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Ocean debris is particularly important for oceanography,
biogeography and forensics. The biofouling communities on floating objects like
logs, pumice, plastic or even corpses can help reconstruct where the objects came
from and their duration at sea. Understanding biofoulers also helps predict the
spread of invasive species. These biofouling communities are often shaped
around Lepas, a genus of goose
barnacles found across the world’s oceans.
Thomas Mesaglio of the University of New South Wales is
investigating how marine biofouling communities ─ especially those that develop
around the goose barnacle genus Lepas
─ can be used in forensics to reconstruct the drift path and duration at sea of
beach-cast objects. His project aims to:
1) Review the pelagic biofouling community and understand
how it changes over time, with a focus on goose barnacle communities.
2) Develop a greater understanding of the goose barnacle genus Lepas
focused on its morphology, growth and life history by combining field
observations with laboratory studies.
3) Determine whether Lepas
can be used as a useful forensic tool for tracking drift objects, combining
calculations of Lepas growth rates
with a study of shell-derived oxygen isotopes to estimate the approximate water
temperature, origin and minimum duration at sea of Lepas-covered drifters.
Historically, ocean drifters have mostly been natural
floating objects like pumice, seeds, and wood (Thiel and Gutow 2005a, Goldstein
et al. 2014). However, in the past
few decades, anthropogenic drifters, predominantly plastics, have increased in
abundance and distribution to become the dominant debris type globally
(Goldstein et al. 2013, Eriksen et al. 2014). Together, the rapid
increase in global shipping and quantity of drifting debris has increased the
transport of marine organisms across the planet (Barnes et al. 2009, Murray et al. 2018).
As a serious threat to marine biodiversity (Molnar et al. 2008) and a part of the IUCN’s Red List criteria (Keith et al. 2013, Rodríguez et al. 2015), the increased spread of
invasive species magnifies the importance of understanding drifter
The barnacle family Lepadidae is one of the most abundant
biofouling taxa. Referred to as goose barnacles, lepadids are obligate
epipelagic rafters, which means they are restricted to living on floating
substrates near the ocean surface (Thiel and Gutow 2005b). Lepadids are a
cosmopolitan family and are able to survive on drifters for long periods of
time and travel large distances (Iljin et
al. 2013). Because of their pervasiveness in the global epipelagic
environment, many studies of biofouling communities are inherently of
Lepadidae, with the genus Lepas of
particular interest. Despite the dominance of Lepas as a biofouler, its ecology is poorly understood. Besides
studies of how Lepas anatifera
cements to substrates (Lacombe and Liguori 1969, Walkera and Youngson 1975,
Jonker et al. 2015), there are few
studies on their growth rates, life history, or interactions with predators or
After the disappearance of Malaysian Airlines flight MH370 in
March 2014, a wing fragment covered in L. anatifera washed ashore 505 days later on the western Indian
Ocean island of Réunion (Poupin 2015, ATSB 2017), strongly supporting the
belief that the flight had terminated in the eastern Indian Ocean. An
oceanographic analysis based on the Global Drifter Program (Trinanes et al. 2016) estimated the possible
origin of the wing fragment in relation to the last recorded position of the flight.
To constrain these oceanographic hindcasts, the Australian Transport Safety
Bureau recommended that the attached Lepas
be studied for their growth rates and their temperature of calcite formation in
an attempt to retrace the path of the fragment. A 2016 study consequently
established a linear relationship between sea surface temperature and the
delta-O-18 (ratio of oxygen-18 to oxygen-16) content of Lepas shells allowed them to conclude that Lepas faithfully record the water temperature during formation of
their shell in the oceanographic conditions of the Indian Ocean.
NSW beaches will be combed for shore-cast drifters to achieve
a better understanding of the pelagic biofouling community, with a strong focus
An offshore mooring will be installed 3 km off the North
Bondi headland. Designed as a biofouling substrate, the mooring will be sampled
monthly from a boat launched from SIMS, allowing observations of live
biofouling communities and how these communities change over time. Also Lepas will be reared in the SIMS Ian Potter Research Aquaria
for six weeks using three temperature regimes to understand how temperature
affects growth and allow the calculation of a growth curve.
Finally, an isotopic analysis will be conducted at UNSW’s Mark Wainwright Analytical Centre. The delta-O-18 content of Lepas shells will be measured and these
data validated against the known sea surface temperatures recorded at each
sampling site to establish the accuracy of the isotope thermometer, and then
checked against each specimen’s size, and thus age, to further confirm the
accuracy of the settlement time estimation.
In combination with delta-O-18 data, calculating the age of
any attached Lepas and referring to
known growth rates allows the calculation of minimum duration at sea and a
prediction of place of origin for forensically important objects like corpses
or aircraft debris, creating a novel, forensic tool with strong potential for
Understanding pelagic biofouling communities and the factors
facilitating long-distance drifter transport will help identify the threats
posed by the emergence of plastic as a cosmopolitan, hyper-abundant debris type
and extreme events like tsunamis, the combination of which can facilitate the
transport of debris, and thus invasive species, across entire oceans.
This study will represent the finest temporal resolution
study ever conducted on mooring biofoulers, as well as the first ever
convergence of drifter, mooring and laboratory studies for not only Lepas, but biofoulers in general. The
combination of data from all three analyses will allow cross-checking of all
findings against each other and strengthen the conclusions drawn.