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Consideration of the Hawaiian Collector Urchin, Tripneustes gratilla, as a Biocontrol Agent.

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Title:Consideration of the Hawaiian Collector Urchin, Tripneustes gratilla, as a Biocontrol Agent.
Authors:Westbrook, Charley E.
Contributors:Marine Biology (department)
Feeding Preference
Date Issued:Aug 2018
Publisher:University of Hawaiʻi at Mānoa
Abstract:We investigate the survivorship, growth and diet preferences of hatchery-raised juvenile urchins,
Tripneustes gratilla, to evaluate the efficacy of their use as biocontrol agents in the efforts to
reduce alien invasive algae. In flow-through tanks, we measured urchin growth rates, feeding
rates and feeding preferences among diets of the most common invasive algae found in Kāneʻohe
Bay, Hawaiʻi: Acanthophora spicifera, Gracilaria salicornia, Eucheuma denticulatum and
Kappaphycus clade B. Post-transport survivorship of outplanted urchins was measured in paired
open and closed cages in three different reef environments (lagoon, reef flat and reef slope) for a
month. Survivorship in closed cages was highest on the reef flat (∼75%), and intermediate in the
lagoon and reef slope (∼50%). In contrast, open cages showed similar survivorship on the reef
flat and in the lagoon, but only 20% of juvenile urchins survived in open cages placed on the reef
slope. Urchins grew significantly faster on diets of G. salicornia (1.58 mm/week ± 0.14 SE) and
Kappaphycus clade B (1.69 ± 0.14 mm/wk) than on E. denticulatum (0.97 ± 0.14 mm/wk), with
intermediate growth when fed on A. spicifera (1.23 ± 0.11 mm/wk). Interestingly, urchins
display size-specific feeding preferences. In non-choice feeding trials, small urchins (17.5–22.5
mm test diameter) consumed G. salicornia fastest (6.08 g/day ± 0.19 SE), with A. spicifera (4.25
± 0.02 g/day) and Kappaphycus clade B (3.83 ± 0.02 g/day) intermediate, and E. denticulatum
was clearly the least consumed (2.32 ± 0.37 g/day). Medium-sized (29.8–43.8 mm) urchins
likewise preferentially consumed G. salicornia (12.60 ± 0.08 g/day), with less clear differences
among the other species in which E. denticulatum was still consumed least (9.35 ± 0.90 g/day).
In contrast, large urchins (45.0–65.0 mm) showed no significant preferences among the different
algae species at all (12.43–15.24 g/day). Overall consumption rates in non-choice trials were
roughly equal to those in the choice trials, but differences among feeding rates on each species
were not predictive of feeding preferences when urchins were presented all four species
simultaneously. In the choice feeding trials, both small and medium urchins clearly preferred A.
spicifera over all other algae (roughly twice as much consumed as any other species). Again,
however, differences were less pronounced among adult urchins, with adults showing a
significant preference for A. spicifera and Kappaphycus clade B compared to the other two algal
species. These findings indicate that outplanted urchins are surviving on the reef flats and eating
a variety of alien invasive algae as intended. Although juvenile urchins show stronger feeding
preferences, these animals grow quickly, and adult urchins are more generalist herbivores that
consume all four alien invasive algae.
Description:M.S. Thesis. University of Hawaiʻi at Mānoa 2018.
Rights:All UHM dissertations and theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission from the copyright owner.
Appears in Collections: M.S. - Marine Biology

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