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A meeting of The Malacological Society of London, 28-30 March 2003
O rganized by Professor Alan Hodgson (Grahamstown) and Dr Hugh Jones
(Manchester) at the Universities Marine Biological Station, Millport,
Isle of Cumbrae, Scotland.
The Marine Station
on Cumbrae Island in the Clyde estuary gave a warm welcome to participants
from over a dozen countries who enjoyed meeting in a quiet and convivial
atmosphere, amid beautiful scenery. The sessions covered morphology,
systematics, ecology and conservation; reproduction and genetics;
and feeding biology and behaviour, with invited talks from David Lindberg,
Richard Hartnoll, Steve Hawkins, George Branch, Gerhard Haszprunar
and Alexander Nederbragt.
Abstracts
of Presentations:
(alphabetical order of first author)
1. The effect of alkaline seawater on maturation
and fertilization rates of oocytes from two Patella species
ROSANA AQUINO-SOUZA1,2 AND PAUL A. TYLER1
1.University of Southampton, Southampton
Oceanographic Centre.
2.Marine Biological Association of the
UK.
In Patella, the only possible way to obtain regularly a large number
of gametes is through artificial spawning, which yields a substantial
amount of unripe gametes. This fact makes it difficult to carry out
fertilisation kinetics bioassays because of very low fertilisation rates.
In many invertebrates including Patella species, it has been shown that
the maturation process involves an alkalinization of cytoplasm, and
that artificial alkalinization can unblock meiosis. Studies performed
with P. aspera have shown that this method increases fertilisation rates
and therefore could be useful for fertilisation kinetics assays. The
first study on development of Patella revealed that oocytes from artificially-spawned
individuals appear very irregular in shape. In order to attain suitable
fertilisation rates, these must become spherical and the chorion must
disappear in patches, which are signs of maturation. Using P. depressa
and P. vulgata, this work examined the potential use of oocyte alkalinization
on fertilisation kinetics research. Three approaches were done: a) Investigation
on whether alkalinization accelerates the process of shape change and
chorion disintegration, using media at different pH values; b) tests
of the effect of alkalinization, performed at different pH, on fertilisation
rates; c) analysis of the influence of alkalinization on fertilisation
rates, at different sperm concentrations. Results from P. depressa experiments
show that immersion in a variety of alkalinization media (with different
pH values) induces oocytes to become spherical and the chorion to disappear
within a shorter period of time than immersion in control media. The
optimum pH was 9.5. The effects of alkalinization, by immersion in pH
9.5, on shape and chorion were also tested in P. vulgata showing similar
results. In P. depressa, alkalinized oocytes showed significantly higher
(p<0.05) fertilisation rates than those kept in control media or
those recently spawned. Quantitative and qualitative experiments revealed
that, at various immersion time treatments (1, 2.5 and 5.5 min.), alkalinization
at pH 9.5 yields the highest fertilisation rates than other pH treatments
(normal, 9.0, 9.5, 10). The effects of alkalinization at pH 9.5 and
sperm concentration on fertilisation rates were tested in P. vulgata
through a two-way ANOVA. There was a strong interaction between the
two factors: the effect of alkalinization was enhanced with increasing
sperm concentration. The highest fertilisation rates in both treatments
were achieved at the same sperm concentration value, which matched that
found in an earlier work using non-treated oocytes. After attaining
a peak, fertilisation rate appears to have a tendency to decrease with
increasing sperm concentration, in accordance with previous results.
This work shows that oocyte alkalinization can improve the effectiveness
of fertilisation kinetics research in species that cannot be induced
to spawn naturally.
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2.
Isolating
the effects of larval dispersal on phylogeographic patterns in patellogastropods
EMINA BEGOVIC AND DAVID R. LINDBERG
University of California Berkeley
Using the cytochrome oxidase I gene (COI) from three North Pacific
patellogastropod species that co-occur on coralline substrata in the
nearshore subtidal throughout the Aleutian Islands, we examined how
differences in larval dispersal ability affect the population structure
of nearshore marine taxa with diverse life histories. We also examined
currents as vectors of larval dispersal and their impact upon the
genetic population structure of broadcasting versus brooding taxa.
