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PHYCOLOGIA 9 (3/4)
1970
Diatoms attached to floating Sargassum in the western Sargasso Seal
EDWARD J. CARPENTER
Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, U.S.A.
Accepted August 19, 1970
Thirteen species of diatoms, including two new species, were observed as epiphytes on Sargassum collected
at seven locations in the western Sargasso Sea. The most widespread species was Mastogloia binotata (Grun.)
CI., being found at all seven locations. Eight species of Mastogloia were observed along with one each of
Cyc/otella, Cocconeis, Nitzschia, Synedra, and Navicula. In comparison with epiphytic diatoms from inshore
and freshwater areas, the number of species of diatoms on floating Sargassum is relatively low.
Phycoiogia, 9(3/4): 269-274 (1970)
Introduction
Many investigations have been carried out on
littoral or epiphytic diatoms from inshore areas,
but few have been made on epiphytic diatoms
of pelagic seaweeds, such as Sargassum. Hent­
schel (1921) found Cocconeis sp. attached to
floating Sargassum in the Sargasso Sea, but no
further literature could be found on epiphytic
diatoms on floating Sargassum. The purpose of
this study was to determine the identity of such
diatoms from the western Sargasso Sea.
Methods
Sargassum was collected with a hand net at
seven locations (Table 1) on cruise No. 56 of
Atlantis II between Woods Hole and St.
Thomas, U.S. Virgin Islands. Sargassum fiui­
tans was collected at five locations and S.
natans was obtained at two. The Sargassum
1
Contribution No. 2536 from the Woods Hole Ocean­
ographic Institution, Woods Hole, Massachusetts
02543. This study was supported by National Sci­
ence Foundation Grant GZ ]]31.
was preserved in distilled water containing
formalin at a concentration of 3 per cent. To
clear the diatoms for microscopic examination
and remove them from the Sargassum, an ultra­
violet-light oxidation procedure similar to that
described by Swift (1967) was used. A I-cm
length of Sargassum stipe, two pneumatocysts
(flotation bladders), and five blades were re­
moved from the algae collected at each station.
These parts were placed in quartz tubes with
about 50 ml distilled water and 7-8 drops of
30 per cent H202• The tubes were irradiated
with ultraviolet light for twelve hours during
which time they were shaken periodically to
assure that all plant surfaces were irradiated.
After oxidation, Sargassum was visibly eroded,
and attached diatom frustules were released
into the water. The plant parts were washed
with distilled water to remove any diatoms that
remained on their surfaces and then examined
with a light microscope to be sure that no dia. toms remained. Before irradiation, dense popu­
lations of diatoms could be seen on the plant
surface.
TABLE 1
Location, date of collection, and species of Sargassum from which diatom samples are taken
Sample Number
1
2
3
4
5
6
7
Location
Species
Date (1970)
S. fluitans
36°42.5'N, 69°55.0'W
Feb. 5
S. fluitans
32°17.0'N, 68°49.0'W
Feb. 6
S. fluitans
30° 14.0'N, 67"41.5'W
Feb. 7
S. natans
28°06.0'N, 66°41.0'W
Feb. 7
S. natans
26°06.5'N, 65°28.0'W
Feb. 8
S. fluitans
24°00.0'N, 65°16.0'W
Feb. 8
S. natans
20000.0'N, 64°28.0'W
Feb. 9
269
CARPENTER: Diatoms on floating Sargassum
PHYCOLOGlA, VOL. 9(3/4), 1970
Mastogloia pusilla Gron. Cells about 1 3 p'm
long, 7 p'm wide, with 25 striations/10 p.m.
Present at five locations. Also found in the
Caribbean Sea (Hagelstein, 1938) and the
Mediterranean Sea (Peragallo and Peragallo,
1897).
Mastogloia gomphonemoides Hust. Found in
one sample. About 17 p'm long, 4 p'm wide,
with 36 striaellOp.m. Also seen at the South
Pacific island of Funafuti (Hustedt, 1959).
Apparently this is the first record for this
species in the Atlantic Ocean.
