Seasonal, annual, and spatial variation in the development of hard ...

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In 1981 they recovered, and settlement increased again, but the cold winter ... variation, of seasonal epibenthic community development, and it is a preliminary.
HELGOI_flL'NDER MEERESUNTERSUCHUNGEN Helgolfinder Meeresunters. 36, 137-150 (1983)

Seasonal, annual, and spatial variation in the development

of h a r d b o t t o m c o m m u n i t i e s *

J. Harms I & K. Anger 2 I Zoologisches Institut," Technische Hochschule Darmstadt; Schnittspahnstr. 10, D-6100 Darmstadt 2 Biologische Anstalt Helgoland (Meeresstation); D-2192 Helgoland, Federal Republic of G e r m a n y

ABSTRACT: The development of hard bottom comnlunities has b e e n studied on test panels in Helgoland Harbour (German Bight) since 1977. Settlement and growth of epibenthic species was e x a m i n e d monthly. Natural variation in different seasons, years, and at three stations (the latter, only in 1981 and 1982) was investigated. At Station A (Binnenhafen), barnacles (Balanus crenatus) and polychaetes (Polydora cillata) were always among the first settlers in spring. They were followed by other barnacles (Elminlus modestus, Balanus improvisus] and by colonial ascidians (Botryllus schlosseri). The latter species often dominated from August to October, and t e n d e d to overgrow the barnacle populations. E. modestus showed strong annual variation, probably due to extremely low winter temperatures: after the cold winter of 1978/79, its populations were less d e n s e than in previous years. In 1981 they recovered, and settlement increased again, but the cold winter 1981/82 d a m a g e d the population again. At Station B (Nordosthafen), mussels (Mytllus edulls) soon covered barnacles and empty space. By October they had monopolized the fouling community. At Station C (Siidhafen}, barnacle settlement in spring was followed by an overgrowth of hydrozoans (Laomedea spec.). In summer, ascidians (Clona lntestinalls and Ascldlella aspersa) settled and b e g a n to dominate. Barnacles w e r e w e a k e r in the competition for space as opposed to later colonizers at all three stations.

INTRODUCTION T h e c o l o n i z a t i o n of a r t i f i c i a l h a r d s u b s t r a t u m h a s b e e n s t u d i e d o n t h e i s l a n d of H e l g o l a n d ( G e r m a n B i g h t , N o r t h Sea) s i n c e 1977. A p r e l i m i n a r y r e p o r t w a s g i v e n b y A n g e r (1978), w h o a l s o r e v i e w e d r e l e v a n t l i t e r a t u r e . T h e m a i n p u r p o s e of t h i s l o n g - t e r m i n v e s t i g a t i o n h a s b e e n to a n a l y z e r e c u r r e n t p a t t e r n s i n c o m m u n i t y d e v e l o p m e n t d u r i n g t h e s e a s o n a l c o u r s e of e p i b e n t h i c c o l o n i z a t i o n . T h e c o n s e q u e n c e s to c o m m u n i t y s t r u c t u r e of a n n u a l v a r i a t i o n i n r e c r u i t m e n t s u c c e s s of p o t e n t i a l l y d o m i n a t i n g s p e c i e s a r e o n e of t h e m o s t i n t e r e s t i n g a s p e c t s of t h i s s t u d y , s i n c e t h e y m a y s h e d l i g h t o n t h e e f f e c t i v e n e s s of i n t e r s p e c i f i c i n t e r a c t i o n s s u c h as c o m p e t i t i o n for s p a c e s h a p i n g e p i b e n t h i c a s s e m b l a g e s . * Dedicated to the memory of Dr. J. A. Petersen (Sho Paulo, Brazil), who died on 11 February, 1983 in an accident during his work on hard bottom communities. © Biologische Anstalt Helgoland

138

J. H a r m s & K. A n g e r

Since 1981, the study h a s b e e n e x t e n d e d to three stations located i n different h a r b o u r s of the island. Thus, spatial v a r i a t i o n is also considered. This m a y c o n t r i b u t e towards further k n o w l e d g e of the competitive interactions a n d other factors i n f l u e n c i n g the direction of c o m m u n i t y d e v e l o p m e n t . T h e p r e s e n t p a p e r is a n i n t e r m e d i a t e report on recurrent p a t t e r n s a n d a n n u a l variation, of seasonal e p i b e n t h i c c o m m u n i t y d e v e l o p m e n t , a n d it is a p r e l i m i n a r y a c c o u n t of spatial v a r i a t i o n i n these particular hard bottom c o m m u n i t i e s .

