Biodiversity of a Wreck from the Belgian Continental Shelf: Monitoring Using Scientific Diving
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BULLETIN DE L’INSTITUT ROYAL DES SCIENCES NATURELLES DE BELGIQUE, BIOLOGIE, 72: 67-72, 2002 BULLETIN VAN HET KONINKLIJK BELGISCH INSTITUUT VOOR NATUURWETENSCHAPPEN, BIOLOGIE, 72: 67-72, 2002 Biodiversity of a wreck from the Belgian Continental Shelf: monitoring using scientific diving. Preliminary results by Cl. MASSIN, A. NORRO & J. MALLEFET Abstract Introduction Scientific diving from aboard the r/v Belgica has been employed to Biodiversity of the Belgian marine benthos is well docu carry out a preliminary study of the macrofauna living on a wreck mented for the meiobenthos and the small macrobenthos (up (the Birkenfels) located on the Belgian Continental Shelf (BCS). to a few mm long) from soft bottoms (see CATTRIJSSE & The study revealed an extremely rich sessile and slow moving fauna VlNCX, 2001 for extensive literature review). Large (at least 40 species), 3 jellyfish species and 8 fish species. The pres epibenthos and sessile fauna have been collected for more ence of at least 51 species represents a biodiversity of macrofauna than a century (Van Beneden, 1883; GILSON, 1900) but few on the wreck that is much higher than that found in nearly all known surrounding soft bottom communities belonging to the BCS. The papers have been published until now, e.g. COENJAERTS covering of large parts of the wreck is represented by three species: (1997),D e g r a e r (1999)D e g r a e r et a l (1999) andB e y s t Sarsia eximia (Hydrozoa) and Jassa herdmanni (Crustacea) associ (2001). The collection of samples in these studies were all ated with Tubularia indivisa (Hydrozoa). It should also be pointed based on the same method (the V a n V e e n grab). Previous out that 53 % of the species identified in this study are species not studies on epibenthos were earned out by the Departement included as members of the Belgian marine fauna in a recent list voor Zeevisserij (formerly Rijksstation voor Zeevisserij) dealing with offshore fauna. Moreover, some, such as Sarsia eximia Oostende (DvZ). They focussed their attention mainly on or Epithonium clathratulum, previously thought to be rare, have commercially important species (Crangon crangon, been found in large numbers. Furthemore, Diadumene cincta and Pleuronectidae, Soleidae, Gadidae, Clupeidae) and occasion f Caprella tuberculata are new species for the Belgian marine fauna. ally on by-catches (Hydrozoa, Anthozoa, Annelida, Bryozoa, Key-words: biodiversity, Belgian Continental Shelf, wreck, scien Crustacea, Mollusca and Echinodermata)(see among others tific diving. De Clerck, et a l, 1973; 1974a; 1974b; 1975;M a e r t e n s , 1987). These samples were either collected by means of dif ferent trawls or by VAN V e e n grab. Most of their results were Résumé published in «grey» literature. Since G i l s o n (1900), collecting methods for the study of L’utilisation de la plongée scientifique à partir du r/v Belgica a per marine benthic biodiversity have not varied much: VAN mis une étude préliminaire de la macrofaune vivant sur une épave V e e n (le Birkenfels) située sur le plateau continental belge (PCB). Cette grabs, box corers, trawls and sledges. These methods étude a révélé une faune sessile et une faune à mouvements lents may be sufficient to give an overview of the soft bottom très riches (au moins 40 espèces), plus 3 espèces de méduses et 8 benthic fauna on the Belgian Continental Shelf, but are to espèces de poissons. La présence d’au moins 53 espèces représente, tally inappropriate or result in underestimations for hard bot pour l’épave, une biodiversité de la macrofaune bien supérieure à toms (rocks and wrecks) and particularly for sessile fauna. celle de presque toutes les communautés benthiques de substrats Furthemore, data concerning this sessile epifauna are very meubles connues du PCB. L’essentiel de la couverture de l’épave scarce (CATTRIJSSE & VlNCX, 2001). est représenté par trois espèces: Sarsia eximia (Hydrozoa) et Jassa Scientific diving on wrecks with direct observations of herdmanni (Crustacea) associée à Tubularia indivisa (Hydrozoa). Cinquante trois % des espèces identifiées dans cette étude ne sont benthic and particularly sessile fauna has been performed by pas mentionnées comme appartenant à la faune marine belge dans Dutch scientists (WAARDENBURG, 1988;VAN MOORSEL et une liste récente traitant de la faune du large. De plus, certaines es a l, 1989; 1991). They prospected 22 wrecks along the Dutch pèces comme Sarsia eximia ou Epithonium clathratulum, suppo Coast. Biodiversity was estimated in situ and on video tapes. sées rares, ont été trouvées en grand nombre. Diadumene cincta et Surprisingly, only a few samples were collected for identifi Caprella tuberculata sont des espèces nouvelles