Mastogloia erythraea Grun. Frustule has two
and sometimes four enlarged loculi. Length 36
p'm, width 13 p'm, with 22 striae/10 p.m. Found
at five locations. Also found in the Caribbean
Sea, and the Red Sea (Hagelstein, 1938).
Mastogloia angulata Lewis. The specimens
observed in this study were smaller than those
described by Hustedt (1959). The frustules on
Sargassum were from 22-26 p'm long, and
10-12 p'm wide. Hustedt describes this species
as ranging from 35-80 p'm long and 25-30 p'm
wide. The areolae were difficult to see. They
could only be resolved in a few large indi­
viduals, so the species is drawn (Fig. 1) as the
majority of individuals appeared. Also found
in the Caribbean Sea and the Atlantic Coast of
North America (Hagelstein, 1938).
Mastogloia guillardi sp. nov. Valve elliptical,
ends obtusely rounded, 12-16 p'm long and
3.5-4.5 p'm wide. Striae slightly radiate, 30 in
10 p.m. Five coarse striae in median area. Lo-
For each sample the diatom frostules were
concentrated by settling and mounted on eight
glass slides in Hyrax. A transect was made
through each slide using an oil immersion ob­
jective of high resolution at X 1,350 magnifi­
cation, and the occurrence of each species was
recorded. From 200 to 800 cells were counted
for each station, and low magnification scans
assured that all species had been observed.
Electron micrographs were made of some of
the species. The cleared diatoms were placed
directly on a carbon coated grid with 60 p.
apertures and photographed at magnifications
of X54,300 and X70,000.
Results
The following diatoms were found:
Mastogloia binotata (Gron.) C l . This was
the most abundant diatom on Sargassum. It
was present at all stations and averaged 71 per
cent of the cell numbers. It ranged from 93 per
cent of the cell numbers at station four to 4.3
per cent at station five (Table 2). From 17-20
p'm long and from 12-14 p'm wide. Also found
in the Caribbean Sea (Hagelstein, 1938), and
in all coastal waters of France (Peragallo and
Peragallo, 1897).
Mastogloia ovulum Hust. About 17 p'm long,
8 p'm wide, 24 striae/ lOp., with 6 loculi per
side. Present in two samples. Also found in the
Mediterranean Sea, the Indo-Malayan region,
and at Beaufort, North Carolina (Hustedt,
1955).
TABLE 2
Distribution of diatoms on Sargassum and the per cent occurrence of species at each station
Location of Collection
Mastogloia binotata (Grun.) CI.
1
2
3
4
89.4
79.1
86.2
93.2
Mastogloia ovulum Hust.
Mastogloia pusilla Grun.
0.2
1.4
3.4
Mastogloia angulata Lewis
3.5
Mastogloia guillardi sp. nov.
0.3
3.1
2.8
0.7
24.1
0.5
1.4
Mastogloia gomphonemoides Hust.
59.8
5.7
10.7
3.8
22.7
1.4
4.0
1.2
5.0
0.2
Cocconeis dirupta Greg.
1.9
1.5
Nitzschia sp.
0.8
Synedra sp.
Navicula sp.
86.7
5.0
Mastogloia hulburti sp. nov.
Cyclotella meneghiniana Kutz.
7
21.9
0.5
1.4
4.3
6
12.8
0.5
Mastogloia erythraea Grun.
5
1.9
1.5
6.4
270
15.0
8.6
3.4
20.7
1.4
CARPENTER: Diatoms on floating Sargassum
PHYCOLOGIA, VOL. 9(3/4), 1970
c
A
B
]
J
]
J
L
]
FIG. 1. Diatoms found on Sargassum spp. A , Mastogloia gomphonemoides. B, M. binotata. C, M. angulata.
D, M. ovulum. E, M. pusi/la. F, M. erythraea. G, M. hulburti. H, M. guillardi. I, Synedra sp. J, Cocconeis
dirupta, two valves. K, Cyclotella meneghiniana. L, Navicula sp. M, Nitzschia sp. (Scales, all 101-'.)
