Postilla

ED . WOODS HOLE OCEANOGRAPHIC INSTITUTION

)

Peabody Museum

of Natural History

Yale University

New Haven,-GT-0651 1

NIORI

(Received 20 April 1988)
Abstract

The discovery of the freshwater amphipod H.
azteca in Bermuda Is reported. No freshwater
amphipods have previously been recorded
from open water pond habitats on this
western Atlantic island. H. azteca in Bermuda
presumably dispersed from nearby North
American populations; several possible
methods for dispersal are discussed.
Distinctive morphological features of Bermuda
H. azteca are compared with similar
characters reported for other New World
populations.

Key Words

Hyalella azteca, Amphipoda, Bermuda,
introduced species, dispersal mechanism.

Introduction

During a collecting trip to Bermuda in 1987,
the authors found a large population of the
freshwater amphipod Hyalella azteca

Contribution No. 1199 from the Bermuda Biological
Station for Research.

© Copyright 1989 by the Peabody Museum of
Natural History, Yale University. All rights reserved.
No part of this publication, except brief quotations
for scholarly purposes, may be reproduced without
the written permission of the Director, Peabody
Museum of Natural History.

ISBN No. 0-912532-16-5

Posti | la Number 204

10 July 1989

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First Report of a Freshwater Amphipod
(Gammaridea: Hyalellidae), Hyalella
azteca (Saussure), from Nonanchihaline
Waters of Bermuda

Eric A. Lazo-Wasem
Michael F. Gable

(Saussure) (YPM 8432, Fig. 1). The amphipods
were discovered in Seymour Pond,
Southampton Parish, one of the few
freshwater ponds in Bermuda. According to a
survey taken in 1900 (the Savage map), this
pond covered 0.7 acres; with subsequent
partial fill by garbage tip its 1980 size had
been reduced to 0.5 acres (Sterrer and
Wingate 1981). The pond was purchased by
the Bermuda Audubon Society after 1953 and
is being maintained as a nature reserve
(Altrusa Club 1972). Seymour Pond is rain-fed
and has only a slight salt content, probably
from wind-carried salt spray; there are no
known subterranean fissures connecting the
pond to the ocean (D. Wingate, personal
communication).

The discovery of H. azteca represents the
first recorded occurrence of a freshwater
amphipod from an open pond habitat in
Bermuda and a new distributional record for
the species. Several amphipod species with
freshwater affinities have been described
recently from Bermuda (Stock et al. 1987), but
these species are from the freshwater lenses
of flooded caves or other anchihaline habitats.
Freshwater open ponds are not abundant in
Bermuda; some, such as Seymour Pond,
occur naturally, whereas others have been
constructed in the last few decades as golf
course water traps or wildlife reserves (Wyers
1981). An investigation of ponds other than
Seymour Pond may result in the discovery of
additional populations of H. azteca. Open
ponds that are brackish, however, such as
Spittal Pond, have been investigated and lack
populations of H. azteca. The distributional

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Peabody Museum
of Natural History
Yale University

New Haven,-CT-0651 1

c TH
NIOSIE

> . WOODS HOLE OCEANOGRAPHIC INSTITUTION

Posti | la Number 204

10 July 1989

ee er

(Received 20 April 1988)
Abstract

The discovery of the freshwater amphipod H.
azteca in Bermuda Is reported. No freshwater
amphipods have previously been recorded
from open water pond habitats on this
western Atlantic island. H. azteca in Bermuda
presumably dispersed from nearby North
American populations; several possible
methods for dispersal are discussed.
Distinctive morphological features of Bermuda
H. azteca are compared with similar
characters reported for other New World
populations.

Key Words

Hyalella azteca, Amphipoda, Bermuda,
introduced species, dispersal mechanism.

Introduction

During a collecting trip to Bermuda in 1987,
the authors found a large population of the
freshwater amphipod Hyalella azteca

Contribution No. 1199 from the Bermuda Biological
Station for Research.

© Copyright 1989 by the Peabody Museum of
Natural History, Yale University. All rights reserved.
No part of this publication, except brief quotations
for scholarly purposes, may be reproduced without
the written permission of the Director, Peabody
Museum of Natural History.

