton due to low er accuracy of its determ ination. F o r this reason, / 441/675 is determ ined m ainly for approxim ate description of the shape of phytoplankton absorption curve and for an evaluation of the possibility of determ ination of the content of C hi a on the basis of total absorption w ithin the blue spectral range. A nother relative param eter, viz a*(675)/(ô)* = a(675)/a, allows to calculate a m ean value of absorption coefficients within the PAR range on the basis of absorption curve and for an evaluation of the possibility of determ ination of the the accuracy o f a calculation of a m ay be estim ated by the value of a (675). A m ong recent papers on phytoplankton light absorption ability and other absorption properties, the following papers should be m entioned: M orel, Bricaud, 1986;M aske, H aard t, 1987;K ishino etal, 1984; S athyendranath etal, They contain the results of experim ental m easurem ents perform ed both on cultures and on n atu ral phytoplankton, as well as literature reviews. 2. Materials and Methods Tw o hundred and thirty sam ples draw n at two stations in the G ulf of G dańsk in the beginning of M ay, 1987, from depths of 0, 1, 2, 3, 5, 7, 10, 15, 20, and 30 m were used in the experim ents. At station G -2 (open p art of the Gulf), sam ples were

draw n every 6 hours since m idnight of M ay 1 till m idnight of M ay 4. At station Z in the internal p art of the G ulf sam ples were draw n also every 6 hours since 6 pm M ay 4, till m idnight.

3 draw n every 6 hours since m idnight of M ay 1 till m idnight of M ay 4. At station Z in the internal p art of the G ulf sam ples were draw n also every 6 hours since 6 pm M ay 4, till m idnight. M ay 7. Samples of were filtered through W hatm an glass-fiber filters (G F/F), 47 mm in diam eter. Each filter was cut into tw o unequal parts. T hree quarters of a filter were used for the determ ination of a Chi a content by an extraction m ethod. O ne fourth of a filter was directly used for recording the spectrum of optical density and subsequent calculation of light ab so rp tio n coefficients. The chlorophyll concentration was m easured by a standard extraction m ethod (SC O R -U N E SC O, 1966; E dler L. (ed.), 1979). M easurem ents of absorption spectra of the extracts were carried o ut using a S P E C O R D UV/V IS spectrophotom eter (K arl Zeiss JEN A, GDR). O ptical density spectra of seston, ie p h y toplankton together with the rem aining suspended m atter deposited on a filter, were recorded using an SP-18 double-beam spectrophotom eter (L O M O, USSR). A wet filter was placed on a glass holder in the centre of a light integrating sphere of the spectrophotom eter. A wet filter w ithout seston was used as a blank. A bsorption spectra were recorded before and after decolorization of p h y to p lan k ton pigm ents, carried o ut by m eans of UV irradiation in the presence of H O ptical density spectra of seston deposited on a filter do not coincide w ith the absorption spectra of phyto p lan k to n in situ. In order to determ ine a real shape of the latter, it is necessary first of all to substract the spectrum of decolorized seston. T hen it is im p o rtan t to take into consideration the effect of reflection of light from a filter and broadening of a light beam due to scattering by seston particles and filter m aterial a t various w avelengths an d various optical densities. T he follow ing form ulas were used for calculations: a(k) = 2.3 D(tylkf, (1) where: a {k)~ the spectral absorption coefficient (natural logarithm ) [m _1], D{X) the spectral optical density (com m on logarithm ), 2.3 a coefficient of conversion of com m on logarithm into natural one, kf a correction factor, I the length of the recovered light beam pathw ay w ithout a correction for light scattering (X). l=k/sf, (la) where Vs is a volum e of w ater sam ple; Sf is the filtration surface of a filter. In o u r experim ents I varied from 1.4 to 3.1 m. 700 d = 3^0 a ^ d /l W where a [m *] is an absorption coefficient averaged over the PA R spectral range. a*(k) = a(x)/ba, (3) where a*(a) is the specific spectral absorption coefficient [m 2 m g _1], Ba is the Chi a concentration [m g m -3 ].

(a)* = a/b a, (4) where (â)* (com m only denoted as K c) is a specific absorption averaged over the PA R range [m 2 m g -1 ]. ^ 441/675 = a(441)/fl(675), (5) where / 4 4i /675 is the pigm ent index.

