Further Observations with the Electron Microscope on Spermatozoids in the Brown Algae

Observations are recorded for Ascophyllum, Pelvetia, Himanthalia,and Dictyota in addition to Fucus which has already been describedin a previous paper. Fibrillar disintegration of cilia has beenobtained in all except Pelvetia, in each case to give nine peripheralstrands and a central pair. This corrects a previous error forthe hind flagellum of Fucus. Some facts are given regardingthe internal organs associated with the parts of the cilia insidethe body in Himanthalia and Dictyota. A proboscis similar tothat previously described for Fucus has been demohstrated inAscophyllum and Pelvetia, but is absent from Himanthalia andDictyota. Himanthalia differs from the other Fucoids in therelative lengths of front and hind flagella. Dictyota has onlya single flagellum. In all, the front flagellum is a Flimmergeisselwith two rows of hairs, which, in certain cases, notably Himanthalia;have very long hair points. In Himanthalia there is a largespine near the distal end of the front flagellum borne on onefibril of the peripheral series. In Dictyota there is a rowof smaller spines at the front end of the flagellum borne ina line between the two lateral rows of hairs. These spines inDictyot can be used as evidence regarding the internal symmetryof the whole cilium which is summarized in a diagram.     

Further experiments on larval behaviour of the tubicolous polychaete Spirorbis inornatus L'Hardy & Quiévreux

Laboratory experiments indicate that there are many ecologically isolated populations of Spirorbisinornatus L'Hardy & Quiévreux, each tending to select the algal substratum which supported their parents. In some algae certain parts of the thallus are particularly favourable for settlement and, in some areas, this involves adaptation of the local population, e.g. to settle on fronds of Laminaria in sheltered localities. Other parts are unfavourable and these are generally the parts which are most illuminated in their natural orientation (e.g. the upper sides of Himanthalia buttons and the outer sides of Laminaria holdfast branches). These parts are active in producing antibiotics, which may thus have an antifouling role, deterring settlement of larvae whether or not those larvae come from populations adapted to settling upon other parts of the thallus.Most larvae from populations on the turf-alga Chondrus settle without any pelagic phase, whereas the majority from populations on Himanthalia and Laminaria holdfasts become pelagic. The proportions choosing holdfasts in laboratory experiments are high, however, suggesting that the need for skill in such choice, by these pelagic populations, more than balances any effect from outcrossing.     

THE ECOLOGY OF THE HONG KONG LIMPETS CELLANA GRATA (GOULD, 1859) AND PATELLOIDA PYGMAEA(DUNKER, 1860): DISTRIBUTION AND POPULATION DYNAMICS

Cellana grata is a high-zoned, exposed-shore limpet with a lifespanof 3 years. Patclloida pygmaeais a low-zoned, sheltered-shorelimpet with a lifespan of I year. C. grata migrates up-shorein winter, but occurs lower on the shore in summer. This migrationis synchronized with variations in algal availability high onthe shore; such variations are, however, themselves relatedto seasonal changes in wave height. P. pygmaea is restrictedto the low shore, year round. The movements upwards in winterand downwards in summer are still evident. Algal species richnessincreased from September to reach a peak between December andMarch, and to abruptly diminish between May and June. The encrustingalgae Brachytrichia maculans, Hildenbrandia prototypus, Lithothamnionsp. and Ralfsia vcrrucosa were present year round. The timingof juvenile recruitment of C. grata and P. pygmaea was fromOctober to July and February to October, respectively. Temperaturemay be important in enhancing juvenile survival by affectingthe seasonal pattern of algal occurrence on the shore. Seasonalfluctuations in the rate of growth were recorded for both specieswith the time of fastest growth of C. grata and P. pygmaea occurringbetween October and March and September and February, respectively.Mortality of both species occurred mainly in summer. Summerheat, predation and intra-specific competition for food appearto be the major causes of death. (Received 1 December 1992; accepted 5 May 1993)     

RELATIONSHIPS BETWEEN SHELL SHAPE, WATER RESERVES, SURVIVAL AND GROWTH OF HIGHSHORE LITTORINIDS UNDER EXPERIMENTAL CONDITIONS IN NEW SOUTH WALES, AUSTRALIA