Taxa were chosen based upon their similar geographic ranges, presumed
ecological similarities, and phylogenetic position. Tectura testudinalis,
Erginus sybaritica and Erginus apicina all feed on coralline algae,
however T. testudinalis is a broadcast spawner and E. sybaritica and
E. apicina are brooders. We hypothesize that these differences in
reproductive strategy would be reflected in each species' genetic
population structure. Our COI data indicate that population structure
is directly affected by reproductive life history strategies when
the ecological context of the study organisms is held constant and
phylogenetic effects are accounted for, giving us a better measure
of dispersal's contribution to population structure.
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3.
How good are we at predicting the effects of alien species? The case
of Mytilus galloprovincialis versus endemic limpets
GEORGE M BRANCH AND C NINA STEFFANI
Department of Zoology, University of Cape Town, Rondebosch 7701, South
Africa
The alien invasive Mytilus galloprovincialis has encroached on much
of the west and south coasts of South Africa. Four approaches were
used to predict its impacts. First, the history of its effects elsewhere
led to predictions that it is likely to be invasive and dominate shores
elsewhere in the world, particularly rocky, exposed, temperate shores.
Second, studies of its biology led to the prediction that it will
be competitively superior to endemic mussels because of its fast growth,
high reproductive output and tolerance to desiccation. Third, the
fact that filter-feeders in general, and mussels in particular, favour
wave-exposed shores led to the prediction that the interaction between
M. galloprovincialis and an endemic limpet, Scutellastra argenvillei
will be moderated by wave action. Fourth, the impacts of this mussel
on limpets will be influenced by the sizes of the respective species,
as can be illustrated by its effects on a large species, S. argenvillei,
and a relatively small species, S. granularis. Data from the west
coast show that all four approaches to forecasting the effects of
M. galloprovincialis were successful in predicting its effects. But
lest we indulge in too much congratulatory back-patting about our
predictive abilities, there is one last case to consider. M. galloprovincialis
is a sessile, rocky-shore filter-feeder. What predictions would we
venture concerning its effects (or lack of effects) on a predatory,
mobile, sandy-beach crab, Ovalipes trimaculatus? I leave the outcome
open, with a challenge to make your own forecast – and the reasons
for it.
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4.
Causes of rarity and range restriction in an endemic, threatened limpet,
Siphonaria compressa: the role of interactions between eelgrass and
sandprawns
GEORGE M. BRANCH, TIMONY SIEBERT AND ANDREA ANGEL
Department of Zoology, University of Cape Town, Rondebosch 7701, South
Africa
The eelgrass Zostera capensis is restricted to high-shore beds in
Langebaan Lagoon on the west coast of South Africa, and we hypothesized
that the main reason for this is that bioturbation by the sandprawn
Callianassa kraussi prevents it from living further down the shore.
To test this, experimental transplants of Zostera were introduced
into lower-shore areas that were either occupied by sandprawns or
had been experimentally cleared of sandprawns. The eelgrass grew prolifically
in areas lacking sandprawns and established dense and expansive beds,
thus confirming the hypothesis. The formation of these beds also led
to entirely different communities developing in previously sandprawn-dominated
sandflats. More interestingly, these low-shore beds were colonized
by extraordinarily high densities of a normally rare siphonariid limpet,
Siphonaria compressa, which occurs exclusively in Langebaan lagoon
and only on eelgrass. Further experiments explored the possibility
that this limpet is rare in the high shore because of a combination
of physical stress and competition with an abundant gastropod, Assiminea
globulus. Using a combination of transplants and caging proved the
former true and the latter false. Siphonaria compressa is thus caught
between a rock of physical high-shore stress and a hard place of Callianassa
bioturbation in the low shore. This is one of the few experimental
demonstrations of the causes of rarity in any marine invertebrate.
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5.
