Eat what‘s on your plate!
Feeding of demersal fish in different habitats
Philipp Krämer *, Jennifer Dannheim & Alexander Schröder
Alfred-Wegener Institute for Polar and Marine Research, Bremerhaven, Germany
*email: philipp.kraemer@awi.de
Study site
Diets of whiting (Merlangius merlangus), grey gurnard
(Chelidonichthys gurnardus), plaice (Pleuronectes platessa) and dab (Limanda limanda) were compared by the following methods:
• stomach content analysis
- “dietary snapshot”: identifies recently ingested prey items (b) nitrogen stable isotopes analysis
- integrates diet over longer time scales: tissue-δ15N (15N/14N) indicates an organism’s position within the trophic hierarchy of an ecosystem (15N is enriched with assimilation)
Material and methods
Demersal fish were sampled with otter and beam trawl.
Sampling proceeded in April 2007 in a coarse sand area and a fine sand area at the Sylter Outer Reef. Both areas were separated by a distance of 9.4 km.
6°30´ 7°00´ 7°30´ 8°00´ 8°30´ 9°00´
53°40´
54°00´
54°20´
54°40´
55°00´
55°20´
study site
German Bight
Sylt
Helgoland
Bremerhaven
fine sand coarse sand
Results from dab were inconsistent. Different site specific trophic positions despite similar prey compositions in both habitats might
indicate structural differences on lower trophic levels of the local food webs. An artefact due to empty stomachs and advanced digestion, however, cannot be excluded for this species.
Demersal fish species such as plaice and whiting are stationary predators with habitat dependent food spectra.
Others such as the grey gurnard roam different feeding grounds potentially connecting local food webs of sites seperated by tens of kilometres.
Conclusion
Trophic interactions are major structuring factors in benthic communities. A wide spectrum of benthic organisms provides diverse food resources for demersal fish.
Due to their mobility fish potentially migrate between spatially separated feeding grounds.
Are demersal fishes stationary predators or do they connect benthic food webs by browsing different habitats?
Introduction
spp.
Dab (Limanda limanda) Diet consisted mainly of Echinoidea (a)(b).
Higher trophic position in the coarse sand habitat (p < 0.05) (c)
Higher trophic range in the fine sand habitat (c)
fine coarse
(c) Trophic position (b) Stomach content
δ15 N
ANOSIM: R = 0.085; p = 15.1%
Diet consisted mainly of Crangon spp. (a)(b).
Trophic positions not different (p > 0.05) (c)
Higher trophic range in the coarse sand habitat (c)
Grey gurnard (Chelidonichthys gurnardus)
fine coarse
(b) Stomach content (c) Trophic position
δ15 N
ANOSIM: R = 0.175; p = 7%
Diet consisted mainly of sandeels on fine sand and of Crangonidae on coarse sand (a)(b).
Higher trophic position in the fine sand habitat (p < 0.05) (c)
Higher trophic range in the coarse sand habitat (c)
Whiting (Merlangius merlangus)
(c) Trophic position
δ15 N
(b) Stomach content
fine coarse
ANOSIM: R = 0.691; p = 0.1%
Plaice (Pleuronectes platessa)
(c) Trophic position (b) Stomach content
fine coarse
ANOSIM: R = 0.501; p = 0.1%
Diet consisted mainly of polychaetes (a).
Food composition varied between habitats (b).
Higher trophic position in the coarse sand habitat (p < 0.05) (c)
Higher trophic range in the fine sand habitat (c)
δ15 N
Differential intra-specific feeding in different habitats (fine and coarse sand)
Results
(a) Major prey items
0 20 40 60 80 100
coarse fine
%
Crangon crangon Ammodytidae
Branchiostoma lanceolatum
0 20 40 60 80 100
coarse fine
(a) Major prey items
Scolelepis spp.
Branchiostoma lanceolatum Notomastus latericeus
Spiophanes bombyx Magelona johnstonii
%
0 20 40 60 80 100
coarse fine
(a) Major prey items
Echinoidea Liocarcinus spp.
Nephtys spp.
Nereis spp.
%
0 20 40 60 80 100
coarse fine
(a) Major prey items
Crangon spp.
Pomatoschistus spp.
Pleuronectiformes Gadidae
%
Stomach content
flatfish
dab plaice
grey gurnard whiting
ANOSIM: R = 0.452; p = 0.1%
plaice dab gurnard whiting
14 15 16 17 18 19
flatfish round fish
N = 20 N = 19 N = 19 N = 20
round fish
Differential feeding in flatfish and round fish
δ15 N
Low trophic position Low trophic variability
Higher trophic position Higher trophic variability
round fish
Stable isotope measurement
flatfish
High prey item diversity Lower prey item diversity