The shell morphologies of the highshore littorinids, Littorinaunifasciata Gray and Nodilittorina pyramidalis (Quoy & Gaimard)have previously been shown to vary at a variety of spatial scales,including among replicate sites at the same height, from heightto height and from shore to shore. In this study, the relationshipsbetween morphology of the shell, the reserves of water heldwithin the shell, the size of the foot and survival on differentshores and rates of growth in different habitats were examinedfor L. unifasciata and, to a lesser extent, N. pyramidalis.Reserves of water were not consistently related to size or shapeof the shell, but did increase as relative weight of shell increased.This may be due to the relatively smaller body providing moreinternal volume for extra-corporeal water. Water reserves andthe amount of free water held in the shell were also not relatedto loss of water or survival during extended periods of emersion.Although the shape of the shell on sheltered and exposed shoreswas correlated with size of the foot, with the snails on anexposed shore having larger apertures and feet than those ona sheltered shore, transplant experiments did not show differentialmortality between morphs from the different shores. All translocatedand transplanted snails disappeared from the exposed shore ata greater rate than from the sheltered shore, but this was probablydue to the snails dispersing out of the experimental areas ratherthan due to mortality. Therefore, many of the large-scale modelsthat have previously been used to describe patterns of shellshape in intertidal gastropods do not appear to be importantin these highshore littorinids. Finally, field experiments ongrowth of juvenile L. unifasciata indicated that rate of growth,largely governed by opportunity to feed rather than type andquantity of food, is the most likely explanation for the small-and large-scale patterns of shell shape that have been previouslydescribed in this species. (Received 22 October 1996; accepted 19 February 1997)     

The influence of the Pseudo-nitzschia toxin,domoic acid,on microzooplankton grazing and growth: A field and laboratory assessment

We conducted field and laboratory experiments to determine whether the Pseudo-nitzschia-derived metabolite, domoic acid (DA), functions as a microzooplankton grazing suppressant. Using the seawater dilution technique in natural plankton communities along the Pacific Northwest coast, we found no significant relationship between dissolved DA and microzooplankton grazing rate on Pseudo-nitzschia spp. Dilution experiments amended with either 50 or 80 nM dissolved DA also showed no evidence that microzooplankton community grazing was affected by DA. The relationship between Pseudo-nitzschia spp. intracellular DA and microzooplankton grazing was less clear. On a subset of data where small Pseudo-nitzschia spp. cells dominated community composition, an apparent negative relationship between intracellular DA and microzooplankton grazing was observed. However, we provide evidence that this relationship is a microzooplankton response to Pseudo-nitzschia spp. growth rate, rather than cellular DA. In laboratory experiments, two diatom-consuming dinoflagellates, Protoperidinium excentricum and P. pellucidum, were fed single and mixed diets of a toxic and non-toxic Pseudo-nitzschia species and an optimal prey, Ditylum brightwellii. P. excentricum did not grow or ingest either the toxic or non-toxic Pseudo-nitzschia. However, P. pellucidum grew as well on the toxic Pseudo-nitzschia multiseries as it did on D. brightwellii, but did not grow on the non-toxic Pseudo-nitzschia pungens. Both dinoflagellates were capable of growing if Pseudo-nitzschia spp. diets were mixed with D. brightwellii. Addition of dissolved DA also had no negative effect on dinoflagellate growth when fed the optimal diatom diet. We conclude that domoic acid has no functional role in deterring microzooplankton grazing or growth rates. Further, our findings highlight the difficulty of defining the complex mechanisms that regulate predator and prey interactions within microplankton food webs.     

Cytological Studies in the Laminariales

A cytological investigation of British members of the orderLaminariales has revealed the presence of a very large X-chromosomein dividing nuclei of female gametophytes and young sporophytesof Saccorhiza polyschides. This chromosome pairs with a smallY-chromosome at meiosis. A chromosome which is conspicuouslylarger than the others has also been detected in the femalegametophytes (and young sporophytes) of Laminaria spp., Chordafilum, and Alaria esculenta. There is some evidence that thisalso pairs with a smaller chromosome. Chromosome numbers determinedduring the work are as follows: Laminaria digitata, L. saccharina,L. hyperborea, L. ochroleuca, Saccorhiza polyschides, hap-loid31 and diploid 62; Alaria esculenta, haploid 28 and diploid56; Chorda filum, haploid c. 28 and diploid c. 56     

