Fish or jellies - a question of visibility?

Article Abstract:

A question of visibility related to fish and jellies and why some pelagic ecosystems support large stocks of fish while others are dominated by jellyfish is discussed. Two fjords of the same size with quite different pelagic food webs were studied. In one fjord a slightly greater influence of coastal water in the basin water causes the exponential light absorbance coefficient below 100 m to be 2-3 times as high as that in other fjords. Reduction in light flux of several orders of magnitude reduces possibility of visual foraging, but predation in jellyfish is tactile and is not influenced. The visibility regime is decisive.

Norway, Statistical Data Included, Light, Jellyfishes

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The influence of fish-exuded chemical signals on the carbon budget of Daphnia

Article Abstract:

No differences were found between Daphnia magna juvenile instars cultivated in fish-treated or control medium. Respiration and carbon assimilation rates are positively correlated with body size in both the fish-influenced and control daphnids. The observed life-history changes in Daphnia on exposure to fish exudates appear to be facultative changes and not responses to the stress of laboratory conditions, indirect effects of other defense mechanisms induced by predators or toxic effects of fish exudates.

Cladocera, Semiochemicals, Carbon cycle (Biogeochemistry), Carbon cycle

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Coral reef sponges: do predatory fishes affect their distribution?

Article Abstract:

Predatory fishes can limit the distribution of some Caribbean sponges. Fifteen sponge species were transplanted from habitats where spongivorous fishes are rare to habitats where they are common. Nine sponge species had significant loss of wet mass in the uncaged sponges after three days because of spongivore predation. Seven species suffered a mean consumption of tissue that was greater than 50%.

Predation (Biology), Coral reef ecology, Coral reef ecosystems, Sponges, Sponges (Animals)

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