pour la faune ma cation; as a consequence, this work reveals only a part of the rine belge. biodiversity. Nevertheless, the results clearly indicate that Mots-cléfs : biodiversité, Plateau Continental Belge, épave, plon wrecks are much richer than the surrounding sand and appear gée scientifique. an oasis for marine life. 68 CL. MASSIN, A. NORRO & J. MALLEFET To fill the gap of our knowledge on the sessile macrofauna of Discussion & conclusions the BCS, a preliminary campaign on board of r/v Belgica was performed in July 2001 to test the feasibility of a study of With at least 51 species identified in only 3 samples, the sessile macrofauna by means of scientific diving. biodiversity of the Birkenfels’s macrofauna is considerably higher than that of nearly all the prospected soft bottom com munities on the BCS. CATTRIJSSE & DEGRAER (2001) report Material & Methods an average of 8 to 30 macrobenthos species per prospected zone, the number of observations per zone varying between The target wreck was the «Birkenfels» (ED50, N 51 ° 39’,040- 13 and 209. Regarding the epibenthos species, CATTRIJSSE E002°32’,350; 156 m length; 42 m depth HW). It was pros (2001) reports an average of 12 to 18 species per prospected pected twice by two teams of divers. Three samples were zone, the number of observations per zone varying between 3 taken on horizontal surfaces at 22, 28 and 29 m depth. Only and 67. Intensive sampling of the wreck will certainly bring macro-organisms (visible with the naked eye) were taken more species. Sarsia eximia and Epitonium clathratulum into account. were considered rare species for the Belgian fauna. S. eximia Three complementary techniques were used: was mentioned only once by L e l o u p (1947) on mussel shells 1. Photography:surfaces delimited by a frame 50 X 50 cm collected on the West-Hinder lightship in 1905 (this informa were photographed (using digital video camera). Species di tion is repeated in L e lo u p , 1952). According to our observa versity can be estimated from these photographs. tions it is a common species in offshore Belgian waters. 2. Estimate of covering: within the same 50 X 50 cm frame, Before the present study, E. clathratulum was only known divers estimated the rate of coverage (fig. IB) with the main from a few stranded specimens (Backeljau, 1986; benthic sessile organisms using the techniques established by Vanhaelen, 1989) and by a single living specimen col D a h l (1981). lected on a breakwater at Koksijde (JONCKHEERE, 2001). 3. Sampling:within each 50 X 50 cm frame, a surface of 25 Jassa herdmanni was very recently ascribed to the Belgian X 25 cm was scraped off (fig. 1C) in order to collect all the fauna ( d ’U d e k e m d ’A c o z , 1993). It has been found associ sessile fauna and slow moving vagile fauna. On board, each ated with Tubularia spp. on rocky substrate along the coast. sample was properly labelled, animals anaesthetized in 3% This species is much more common than predicted but it has magnesium chloride and preserved in buffered formalin. very often been confused with Jassa falcata. Caprella Later the material was transferred to buffered alcohol, identi tuberculata is a rare species in the North Sea and should be fied and for a few species the number of specimens/surface considered as a new species for the Belgian marine fauna. unit was counted. Diadumene cincta is very common on the wreck. However, it Fishes living in open water were identified in situ by divers. has not previously been mentioned as belonging to the ma rine Belgian fauna ( L e lo u p , 1947; 1952;D a r o , 1969; Topography of the wreck was carried out using the onboard M a n u e l , 1981; Hayward & Ryland, 1995). Checking the Belgica Kongsberg Simrad EM1002S multibeam sonar (fig. «grey» literature it is possible to find 3 references 1A). Such a technique requires tidal reduction. Maps were (Huysseune, 1978;M e ir e , 1981; Vanderperren, 1991) produced with the help of the Fund for sand extraction (Bel listing D. cincta from the Belgian coast (Bredene, St gian Ministry of Economics Affairs). Idesbald, Ostende). However, these observations were not checked by a specialist and confusion with some Sagartia species cannot be excluded ( K e r c k h o f pers. comm.). D. Results cincta must be considered a new species for the Belgian ma rine fauna. Its presence along the coast line is still to be con The dominant species on vertical and horizontal surfaces firmed. were Sarsia eximia and Jassa herdmanni associated with Twenty seven species in table 1 (53% of the observed spe Tubularia indivisa (fig. 1D-E). They represented more than cies), are not recorded in the species list of the CBS estab 80% of the covering. Sea anemonies (particularly lished by CATTRIJSSE &VINCX (2001) and based on offshore Diadumene cincta and Metridium senile; figs IF, 2E) repre records from 1970 to 1998.