MATERIAL AND METHODS W o o d e n frames with 12 test p a n e l s (100 cm 2 plexiglas) were s u s p e n d e d from rafts, so that they floated i n a vertical position, ca 1 to 1.5 m b e l o w the water surface. The schedule for s u s p e n d i n g a n d s a m p l i n g the p a n e l s was described i n detail b y A n g e r (1978). Every m o n t h two p a n e l s were r e m o v e d a n d the f o u l i n g c o m m u n i t i e s were e x a m i n e d u n d e r a stereo microscope: one after b e i n g exposed for one m o n t h only, a n o t h e r one after b e i n g s u b m e r g e d since the b e g i n n i n g of the e x p e r i m e n t ("Series A" panels). At Station A (Binnenhafen), e x p e r i m e n t s were c o n d u c t e d d u r i n g the periods May 10, 1977 to May 11, 1978 (see Anger, 1978); May 17, 1978 to October 16, 1978; M a y 16, 1979 to October 13, 1979; J a n u a r y 15, 1980 to N o v e m b e r 15, 1980; March 9, 1981 to April 6, 1982, a n d from April 6, 1982. At Stations B (Nordosthafen) a n d C (Siidhafen), colonization of the test p a n e l s has b e e n s t u d i e d since 1981 with the same i n v e s t i g a t i o n periods as above, i n order to record spatial variation. The density of i n d i v i d u a l s or colonies on o n e - m o n t h p a n e l s will b e t e r m e d " p r i m a r y

N

~o metres

Fig. 1. The investigation area: Island of Helgoland (left; with Stations A, B, and C) and Diine Island (right)

Rissoa inconspicua (B, C) Facelina spec. (B, C)

Gastropoda

Anthozoa u n d e t d , (A, B)*

Aurelia aurita? (A, B)*

Scyphozoa

Tubularia larynx (A, B, C) * Clara multicornis (A) * Perigonimus repens (A) * Campanularia johnstoni (A, B) * Laomedea longissima (B, C) * Laomedea geniculata (A, B, C) * Laomedea gelatinosa {C) * Laomedea flexuosa (A, B, C) *

Hydrozoa

C a l c a r e o u s s p o n g e (undetd.) (A, B) *

Sycon ciliatum (A, B, C) *

Porifera

Balanus crenatus (A, B, C) * Balanus improvisus (A, B, C) * Balanus balanus (A, B) * Hlminius modestus (A, B, C) * Ven-uca stroemia (A, B) *

Cirripedia

Pantopoda u n d e t d . (B)

Botryllus schlosseri (A, B, C) * Botrylloides leachi (B) * Ascidiella aspersa (A, B, C) * Ciona intestinalis (A, B, C) * Molgula citrina (A, B, C) *

Ascidiacea

Psarnmechinus miliaris (B, C)

t~chinoidea

Harmothoe impar (A) Anaitides spec. (A, B, C) Algae Amphipoda Bulalia viridis (A, B, C) Jassa falcata (A, B, C) * Acrosiphonia arcta (B)" Autolytusprolifer (A, C) Ulva curvata (B)* Corophium insidiosum (A, C) * Nereis pelagica (B) Hnterornorpha spec. (C)* Nereis diversicolor (B, C) Punctaria hiemalis (B) * Isopoda Ophryotrocha puerilis (A, B) Limnoria lignorum (A)* Sc~osiphon spec. (B) * Polydora ligni (A, B) * Ceramium rubrum (B, C) * Polydora ciliata (A, B, C)* PoIysiphonia urceolata (B)* Decapoda Capitella capitata (A, B) Polysiphonia nigrescens (C) * Crangon crangon (A) Nicolea venustula (C) * Potysiphonia elongata (B)* Hyas araneus (A) Nicolea zostericola (C) * Goniotrich um alsidii (C)* Carcinus maenas (A, B, C) Lanice conchilega (A, B) * Fabricia sabella {A) * Pomatoceros triqueter (A, B, C) *

Polychaeta

Dinophilus gyrodfiatus (B)

Archiannelida

Mytilus edulis (A, B, C) * Saxicava arctica (A)*

Bivalvia

T a b l e 1. S u r v e y of t h e h a r d b o t t o m c o m m u n i t y . A, B, C: stations at w h i c h a s p e c i e s w a s f o u n d (cf. Pig. 1)• * S e s s i l e a n d h e m i s e s s i l e f o u l i n g s p e c i e s or g r o u p s

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