H E L G O I ~ N D E R MEERESUNTERSUCHUNGEN Helgol/inder Meeresunters. 42, 637-643 (1988)
S o m e c h a n g e s in the flora and v e g e t a t i o n of a l g a e in
freshwater environments*
Ursula Geissler
Institut [fir S y s t e m a t i s c h e B o t a n i k und P f l a n z e n g e o g r a p h i e der Freien Universit~t Berlin; Altensteinstr. 6, D- I O00 Berlin 33
ABSTRACT: Changes in the flora and vegetation of algae are discussed with regard to the following aspects: (1) Changes in the distribution of an individual taxon (new colonizations and extinctions); (2) Changes within one group of algae over some decades [examples: desmids of two nature reserves b e t w e e n 1925 and 1980, and charophytes in the region of Berlin since 1800)or over longer periods of time (for example: analysis of diatom frustules in lake sediments since the glacial periods); (3) Changes in the algal flora within a region (for example: the phytoplankton of a small lake in Berlin in 1909 in connection with the restoration of this lake by R. Kolkwitz as compared with the phytoplankton in 1983, or the attempt to show the development in the algal flora in Berlin (West)by a survey of all data available and by planned investigations). - The interpretation of these data often proves difficult due to the problems regarding nomenclature, taxonomy and determination as well as the discontinuity in research, and the different methods apphed. Finally, the importance of old reports and the need for modern research are emphasized. "Red Lists" of algae point to the urgent necessity of maintaining as many natural ecosystems as l~ossible.
I N T R O D U C T I O N
C h a n g e s in t h e flora a n d v e g e t a t i o n of a l g a e c a n o c c u r c o n t i n u o u s l y a n d v e r y fast, e s p e c i a l l y in m i c r o p h y t e s w i t h t h e i r s h o r t s e q u e n c e s of g e n e r a t i o n . In t h e p r e s e n t p a p e r , n e i t h e r d i u r n a l c h a n g e s will b e d i s c u s s e d (such as p l a n k t o n m i g r a t i o n s or m i g r a t i o n s of i n t e r t i d a l d i a t o m s ) n o r s e a s o n a l c h a n g e s (such as s p r i n g or m i d s u m m e r a s p e c t s of a site) n o r t h e d i f f e r e n c e s in t h e o c c u r r e n c e o f a l g a e in a p a r t i c u l a r h a b i t a t o v e r t w o s u b s e q u e n t y e a r s . I n s t e a d , t h e l o n g - t e r m c h a n g e s will b e d e s c r i b e d h e r e , b o t h t h o s e c a u s e d n a t u r a l l y (such as b y t h e p h a s e s of s u c c e s s i o n of a lake) a n d t h o s e c a u s e d m o s t l y b y m a n . T h i s s t u d y w i l l f o c u s o n c h a n g e s in t h e flora t h a t is in t h e s p e c t r u m of s p e c i e s i n a s p e c i f i c r e g i o n , u n d e r t h r e e d i f f e r e n t a s p e c t s .
C H A N G E S IN T H E D I S T R I B U T I O N O F A S I N G L E T A X O N
C h a n g e s in t h e d i s t r i b u t i o n of a t a x o n , b o t h e x t e n s i o n s a n d r e d u c t i o n s of a r e a s , h a v e b e e n r e c o r d e d in m a n y m a r i n e s p e c i e s (i.a. s e e Boalch, 1987; J o n e s , 1974; L f i n i n g , 1985). U p to n o w , t h e r e is little i n f o r m a t i o n c o n c e r n i n g f r e s h w a t e r s p e c i e s .
638 Ursula G e i s s l e r
T a x a are a b l e to colonize n e w r e g i o n s b y m i g r a t i n g step b y s t e p or t h e y c o n q u e r n e w b i o t o p e s b y o v e r c o m i n g l a r g e distances. F i n d s are a l w a y s p a r t i c u l a r l y s t r i k i n g w h e n t h e y a r e d i s c o v e r e d far a w a y from a n original habita't; e.g. the r e d a l g a Cornpsopogon hookeri
M o n t a g n e in t h e river "Erft" w a r m e d u p b y cooling w a t e r s (a t r i b u t a r y of t h e "Rhine" in t h e w e s t e r n p a r t of G e r m a n y ; Priedrich, 1966), a n d t h e b r o w n a l g a P.ctocarpus confer- voides (Roth) K j e l l m a n in the s a l t - s t r e s s e d river "Werra" (a h e a d s t r e a m of t h e " W e s e r " in the w e s t e r n p a r t of G e r m a n y ; Geissler, 1983). For t h e biologist, two a s p e c t s a r e inter- esting:
- H o w did the s p e c i e s m a n a g e to arrive at the n e w site? - W h a t conditions at the site e n a b l e d its colonization?