Modelling foraging decisions in limpets
MICHAEL T. BURROWS1 AND GIACOMO SANTINI2
1.Scottish Association for Marine Science,
Dunstaffnage Marine Laboratory, Oban, Argyll, PA37 1QA, U.K
2.Dipartimento di Biologia Animale e
Genetica, Università degli Studi di Firenze, Via Romana 17,
I-50125, Italy
Foraging excursions in homing limpets can be seen as a hierarchy of
behavioural decisions. A decision is made to leave the home scar at
the beginning of each excursion, while at some point during foraging
a decision is made to return home. We have developed a model that
predicts optimal strategies of time budgeting of foraging bouts in
contrasting conditions. The model incorporates energetic costs of
movement and metabolism, energetic benefits of and constraints on
ingestion and digestion, and risks of predation in changing tidal
environments by day and night.
Once a decision to forage has been made, limpets may choose a direction
to embark upon. This decision may be influenced by prior experience
of returns from different parts of the foraging ambit, and the predictability
or patchiness of the food resource in successive visits to the same
areas. These influences have been included in a further model. This
predicts that limpets should return outward along the previous inward
track only when microalgal standing crop is predictably patchy, such
that the animal will get an above-average reward by returning to the
same area. Limpets that avoid the last track will be more successful
than random foragers when returns from sequential visits are negatively
autocorrelated, either by patch depletion or particular small-scale
spatial distributions.
Sequential non-random revisiting of previously exploited foraging
patches has been seen in Onchidium sp., Patella vulgata and the chiton
Acanthopleura gemmata. In contrast, the Mediterranean high shore limpet
Patella rustica shows a pattern of cropping based on random angular
selection, weakly biased towards avoidance of the last foraging excursion.
Our model suggests that a better understanding of the spatial patterns
of the food resource may explain the foraging patterns of different
species.
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6.
Size distributions in populations of Patella sp from the Scottish
west coast and Western Isles from digital photography
MICHAEL T. BURROWS AND LINDA ROBB
Scottish Association for Marine Science, Dunstaffnage Marine Laboratory,
Oban, Argyll, PA37 1QA, U.K.
Large-scale effects such as those associated with climate change may
also influence populations of susceptible species along latitudinal
and regional gradients. Size-frequency data and population density
estimates were collected in summer 2002 to detect such potential large-scale
influences on populations of intertidal grazing limpets, over an area
encompassing the Scottish west coast and Western Isles. On the mainland,
sites were selected around 12 sea lochs spanning the coastline from
the Firth of Clyde to beyond Cape Wrath. Four sites were selected
in each loch: two on the open coast to each side of the mouth of the
loch, one in the lower region of the loch and one in the middle region
of the loch. The location of sites within lochs was designed to detect
differences due to smaller-scale gradients from open coastal, exposed,
conditions to sheltered sea loch conditions. Comparison among lochs
from different regions would detect larger scale effects.
All limpets in digital photographs of areas (500 cm2 to 10000 cm2,
mean 3000 cm2) from the lower (5) and upper (5) middle shore were
measured, giving average size and density estimates for more than
500 areas. Size and density were strongly negatively related. Analyses
of variance showed there was no significant large-scale differences
in size or density among regions comprised of adjacent lochs, although
shifts in boundaries among regions may produce such differences. There
were however large and significant differences between sites within
lochs, and also significant differences between shore levels in the
range of sizes (lower shore samples had larger standard deviations
of size). Where differences among sites did exist, sites inside lochs
tended to have larger and sparser limpets.
Influences on limpet population density and size structure may thus
be dominated by factors operating at smaller topographical scales
than whole coastlines, such as local conditions influencing larval
settlement and recruitment, and food availability.
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7.
Using bulk stable isotopes to investigate nitrogen assimilation by
the common limpet, Patella vulgata L.
LIZ CAMPBELL1,2, GORDON B. CURRY1 AND TOM PRESTON2
1.Division of Earth Sciences, University
of Glasgow, Gregory Building, Glasgow, G12 8QQ, Scotland
2.Scottish Universities Environmental
Research Centre (SUERC), Rankine Avenue, East Kilbride, Glasgow, G75
0QF, Scotland
Due to increasing levels of nitrogen pollution, a need has arisen
to find a biomonitoring organism which can be used to identify and
monitor sources of nitrogen in estuarine and marine environments.