271
CARPENTER: Diatoms on floating Sargassum
PHYCOLOGIA, VOL. 9(3/4), 1970
culiferous rim 1.5 ",m wide in the middle, and
undulate toward the ends. Five loculi on each
side of valve.
Valvae ellipticae, apicibus obtusis rotundatus, 1216 /Lm longae, 3.5--4.5 /Lm latae. Striae leniter
radiantes, 30/10 /Lm, cum quinque gravibus striis.
Annulus loculorum in media parte 1.5 /Lm latus, ad
extremitates undulatus. Loculi quinque in margine
valve.
This species is widespread, being found at
five of seven stations in the Sargasso Sea. Dedi­
cated to Dr. R. R. L. Guillard, Woods Hole
Oceanographic Institution.
Mastogloia hulburti sp. nov. Valves elliptical
with obtusely rostrate poles, 9-16 ",m long and
3-4 ",m wide. Transapical rows of striae slight­
ly radiate, about 32 in 10 ",m. Three to five
coarse median striae on each side. Loculiferous
rim 1.5 ",m wide in the middle, 0.5 ",m near
the poles. One locule on each side of the valve,
near the middle, placed obliquely to the op­
posite locule.
Valvae ellipticus, polis obtusis rostratus, 9-16 /Lm
longae, 3-4 /Lm latae. Series transapicales lenter
radiantes, circiter 32/10 /Lm cum 3-5 gravibus mediis
striis per marginem. Annulus loculorum in media
parte 1.5 /Lm latus, prope apices 0.5 /Lm latus, loculis
obliquis.
sp. nov. resembles M.
can easily be separated
by the presence of the three five course median
striae in M. hulburti. It differs from Mastogloia
obliqua Hagelstein in that M. hulburti does not
have an expanded central area. M. hulburti was
very common, being found at five of seven
locations. Dedicated to Dr. E. M. Hulburt of
the Woods Hole Oceanographic Institution.
Synedra sp. This diatom measures 60 ",m
long, 3 ",m wide, and has 18 striaell 0 ",m. It
resembles S. affinis Kutz., but it does not have
as broad a pseudoraphe.
Nitzschia sp. Cell is 27-37 ",m long, 3.5-4
",m wide, with 26 striae/10 ",m, and 9-15 keel­
points/10 ",m. The specific identity of this dia­
tom could not be determined.
Cocconeis dirupta Greg. Measures 4.5-10
",m wide and 7-18 ",m long. It is smaller than
the dimensions given by Cleve-Euler (1952)
and Van Heurck (1896). It is a widely distri­
buted species, being found on Atlantic and
Pacific coasts of North America (Hagelstein,
1938) and in the seas of France (Peragallo
and Peragallo, 1897).
Cyclotella meneghiniana Kutz. Measures 10
Mastogloia hulburti
minutissima Voigt, but
",m in diameter and contains 10 striae/10 ",m.
The valve surface is crossed by undulations.
Electron micrographs were made of this species
and compared with those made of C. menegh­
iniana and other Cyclotella species by Helmcke
and Krieger (1953) and Reimman, Lewin, and
Guillard (1963). The Cyclotella from Sargas­
sum was identical to C. meneghiniana except
that the former contained about 10 radial
striae/10 ",m as opposed to about 5 to 7
striae/10 ",m for the latter. The central area
of the frustule usually contained two pores,
spaced near each other. The border between
the marginal zone and central area is well de­
fined and the costae and intercostae in the mar­
ginal zone are similar to those shown by
Helmcke and Krieger (1953). Found at two
of seven locations. This is found in fresh waters
in Holland, England, and Ireland (Van Heurck,
1896), and North Carolina (Whitford and
Schumacher, 1969). Also, it is recorded from
Virginia tidal waters (Mulford, 1962) and has
been shown to grow in full strength seawater
(Reimann et al., 1963).
Navicula sp. Measures 1 ",m wide, 11 ",m
long, with 9-11 heavy craticula/length of cell.