LIFE CYCLE AND HABITAT SHIFT OF THE TROCHID SNAIL DILOMA SUAVIS (PHILIPPI) WITHIN INTERTIDAL MUSSEL ZONES

The life cycle of the trochid snail Diloma suavis (Philippi, 1849),was studied on an intertidal rocky shore at Shirahama, Wakayama Prefecture,where two mytilid bivalves, Septifer virgatus (Wiegmann) andHormomya mutabilis (Gould), formed vertically contiguous musselbeds in the upper-middle and lower zones, respectively. At lowtide in April, the snail density increased with decreasing shoreheight and was greatest at the middle level of the H. mutabilisbed. Then, the density decreased towards the lower littoralfringe. Newly settled juveniles smaller than 2 mm in shell heightappeared abundantly in late summer and autumn within algal turfon the lower shore. As snails grew larger than 2 mm, they appearedwithin the gaps of the H. mutabilis bed and the S. virgatusbed. They increased in size monotonically towards the next summer,but rate of growth in shell height tended to be great in autumnand small in winter. Seasonal change in the density of snailsfound within the gaps of the mussel beds was remarkable during athree year period, increasing from autumn to winter and then decreasingtowards next summer. Reproduction occurred in summer, and adultsnails disappeared by September. It is thus suggested that this specieshas a one year lifespan and shows a habitat shift from algal turfto the gaps of the mussel beds with growth. (Received 12 October 1998; accepted 2 March 1999)     

DISTRIBUTION AND POPULATION DYNAMICS OF THREE POPULATIONS OF SIPHONARIA ON ROCKY INTERTIDAL SHORES IN HONG KONG

The pulmonate limpets Siphonaria japonica and Siphonana siriusoccur over a wide range of local habitat types in terms of exposureto wave action and salinity. This is a study of these two specieson three different shore types in Hong Kong, ranging from anextremely exposed, high salinity (32–35) shore at Caped'Aguilar to a sheltered, low salinity (16–33) shore atTai Lam Chung. Both species are restricted to the low shore,year round. S. japonica is a winter breeder and recruitmentoccurred between October and January. The recruitment of S.sirius could not be recognised from the size-frequency histograms.The algal standing crop at Tai Lam Chung was higher than atWu Kwai Sha during the winter period, i.e., between Octoberand April. Seasonal fluctuations in growth rate were recordedfor both Siphonaria species with the time of fastest growthoccurring in winter. S. japonica grew faster at Tai Lam Chungthan at Wu Kwai Sha. Food availability is thought to be an importantfactor affecting growth. (Received 17 September 1993; accepted 16 June 1994)     

The IJsselmeer and its phytoplankton--with special attention to the suitability of the lake as a habitat for Oscillatoria agardhii Gom

The IJsselmeer (surface area 1200 km², mean depth 4.5 m, residencetime 0.4 year, phosphorus load 7 g m^–2 year^–1) isa very important conservation area. Regular summer bloomingof Oscillatoria spp. can depreciate this value, so the boundsof possibility of this kind of blooming have been investigated.Therefore samples were taken along the shore and in the openwater from 1974 to 1982, continuous temperature profile measurementswere made in the same period in the middle of the lake and insitu primary production was measured in 1976 and 1977. The phytoplanktonconsists of green algae throughout the year, diatoms in spring,and blooms of Microcystis aeruginosa in summer. Blooming ofOscillatoria agardhii Gom occurs regularly in summer along theFrisian shore. In 1976, however, a heavy bloom of this algaoccurred in the whole lake. Comparing the IJsselmeer with shallowerOscillatoria-lakes in the Netherlands distinct differences arepresent concerning biomass, chlorophyll a content, relativevolume of the euphotic zone and light-dark cycle. Not only thelarger depth and extensiveness of the IJsselmeer are unfavourablefactors for Oscillatoria, but also the separation by land reclamationof many of the shallow littoral regions from the main body ofthe lake. High temperature and microstratification are neededto develop a bloom in the whole lake.     