Did the s p e c i e s o c c u p y a n ecoIogical niche, t h a t w a s v a c a n t until then, or d i d it r e p l a c e a n o t h e r species?
T h e a b o v e m e n t i o n e d e x t e n s i o n s of areas, h o w e v e r , ar in c o n t r a s t w i t h r e d u c t i o n s of areas, e v e n g o i n g as far as extinction of the species. For instance, t h e b r o w n a l g a
Pleurocladia lacustris A. Braun, a r a r e s p e c i e s f o u n d in e a r l i e r times in e x t e n s i v e w a t e r s of the N o r t h G e r m a n plain, w a s also f o u n d in t h e s u r r o u n d i n g s of Berlin; t h e l a s t proof, h o w e v e r , d a t e s b a c k to 1882. T h e s a m e a p p l i e s to t h e r e d a l g a Thorea ramosissima Bory, living in slowly flowing, oligo- to m e s o t r o p h i c w a t e r s , w h i c h w a s last f o u n d in Berlin in 1949 (Geissler & Gefloff, 1982). K n o w l e d g e on t h e distribution of m a n y m i c r o p h y t e s is p a r t i c u l a r l y s m a l l t h a t one has to a g r e e w i t h W h i t t o n (1974, p. 134): " A l g a e . . . m i g h t w e l l b e c o m e extinct n a t i o n a l l y w i t h o u t a n y a l g o l o g i s t r e a l i z i n g the situation."
C H A N G E S W I T H I N GROUPS O F A L G A E
T h o r o u g h investigations, w h e n a v a i l a b l e , c o v e r i n g l o n g e r p e r i o d s of time, r e v e a l c h a n g e s w i t h i n a g r o u p of a l g a e at a site r e l a t i n g to c h a n g e s in its e n v i r o n m e n t a l conditions. So, for instance, in the a r e a of the " P e c h s e e " a n d t h e " B a r s e e " , two n a t u r e r e s e r v e s in t h e " G r u n e w a l d " in Berlin (West), t h e n u m b e r of d e s m i d t a x a h a s d e c r e a s e d b y one fifth since 1925. H o w e v e r , not only t h e diversity b u t also the s p e c t r u m of the s p e c i e s h a s c h a n g e d d u r i n g this p e r i o d ; lately, t h e r e h a v e b e e n 21 r e o c c u r r e n c e s of finds a n d 41 losses, b u t also 23 n e w finds. As t h e r e h a s b e e n a c h a n g e in t h e s e two a r e a s e s p e c i a l l y in t h e q u a n t i t y a n d the quality of the w a t e r a n d c o n s e q u e n t l y in t h e p l a n t associations, t h e flora of the D e s m i d i a c e a e has c h a n g e d in different w a y s in t h e v a r i o u s m i c r o h a b i t a t s : w h i l e t h e q u a n t i t y of s p e c i e s living on t h e m u d surface h a s i n c r e a s e d slightly, the q u a n t i t y of s p e c i e s living on s p h a g n u m - c u s h i o n s h a s d e c r e a s e d m o r e distinctly. M o r e o v e r , our c o m p a r i s o n s h a v e s h o w n that e s p e c i a l l y the r a r e s p e c i e s h a v e d e c r e a s e d , w h i l e n e w l y found t a x a c a n often b e c h a r a c t e r i z e d as f r e q u e n t a n d as h a v i n g w i d e e c o l o g i c a l t o l e r a n c e s ( W e d d i g e n & Geissler, 1980).