4 (a)* = a/b a, (4) where (â)* (com m only denoted as K c) is a specific absorption averaged over the PA R range [m 2 m g -1 ]. ^ 441/675 = a(441)/fl(675), (5) where / 4 4i /675 is the pigm ent index. 3. Results and discussion T aking into account high values of the chlorophyll concentration (m ore than 20 m g m ~ 3 at st. G -2 and alm ost 30 m g m - 3 at st. Z) it can be assum ed th at our investigations were carried out in the eutrophic region of the Baltic Sea. The corresponding values of optical properties of phytoplankton presented in Table 1 are also relatively large, which confirm s the assum ption. Table 1 presents the values of absorption coefficients of p h y toplankton allowing an evaluation of their variability depending on the tim e of a day and the depth of sam pling, viz at the surface (0 m), at the depth of occurrence of a m axim um at a vertical profile of the absorption coefficient and at 30 m, ie ju st below the lower limit of euphotic layer. It follows from Table 1 th at the value of an absorption coefficient a(441) in the band of m ost intensive absorption of phytoplankton with a m axim um at 441 nm reached 0.85 m _ 1 (station Z, 5th M ay, h, 3 m of depth). T he m axim um values of a (441) observed at stations Z and G-2 ranged from 0.49 to 0.85 m - 1 (0 7 m) and from 0.29 to 0.46 m - 1 (0 10 m), respectively. A vertical distribution of the value of a(441) corresponded to the distribution of chlorophyll, reflecting th at of p h y toplankton biom ass. T he largest values of a (441) were recorded in the layer of 5 10 m. In the m layer, the value of a(441) considerably decreased (Fig.l). At station Z, which appeared to be richer in p h y toplankton th an th at at station G-2, the m axim um values of a(441) occurred closer to the surface and a decrease of a(441) at the depth of m was m ore pronou nced. Figure 2 illustrates the changes of a(441) with time. At station G-2, a certain regularity of these fluctuations has been noticed. The m inim um values of this characteristics were observed at 6 pm, while the m axim um values were observed over the time interval from 6 am till noon. O bservations at station Z revealed a different tim e distribution of a (441) in time. T he changes of a (441) were not cyclic. M oreover, the m axim um values of a(441) were observed at 6 pm, ie at the sam e tim e when they were m inim um at station G-2. It follows from Table 1 and Figure 1 and 2 th at the changes of a at 441 nm and at other characteristic w avelengths, ie at the chlorophyll red m axim um (675 nm) and at a m inim um of phyto p lan k to n absorption (605 nm), as well as changes of a, were synchronous, although less pronounced.

6 Pigment index a*l 675 Hm2 (mg Chi W 1] Absorption coefficient Im

7 I m Fig. 1. Depth profiles: A station G-2, 0 h, May 3; B station Z, 18 h, May 6 1 chlorophyll a, Ba, [mg m -3 ]; 2 pigment index / 441/675; 3 specific absorption coefficients a*(675), [m 2 (mg Chi a ) ']; 4 mean specific absorption coefficient (â)* [m 2 (mg Chi a )-1 ]; 5, 6 spectral absorption coefficients a(441) and «(675), [ m ^ 1]

5.05 6.05 Day Fig. 2. D aily variability of abso rp tio n coefficients a(x) and à in surface layer at statio n G -2 (A) and statio n Z (B) 1 a(441), 2 a(605), 3 -a (6 7 5 ), 4 - a 3.

8 Day Fig. 2. D aily variability of abso rp tio n coefficients a(x) and à in surface layer at statio n G -2 (A) and statio n Z (B) 1 a(441), 2 a(605), 3 -a (6 7 5 ), 4 - a 3.1 Specific values a*(k) and (a)*. O f all the spectral values of only a*(675) directly reflects the specific absorption of Chi a. At other vaw elengths a*(/.) depends on the relative content and light absorption properties of o ther pigm ents contained in phytoplankton. F o r this reaso n only the variability of a*(675) is considered here in detail. Changes in a*(675) depend neither on time, nor on depth. Figure 3 presents the m ean vertical distributions of a*(675) for both stations. A m ean value for the 0 20 m layer is equal to m 2 (mg Chi a )_ 1. At a depth of 30 m, the m ean value is slightly low er (0.014 at st. Z), which is apparently due to the fact th at this depth is situated below the euphotic layer. M axim um values of a*(675) were found at various depths of the euphotic layer, yet m ost often close to the surface. The range of a*(675) variability was rath er wide from 0.01 to m 2 (mg Chi a )- 1, except one determ ination at 30 m, where a*(675) was equal to T he occurrence of a negative linear co rrelatio n betw een a*{675) and the

0*1675) [ m2 l mg C h lv )-1] 0 0.01 0,02 0.03 Fig. 3.

