Hong Kong Baptist University’s discovery of new coral and nudibranch species reflects Hong Kong’s rich marine biodiversity

HONG
KONG SAR – Media OutReach – 25 October 2021 – Biologists from
Hong Kong Baptist University (HKBU) have discovered in Hong Kong waters a new species of hard coral and two new
species of nudibranch, a type of marine mollusc, that have never been
identified anywhere else in the world. The discoveries of new species from these
commonly seen animal groups are a vivid reflection of Hong Kong’s rich marine
biodiversity.

Professor
Qiu Jianwen (right) and Mr Yiu King-fung, a member of the research team and a
research postgraduate student (left) introduce the new coral and nudibranch
species.

The new marine
species were identified by research teams led by Professor Qiu Jianwen,
Professor of HKBU’s Department of Biology. The descriptions of the new coral
and nudibranch species were published in the academic journals Zootaxa and Zoological Studies, respectively.

First new hard coral species discovered
and named in Hong Kong in the past two decades

The
new coral species belongs to the genus Tubastraea, which is commonly
known as sun coral due to its bright orange polyps (individuals making up the
colony) and the circle of tentacles that surround its mouth. HKBU biologists
discovered the new species while conducting underwater surveys at the Breaker
Reef in the eastern waters of Hong Kong in the summer of 2020.

The
team named the coral Tubastraea megacorallita, with “mega” and “corallite” meaning “big” and “skeletal cup”, respectively. The
species name reflects the fact that it has the biggest and most structurally
complex corallite among the eight recognised
Tubastraea species around the world. This species forms small colonies of between
three and 12 polyps, and they share a common calcareous skeleton.

Sun
corals are different from most reef-building corals, as they do not host
symbiotic algae that produce energy via photosynthesis. Instead, these corals
gain energy and nutrients by capturing small animals called zooplankton from seawater
using their tentacles. While reef-building corals in Hong Kong typically
inhabit shallower waters up to a depth of 10 metres, sun corals live in deeper
waters at a depth of between 10 and 30 metres.

“Although
98 species of hard coral have been recorded in Hong Kong, the last time a new
coral species discovered in Hong Kong waters was in 2000. It is in over around
20 years a new hard coral species discovered and named in Hong Kong,” said
Professor Qiu.

Two new nudibranch species

Nudibranchs,
commonly known as sea slugs, are gastropod molluscs that only have a shell
during their larval stage. They are eye-catching animals, and they can often be
spotted on coral reefs due to their vivid body colour patterns.

The
HKBU team also discovered in Hong Kong waters two coral-eating species of
nudibranch, both belonging to the genus Phestilla
that has only nine recognised species prior to these discoveries. One of them, named Phestilla
goniophaga, was collected from Sharp Island and Chek Chau. The word “goniophaga”
derives from the name of the host coral, “Goniopora“,
which is commonly known as flowerpot coral, and the Latin word “phaga“, which means “eat”.

Phestilla goniophaga is
rather big, and its body is around three centimetres long. It can be
distinguished from other species of the genus by the large number of long
finger-like, brown and white striped projections called cerata, and the white
rounded hump on its back. The hump resembles the host coral’s mouth, while the
cerata resemble the coral’s tentacles. This mimicry makes it difficult for its
potential predators, such as fish, to spot them. Its egg masses, however, are bright
orange in colour and they can normally be found glued to the coral skeleton.

The other newly discovered nudibranch
species is smaller in size, and its
body is less than one centimetre long. It lays eggs and feeds on the tissue of
the leaf coral Pavona decussata. It
has a white body with brown stripes and exhibits excellent mimicry against the
colour pattern of its coral host. It was named Phestilla fuscostriata, with the species epithet adopting the
Latin words “fuscus” and “striatus”, which mean “brown” and “streaky”.

This new species was discovered while culturing
the leaf coral samples collected from Sharp Island during a study of coral
bleaching mechanisms. The HKBU team discovered the new nudibranch species and
its crescent-shaped white egg masses after noticing the wounds on the coral
surface caused by its feeding.

While
the seas around Hong Kong are only 1,651 square kilometres in size, the territory has around
six thousand marine species – one-quarter of all the marine species recorded in
China.

The
work conducted by Professor Qiu’s team highlights the rich biodiversity found in
Hong Kong, and reflects the urgent need to train local young talent to
implement the Hong Kong Biodiversity Strategy and Action Plan.