Barnacles (Cirripedia) are crustaceans, with sessile adult forms that are permanently attached to hard substrata or to other living organisms. They are adjusted to various lifestyles, from parasites of decapod crustaceans to free-living groups. As cosmopolite animals, barnacles are abundant, with over 1000 species found worldwide in polar, tropical, and temperate waters, from the ocean shore to its depths. However, knowledge of the barnacle fauna of the Maluku Islands, eastern Indonesia (also known as the Moluccas), remains sparse. The lack of studies on barnacles in the Moluccas is unfortunate, given that the exceptionally high marine biodiversity of this region—part of the global epicentre of marine biodiversity—suggests that many barnacle species may not yet have been discovered.
In the doctoral thesis presented here, barnacles from the Moluccas Islands were studied to establish a taxonomic checklist, including information on their morphology, distribution, and substrate. This doctoral thesis is divided into three major sections. In its first section, it focuses on integrative biodiversity discovery of barnacles from the Moluccas, including morphological and molecular data of recently collected material. In the second section, deepsea barnacles collected from the Moluccas by previous scientific expedition and deposited in the Muséum National d’Histoire Naturelle, Paris were investigated. In the third section of this thesis, a modern non-destructive imaging method, X-ray micro-computed tomography (Micro-CT scanning), was used to study sponge-dwelling barnacles from the Moluccas that still embedded in their sponge host.
The first section provides the most comprehensive overview of barnacle species from the Moluccas Islands to date. Morphological analysis of recently collected material revealed 24 intertidal species and one deep-water species from three families of stalked barnacles (Heteralepadidae: one genus and species; Lepadidae: two genera and species; Pollicipedidae: one genus and species) and four families of acorn barnacles (Pachylasmatidae: one genus and species; Chthamalidae: five genera and species; Tetraclitidae: five genera and eight species; Balanidae: two genera and seven species). Including previous records from the literature, a total of 97 species from the Moluccas Islands are recorded from the superorder Thoracica (free living or epizoic). Of these, 21 species are new records, and two (Amphibalanus sp. and Microeuraphia sp.) are currently unidentified.
The second section examines the deep-sea barnacles collected by the Karubar expedition (1991) and deposited in the Muséum National d’Histoire Naturelle, Paris. It identifies 40 species from three families of stalked barnacles (Heteralepadidae: two genera, three species; Poecilasmatidae: four genera, five species; Scalpellidae: 12 genera, 21 species) and five families of acorn barnacles (Verrucidae: two genera and species; Pachylasmatidae: one genus and species; Archaeobalanidae: three genera, six species; Pyrgomatidae: one genus and species; Balanidae: one genus and species). Thirty of the species are new records for the Indonesian Kei Islands and Tanimbar Island, which increases the total number of species recorded from Kei, Aru, and Tanimbar to 40.
The third section explores the sponge-dwelling barnacles of the Moluccas using a modern non-destructive imaging method, X-ray micro-computed tomography (Micro-CT scanning). The results reveal the advantage of using micro-CT scanning when examining sponge barnacles, as their deep anchors in sponge tissue makes it almost impossible to pull out the barnacle without breaking it. Although there are some methodological limitations regarding contrast-enhancing techniques, this study demonstrates that micro-CT is a useful non-destructive technique for the integrative taxonomy of the sponge-inhabiting barnacles.
Overall, this doctoral thesis demonstrates that 126 species now are recorded from the Moluccas Islands, including 46 new records; five further species are proposed. This shows that the Indo-Malayan region (including the Moluccas) has not been replaced by other areas as the centre of benthic biodiversity. However, a comparison of the number of species previously recorded from the Moluccas with those recorded in this study indicates that species diversity for each island has been heavily underestimated. Molecular results also indicate that the barnacle fauna of the region is understudied. Nonetheless, a modern non-destructive imaging method, X-ray micro-computed tomography (Micro-CT scanning) is proven to be a very useful technique for studying the morphology and taxonomy of barnacles from the Moluccas. When paired with classic morphological examination, this technique has the potential to be an extremely useful tool for understanding the integrative taxonomy of barnacles and helping identify further species of barnacles.