Alternate life history phases of a common seaweed have distinct microbial surface communities

Macroalgal life histories are complex, often involving the alternation of distinct free‐living life history phases that differ in morphology, longevity and ploidy. The surfaces of marine macroalgae support diverse microbial biofilms, yet the degree of microbial variation between alternate phases is unknown. We quantified bacterial (16S rRNA gene) and microeukaryote (18S rRNA gene) communities on the surface of the common intertidal seaweed, Mastocarpus spp., which alternates between gametophyte (foliose, haploid) and sporophyte (encrusting, diploid) life history phases. A large portion (97%) of bacterial taxa on the surface Mastocarpus was also present in samples from the environment, indicating that macroalgal surface communities are largely assembled from the surrounding seawater. Still, changes in the relative abundance of bacterial taxa result in significantly different communities on alternate Mastocarpus life history phases, rocky substrate and seawater at all intertidal elevations. For microeukaryote assemblages, only high intertidal samples had significant differences between life history phases although sporophytes were not different from the rocky substrate at this elevation; gametophytes and sporophytes did not differ in microeukaryote communities in the mid and low zones. By sequencing three host genes, we identified three cryptic species of Mastocarpus in our data set, which co‐occur in the mid‐to‐low intertidal zone. In these samples, M. alaskensis sporophytes harboured distinct bacterial communities compared to M. agardhii and M. intermedius sporophytes, which were not distinguishable. Conversely, microeukaryote communities did not differ among species.     

AGE, GROWTH AND MATURATION OF THE SQUID ENOPLOTEUTHIS LEPTURA (OEGOPSIDA: ENOPLOTEUTHIDAE) FROM THE CENTRAL-EAST ATLANTIC

Fifty-nine specimens of the tropical epipelagic eno-ploteuthidEnoplotcuthis leptura were collected in the central-east Atlanticbetween 1986–1988. Statoliths were extracted from allspecimens (mantle length (ML) 4.1–92 mm) and processedunder the statolith ageing technique. The characteristic featureof statolith morphology in E. leptura is a sculpture of therostrum, which is covered by numerous tiny spines and knobs.In the ground statolith it was possible to distinguish fourmain growth zones consisting of narrow growth increments likethose in other squids studied. Allometric growth of statolithsversus ML is negative. E. leptura is a short-lived squid witha half-year life span. Growth rates of E. leptura are high atjuvenile stage (instantaneous rate of growth (G) of body weight(BW) 0.04–0.06). An early maturation of males (at age45–60 days) and females (at 80–90 days) causes asharp decrease of somatic growth of E. leptura, and mature squidhave low growth rates (G of BW - 0.OO3-O.0O5). Spawning takesplace between January and September with two peaks: in Januaryand in June-July. (Received 22 November 1992; accepted 15 February 1993)     

Diet selection by copepods in the presence of cyanobacteria

Boeckella, the dominant calanoid in many Southern Hemispherelakes, can survive, grow and reproduce to varying extents onmonocultures of cyanobacteria. In this study, we determinedthe effects of algal and cyanobacterial foods of different nutritionalvalue and concentration on food preferences of adult femaleBoeckella trianiculata and Boeckella hamata. Four species ofcyanobacteria (Anabaena flos-aquae, Nostoc sp. 2, OscillatoriatenuisandMicrocystis aeruginosa) were offered alone and mixedwith equal biomasses of Cryptomonas sp., Choricystis or a cyanobacterium.Food preferences were calculated as ratios of the rates at whichthe copepods removed each food at high and low food concentrations.In high-concentration mixtures with cyanobacteria, Cryptomonaswas consistently preferred by both Boeckella spp. In low-concentrationmixtures, both Boeckella spp. preferred Anabaena and Nostoc,which they removed at high rates(81–142 ml mg^–1h^–1), although Cryptomonas was selected in preferenceto Oscillatoria and Microcystis. When fed mixtures of filamentouscyanobacteria, both species of Boeckella showed invariant discriminationagainst Nostoc, andshifts in preference between Anabaena andOscillatoria that were related to food concentration. Microcystis,the least favouredfood, appeared to have a toxic effect on B.triarticulata. ¹Present address: Nursing and Midwifery Department, Otago Polytechnic,Forth Street, Dunedin, New Zealand     