ISBN No. 0-912532-16-5

First Report of a Freshwater Amphipod
(Gammaridea: Hyalellidae), Hyalella
azteca (Saussure), from Nonanchihaline
Waters of Bermuda

Eric A. Lazo-Wasem
Michael F. Gable

(Saussure) (YPM 8432, Fig. 1). The amphipods
were discovered in Seymour Pond,
Southampton Parish, one of the few
freshwater ponds in Bermuda. According to a
survey taken in 1900 (the Savage map), this
pond covered 0.7 acres; with subsequent
partial fill by garbage tip its 1980 size had
been reduced to 0.5 acres (Sterrer and
Wingate 1981). The pond was purchased by
the Bermuda Audubon Society after 1953 and
is being maintained as a nature reserve
(Altrusa Club 1972). Seymour Pond is rain-fed
and has only a slight salt content, probably
from wind-carried salt spray; there are no
Known subterranean fissures connecting the
pond to the ocean (D. Wingate, personal
communication).

The discovery of H. azteca represents the
first recorded occurrence of a freshwater
amphipod from an open pond habitat in
Bermuda and a new distributional record for
the species. Several amphipod species with
freshwater affinities have been described
recently from Bermuda (Stock et al. 1987), but
these species are from the freshwater lenses
of flooded caves or other anchihaline habitats.
Freshwater open ponds are not abundant in
Bermuda; some, such as Seymour Pond,
occur naturally, whereas others have been
constructed in the last few decades as golf
course water traps or wildlife reserves (Wyers
1981). An investigation of ponds other than
Seymour Pond may result in the discovery of
additional populations of H. azteca. Open
ponds that are brackish, however, such as
Spittal Pond, have been investigated and lack
populations of H. azteca. The distributional

2 Freshwater Amphipod,
Hyalella azteca from
Bermuda, First Report

Postilla 204

Fig. 1
YPM 8432. Male Hyalella azteca (Saussure); length,
6.4 mm; from Seymour Pond, Bermuda.

extension of H. azteca to Bermuda is
interesting although not surprising; this
freshwater amphipod is widespread
throughout North America and South America
and is known from other islands in the
western Atlantic, for example, Dominica and
Puerto Rico (Shoemaker 1933).

H. azteca presumably represents a species
introduced to Bermuda; however, one can
only speculate on its mode of introduction.
One possibility is a natural one carried out by
birds. Swanson (1984) proved that H. azteca
can be readily transported for short distances
between freshwater basins of North America
within the feathers of migrating waterfowl.
Although Bermuda is regularly visited by large
numbers of migrating birds, this mode of
dissemination is unlikely because of the

relatively large distance between Bermuda
and the nearest mainland (1000 km). Small
disseminules, attached to various parts of
birds’ bodies in mud, however, are a possible
means of long-distance dispersal (Carlquist
1974). As Seymour Pond is regularly used by
migratory herons, egrets, and waterfowl
(Slaughter 1975), this mode would seem to
have been a possible pathway of dispersal for
H. azteca. Consequently, the amphipod could
have been introduced at any time favorable
geologic and biotic conditions existed. The
Bermuda expeditions of A. E. Verrill, however,
suggest otherwise.

A. E. Verrill of the Yale Peabody Museum
made collecting forays to Bermuda in 1898
and 1901. Verrill had a keen interest in the
animals and plants introduced to the island,

3 Freshwater Amphipod,
Hyalella azteca from
Bermuda, First Report

and wrote extensively on these alien
organisms (Verrill 1903). An assiduous
collector, he amassed specimens of the native
and introduced biota from nearly every
conceivable habitat. He discovered many
inconspicuous animals, including ostracods
from cisterns and several marine amphipod
species that have yet to be recollected. Verrill
even ascertained through gut content analysis
that the principal food of the endemic skink,
Eumeces longirostris, was at that time the
amphipod beach hopper Orchestia agilis
[=Platorchestia ?platensis (Kroyer)]. Verrill
was obviously no stranger to amphipods. It
seems most probable, then, that Verrill would
have uncovered the presence of H. azteca if
this species had been introduced to the
islands by the time of his 1901 expedition. An
argument for the natural introduction of the
amphipod prior to this century, therefore,
seems a weak one.

Two human-mediated accidental
introductions of H. azteca in the twentieth
century can be considered. First, freshwater
was initially imported from North America to
Bermuda in 1938 (Wyers 1981). The likelihood
for the introduction of H. azteca in this
manner is low, however, because of the
necessary concurrence of many obvious
variables. A second, and more probable,
scenario would have been the coincidental
introduction of H. azteca when the mosquito
fish, Gambusia affinis, was imported. G. affinis
was introduced to Bermuda for mosquito
control in marshes, ponds, drainage ditches
and individual cisterns (Sterrer 1986),
presumably after 1933 (George 1971).
Shipments of these fish in water from North
America, particularly if bits of aquatic
vegetation were present, would seem to have
been the most likely means of introduction for
H. azteca.