I n v e s t i g a t i o n s c a r r i e d out in S w i t z e r l a n d (Werner, 1977) a n d t h e N e t h e r l a n d s (Coesel et al., 1978) r e v e a l e d similar t e n d e n c i e s ,
C h a n g e s i n flora a n d v e g e t a t i o n of algae 639 that i n t h i s g r o u p of algae the greatest c h a n g e s h a d already t a k e n place before 1910, w h e n the city of Berlin h a d d e v e l o p e d into a metropolis a n d into a centre of industry, i n 1985, a c o m p r e h e n s i v e exploration at more t h a n 100 potential sites in Berhn (P15ter, 1985) r e v e a l e d that i n that y e a r 5 different Chara- a n d
Nitella-species
w e r e p r e s e n t at 13 sites, so that the d i a g r a m could a g a i n b e shghfly altered (Fig. 1). Obviously, at least some taxa of the C h a r o p h y c e a e are more tolerant ecologically t h a n h a d b e e n realized so far. Moreover, several species are able to colonize e v e n strongly a n t h r o p o g e n i c sites (such as gravel pits, d r a i n a g e ditches, artificial ponds).+ 5 Chara vulgari$ L. 7 N i t e l l o p s i s obtusa (Desv. in Louis) J. Gr.
+ 4 Chara hispida L. - 8 N i t e l l a translucens (Pers.) Agh.
+ 3 Chara globularis T h u t l l . 9 N i t e l l a tenuissima (DeSv.) KQtz.
+ 2 N i t e l t a mucronata (A.Br.) Miquel - 10 N i t e t l a capitata (N. v . E.) Agh.
+ I N i t e l l a syncarpa ( T h u i l t . ) Chevat - 11 N i t e t t a opaca Agh.
- 12 Chara acuteolata KEtz.
I Totypella i n t r i c a t a (Trentep. ex Rotb) Leonh. - 13 Chara intermedia A. Br.
2 N i t e ! t a f l e x i t t s (L.)Agh. - 14 Chara deltcatula Agh.
- 3 Chara tomentosa L. - 15 N i t e l l a batrachosperma (Reich.) A. Br.
- 4 Lychnothamnus barbatus (Meyen) Leonh. - 16 Chara aspera Deth. ex Willd.
- 5 Chara braunii Gmelin - 17 Chara contrara A. Br.
- 6 Chara baueri A. Br. - 18 N i t e l t a g r a c i l i s (Smith) Agh.
1 0
0
O u
- l O -
'~ - 2 0
... 9 - : : : - ... = : ' - !i ... ... : ... I
9
$.~1 ~ I ...1
Year
I I I I I I I I I I I " I " I I " I
1 8 1 0 1 8 5 0 1 9 0 0 1 9 3 0 1 9 5 0 1 9 8 0
Fig. 1. Records on Charophyta in Berlin (West) over the past 188 years. Each point represents a record of a particular taxon (y-axis) in a particular year (x-axis). The species recorded have been numbered (see list and y-axis). The disappeared taxa are lined beneath the zero h n e (with a minus
sign) and the taxa still existing above the zero line (with the plus sign)
Investigations over very l o n g periods are of special interest, as they help to charac- terize the d e v e l o p m e n t of waters a n d landscapes. Diatoms (in a d d i t i o n to the r e m a i n s of other organisms) are especially suited as their valvae r e m a i n well m a i n t a i n e d i n the sediment. Thus, w i t h i n a n i n t e r d i s c i p h n a r y project the analysis of the flora of diatoms of late pleistocene a n d h o l o c e n e s e d i m e n t s from the river "Havel" in B e r h n was a contribu- tion to the research of the post-glacial d e v e l o p m e n t of this river system (Bertzen, 1979, 1985).
