PORCUPINE MARINE NATURAL HISTORY SOCIETY NEWSLETTER

22
and only 2-3cm long, the shrimp has some
clear distinguishing features. The chelae are
blue and white striped whilst the thorax is
covered with small blue spots. Its abdomen is
ornated by pinky-white stripes, one of which
is v-shaped and points toward the tail. Finally
the telson is edged by a further blue and white
arrow shaped stripe pointing back toward the
thorax.
Sighting details
An individual P.sagittifer (Norman, 1861)
shrimp was observed on the oral disc of a
solitary A.viridis under the new Swanage Pier
in Swanage, Dorset, UK (grid reference SZ
035 787; 50° 36.501’N, 001° 57.056’W) (Plate
1). Seasearch diver Polly Whyte made the
sighting on 22 September 2007 at 1242h GMT.
Water depth was approximately 3m and the
temperature was approximately 17°C (Suunto
Vyper dive computer).
Plate 1: The actual shrimp observed in its host anemone
beneath Swanage Pier, © Matt Doggett.
The authors recorded the sighting,
identified the species and records have
been sent to the Marine Life Information
Network (MarLIN) at the MBA, Plymouth
and to Seasearch. The sighting has been
acknowledged as the first recorded sighting in
UK mainland coastal waters by Dr. Roni Robbins
of London Natural History Museum and Chris
Wood, National Seasearch co-ordinator at the
Marine Conservation Society.
Discussion
The shrimp observed beneath Swanage
Pier was positioned on the oral disc of its host
anemone. This contrasts with the study by
Calado et al. (2007) in which the specimens
of P.sagittifer were never observed on the
PMNHS Newsletter No.24 Summer 2008
oral disc but mainly on the tentacles and
column of its host. Whilst it is possible that
the shrimp moved to the centre in response to
the approaching divers, detritus was present
on the oral disc upon which the shrimp may
have been feeding. Other species frequently
observed with A.viridis such as Eualus occultus,
Necora puber, Eualus cranchii and Clibanarius
erythropus are often located near the base,
possibly as they take shelter from approaching
divers (Calado et al., 2007). The presence of
our specimen on the oral disc enforces its
close association with A.viridis and further
careful observations can determine whether
its presence on the oral disc is a common
occurrence. It is possible that a lack of detritus
under aquarium conditions might explain why
the shrimp were never previously observed on
the oral discs.
Although our observation is the first
recorded UK sighting, anecdotal evidence does
exist of a previous observation near Brixham,
Devon approximately 3-5 years previously
by Chris Proctor. No images exist and the
sighting was not recorded. Further dives have
been conducted beneath Swanage Pier by the
authors since the original sighting but as yet,
have failed to yield further observations.
These sporadic sightings along the British
south coast suggest that P.sagittifer is likely to
be at the extreme northern most extent of its
present range. As a result of the observation
the species has been added to the Seasearch
list of climate change indicator species moving
northward, which already included its host
anemone A.viridis.
In 2002, P.sagittifer was also recorded for
the first time in the Azores and was observed
to inhabit various hydroids, algae and the
black coral Antipathes wollastoni (d’Udekem
d’Acoz & Wirtz, 2002). It is hoped that further
information can be provided by UK divers to
provide a clearer picture of the distribution
of P.sagittifer and indicate whether or not
the species is extending its range. The finding
proves the important role that divers can play
in providing information regarding marine
ecosystems and their inhabitants.