COMPETITIVE GRAZERS AND THE PREDATORY WHELK LEPSIELLA FLINDERSI (GASTROPODA: MURICIDAE) STRUCTURE A MUSSEL BED (XENOSTROBUS PULEX) ON A SOUTHWEST AUSTRALIAN SHORE

On a southwest Australian exposed rocky shore within King GeorgeSound, the predatory muricid Dicathais orbita was observed feedingnon-selectively on an array of sessile prey, including Austromegabalanusnigrescens, Galeolaria caespitosa, Patelloida nigrosulcata,Serpulorbis sipho, Siphonaria sp. and the mussel Xenostrobuspulex. On a more sheltered, contiguous, platform of the same shore,however, a mat of Xenostrobus pulex occurred which was beingpredated by another muricid, Lepsiella flindersi. X. pulex occupieda wide vertical range on this shore. Higher-zoned, supralittoral,individuals were small and occurred as clusters in crevicesand pits in the rock. A mat of mussels in the lower eulittoralzone was heavily predated by the drilling L. flindersi whichattacked selectively the largest individuals. Between, in thehigh eulittoral, the mussel bed was formed into patches whichwere isolated by the grazing activities of an array of herbivorousgastropods. Recruitment here by X. pulex was to the patch edgesand the grazer's habits of clustering against them, furtherkept them discrete. Little predation by L. flindersi occurredat this shore level. The Xenostrobus pulex community was, therefore, highly structureddown the shore sequentially by: (a), physiological stresses;(b), competitive grazing pressures and (c), predation. (Received 2 February 1998; accepted 5 January 1999)     

Evolution of group size in the dolphins and porpoises: interspecific consistency of intraspecific patterns

I investigated group size variability in dolphins and porpoisesusing intraspecific comparisons. Explanatory factors consideredin the analysis were variables of the physical environment,the diet, and the life history of the species. Open habitatand small body size were viewed as increasing predation risk.This pattern was apparent in Risso's dolphins (Grampus griseus) and weakly apparent in bottlenose dolphins (Tursiops spp.).Group size was negatively correlated with body size in pilotwhales (Globicephala spp.) and positively correlated with theopenness of habitat in killer whales (Orcinus orca), stripeddolphins (Stenella coeruleoalba), and common dolphins (Delphinus spp.). No such relationship was found for harbor and Dall'sporpoises (Phocoena phocoena, P. dalli). Group size also seemedto vary depending on other physical measures of the habitat,which may indirectly reflect diet; group size showed U-shapedpatterns if related to temperature. The predictive power ofvariables comprising detailed prey information on group sizewas variable. For example, pilot whales had smaller group sizes when they fed more on mesopelagic fish and less on mesopelagiccephalopods, and common dolphins had larger groups if theyfed on varying types of fish. In most Delphinoidea species,group size could be described by the variables considered inthis study. But each species showed its own pattern of correlationsbetween group size and a specific set of explanatory variables. Thus, no general and consistent relation between group sizeand the other variables was found. It remains unknown whetherthese species-specific patterns result from a historical processor whether they are specialized adaptations.     

Maturation, Spawning and Development in Siphonaria Pectinata Linnaeus (Gastropoda: Pulmonata) at Gibraltar

A comparative study of some aspects of the reproductive biologyof Siphonaria pectinata was carried out at Gibraltar. Maturationoccurred at 5-6 mm shell length corresponding to an age of 6-12months. At the more sheltered Atlantic site spawning was evidentfrom March to June 1992 with peak spawning occurring in May-June1992. The patterns of spawning activity for the following twoyears were very similar. Egg ribbons were very scarce at themore exposed Mediterranean site and were found in considerablyless quantities than at the Atlantic site. Individuals at bothsites contained mature eggs in their gonads at the onset, andthen throughout the duration of the spawning season, but exhibitedspent gonads by October. The spawn of S. pectinata consistedof small oval ribbons filled with numerous egg-shaped capsulesspaced irregularly in a jelly-like matrix. Spawn was depositedmainly away from the home scar in shallow depressions, cracksand crevices and between barnacles and mussels. S. pectinataexhibited planktonic development. The fertilised eggs took between14 and 21 days to develop at ambient temperature (14-19°),and hatched as free-swimming planktotrophic veligers. The timingof spawning activity and the placement of egg masses in protectivemicrohabitats on the shore are discussed in terms of adaptationsto reduce desiccation stress, predation and possible food shortages.The mode of development in S. pectinata is placed in contextwith current theories regarding siphonariid ancestry and evolution. (Received 6 January 1998; accepted 25 June 1998)     