C H A N G E S IN THE FLORA OF ALGAE WITHIN A REGION
640 Ursula Geissler
b y "rinsing" the lake with g r o u n d w a t e r poor in nutrients. His p u b l i c a t i o n s (Kolkwitz, 1909, 1914) s e e m e d suitable for a comparison with the results of a r e i n v e s t i g a t i o n ( H e c k e l m a n n , 1983). Based on the data p r e s e n t e d u p to n o w i.a. the f o l l o w i n g results were obtained:
(1) essential c h a n g e s i n the chemical p a r a m e t e r s of the lake c a n n o t b e r e c o g n i z e d ; (2) possibly, p h y t o p l a n k t o n diversity has increased: in 1983 more taxa w e r e identified
t h a n h a d b e e n recorded b y Kolkwitz; however, the different m e t h o d s u s e d s h o u l d be c o n s i d e r e d
(3) the s p e c t r u m of the species has c h a n g e d ; i n the two i n v e s t i g a t i o n s t h e r e w e r e only four species i n c o m m o n ;
(4) the proportion of t h e various groups of algae to the whole s p e c t r u m of s p e c i e s h a s also c h a n g e d considerably: w h i l e the taxa of the Chlorophyceae h a v e a l w a y s p r e s e n t e d the largest part, the proportion of species in the C y a n o p h y c e a e a n d in the various groups of flagellates has c h a n g e d significantly;
(5) in late s u m m e r the m e m b e r s of the g e n u s Oscillatoria still d o m i n a t e w h i l e in the w i n t e r p l a n k t o n the species previously d o m i n a n t h a v e n o w b e e n r e p l a c e d b y differ- e n t ones;
(6) n u t r i e n t l o a d i n g is high; t h e d e g r e e of saprobity is still w i t h i n m e s o s a p r o b i c range. For some time now, w e h a v e b e e n trying to compile a survey, as c o m p r e h e n s i v e as possible (Gutowski, 1984; G u t o w s k i & Geissler. 1987) c o n c e r n i n g the data o n atgal finds i n Berlin (West). Principally, this r e g i o n seems to b e well investigated; h o w e v e r , over the decades there h a v e b e e n c o n s i d e r a b l e differences as to the r e s e a r c h (intensity, issues. waters, a n d methods; see "Discussion").
T h e p r e l i m i n a r y results a r e as follows:
(1) In Berlin (West) a total of 875 algal taxa has b e e n r e c o r d e d so far. T h i s exceeds c o m p a r a b l e checkhsts (cf. W h i t t o n ,[1974] for the Isle of Mull) with r e g a r d to the absolute q u a n t i t y of taxa as well as to the n u m b e r of taxa p e r k m 2. This m a y b e the result of a l o n g resea[ch tradition on algae a n d limnology a n d a b r o a d diversity of biotopes i n Berlin.
(2) As in the checklist o n the Isle of Mull the greatest n u m b e r of species in B e r l i n c a n b e found i n the Bacillariophyceae; a p p r o x i m a t e l y 370 species of diatoms r e p r e s e n t a b o u t 42 % of all species; this is followed b y the n u m b e r a n d proportions of s p e c i e s i n the Chlorophyceae, C o n j u g a t o p h y c e a e a n d C y a n o p h y c e a e .
(3) C o m p a r i n g records up to 1930 with those since 1951 w e find, to o u r surprise, i n c r e a s i n g n u m b e r s of taxa i n several classes. This should b e r e e x a m i n e d : it m i g h t b e the result of a n i n c r e a s e i n research rather t h a n in the diversity of algae.
(4) Detailed c o m p a r i s o n s show that in some groups of algae the species n u m b e r s m a y b e a p p r o x i m a t e l y constant, b u t the composition of the species s p e c t r u m h a s c h a n g e d . T h e graphic m e t h o d u s e d here offers good possibihties for t h e i n t e r p r e t a t i o n of these finds over a l o n g e r period of time (cf. the a b o v e discussion on charophytes, a n d Fig. 1). T h e diversity w i t h i n a group of algae, the c o n s t a n t occurrence of species, t h e d i s a p p e a r - a n c e of species, the r e a p p e a r a n c e of species a n d a c h a n g e in the s p e c t r u m of species are depicted.
