Advisory Committee Chair
James B McClintock
Advisory Committee Members
Charles D Amsler
Robert W Thacker
Bill J Baker
Micha Ilan
Document Type
Dissertation
Date of Award
2011
Degree Name by School
Doctor of Philosophy (PhD) College of Arts and Sciences
Abstract
Palatability of outer tissues of 12 species of ascidians from the Western Antarctic Peninsula was evaluated using the sympatric, omnivorous predator fish Notothenia coriiceps and sea star Odontaster validus. Tissues of 100% of those tested were unpalatable to fish, while 58% were unpalatable to sea stars. Lipophilic and hydrophilic extracts of 11 species were incorporated into pellets and tested in fish and sea star bioassays. Only the lipophilic extract from Distaplia colligans caused sea star and fish feeding deterrence. Organic extracts from 10 ascidian species were also examined in food pellet assays using the sympatric, omnivorous amphipod Gondogeneia antarctica. Only the lipophilic extract of Distaplia cylindrica was deterrent. Five of the ascidians possessed acidified outer tunics (pH < 3). In acidified food pellet bioassays, acidity deterred feeding by the sea star, but not by the fish. Furthermore, bioactivity of whole body extracts from six solitary and eight colonial ascidian taxa against sympatric marine bacteria and diatoms from the Western Antarctic Peninsula. All ascidians had lipophilic and hydrophilic extracts assayed at 3X natural concentration against twenty bacterial strains. The extracts were fractionated into seawater soluble and insoluble fractions and assayed at three concentrations (3X, 1X and 0.3X natural concentration) against the chain-forming, pennate diatom Syndroposis sp. Only the lipophilic extract of D. colligans showed broad-spectrum antimicrobial activity against all strains. Extracts from all but one ascidian taxa caused significant diatom mortality in at least one fraction. The palatability of two solitary and three colonial species of ascidians commonly found in sub-tropical seagrass meadows were evaluated using the sympatric, omnivorous pinfish Lagodon rhomboides. Pieces of fresh tissues of both solitary and one of the three colonial ascidian species were unpalatable to fish. Organic extracts of the three unpalatable species did not deter feeding. The toughness of the tunic of all ascidians was evaluated using a penetrometer. Tunic toughness is likely to explain the lack of palatability of the solitary species. Distaplia bermudensis, the one colonial ascidian that was unpalatable to fish, had an acidified outer tunic (pH=1.5). Acidified food pellets did not deter feeding by the fish.
Recommended Citation
Koplovitz, Gil, "An examination of secondary metabolites and inorganic acids as chemical defenses against predation and fouling in Antarctic and sub-tropical ascidians" (2011). All ETDs from UAB. 2177.
https://digitalcommons.library.uab.edu/etd-collection/2177