Hiding and feeding in floating seaweed: Floating seaweed clumps as possible refuges or feeding grounds for fishes

Abstract

Paper in pressVandendriessche S., Messiaen M., O'Flynn S., Vincx M., Degraer S.Hiding and feeding in floating seaweed: floating seaweed clumps as possible refuges or feeding grounds for fishes ABSTRACTFloating seaweed is considered to be an important habitat for juvenile fishes due to the provision of food, shelter, a visual orientation point and passive transport. The importance of the presence of the highly dynamical seaweed clumps from the North Sea to juvenile neustonic fishes was investigated by analysing both neuston samples (without seaweed) and seaweed samples concerning fish community structure, and length-frequency distributions and feeding habits of five associated fish species. While the neustonic fish community was mainly seasonally structured, the seaweedassociated fish community was more complex: the response of the associated fish species to environmental variables was species specific and probably influenced by species interactions, resulting in a large multivariate distance between the samples dominated by Chelon labrosus and the samples dominated by Cyclopterus lumpus, Trachurus trachurus and Ciliata mustela. The results of the stomach analysis confirmed that C. lumpus is a weedpatch specialist that has a close spatial affinity with the seaweed and feeds intensively on the seaweed-associated invertebrate fauna. Similarly, C. mustela juveniles also fed on the seaweed fauna, but in a more opportunistic way. The shape of the size-frequency distribution suggested enhanced growth when associated with floating seaweed.Chelon labrosus and T. trachurus juveniles were generally large in seaweed samples, but large individuals were also encountered in the neuston. The proportion of associated invertebrate fauna in their diet was of minor importance, compared to the proportions in C. lumpus. Individuals of Syngnathus rostellatus mainly fed on planktonic invertebrates but had a discontinuous size-frequency distribution, suggesting that some of the syngnathids were carried with the seaweed upon detachment and stayed associated. Floating seaweeds can therefore be regarded as ephemeral habitats shared between several fish species (mainly juveniles) that use them for different reasons and with varying intensity.

The effect of temperature and fish size on growth of juvenile lumpfish (Cyclopterus lumpus L.)

“…Ingolfsson and Kristjansson (2002) found that only 28 % of 1482 juvenile lumpfish collected in June-September had food in their stomachs, whereas 27 % of the juveniles in the same study had remains of food in their stomach. This may indicate a rapid degradation of prey in juvenile lumpfish, as a study by Vandendriessche et al (2007) observed food in all stomachs, also in winter.…”

“…Juvenile lumpfish feed throughout the year (Vandendriessche et al 2007). Small juvenile lumpfish with yolk sacks are found to feed on small crustaceans (harpacticoid copepods) before shifting to amphipods (Callopius laeciusculus and Parathemisto gaudichaudi) with increasing size (Daborn & Gregory 1983;Ingolfsson & Kristjansson 2002).…”

Habitat Selection Among Fishes and Shrimp in the Pelagic Sargassum Community: The Role of Habitat Architecture

“…Previous algal studies have used patch sizes ranging from a single algal thallus to greater than 100 g (Roberts and Poore, 2005;Christie et al, 2007;Vandendriessche et al, 2007a;Christie et al, 2009;Jobe and Brooks, 2009). Habitat sizes of either 20 g 6 0.5 g or 30 g 6 0.5 g were used for habitat selection experiments.…”

“…attract and concentrate fauna (Hunter and Mitchell, 1968;Kingsford, 1995;Lapointe, 1995;Ingólfsson, 1998;Casazza and Ross, 2008) by increasing the complexity of the pelagic environment (Kingsford, 1995;Ingólfsson, 1998). Generally, the fish community is more diverse and abundant below floating seaweeds than below other floating items (Dooley, 1972;Fedoryako, 1989;Lapointe, 1995;Vandendriessche et al, 2007a). Adrift alga is also important as a dispersal agent for nearshore fauna (Helmuth et al, 1994;Parker and Tunnicliffe, 1994;Ingólfsson, 1995Ingólfsson, , 1998.…”

“…In the marine environment, structure, in general, attracts and concentrates fauna (Hunter and Mitchell, 1968;Lapointe, 1995;Ingó lfsson, 1998;Roberts and Poore, 2005;Norderhaug et al, 2007;Vandendriessche et al, 2007a;Casazza and Ross, 2008;Christie et al, 2009). Specifically, objects floating in the ocean (e.g., Sargassum spp.)…”