9 0*1675) [ m2 l mg C h lv )-1] , Fig. 3. D epth profiles of specific absorption coefficient a*(675) averaged over the entire period studied chlorophyll concentration has been established. T he slope of the regression line decreased gradually w ith depth. As an example, Figure 4 presents the dependence of a*(675) on the chlorophyll a content for two layers: 0 5 m and m, the regression lines being described by the follow ing equ ation s: a*(675) = B a, a*(675) = B a. The course of the rem aining regression lines m ay be determ ined on the basis of separate sets of d ata for particular depths. The specific absorption coefficient at 441 nm varied over the range of m 2 (mg C hi a ) ~ 1 in the 0 20 m layer. At a depth of 30 m it varied over the range of , the m ean value being m 2 (mg Chi a ) - ^T his param eter also did not exhibit any regular dependence on the time of a day and depth. However, a specific feature m ay be observed for vertical distributions of a*(441) and a*(675), viz in the 0 2 m and 30 m layers their values were lower th an at the rem aining depths. 3 Oceanologia

10 c o Q. O MM 700 g o ^ s o1 «. s ' I _ O.C 0 O O.. 8 J3 g 1 o a) rn a, u * Q.c,gf E <

T he m ean specific absorption coefficient (a)* revealed sim ilar properties as a*(675) and a*(441). Its value ranged from 0.007 to 0.028 m 2 (mg Chi a )-1, the m ean being equal to 0.

11 T he m ean specific absorption coefficient (a)* revealed sim ilar properties as a*(675) and a*(441). Its value ranged from to m 2 (mg Chi a )-1, the m ean being equal to m 2 (mg Chi a ) - 1 a d varying from to m 2 (mg Chi a ) - 1 at various depths. T he variations range of K c reported herein is shifted to larger values com pared to d ata of Atlas and B annister (1980), who reported the values of to m 2 (mg Chi a ) -1. Sim ilarly to the case of a*(675), the value of (a)* revealed a negative correlation with Ba, viz for the 0 7 m layer: a* = Ba (station Z), a* = Ba (station G-2), and for the m layer (both stations): d* = B a. T he slope of the regression line for a* with chlorophyll a concentration increased with depth sim ilarly to the cases of the characteristics considered above. 3.2 Relative values T he values of the pigm ent index varied within a considerably narrow er range: from 1.29 to 2.04 (a m ean for 230 sam ples was equal to 1.6). V ariations of the pigm ent index seemed random in a case of individual experim ental d ata sets. However, if m ean values at certain depths are taken into account for the two stations, certain regularities of their distribution can be established. A difference between the m ean values of / 441/675 determ ined at the tw o stations is evident (within the 0 20 m layer at st. G -2 / 441/675 = , while at st. Z / 441/675 = ). M oreover, the value of this characteristic was practically constant for all the sam ples from the 0 5 m layer. At greater depths a small, yet steady increase of 1441/675 up to 1.7 was observed. This increase of the value of the pigm ent index with depth has been confirm ed by the d ata on pigm ent index of the extracted pigm ents. The a(675)/a ratio has been the last of the characteristics considered in the research. F ro m a dispersion of the results presented in Figure 5, the value of a m ay be calculated using the d ata on a(675) with an erro r sm aller than 15%, assum ing th at the value of the a(675)/a ratio is equal to 1.2. The accuracy of the calculation can be higher provided the dependence of the m ean value of a(615)/a on a is taken in to consideration. a(615)/d = 2.84a (for a < 0.12), a(675)/a = 0.54a (for a > 0.12). A relatively constant value of the a(675)/a ratio indicates th at the vertical profiles of a*(675) and their dependence on Ba correspond to the dependence of a* or K c, which is illustrated in Figures 3 and 4.