C h a n g e s in flora a n d v e g e t a t i o n of a l g a e 641
D I S C U S S I O N
Primarily, t h e b a s i s of s u c h c o m p a r a t i v e s t u d i e s o n t h e flora of a l g a e is f o r m e d b y all facts p u b l i s h e d . M o r e o v e r , h e r b a r i u m m a t e r i a l , slides, c o n s e r v e d m a t e r i a l as w e l l as c o r e s f r o m w a t e r s e d i m e n t s m a y b e a n a l y s e d . H o w e v e r , it o f t e n t u r n e d o u t t h a t d a t a a n d m a t e r i a l w e r e n o t a v a i l a b l e in s u f f i c i e n t q u a n t i t i e s or c o u l d o n l y b e u s e d w i t h r e s t r i c t i o n s . D i f f i c u 1 t i e s i n c o m p a r i n g : T h e c o m p a r i s o n of r e c o r d s o n a l g a l t a x a f r o m d i f f e r e n t p e r i o d s o f t e n m e e t s w i t h g r e a t difficulties. T h e n o m e n c 1 a t u r e is a n i m p o r t a n t a s p e c t h e r e : a lot of s y n o n y m s h a v e to b e e h m i n a t e d first, a n d it c a n n o t a l w a y s b e a s c e r t a i n e d b e y o n d d o u b t w h i c h t a x o n t h e r e s p e c t i v e s c i e n t i s t d i d o b s e r v e . T h e r e a s o n for this m a y also lie in t h e t a x o n o m y , for o f t e n t h e u n d e r s t a n d i n g of a s p e c i e s h a s c h a n g e d o v e r t h e last d e c a d e s , s o m e t i m e s e v e n s e v e r a l times. In s o m e g r o u p s of a l g a e , p r o b l e m s of i d e n t i f i c a t i o n p l a y a part: t h e fact t h a t t h e r e a r e n o or f e w r e c o r d s m a y j u s t m e a n t h a t t h e t a x a c a n n o t b e i d e n t i f i e d easily. T h i s m i g h t b e t h e r e a s o n for t h e c u r r e n t s p a r s e n u m b e r of r e c o r d s of b l u e a l g a e in t h e r i v e r s a n d l a k e s of Berlin. T h u s , o u r d i a g r a m s s o m e t i m e s s h o w a d i s t i n c t a c c u m u l a t i o n of p o i n t s in t h e p e r i o d a f t e r a n e w flora h a d b e e n p u b l i s h e d (i.e. in t h e X a n t h o p h y c e a e a f t e r Ettl, 1978). In a d d i t i o n , t h e d i s c o n t i n u i t y o f r e s e a r c h m u s t b e i n c l u d e d in t h e i n t e r p r e t a t i o n of t h e d a t a : o v e r t h e y e a r s n o t o n l y t h e p r o b l e m s (i.e. o c c u r r e n c e of d e s m i d s , of i n d i c a t o r s of t h e s a p r o b i c s y s t e m , i n v e s t i g a t i o n of d i f f e r e n t b i o c o e n o s e s s u c h as p l a n k t o n or p e r i p h y t o n ) h a v e c h a n g e d , b u t also t h e w a t e r s i n v e s t i g a t e d , e v e n in s u c h as r e l a t i v e l y s m a l l r e g i o n as t h e w e s t e r n p a r t of Berlin. F u r t h e r m o r e , in o u r city t h e p r o b l e m s i n v o l v e d h a v e b e e n d e a l t w i t h s o m e t i m e s b y a lot of scientists a n d s o m e t i m e s o n l y b y a f e w , all of t h e s e p u r s u i n g v a r y i n g i n t e r e s t s a n d p o s s e s s i n g d i v e r g i n g a r e a s of k n o w l e d g e . T h u s , it is q u i t e o b v i o u s t h a t a d i s t i n c t p e a k in o u r d i a t o m d i a g r a m c a n n o t b e a t t r i b u t e d to t h e f a c t t h a t t h e s e a l g a e h a v e s u d d e n l y i m m i g r a t e d to a l a r g e r e x t e n t into o u r r i v e r s a n d l a k e s b u t to t h e fact t h a t s i n c e t h e m i d - f i f t i e s m o r e b o t a n i s t s ( i n c l u d i n g t h e m e m b e r s of m y s c i e n t i f i c t e a m ) h a v e b e e n d o i n g r e s e a r c h into this field. H o w e v e r , t h e m e t h o d s of t h e s e s c i e n t i s t s differ g r e a t l y , e.g. w i t h r e g a r d to t h e t y p e s of s a m p l i n g , t i m e a n d f r e q u e n c y of s a m p l i n g , e v a l u a t i o n of t h e s a m p l e s , c o n s e r v a t i o n state of t h e s a m p l e s . T h i s affects e s p e c i a l l y t h e e v a l u a t i o n of t h e c h a n g e s in t h e a l g a l v e g e t a t i o n .