The common limpet, Patella vulgata L., could potentially be used by
measuring bulk stable nitrogen isotopes (d15N, the ratio 15N/14N)
in its tissues. By measuring d15N (and d13C, the ratio 13C/12C) in
each sample, it may be possible to identify the sources of nitrogen
assimilated by each limpet. However, before we can use this species
as a biomonitoring organism for nitrogen pollution, seasonal variations
in nitrogen assimilation, and their effects on d15N and d13C in P.
vulgata L., must be fully investigated.
Specimens were collected on a monthly basis over a two-year period
from a rocky shore in the Firth of Clyde, Scotland. d15N and d13C
was measured in various tissues, and compared with corresponding biochemical
and biometric data. Preliminary results show that d15N and d13C vary
seasonally, and are inversely related in certain months in correspondence
with changes in limpet biometrics. Further investigations into nitrogen
assimilation by P. vulgata L. will include: (i) measurements of d15N
and d13C in the epilithic mat food source, and (ii) labelling the
food source with 15N tracer in aquaria to gain further insight into
how limpets assimilate nitrogen into their various tissues.
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8.
Aggregation by limpets results in a reduced vulnerability to predation
R.A. COLEMAN AND T. THEOBALDS
Marine Biology and Ecology, University of Plymouth
Defences against predators may be physiological, morphological, behavioural
or combinations thereof and are nearly always induced, at least in
part, by prey perception of predation risk. One anti-predation behaviour
is to group; however the way in which this translates into a reduction
in risk to an individual is not fully understood. Here we demonstrate
a novel aspect of grouping as a defence, using aggregated limpets
as a test system. Although not having experienced the predator directly,
potential prey in aggregations may detect the vibrations of an attack
on a group member and reduce their vulnerability to predation. This
effect travels further and lasts longer than would be expected. Our
results imply that for a prey showing a mix of distributions (some
solitary and some aggregated) aggregations may be easier to find,
but actually represent a single predation opportunity.
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9.
Variability in Patella gomesii Drouet, 11858 (Patellogastropoda: Mollusca):
species or ecomorphs? Preliminary results on morphological data
J. CÚRDIA, J1, J.M. COSTA1,3 AND A.M.F. MARTINS2
1. Department of Technological Sciences
2. Department of Biology, Universidade
dos Açores, Rua Mãe de Deus, Apartado 1422, 9501 - 801
Ponta Delgada, Portugal: jcur...@notes.uac.pt
3. CIBIO, Center for Research in Biodiversity
A preliminary evaluation on habitat partitioning and degree of differentiation
of two ecophenotypes of the endemic azorean Patella gomesii was presented.
96 limpets were collected from 3 habitats (Água d’Alto,
São Miguel): sheltered; highly exposed in the upper eulittoral;
medium exposed in the midshore. Five parameters were analysed: shell
length (SL), width (SW) and height (SH); radula length (RL) and number
of radular teeth rows (RT). Clear differences among groups were detected.
Principal Components Analysis clearly separates specimens from exposed
and sheltered areas, mainly in the second factorial axis associated
to RT (92%). The former are smaller in size (SL and SW, ANOVA p<0.001)
but present longer radulas and more rows of teeth than the latter
(RL and RT, ANOVA p<0.001). Limpets from the intermediate exposed
area are larger than those from the exposed area (SL and SW, ANOVA
p<0.01) and have different radulas (RL and RT, ANOVA p<0.001).
To avoid shell size effect, analyses were repeated for individuals
with shell lengths between 17 and 22 mm, showing that RL, RT and SH
for exposed and sheltered areas are significantly different (ANOVA,
p<0.001). The data suggest the presence of ecomorphs.
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10.
Some chromosome studies on the genus Fissurella
1C.E. DIUPOTEX, 2S.A. HERNANDEZ AND 1A.M. URIBE
1.Instituto de Ciencias del Mar y Limnología
Universidad Nacional Autónoma de México
2.Instituto de Química U.N.A.M.
