HUW I. GRIFFITHS
DAVID S. MARTIN
Ness and Morar Project
the early years of this century the late Sir John
Murray commenced pioneer investigations into many
aspects of Loch Ness (Murray, 1904 and 1908; Murray
and Pullar, 1910), and some seventy-five years
later this was followed by the extended survey
carried out by Dr. Peter Maitland and his colleagues
(Maitland, 1981), but much of the most recent
work, particularly in the study of the benthic
fauna, has not yet been published.
A preliminary analysis by Shine and Martin
(1988) indicated that ostracod Crustacea ('seed
shrimps') appeared to be an important component
of the zoobenthos, numerically comprising almost
60% of the invertebrates in the deepest parts
of the loch. Subsequently, both quantitative and qualitative studies of the ostracod
fauna of Loch Ness were undertaken (Griffiths,
Martin, Shine and Evans, 1993), and since then,
additional data on the ostracods of the loch have
become available, as well as a small dataset based
on samples taken from the profundal benthos of
Loch Morar. This
current paper uses all these data to further investigate
the patterns of distribution and community structure
in benthic lacustrine ostracods.
were collected both qualitatively, by dredging,
and quantitatively, with a 15 x 15 cm Ekman grab,
and a custom-built 10.3 cm diameter gravity corer. Ostracods were extracted
by passing sediment samples through a bank of
sieves down to 125 m , and then by individually hand-picking specimens from
sediment residues under a low-power dissecting
microscope. Ostracods were killed in 30% ethanol, fixed
in 70% ethanol, and identified using Henderson
(1990), and Meisch
(1985) for Potamocypris sp. Taxonomic nomenclature follows Griffiths and
Quantitative samples were used to
assess ostracod densities in different areas of
the loch. Qualitative
data allow investigation of the proportional composition
of the ostracod community, both as a whole (Figure
1, 24K), and in Urquhart Bay in the North
On two occasions it was possible to extrude
cores in such a way as to allow examination of
the depth distributions of ostracods within sediments
in ostracod densities in various parts of the
loch were examined by Student's t-test (Parker,
Both the samples from Loch Morar result from
qualitative sampling, but are treated in the same
way as those from Loch Ness.
Ostracod diversity from these samples was
assessed by Brillouin's Index (HB) (see Magurran,
1988), allowing comparison with diversity values
obtained from Loch Ness (Griffiths et al., 1993).
the course of these studies, only the undernoted
seven ostracod species were recovered from Loch
Candona angulata G.W. Müller, 1990
Candona candida (O.F. Müller, 1776)
Cryptocandona reducta (Alm, 1914)
Cypria ophthalmica (Jurine, 1820)
Cyclocypris ovum (Jurine, 1820)
Potamocypris smaragdina (Vavra, 1891)
Psychrodromus robertsoni (Brady and Norman, 1889)
In addition, Candona
neglecta Sars, 1887 was reported from the
loch in samples taken during the early 1980s,
but has not been identified since. Of these taxa, specimens of the lotic water species P. robertsoni have only been recovered
from the guts of Three-spined Sticklebacks Gasterosteus
aculeatus, and are thought to have been ingested
in one of the many streams which feed into the
benthopelagic species Cypria
ophthalmica is the commonest ostracod in Loch
Ness, making up over 61% of the entire fauna recovered.
In contrast, P. smaragdina and C. ovum have only been encountered as one and two specimens, respectively.
The overall density of benthic ostracods in Loch Ness
was reported as 262 340 individuals/m2 by Griffiths et al. (1993), who noted a clumped distribution
within the ostracod taxocene as a whole. It has now been possible to examine densities in three areas within
the loch: the
South Basin, the North Basin, and Urquhart Bay.
The highest ostracod density yet identified is that of
the South Basin (mean = 1,835 ostracods/m2; extrapolated range between 0 and 7,284 individuals/m2). The overall mean density in the North Basin
is 125 ostracods/m2 (extrapolated range between 0 and 657 individuals/m2), but rather
lower densities occur in Urquhart Bay (mean =
88 ostracods/m2; extrapolated
range between 0 and 205 individuals/m2). Density comparisons within the North Basin
are not statistically significant (P >0.05),
whereas a significant difference exists between
the densities observed in the North and South
Basins (t = 2.76, P <0.05).
Ostracod distributions are clumped in all
these sub-divisions of the loch.
The two vertically sub-divided cores provide comparatively
little information on depth distributions. The first 6.0 cms were examined of a core taken
from 215 m in the North Basin (Figure
3a, 6K). Here C. ophthalmica occurred
throughout the sediments, presumably burrowing
deeply to feed. Candona
angulata occurred to a depth of 5.0 cm, but
C. reducta (which belongs to an infaunal genus) was only represented
by a single individual.