It resembles Navicula cuspidata Kutz. in that
it contains craticula, but it is much smaller and
is linear-elliptic whereas N. cuspidata is lance­
olate. A raphe could not be resolved in light
microscope preparations but could be seen
clearly in electron micrograph preparations,
thus indicating that this diatom was not of the
genus Denticula. The specific identity of this
diatom could not be determined.
Discussion
Thirteen species of six genera of the epi­
phytic diatoms on Sargassum have been ob­
served in this study as opposed to the one
species of Cocconeis that Hentschel (1921)
found. However, there are fewer species of
diatoms epiphytic on floating Sargassum than
on inshore marine and freshwater plants. For
example, Jorgensen (1957) collected 57 species
belonging to 19 genera of diatoms from Phrag­
mites stems in two lakes in Denmark. Takano
(1961) found 42 species of 25 genera of dia­
toms on Japanese agar seaweeds from eight
localities on the Japanese coast. He later found
over 90 diatom species, 32 of which were the
main members of the epiphytic community, on
seaweeds from rock pools and intertidal zones
272
CARPENTER: Diatoms on floating Sargassum
PHYCOLOGIA, VOL. 9(3/4), 1970
at thirteen localities near Japan (Takano,
1962). Grunow (1867) has reported 35 species
of 18 genera of diatoms epiphytic on attached
Sargassum in the coastal waters of Honduras.
Since the distance between the northernmost
and southernmost sample locations in the pres­
ent study was about 2,000 km, and Sargassum
from seven locations was examined, it is sur­
prising that so few species of diatoms were
found on floating Sargassum. Apparently the
epiphytic diatoms of the western Sargasso �ea
are few in species and, since six of the specIes
were found at five or more stations, relatively
homogeneous in their distribution over this
rather large area.
Specimens of two of the species, Mastogloia
angulata and Cocconeis dirupta, were smaller
than specimens that have been observed pre­
viously from inshore areas. Possibly the reduc­
tion in size of the Sargasso Sea diatoms is an
adaption to the relatively low nutrient concen­
trations that are found there, although no
literature could be found that supports this
suggestion.
On microscopic examination, diatoms could
be seen covering whole areas of the Sargassum
plant surface. These dense concentrations a�e
of interest, since Fitzgerald (1969) found III
field and laboratory studies that freshwater
aquatic plants, Myriophyllum sp. Ceratophyl­
lum sp., Lemna minor, Cladophora sp., and
Pithophora oedogonium, remained relatively
free of epiphytes if the surrounding water was
deficient in nitrogen. He believes that the
aquatic weeds or filamentous green algae pre­
vent the growth of epiphytes by being better
able to use the limited nitrogen compounds
available. Since the Sargasso Sea is an area of
relatively low nutrients, it is surprising that the
Sargassum contains heavy growths of diatoms.
A possible explanation for the epiphytes on
Sargassum is given by Culliney (1970) who
found that the phosphate (PO-P) concentra­
tions from water in a floating Sargassum patch
was two to three times greater than that in the
surrounding water. Apparently, diffusion of
phosphate from Sargassum or from the ex­
cretory products of the animals associated with
Sargassum significantly enriches the immedi­
ately surrounding water. In contrast to the
freshwater plants that Fitzgerald (1969) stud­
ied, it is possible that the Sargassum acts to
provide a favourable environment for epiphytes.
Acknowledgements
I would like to extend my appreciation to
Mr. W. Gary Metcalf, Chief Sctentist on Cruise
56 of Atlantis II for allowing me to participate.
Also, I thank Dr. Charles Remsen for the
electron micrographs of the diatoms, Dr. E. M.
Hulburt for writing the latin descriptions of the
species, and Dr. Paul Hargr;;tve.s of t�e U�i­
versity of Rhode Island for aId III the IdentIfi­
cation of some of the species. I thank Drs. L.
Hobson, G. Grice, T. Lawson, and W. Dun­
stan for reviewing the manuscript.
Addendum
I have recently observed two other diatoms,
(Breb.) Ralfs and
on Sargassum from
the western Sargasso Sea.
Asteromphalus heptacis
Licmophora sp. epiphytic
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