Lepas testudinata

Lepas testudinata is a species of goose barnacle in the family Lepadidae, genus Lapas. The species was likely first described in 1834 by Jean René Constant Quoy and Joseph Paul Gaimard, and was initially named Lepas elongata. In 1892, Carl Wilhelm Samuel Aurivillius classified the species as Lepas testudinata, with its official classification as Lepas (Lepas) testudinata. In 1978, Brian Arthur Foster declared Lepas elongata a nomen oblitum since it hadn't been used since the 1920s. Foster concluded that the name was likely synonymous with Lepas testudinata due to their similar geographical distribution and peduncle structure. In this same paper, Foster also declared Lepas affinis (named by Lancelot Alexander Borradaile, 1916) a synonym as well.[1]

Lepas testudinata is a plantonic filter feeding barnacle. They have a calcite shell and employ a photoreceptive naupliar eye.[2]

Lepas testudinata have two different peduncle (stalk) structures depending on substrate they've affixed to. When affixed to kelp, the peduncles are smooth and long; with some measuring as long as 25 centimetres (9.8 in) in length. This compares to non-kelp forms that have short, spiny pendicles. It is still unclear if these represent two distinct lineages within the species or indicates a yet to be described morphological adaptation.[3]

Similar to other species of barnacles, Lepas testudinata forms colonies along tidewrack, driftwood, and man-made items.[5][6][7] They do not affix themselves to stationary objects, instead they exclusively prefer mobile, floating objects. This preference has allowed the species to become widespread across temperate oceans in the Southern Hemisphere.[3] L. testudinata, in particular, shows a preference to colonize on the kelp species Ecklonia maxima. It can regularly form colonies greater than 1000 members and have a tendency to colonize plastic pollution when available. Their colonization of man-made objects is a driving force in the species' dispersal throughout the south African region.[5] Off the coast of New Zealand, Fiona pinnata predates Lepas species barnicles, and L. testudinata is often found colonizing the kelp species durvillaea antarctica.[6][8]

Along with other species of Lepas barnicles, Lepas testudinata plays a major risk to biofouling damage, as colonies can form on man-made structures. L. testudinata also functions as a foundation species when their colonies wash ashore, where they are then consumed by scavengers. A 2021 study in Marine Biology found that the presence of washed-up L. testudinata colonies on beaches result in ecological succession that significantly increases the species diversity of the local environment.[9]

L. testudinata is cosmopolitanly distributed throughout the Southern hemisphere, though it is strictly limited to pelagic, temperate waters. More specifically, it is broadly distributed throughout the China Seas, Australian Sea, and the Indo-West Pacific.[4][10][3] The species was not observed in China's seas until the 1990s, and ongoing research seeks to determine if it was accidentally introduced to this region or not.[3] Despite this wide range, L. testudinata is generally considered a rarely observed species.[11]

Mitochondrial data of L. testudinata shows that there are two subgroups within the species, one in South African waters, and one in Australian waters. This is because L. testudinata's range is noncontinuous and is likely broken up by the Antarctic current system, in which it cannot survive.[11] The species has not been evaluated by the IUCN Red List.[4]

Analyses of the 18S gene places L. testudinata within an ingroup to L. anatifera but analysis of the 28S sequence places it within an ingroup to L. australis. Due to the broad similarities in morphology between these three species, their overall phylogeny is considered to be very closely related and is the subject of continued research.[11] The following cladogram shows the phylogenetic position of L. testudinata among select members of the Lepas genus, based upon comparison of 18S gene:[11]