Distribution in relation to life history in the directdeveloping gastropod Batillaria cumingi (Batillariidae) on two shores of contrasting substrata

Population structure and spatial distribution with growth ofthe direct-developing gastropod, Batillaria cumingi, were investigatedon two shores of differing substrata. Sand-mud shore and rockyshore populations differed in size structure; first-year snailswere ca. 7 mm in shell length (SL) in both populations, whereassecond-year snails, merging with older cohorts, measured 15–25mm SL in the sand-mud shore population and ca. 15 mm SL in therocky shore population. Egg distribution matched adult distributionin the sand-mud shore population, but was more restricted thanthat of adults in the rocky shore population. The distributionof newly-hatched juveniles (0–1 mm SL) was restricted inboth populations, but the growth stage at which snails extendedtheir distribution differed between the two populations; 1–2.5mm SL on the sand-mud shore and 5 mm SL on the rocky shore. Floatingachieved by early juveniles (ca. 2 mm SL), was commonly observedin the sand-mud population, but rarely in the rocky shore population.The sudden expansion in distribution of the 1–2.5 mm SLgrowth stage in the sand-mud shore population is consideredto have been caused by floating, while expansion of the distributionof older growth stages (>5 mm SL) in the rocky shore populationprobably occurs by crawling. (Received 13 May 1998; accepted 25 August 1998)     

Statolith shape and microstructure in studies of systematics, age and growth in planktonic paralarvae of gonatid squids (Cephalopoda, Oegopsida) from the western Bering Sea

The microstructure, morphology and ontogenetic development ofstatoliths and age and growth of 405 planktonic paralarvae and117 juveniles belonging to 10 species of gonatid squids (Cephalopoda,Oegopsida) were studied in the region of the continental slopein the western part of the Bering Sea (57°00'–61°30'N,163°00'E–179°20'W). The statolith microstructureof all species was characterized by the presence of a largedroplet-shaped nucleus and bipartite postnuclear zone dividedinto two by the first stress check, except for Berryteuthismagister which had only one stress check and an undivided postnuclearzone. In Gonatus spp., completion of development of the postnuclearzone coincided with full development of the central hook onthe tentacular club. Daily periodicity of statolith growth incrementswas validated by maintaining 13 paralarvae of the four mostabundant species in captivity. All species might be subdividedinto two groups based on statolith microstructure, i.e. specieswith a central position of the nucleus within the first statolithcheck (Gonatopsis spp., Egonatus tinro and B.magister) and specieswith the nucleus shifted to the inner side of the first statolithcheck (Gonatus spp.). Comparative analysis of statolith morphologyshowed that paralarval statoliths have species-specific charactersthat allowed the construction of keys to identify species ofgonatid paralarvae based on their statoliths. Analysis of paralarvalgrowth using statoliths revealed that these cold-water planktonicgonatid paralarvae have fast growth rates, attaining a mantlelength of 7–10 mm at 15–20 days and 20–25mm at 35–70 days.     

Spatio-temporal distribution and production of calanoid copepods in the central Baltic Sea

The aim of our study was the exploration of species-specificdistribution and production patterns of dominant copepods inthe Central Baltic Sea (Bornholm Basin). Spatio-temporal distribution,egg and secondary production were studied by means of net-samplingand egg production experiments from April to August 1999. Verticaland horizontal distribution patterns appeared to be linked witheach other and were primarily species-dependent. Both Acartiaspp. and Temora longicornis preferentially inhabited the upper30 m of the water column and the shallower marginal regionsof the Bornholm Basin. In contrast, the C4–5 and C6 ofPseudocalanus spp. preferentially inhabited the halocline region(50–70 m) and the deep central part of the area. Observeddifferences in horizontal distribution among these three copepodsappear to result from different depth preferences and depth-dependentwater circulation patterns. Egg production rates (EPR) clearlyexhibited seasonal differences with maximum EPR in May and minimumEPR in July. Mean EPR was significantly different between species,being highest in Acartia spp. and lowest in Pseudocalanus spp.The variability in EPR was related to differences in hydrographyand modelled food environment.     