Karyotypes in Fissurella of the family Patellaceae have been studied.
In this genus, chromosome numbers of 14(n) to 16(n) and 28(2n) to
32(2n), were observed. The metaphase chromosome complement of Fissurella
consists of 5 pairs of metacentrics, 3 pairs of sub-metacentrics,
two pairs of submeta- or metacentrics and two pairs subtelo- or submetacentrics.
No sex chromosomes were found. Chromosomes are generally small to
medium-small, with the occasional presence of medium-large chromosomes.
The metaphase chromosome complement of Fissurella consists of 10 pairs
of metacentric and two pairs of meta- or submetacentrics The value
of chromosome numbers as a character for the examination and analysis
of karyotypes, for future comparative studies in phylogenetic systematics
in the Patellacea, the evolutionary trends in chromosome number and
morphology, to enhance our understanding of the speciation process
are discussed.
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11.
How many limpets can we catch in the islands of Faial and Pico in
the Azores?
ROGÉRIO R. FERRAZ1, RICARDO S. SANTOS1, STEPHEN J. HAWKINS2
AND GUI MENEZES
1Department of Oceanography and Fisheries, University of the Azores
2Marine Biological Association of the United Kingdom
Limpets (Patella aspera) are appreciated as a gastronomic delicacy
by local people in the Azores. Since the mid-80’s, the demands
for these gastropods has lead to increased harvesting. Some management
rules have been implemented in order to deal with the depletion of
the stock. These rules were supported by studies of density and biology,
and for this a method for biomass estimation was developed. A monitoring
program was established in 1998 according to this method which is
based on 15 (or 30) minutes catch dives, performed by a former limpet
harvester, who catches all the limpets seen in a surveyed area (50
or 100 metres of coastline dependent on the time frame). In 1998 and
1999 the method was evaluated in Faial and Pico Island prior to (April
and May) and after (October and November) the harvesting period in
order to detect if the method was adequate for dealing with stock
management. Analyses of the data showed that the sampling effort (number
of dives) was not sufficient to show statistical significance. However,
the results proved that the method can detect and roughly quantify
the commercial catches made during the harvesting period. In 1998
the biomass estimation for Faial showed that the commercial exploitation
was very low, which was confirmed by the official commercial sales.
Some commercial harvesters confirmed that this low activity was due
to the danger offered by the collapse of cliffs (a consequence of
the 1998 earthquake). During the same period, and using the same method
in Pico Island, we found differences between pre- and post-capture
period. Even differences between sex ratios after the capture period
(fewer females) were detected. This could be easily explained by the
fact that this species is protandrous, and females are the main target
of limpet harvester’s due to their greater size. The accuracy
of the method was enhanced after the number of sampling stations increased
and is currently used to monitor and manage this resource. The continuous
application of this method for biomass estimation has shown that when
the implemented management rules are kept, limpet populations remain
close to sustainable levels.
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12.
The importance of a crevice environment to the prosobranch limpet
Helcion pectunculus
1.DAVID R. GRAY AND 2.ALAN N. HODGSON2
1.Department of Zoology & Entomology,
Rhodes University, Grahamstown 6140, South Africa
E-mail: a.ho...@ru.ac.za
2. Department of Animal Science, Hartpury
College, University of the West of England, Gloucester, GL19 3BE,
U.K.
Helcion pectunculus have an organized distribution within crevices
with smaller, younger limpets being towards the back of the crevice
and larger, older limpets towards the crevice mouth. The crevice refuge
supplies H. pectunculus with a stable and buffered environment with
higher relative humidities and lower rock surface temperatures than
adjacent exposed rock surfaces. Limpet body temperatures were significantly
lower in crevice refuges compared to limpets on adjacent exposed rock
surfaces. Body temperatures never exceeded the rock surface temperatures.
It is suggested that this is a result of morphological adaptations
such as shell ornamentation and allometric growth. Helcion pectunculus
is one of the least tenacious limpets occurring along the South African
coast and it is suggested that wave action is a major factor in governing
both the activity patterns and homing behaviour of this limpet. Limpets
deprived of a crevice refuge experienced extremely high mortalities,
with 45% of limpets being lost during the first high tide period.