In the first 2.0 cms of the core taken
from 150 m in the South Basin (Figure
6K), ostracods were present at higher densities. Only C. ophthalmica and
were present, the former in comparatively high
numbers in the top 1.0 cm layer. The depth
to which ostracods actually penetrate Loch Ness
benthic sediments is currently unknown, although
it is surprising to find the benthopelagic form
C. ophthalmica at these depths in the sediments.
The Loch Morar samples were both taken from a depth of
300 m on 8th June 1992, and the fauna identified
in the two samples are listed below:
The fauna of the two Loch Morar samples are fairly similar
to the samples from Loch Ness, except that one
benthic species (C. angulata) is absent, although the free-swimming
ovum is present in relatively high numbers.
Species richness (four taxa) is similar
to that found in much of Loch Ness, and in other
105, The Scottish Naturalist: Benthic Ostracods
in the Profundal Zone of Loch Ness p144
oligotrophic temperate lakes, but HB values are within
the upper range of the values reported from Loch
Ness (Griffiths et al., 1993). As far
as we are aware, these samples (from 300 m) represent
the deepest records yet known for C.
Griffiths et al.
(1993) have shown that no correlations exist
between depth and either ostracod diversity or
the abundance of individual species within the
loch. Comparison of the ostracod communities in the
North and South Basins (Figure
1) shows that species-richness is lowest
at the southern end of the South Basin, where
the influence of the River Oich is greatest (Bennett,
remains at either 3.0 or 4.0 throughout much of
the loch's length, only reaching 5.0 in the upper,
shallower reaches of the North Basin. Within Urquhart Bay (Figure
2), which comes under the influence of
the Rivers Enrick and Coiltie, the community appears
to be a little more uniform in composition, although
ostracod distributions are still clumped (see
It is clear that ostracod densities are considerably
higher in the South Basin than in the North, and
this is believed to reflect the higher sedimentation
rate of the South Basin, coupled with quantitative
increases in the levels of organic inputs.
105, The Scottish Naturalist: Benthic Ostracods
in the Profundal Zone of Loch Ness p145
However, this increase is not accompanied by increases
in either diversity or species-richness.
The latter never rises above 4.0 in the
South Basin, and several samples consisted only
of C. ophthalmica
and C. angulata, both of which are eurytopic,
Candona candida was largely absent from
the South Basin, except in deep-water samples,
possibly suggesting that C. candida is sensitive to some aspect
of the conditions associated with higher levels
of sediment deposition.
The sediments of the deeper parts of the loch are primarily
of laminated muds, with areas of sand or organic-rich
sands in the vicinities of river mouths (Bennett,
there appears to be little linkage of fauna and
sediment type, even when the sandy, organic substrata
of Urquhart Bay are compared with the remainder
of the loch.
This provides further evidence that the
restricted ostracod fauna of Loch Ness is (to
some degree at least) a product of the homogeneity
of the benthic sediments (Griffiths et
The use of ostracods in palaeolimnological analysis at
Loch Ness has so far proved impossible.
The sediments are predominantly acidic,
which causes rapid post-mortem degradation of ostracod valves.
Despite this, it is believed that the loch
has represented a comparatively stable environment,
at least since 1868, when a catastrophic flooding
event (Anon., 1868; Barron, 1985) resulted in
the deposition of a layer of clay throughout the
benthos (Bennett, 1993).
The benthic fauna of a given water-body must largely
be determined by site-based variables (abiotic
interactions), the influence of biotic constraints
becoming more apparent over time (Forester, 1991). Griffiths and Evans (1992) have argued that
the co-occurrence of several related ostracod
species (e.g. congeners) reflects niche-packing,
since species which are essentially similar in
their modes of life partition the resources available.
At Loch Ness, many of the benthic samples contain three
closely-related species: C.
angulata, C. candida and C.
reducta, plus C. ophthalmica. Of these,
the first two are semi-infaunal, and C.
reducta is markedly so.
Cypria ophthalmica, however, is free-swimming
and hardy. Combinations
of these species (or a variant composed of C.
neglecta rather than C.
angulata) are also present in Loch Morar,
at Cosemeston Lakes in South Wales (Griffiths
and Evans, 1991) and elsewhere (e.g. Löffler,
1975; Jónasson, 1978; Danielopol et al., 1985). This may suggest some sort of 'stable' ecological
unit, pre-adapted to partitioning simple benthic
habitats. Since this faunal unit is so widespread, it
also suggests the question, - to what extent are
benthic niches pre-empted? - (see Krebs, 1985).
The presence of this fauna may simply reflect
the inability of other groups to survive in
105, The Scottish Naturalist: Benthic Ostracods
in the Profundal Zone of Loch Ness p146
these environments, but its recurrence perhaps
does suggest a colonising fauna which, once established,
is difficult to displace.
The presence of such a faunal element,
exhibiting a high degree of niche pre-emption,
would also act to limit benthic colonisation,
and restrict incoming colonists to littoral habitats,
or to other, possibly less favoured, niches.
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Huw I. Griffiths, Department of Genetics,
of Leeds, Woodhouse Road, LEEDS LS2 9JT.
David S. Martin, Loch Ness and Morar Project,
Ness Centre, DRUMNADROCHIT, Inverness-shire IV3