The effect of ultraviolet radiation on the vertical distribution and mortality of estuarine zooplankton

The effect of UV-B radiation on the vertical distribution ofthree calanoid copepod species (Tortanus dextrilobatus, Acartiuraspp. and Acanthacartia spp.) and three larval stages of Pacificherring, Clupea pallasi (1-, 7-, and 14-day-old larvae) wasinvestigated. A series of 2 m high columnar tanks equipped withinfra-red light and video-microscopy was used to investigatethe vertical distribution of zooplankton in the presence andabsence of UV-B radiation. In the presence of UV-B radiation,T.dextrilobatus and 1-day-old C.pallasi resided about 50 cmdeeper than in the absence of UV-B, while Acartiura spp. andAcanthacartia spp. showed no (or only minimal) change in verticaldistribution. Mortality experiments were also conducted outdoorsin which each copepod species was exposed to full or reducednatural radiation levels. Only T.dextrilobatus showed an increasein mortality when exposed to full radiation. Our results showedthat T.dextrilobatus and 1-day-old C.pallasi larvae were sensitiveto UV radiation (UVR), and to reduce or eliminate UV-inducedstress, they avoided the surface of the water column when UV-Bradiation was present. Copepod species were chosen to span arange of pigmentation: T.dextrilobatus (heavily pigmented),Acartiura spp. (moderately pigmented) and Acanthacartia spp.(not pigmented). The pigmentation did not appear to play a rolein UVR tolerance of the copepods, but may be a factor determiningUV tolerance of C.pallasi.     

SPATIAL PATTERNS OF SHELL SHAPE OF THREE SPECIES OF CO-EXISTING LITTORINID SNAILS IN NEW SOUTH WALES, AUSTRALIA

The shape and relative weight of the shell have been shown tovary intraspecifically and interspecifically in a number ofspecies of gastropods, including many different littorinids.These differences give rise to different shell forms in differenthabitats. In those species which have non-planktotrophic development,differences in shell form among shores have been usually explainedin terms of natural selection because exposure to waves supposedlyfavours light shells with large apertures, while predation bycrabs on sheltered shores favours elongated, thick shells withsmaller apertures. Differences in shell shape among speciesfound at different heights on the shore have been explainedin terms of resistance to desiccation and temperature. Suchvariables would tend to act on a relatively broad-scale, i.e.causing differences among heights on a shore or among shores.Rates of growth, which might vary at much smaller scales withina shore, have also been shown to affect the shapes of many shells. In this study, the shape and relative weight of shells of threespecies of co-existing littorinids (Littorina unifasciata, Bembiciumnanum and Nodilittorina pyramidalis) were measured. These speciesall haveplanktotrophic development and they are found on manyshores where there is no evidence that they are preyed uponby crabs. Before explanations of shell shape are proposed, itis necessary that patterns of variation, within different partsof ashore and among different shores are clearly documented.These patterns were measured at a number of different spatialscales within and among replicate shores with different amountsof wave exposure. Large and small specimens were included toallow intraspecific comparisons among snails of different sizesfound at different heights on the shore. The results showedsignificant differences among shores in shape and relative weightof shells, but these differences could not be explained by exposureto waves. In addition, snails of different sizes and differentspecies did not show the same patterns although they were collectedfrom the same sites. Importantly, the shell shape of Liuorinaunifasciata varied significantly among sites at approximatelythe same height within a shore. These differences could notbe clearly correlated with density, mean size nor exposure towaves. The only consistent pattern was a decrease in relativeaperture size in specimens living higher on the shore. Modelsthat have commonly been proposed to explain shape and relativeweight of shells in other species of gastropods are not adequateto explain the small- and large-scale variation of the measurementsdescribed here. It is proposed that any selective advantageof shell morphology and the effects of any variables on thedevelopment of shell morphology in these species can only beidentified after appropriately designed and replicated fieldexperiments. (Received 4 March 1994; accepted 13 September 1994)