Morphological Considerations

Two distinctive morphological features from
the Bermuda population of H. azteca should
be mentioned. First, Bousfield (1973) stated
that the number of dorsal teeth on the pleon
varies from one to three and that they are

Postilla 204

totally lacking in H. azteca inermis. Shoemaker
(1933) reported that dorsal teeth vary from
one to four in the dentate form, but he did not
specify the location of the mucronations on
the amphipods. The Seymour Pond
specimens possess two dorsal mucronations,
one each on the second and third segments
of the pleon, prominent even on the smallest
individuals.

Second, Stebbing (1903) described a
nonmucronate species, H. faxoni, from Costa
Rica, which he distinguished from H. azteca
inermis by the possession of three distal
plumose setae on maxilla 1, a feature to
which he attached considerable significance.
Weckel (1907), however, in discussing North
American H. azteca, noted that the number of
distal plumose setae on maxilla 1 is usually
two but occasionally three; subsequently he
synonymized Stebbing’s H. faxoni with H.
azteca. The setation of maxilla 1 on Seymour
Pond specimens agrees in most respects with
North American H. azteca; significantly,
however, all the individuals examined have
three distal plumose setae on the inner plate
of the first maxilla, and some even possess
four.

The maxillary characteristics of Bermuda H.
azteca are noteworthy and add to the
considerable variation described for this
widely distributed species. A comparative
analysis of known populations, especially of
those outside North America, may lead to an
evaluation of the assumed monospecific
status of this amphipod.

Material Examined

YPM 8432. 124622 Seymour Pond,
Southampton Parish, Bermuda. E. A. Lazo-
Wasem and A. J. Baldinger, collectors, 31
May 1987. From algae and submerged board.
YPM 8433. 174622 Seymour Pond,
Southampton Parish, Bermuda. M. F. Gable,
collector, 31 May 1987. 0.5 mm net dippings.

Acknowledgments

This study was supported in part by a Samuel
Riker Fellowship from the Bermuda Biological

4 Freshwater Amphipod, Postilla 204
Hyalella azteca from
Bermuda, First Report

Station to E. A. Lazo-Wasem, and also by the — Foundation. A Connecticut State University
Yale University Peabody Museum and the Research Grant partially supported M. F.
Eastern Connecticut State University Gable.

Literature Cited

Altrusa Club of Bermuda. 1972. As a matter of fact. Privately published. 192 p.

Bousfield, E. L. 1973. Shallow-water gammaridean amphipods of New England. Cornell University Press,
Ithaca, New York. 312 p.

Carlquist, S. 1974. Island Biology. Columbia University Press, New York. 660 p.

George, C. J. 1971. Ramblings on the natural history of Bermuda. Published privately.

Shoemaker, C. L. 1933. Amphipoda from Florida and the West Indies. Am. Mus. Novitates 598: 1-24.
Slaughter, R. A. 1975. Birds in Bermuda. Bermuda Book Store Ltd., Hamilton, Bermuda. 56 p.
Stebbing, T. R. R. 1903. Amphipoda from Costa Rica. Proc. U.S. Nat. Mus. 26(1341):925-31.

Sterrer, W. 1986. Marine fauna and flora of Bermuda. John Wiley & Sons, New York. 742 p.

Sterrer, W. and D. B. Wingate. 1981. Wetlands and marine environments, p. 107-22. In S. J. Hayward,
V.H. Gomez and W. Sterrer (eds.), Bermuda's delicate balance. Bermuda Biol. Sta. Res. Spec. Publ. No. 20.
Stock, J. H., B. Sket and T. M. Iliffe. 1987. Two new amphipod crustaceans from anchihaline caves in
Bermuda. Crustaceana 53:54-66.

Swanson, G. A. 1984. Dissemination of amphipods by waterfowl. J. Wildl. Manage. 48(3):988-91.
Verrill, A. E. 1903. The Bermuda Islands. Their scenery, climate, productions, physiography, natural
history, and geology; with sketches of their early history, and the changes due to man. Trans. Conn. Acad.
Arts Sci. 11:413-911, pls. 65-104.

Weckel, A. L. 1907. The fresh-water Amphipoda of North America. Proc. U.S. Nat. Mus. 32:25-58.
Wyers, S. 1981. Fresh water, p. 123-36. In S. J. Hayward, V. H. Gomez and W. Sterrer (eds.), Bermuda's
delicate balance. Bermuda Biol. Sta. Res. Spec. Publ. No. 20.

The Authors

Eric A. Lazo-Wasem. Division of
Invertebrate Zoology, Peabody Museum of
Natural History, Yale University, New Haven,
CT 06511.

Michael F. Gable. Department of Biology,
Eastern Connecticut State University,
Willimantic, CT 06226.