T h e a b o v e list s h o w s t h a t t h e p o s s i b i l i t i e s of c o m p a r i s o n s a r e r a t h e r r e s t r i c t e d . T h e c a u s e s of t h e i d e n t i f i e d c h a n g e s in t h e a l g a l flora c a n b e s u m m a r i z e d as follows:
(1) loss of b i o t o p e s , esp. of v e r y s m a l l w a t e r s ; (2) e s t a b l i s h m e n t of n e w , m a n - m a d e b i o t o p e s ; (3) c h a n g e s in t h e b i o t o p e s , e.g. b y e m b a n k m e n t s ;
(4) c h a n g e s in t h e w a t e r r e g i m e , e.g. l o w e r i n g of t h e g r o u n d w a t e r l e v e l , c h a n g e s in t h e f l o w v e l o c i t y ;
(5) c h a n g e s in w a t e r quality, e.g. e u t r o p h i c a t i o n , a c i d i f i c a t i o n .
642 Ursula Geissler
it with its p r e v i o u s conditions or special r e s e a r c h into a p a r t i c u l a r g r o u p of a l g a e (see C h a r o p h y c e a e ) should b e c a r r i e d out. Thus, our survey of the d a t a on C h r y s o p h y c e a e c o l l e c t e d so far can b e i n t e r p r e t e d as s h o w i n g that t h e r e has lately b e e n a n e n o r m o u s r e d u c t i o n of this flora in Berhn. This s t a t e m e n t does not s e e m to b e s u b s t a n t i a t e d , for e c o l o g i c a l reasons. In t h e m e a n t i m e , a p l a n n e d s e a r c h e s p e c i a l l y for r e p r e s e n t a t i v e s of the C h r y s o m o n a d a l e s has b r o u g h t forth a c o n s i d e r a b l e n u m b e r of n e w t a x a (for Berlin) a n d their sites (Gutowski, 1984 a n d 1987}. If, d u e to the l a c k of records f r o m p r e v i o u s times, it is n o t possible to m a k e comparisons; w e should t o d a y lay t h e f o u n d a t i o n for future r e s e a r c h .
T h e s e i n v e s t i g a t i o n s i n d i c a t e the e n d a n g e r m e n t or e v e n t h e extinction of species. In contrast to o t h e r groups of organisms, t h e r e are hardly a n y "R e d L i s t s" of algae. Krause (1984) p r e p a r e d a s u r v e y of the C h a r o p h y t a , a c c o r d i n g to w h i c h 28 of t h e 34 taxa f o u n d in G e r m a n y (that is 82 %) are h s t e d as b e i n g e n d a n g e r e d in d i f f e r e n t d e g r e e s . A further "Red List" is a i m e d at the r e d a n d b r o w n a l g a e in f r e s h w a t e r e n v i r o n m e n t s in G e r m a n y (Friedrich et al., 1984), the f o r m e r a n d p r e s e n t distribution of w h i c h is htfle k n o w n to us. It is e s p e c i a l l y striking that t h e r e are hardly any reports on t h e e x p a n s i o n of a k n o w n v e g e t a t i o n or of n e w colonizations (Friedrich et al., 1985). P r o b a b l y , all four species of t h e P h a e o p h y t a in f r e s h w a t e r e n v i r o n m e n t s are t h r e a t e n e d by e h m i n a t i o n , n e a r l y all 28 s p e c i e s of the R h o d o p h y t a are p r e s u m a b l y h i g h l y t h r e a t e n e d .
A d i s a p p e a r a n c e of o r g a n i s m s from the e a r t h - w h i c h w o u l d m e a n a loss of i r r e c o v e r a b l e g e n e t i c m a t e r i a l a n d an i m p o v e r i s h m e n t of c o m p l e x e c o s y s t e m s - should b e c o n s i d e r e d as serious a n d as a l a r m i n g in v i e w of the h i g h a n d r a p i d l y i n c r e a s i n g q u a n t i t i e s of extinct taxa. " R e d Lists" can only d r a w our a t t e n t i o n to the v a r i o u s dangers. As, in contrast to s o m e o t h e r groups of organisms, a p r o t e c t i o n of a l g a l s p e c i e s is impossible, only a c o m p r e h e n s i v e a n d w o r l d - w i d e p r o t e c t i o n o f e c o s y s t e m s c a n slow d o w n this a l a r m i n g developn~ent. M o r e o v e r , w e h a v e to insist t h a t o u r h a b i t a t b e m a i n t a i n e d as a w h o l e a n d as natural as possible.
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