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13.
Extinction risks and harbours as marine reserves?
J.M. GUERRA-GARCÍA1, J. CORZO1, F. ESPINOSA1, D. FA2, J.C.
GARCÍA-GÓMEZ1
1.Laboratorio de Biología Marina,
Departamento de Fisiología y Zoología, Facultad de Biología,
Universidad de Sevilla, Avda Reina Mercedes 6, 41012 Sevilla, Spain.
E-mail: jmgu...@us.es
2.The Gibraltar Museum, 18-20 Bomb House
Lane, Gibraltar.
|
The
mollusc Patella ferruginea, in danger of extinction, is the most
endangered marine invertebrate species on the list of the European
Council Directive 92/43/EEC on the Conservation of Natural Habitat
of Wild Fauna and Flora. Although its relative abundance in Paleolithic
and Neolithic deposits indicates an extensive former distribution
in the Western Mediterranean, its range has progressively contracted.
The populations regression has been attributed to the generalised
increasing pollution levels on the marine coasts, and especially
to human predation through the collections of specimens for food,
fishing bait and decorative purposes, as this mollusc is one of
the nicest limpets of the Mediterranean. |
Today, the species
has practically disappeared in the Iberian Peninsula and the North
African coast of the Strait of Gibraltar . Strikingly, at the coast
of Ceuta, and especially inside the harbour, we have found dense and
stable populations of Patella ferruginea (mean of 11.33 individuals/10
m inside the harbour, 5.54 in North Bay and 6.96 in South Bay). The
values registered inside the harbour were significantly higher than
those registered outside.
Taking into account that P.ferruginea is considered a k-strategist
species, the high density of this mollusc measured inside a harbour
is even more striking. Consequently, the design of the harbour of
Ceuta, provided with a channel which increases the water renovation,
should be taking in consideration for future civil engineering in
order to reduce the negative impact of harbour building on marine
environments.
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14.
A history of limpet research—the Isle of Man connection
RICHARD G HARTNOLL
Port Erin Marine Laboratory, University of Liverpool, Isle of Man
Research on limpets at the Port Erin laboratory falls roughly into
three phases. The first was the work by Orton and colleagues in the
thirties and forties on the basic biology of Patella. The second phase
was by Burrows, Lodge, Jones and Southward in the forties and early
fifties. This was pioneering field experimentation examining the functional
role of limpets as grazers. The final phase commenced in the late
seventies, and again concentrated on the functional role of limpets
via critical field and laboratory experimentation. It culminated in
the major EUROROCK collaboration of the late nineties. Many workers
participated in this final phase, but it is notable that Hawkins had
his finger in most of the pies. Here these various studies are reviewed,
and an attempt is made to place them in a wider perspective and to
evaluate their significance.
 |
Limpet removal
strip, 10 x 115 m, at Callow Point, Port St Mary, Isle of Man,
photographed in mid-July after limpets removed in previous winter.
From Jones NS (1948) Trans Liverpool Biol. Soc. 56, 60-77. |
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15.
North east Atlantic Patella: who they are, where they are and what
they do
STEPHEN J HAWKINS et al.
Marine Biological Association, Plymouth, and University of Southampton
The talk was an ecologists’ view of North East Atlantic and
Mediterranean Patella species summarising work done by S J Hawkins’
research group and collaborators over the last 25 years. Intensive
taxonomic activity over the last 10 years has essentially confirmed
that Christiaens’ names were mostly right. Although biochemical,
molecular and cladistic approaches have generally clarified their
phylogenetic relationships and the status of allopatric subspecies
there are still some unresolved problems. Better taxonomic knowledge
has provided a clearer biogeographic picture. Behavioural and ecophysiological
studies have allowed an individual based approach to modelling. Broadscale
ecological experiments have also demonstrated the important role that
limpets play in the littoral communities of the North Atlantic and
Mediterranean. Limpets remain key model organisms for the study of
phylogeography, ecophysiology, behaviour and ecology including climate
change studies. They are also under threat in many places with knock-on
effects for the communities in which they occur. Key gaps in knowledge
are identified. Much remains for us to do!
