Food preferences and related behavior of the browsing sea urchin <Emphasis Type="Italic">Tripneustes gratilla</Emphasis> (Linnaeus) and its potential for use as a biological control agent |
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Authors: | John Stimson Tamar Cunha Joanna Philippoff |
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Institution: | (1) Zoology Deptartment, University of Hawaii, Honolulu, HI 96822, USA |
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Abstract: | The short-spined toxopneustid sea urchin Tripneustes gratilla feeds on a wide variety of algal species and on sea grasses. However, the urchin does show preferences when offered a selection
of macroalgal species, which it encounters in nature. Preferences among macroalgae were evident in field-collected urchins
exposed to pair-wise tests where the variable was either the consumption rate of the algae or observation of which algal species
the urchins chose to touch with their lantern teeth. Exposure of lab-housed urchins to one of five species of macroalgae for
5 months did not seem to alter preferences of urchins in three of the exposure groups, but those exposed to Padina sanctae-crucis seemed to show an enhanced preference for this species when offered a choice of the five species of macroalgae at the end
of the exposure period, and those exposed to Gracilaria salicornia seemed to avoid the species when offered the choice of the five species. Perhaps more ecologically important than their preferences
were two other observations on these urchins: first, when offered only a single species of algae, the urchins on four of five
diets ate the same quantity per day. Second, when simultaneously offered the choice among the five macroalgal species, the
urchins consumed more macroalgae per day than when offered only one species. These urchins move about a meter a day. They
probably encounter food resources in a relatively coarse-grained fashion and have evolved to eat what is available. Because
of their limited movements, their habitat overlap with grazing fishes, their acceptance of a wide variety of macroalgae and
their preference for macroalgae, these native urchins are thought to have the potential to serve as biological control agents
of alien and invasive macroalgae, which have come to dominate some reef zones normally occupied by corals in Hawaii. |
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