12 Fig. 5. Dependence of the ratio a*((,15)/(a)* on the mean absorption coefficient à

4. Conclusions Vertical distributions of the absorption characteristics at all wavelengths were identical and corresponded to the distribution of phytoplankton in the euphotic layer at the research

13 4. Conclusions Vertical distributions of the absorption characteristics at all wavelengths were identical and corresponded to the distribution of phytoplankton in the euphotic layer at the research stations. Insignificant changes of the absorption characteristics in the 0 5 m layer indicate a hom ogeneity of this layer. The absence of any regular dependence of the vertical distribution of a(x) on the time of a day implies a certain instability of hydrophysical conditions in the regions where the stations were located. This instability has also been confirm ed by fluorim etric d ata (K arabashev et al, 1990). The fact th at the specific absorption coefficients a*(a) did not depend on depth indicate th at their regular variations due to light ad aptatio n of phytoplankton or o th er reasons were m asked by variations due to hydrological instability. An insignificant variability of the pigm ent index and identical changes of a(ż>.) at various wavelengths seem to indicate th at both the taxonom etric content and general physiological state of p h y toplankton were alm ost stable during our investigations. In o ther w ords, factors determ ining the shape of absorption spectra of p h y toplankton did not exhibit significant variations. References A tl a s D., B a n n i s t e r T. T., 1980, Dependence o f mean spectral coefficient o f phytoplankton on depth, water colour and species, Lim nol. O ceanogr., 25, E d le r L. (Ed.), 1979, Recommendation on methods in marine biological studies in the Baltic Sen. P hvtoplankton and chlorophyll. T he Baltic M arine Biologists (W orking G ro u p no. 9), N K a r a b a s h e v G. S., K h a n y c v S. A., P c t r o s o v A. V., 1990, Variability ojjluorescence o f dissolved and suspended substances o f biological origin in the Gdańsk Basin during the International Ecological Experiment '"Sopot' 87, O ceanologia, 28, 61. K i s h i n o M., O k a m i N., T a k a h a s h i M., 1 c h i m u r a S., 1986, Light utilization efficiency and quantum yield o f phvtoplankton in a thermally stratified sea, Lim nol. O ceanogr., 31, K o b l e n t z - M i s h k e O. J., K o n o v a l v B. V., W o ź n i a k B., B o g u c k i D., 1985, Effektivnost ispolzovaniya solnechnoy energii v protsesse fotosinteza chernomorskogo i baltiyskogo Jitoplanktona, IO A N SSSR, M oscow. K o n o v a l o v B. V., B e ly a y e v a G. A., S e r g e y e v a O. M., 1985, Svetopoglitelnaya sposobnost pigm entovku ltu rdiatom ovykhperidiniyevykh izelenykh vodoroslyey. [In :] U svoyeniyesolnechnoy energii r protsesse fotosinteza chernomorskogo i baltiyskogofitoplanktona. IO A N SSSR, M oscow. M a r g a l e f R., 1960, Valeur indicatrice de la composition taxonom ique et propriétés dynamique des populations, Rupp. et Proc.-Verb., Cons. Perm. Int. Explor. Mer., v. 15, M a s k e H., H a a r d t H., 1987, Quantitative in vivo absorption spectra o f phytoplankton: Detrital absorption and comparison with fluorescence excitation spectra, Lim nol. O ceanogr., 32, 3, M o r e 1A., P r i e u r L., 1977, Analysis o f variations in ocean colour, Lim nol. O ceanogr., 22, M o r e l A., B r i c a u d A., 1986, Inherent optical properties o f algae cells including picoplankton: theoretical and experim ental results, P h o tosynthetic picoplankton, C an. Bull. Fish. A quat. Sci., 214, P r i e u r L., S a t h y e n d r a n a t h S., 1981, A n optical classification o f coastal and oceanic waters based on specific spectral absorption curves o f phytoplankton pigments, dissolved organic m atter and other particulate materials, Lim nol. O ceanogr., 26, 4, S a t h y e n d r a n a t h S., L a z z a r a L., P r i e u r L., 1987, Variation in the spectral values o f specific absorption o f phytoplankton, Lim nol. O ceanogr., 32, 2, S C O R -U N E S C O, 1966, Determination o f photosynthetic pigments in sea water, M onographs on oceanography m ethodology, Paris, no. 1, 69. Y e n ts c h C. S The influence o f phytoplankton pigments on l lie colour o f sea water, D eep-sea Res., 7, 1-9.

The effect of pollutants of crude oil origin on the diffusive reflectance of the ocean*

The effect of pollutants of crude oil origin on the diffusive reflectance of the ocean* O C E A N O L O G IA, 23, 1986 PL ISSN 0078-3234 R adiance Oil pollution Diffusive reflectance K r z y s z t o f