Abundance and distribution of ophiuroids off Helgoland, German Bight (North Sea)
K. Boos & H.-D. Franke
Biologische Anstalt Helgoland, AWI, Germany
Ophiuroids significantly influence benthic communities by means of bioturbation, processing of organic matter, and as links in local food chains (Summers & Nybakken, 2000). Their occurrence is related to various factors such as depth, hydrodynamics and temperature. The sediment structure in particular, determines the spatial distribution of single species reflecting their lifestyle and feeding behaviour.
Due to the difficulties in recording distributional patterns of patchy populations, further experimental work will focus on active habitat selection due to grain size, along with possible competition of epibenthic brittlestars.
References
•Gerdes, D. (1977) Zur Verteilung der Echinodermen in der Deutschen Bucht, Dipl.-Arbeit,IfM. Kiel
•Mortensen, Th., (Ph.D.) (1927) Handbook of the Echinoderms of the British Isles, Humphrey Milford Oxford University Press
•Summers, A.C. & Nybakken, J. (2000) Brittlestar distribution patterns and population densities on the continental slope off central California (Echinodermata: Ophiuroidea) in Deep-Sea Research II, 47:1107- 1137 Acknowledgements
Many thanks to the crew of the RV „Uthörn“ and to all, who helped with the poster.
Dredge (D) and sediment samples (G) were taken at eight stations around Helgoland. Abundance and distribution of ophiuroids from the grab samples regarding sediment characteristics, were recorded. Sediment was
characterized according to grain size.
1871 1894 1911 1923/24 1927 1939 1950 1953-70 1968/69 1969 1970 1975 1975/76 2003
A. filiformis - + - + - + + + - + - - + +
A. squamata + + + - + + + + - + - - + +
O. fragilis + + + - - + + - - + - - + +
O. albida - + + + + + + + + + - + + +
O. ophiura + + + + - - - + + + - + + +
A. brachiata - - - - - - - - - - - - + +
A. chajei - - + + - - - - - - - - - -
O. affinis - + - - - - - - - - - - - -
O. sarsi - - + - - - - - - - - - - -
Common spe cie s
Rare species
In total nine species have been recorded for the German Bight by different authors (after Gerdes 1976, mod.). However, little is known about the species preferences for different substrata.
Therefore, the aim of the the present study is to give an overview of the current spectrum of ophiuroids off Helgoland, as well as of their abundances and distribution on different substrata.
5 Ophiura albida Forbes, 1839 2 Acrocnida brachiata
(Montagu, 1804)
4 Ophiotrix fragilis (Abildgaard, 1789)
3 Amphipholis squamata (Delle Chiaje, 1829)
6 Ophiura ophiura (Linnaeus, 1758)
Sand Sand &
Shells
Sand Mud Sand
Mud Silt Mud
Silt Sand, Shells
& Mud Mud
Species
1 2 3 4 5 6
Frequency (%)
0 20 40 60 80 100
N = 12
7.7 % 92.3 %
Species
1 2 3 4 5 6
Frequency (%)
0 20 40 60 80 100 98.9 %
1.1 % N = 90
Species
1 2 3 4 5 6
Frequency (%)
0 20 40 60 80 100
N = 12
15.4 %
84.6 %
Species
1 2 3 4 5 6
Frequency (%)
0 20 40 60 80
100 N = 2 100.0 %
Species
1 2 3 4 5 6
Frequency (%)
0 20 40 60 80 100
38.7 %
61.3 % N = 52
Species
1 2 3 4 5 6
Frequency (%)
0 20 40 60 80 100
18.0 %
82.0 % N = 27
Species
1 2 3 4 5 6
Frequency (%)
0 20 40 60 80 100 N = 93
0.9 % 92.6 %
6.5 %
Species
1 2 3 4 5 6
Frequency (%)
0 20 40 60 80 100 N = 39
7.8 % 2.3 %
89.9 %
1 Amphiura filiformis (Müller, 1776)
Six of nine species previously recorded for the German Bight, were confirmed in this investigation. All ophiuroids classified as “common“, as well as one “rare“ species were found.
The lack of A. chiajei, O. affinis and O. sarsi reflects the species´ scarce occurrence in the German Bight. Ten individuals of O. fragilis were found in dredge D7. This might be due to the broad absence of hard bottom in the German Bight.
With respect to sediment preference, O. albida appeared to be rather generalistic, while other species showed trends towards certain substrata characteristics.
G 6 G 8 G 5 G 3 G 7 G 4 G 1 G 2
100 80 60 40 20 0
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