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16.
Cocculiniform limpets — a 100 years after Thiele’s first
account
GERHARD HASZPRUNAR
Systematische Zoologie, GeoBio-Center/LMU, Zoologische Staatssammlung
München, Münchhausenstrasse 21
In 1903 Johannes Thiele published the first detailed anatomical account
of two cocculiniform limpets resulting in 1909 in the erection of
a new superfamily, Cocculinoidea, nowadays usually called Cocculiniformia.
100 years later our understanding of these enigmatic gastropods has
significantly increased but nevertheless is in an embryonic state.
Contrary to earlier ideas (also by the author himself) cocculiniform
limpets comprise two unrelated taxa, Cocculinida (at present two nominal
families) with uncertain phylogenetic affinities and Lepetelloidea
(about eight nominal families) as an early subtaxon of the Vetigastropoda.
Representatives of both taxa show paedomorphosis in various characters,
and modifications due to the dominating deep-water habitat (e.g. white
colour, reduction of eyes, small size). It is still debatable to what
extend cocculiniform limpets provide insights into the reconstruction
of the Hypothetical Gastropod Ancestor (HAG), particularly concerning
the shape of the shell (limpet-like) and of the ctenidium.
The most exciting features of cocculiniform limpets are the dramatic
modifications of the alimentary tract in certain families resulting
in the use of very unusual and often rare organic matter in the deep
water region as substrata and food (bacterial mats, sponges, sunken
wood, beaks of squids, sunken rhizomes of seagrass, chitinous empty
tubes of polychaetes, whale and fish bone, carapaces of crabs and
turtles, egg-cases of skates or sharks, and even feathers of birds).
This is at least sometimes correlated with quite different kinds of
bacterial endosymbioses, the details of which are entirely unknown.
The oral contribution provides a review of the state of the art of
our understanding of cocculiniform limpets 100 years after Thiele,
shows certain new developments and unpublished results on new taxa,
and will outline future aims of the research on these highly interesting
gastropods by the author and others.
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17.
Egg longevity and early events at fertilization in patellid limpets
ALAN N HODGSON, JOHN D. BISHOP AND STEVE J. HAWKINS
Department of Zoology & Entomology, Rhodes University, Grahamstown,
South Africa (a.ho...@ru.ac.za); Marine Biological Association,
Plymouth, U.K.
Studies on the reproductive biology of prosobranch limpets have tended
to concentrate on gametogenesis, gamete structure and seasonality
of spawning. By contrast little is known about gamete longevity, fertilization
kinetics or early events of fertilization. The lack of such studies
is probably due to researchers not being able to find a reliable method
for spawning limpets under laboratory conditions, and not being able
to achieve high rates of fertilization when gametes are dissected
from animals. This paper firstly reviews work that has been done on
patellid fertilization, highlighting some points upon which authors
disagree with regard to oocyte structure. Results on how in vitro
fertilization rates in Patella aspera can be improved using alkaline
(pH 9) sea water are presented. Other experiments on egg longevity
in P. aspera indicate that eggs are viable for 12-15 hours post release
after which fertilization rates decline markedly. Provisional results
from a microscopic study of the early events at fertilization are
also presented.
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18.
Limpet grazing over large geographic scales: generality of pattern
and process
STUART R. JENKINS
Marine Biological Association, Plymouth
Seasonal patterns of grazing activity in patellid limpets and the
community level effects of grazing were assessed over a geographic
scale in north-west Europe. Similar patterns of seasonal grazing activity
were found in the Isle of Man, south west England and Portugal with
elevated grazing during the summer and autumn. These patterns were
spatially consistent at each location. In northern Spain no seasonality
was observed. The community level effects of limpet grazing were assessed
at a variety of temporal and spatial scales by conducting a grazer
removal experiment at the same European locations. Removal of limpets
led to large changes in community structure with extensive growth
of macroalgae, although species composition varied greatly among locations.
The outcome of grazer removal was highly deterministic at the most
northerly location but showed increasing temporal and spatial variability
with decreasing latitude.
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19.
Fine scale genetic variation and heterozygote deficiency in the Brazilian
acmaeid limpet Collisella subrugosa
J. JOSÉ AND V.N. SOLFERINI
Departamento de Genética e Evolução, Instituto
de Biologia, Universidade Estadual de Campinas, CP 6109, Campinas,
São Paulo, 13083-970, Brazil. E-mail: juj...@unicamp.br
Intertidal marine molluscs usually have large population sizes and
extensive genetic variability low structured along their geographic
distribution. These species would therefore be expected to be panmictic,
with genotypic frequencies that fit Hardy-Weinberg expectations. However,
genetic studies of these populations, especially using allozymes,
have shown marked heterozygote deficiencies for many intertidal molluscs,
including Brazilian limpets. The “breeding groups” hypothesis
was considered to be the most plausible explanation for this pattern
in Brazilian species. In this study, we investigated the causes of
heterozygote deficiency based on the “breeding groups”
hypothesis. The populations were studied on a microgeographic scale,
comparing samples from different microhabitats within each of two
shores, one exclusively marine and the other estuarine. For each shore,
we obtained 11 marine and 8 estuarine samples along a log2 transect.
Analyses were carried out for the sampled points within the shores
and for size specified classes. We analyzed 16 polymorphic loci of
allozymes known to have high genetic variability and heterozygote
deficiency based on a previous study. For scale of variation studied,
the gene diversity and FIS were negatively correlated with the geographic
distance on the marine shore, and positively correlated with the increase
in size among the size classes on both shores. All of the loci showed
high levels of heterozygote deficiency among the sampled points and
some loci were heterogeneous for FIS values among the sampled points
and size classes. Moderated genetic structure was seen between some
of the sampled points and between the extreme size classes. These
results excluded endogamy and the Wahlund effect as causes of the
heterozygote deficiency and supported the “breeding groups”
hypothesis. The results also indicated the importance of the temporal
variation in genetic variability and structure among cohorts as a
process capable of causing heterozygote deficiency in marine gastropods.
However, the observed heterogeneity of FIS among the sampled points
and size classes meant the hypothesis of disruptive selection acting
on some of the allozyme loci studied cannot be excluded.
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20.
Macrogeographic variations in shell shape and allometry in Collisella
subrugosa
(Patellogastropoda: Acmaeidae)
J. JOSÉ, J AND V.N. SOLFERINI
Departamento de Genética e Evolução, Instituto
de Biologia, Universidade Estadual de Campinas, CP 6109, Campinas,
São Paulo, 13083-970, Brazil. E-mail: juj...@unicamp.br
Variations in shell shape and size are common in limpets inhabiting
different microhabitats on rocky shores. These variations are often
related to some phenotypic plasticity in response to environmental
factors such as desiccation stress and water turbulence. Although
variation in shell shape and size is common among individuals on a
given shore, few studies have evaluated the extent of such variation
over wide geographic ranges. We used a macrogeographic approach to
identify and describe the variations in shell shape, size and allometry
in the Brazilian limpet Collisella subrugosa throughout most of its
distribution. We sampled individuals on 14 rocky shores over a range
of 2,700 km. The shell length, width, height and the distance from
the apex to the posterior extremity of the shell base were measured.
Considerable variation in shell shape and size were observed within
and among samples. Among samples, variation was much higher than that
observed within samples, especially for the shell height, but there
was no geographic pattern in this variation. Almost all of the samples
showed allometric relationships for the shell measurements. Although
there were considerable differences in the allometric coefficients
among the samples, the variation in this coefficient was not correlated
with geographic distances or size classes. Contrary to what was expected,
most allometric relationships of shell measurements did not suggest
the same shapes observed in the samples. This may indicate that the
allometric development and the observed shell shape are being determined
by different processes and may also indicate that there would be different
groups of individuals for the allometric coefficient within each shore,
as we observed for the rocky shores sampled.
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