Shore Height Research Articles

Shell-size variation of Notoacmea biradiata (Archaeogastropoda: Acmaeidae) as a response to gastropod density and height in shore in the Colombian Pacific coast

Notoacmea biradiata (Reeve, 1855) is an abundant intertidal limpet on the rocky shore of the Colombian Pacific coast. This paper reports a field factorial experiment on shell-size variation of N. biradiata as a response to two independent factors: intertidal gastropod density and shore height above sea level. Four rocky shores were selected on the Colombian Pacific coast, two in Gorgona Island and two in Utr?Cove. The intertidal gastropods density was determined in each rocky shore using the transect-quadrant technique. Significant differences were observed in the gastropod densities between study sites: low density in the rocky shores of Utr?Cove and high density in the rocky shores of Gorgona Island (P < 0.009). A factorial sampling was conducted to determine the effect of the density and height on the shore over shell-length, shell-height and shell-thickness. A twoway ANOVA and a least-squared regression was used to determine whether the shell-sizes differ between varying densities and shore heights. Intertidal gastropod density was found to be the dominant factor in determining basal shell length (ANOVA, P < 0.001) and shell height (ANOVA P < 0.05) changes. Thus, at low population densities the shells are larger and taller. The height on the shore did not influence the shell-size of N. biradiata (ANOVA, P > 0.30).

Position affects gastropod predation of sessile colonizers on a tropical rocky shore

A long-term experiment was carried out to determine the relative abilities of five sessile animals to colonize cleared plots in the presence or absence of predators. The experiment was done on two adjacent rocky shores, one sheltered and one exposed, on a small tropical island. The effect of predation in maintaining bare space was greatest on the exposed shore/upper mid-intertidal, less on the sheltered shore and absent on the exposed shore/lower mid-intertidal. The barnacle, Tesseropora rosea, recruited heavily at the exposed shore/lower mid-intertidal and was dominant, but was unable to colonize the exposed shore/upper mid-intertidal or the sheltered shore. The barnacle, Tetraclita squamosa, successfully colonized only the exposed shore/upper mid-intertidal and did not appear to be affected by predation. The oyster, Saccostrea amasa, had low colonization levels only on the sheltered shore and exposed shore/upper mid-intertidal, small individuals were susceptible to predation. The barnacle, Chthamalus maylayensis, heavily colonized only the exposed shore/upper mid-intertidal but was removed from this shore height by gastropod predators. The oyster, Saccostrea echinata, colonized only the sheltered shore and was very susceptible to predation. Given the variability found on this small spatial scale, it is suggested that consistent differences in ecological processes between regions (tropical versus temperate) are unlikely but, rather, that differences between localities will be found at the level of species interactions and abiotic effects in particular habits.

Geographic trends in mangrove crab abundance in East Africa

The aim of this work was to determine the abundance of crabs inmangrove communities along a latitudinal gradient along the eastern coastof Africa from 4°S to 32°S. Surveys were made atMombasa (Kenya), Zanzibar (Tanzania), Maputo (Mozambique) and in theTranskei (South Africa). Crabs were estimated at three designated levelsin the mangroves by visual census using a common protocol, and numberswere converted to biomass.Even after standardising the selection of sites and methods of censusthere was still extensive variability in the data, emphasising the complexheterogeneity of mangrove ecosystems. Lunar phase (full versus new moonsprings) did not have a consistent effect on results, but shore height hadseveral effects. Total crab biomass was similar in the two lower shore strataexamined, but about twice as high at the top-Avicennia level. Theratio of grapsid biomass:ocypodid biomass also changed with height: fromnear unity in the lower mangrove, to 0.14 in the middle strata, but to 15at the top.There was no consistent latitudinal trend in total crab numbers, but totalcrab biomass increased from north to south. In addition there was aconsistent and marked change in the grapsid biomass:ocypodid biomassratio: this swung from 0.65 at Mombasa to 6.8 in the Transkei. This hasimplications for the transfer of primary production through the food chain. Grapsids are important macrophagous feeders on the leaves and other partsof mangroves, whereas ocypodids are microphagous deposit feeders.

Interactive effects of wave exposure and tidal height on population structure of the mussel Perna perna

The influence of wave exposure and of tidal height on mussel (Perna perna Linnaeus) population structure (size, density, biomass and adult/juvenile correlations) was examined at 18 sites along the south coast of South Africa. Sites were classified as exposed or sheltered prior to sampling, without reference to the biota, on the basis of aspect, topography and wave regime. A single set of samples was collected from each site during three spring tide cycles. Adult mussels on these shores almost always attach directly to the rocks, and layering of mussels is virtually absent. Shore height always had a strong influence on population structure, but exposure had significant effects only lower on the shore, and almost exclusively on mussel sizes. Principal component analysis (PCA), based on size distribution data for each population, revealed a general upshore decrease in the modal size of the adult cohort. The effects of exposure on size distribution, however, varied with tidal height. PCA separated exposed zones, with larger mussels, from sheltered zones on the low-shore. Farther upshore the two shore types were increasingly confounded. The maximum size of mussels showed a similar pattern, with significant differences (ANOVA, p 15 mm) densities decreased up the shore, with low-, mid- and high-shore zones being significantly different from one another (ANOVA, p 15 mm) densities in all zones and for both exposure regimes ( p < 0.05 in all cases), but there was considerable variability and extremely low predictability in these relationships (r2 generally <0.2). Predictability tended to be greater towards the high-shore, where adults were more clumped. As with density, biomass was not affected by exposure, but decreased upshore as mean size and density decreased. A reduction in the influence of exposure farther upshore may be caused by greater emersion overriding the effects of exposure. The presence of free space within mussel beds and significant correlations between recruit and adult densities suggest that these mussel populations are recruit limited.

SEASONAL AND ZONAL VARIATION IN NITROGEN SOURCE FOR FOUR INTERTIDAL SEAWEEDS FROM NEW ZEALAND

Seasonal patterns in nitrogen uptake by four species of intertidal macroalgae (Stictosiphonia arbuscula, Apophlaea lyallii, Scytothamnus australis, Xiphophora gladiata) from Otago in New Zealand's south island were investigated. Field‐collected material from species occurring at different shore heights was exposed to inorganic (NO−3, NH+4) and organic (urea) nitrogen at different concentrations (5μM, 30μM), and the rate of uptake over 30min intervals for 3hr was determined. Active uptake of nitrate was shown by all species in both seasons but uptake rates were 2–5 times greater in summer compared to winter. Ammonium uptake was highest in all species regardless of season, indicating a preference for this form of nitrogen. For all species, urea uptake was negligible during winter but represented a substantial proportion of the total nitrogen taken up during summer. Comparison of species in relation to their shore position revealed differences in uptake rates for each nitrogen source. These results suggest that intertidal seaweeds growing at different shore positions employ different strategies for procuring nitrogen in an environment where nutrient supply may be limited.

Biodiversity in Littorina species (Mollusca: Gastropoda): a physiological approach using heat-coma

The upper critical thermal limits were measured as heat-coma temperatures in Littorina species as a tool for examining physiological diversity. Thermal tolerance was found to be stable within a population, but extensive variation occurred between populations and species. All species examined displayed heat-coma values of ∼30 °C and did not show a positive correlation with shore height. Eulittoral-fringe species tended to have higher coma temperatures than eulittoral species. Coma temperatures varied both seasonally and geographically. Lethal thermal limits were also investigated; these were ∼10 C° higher than coma temperatures.

Geographical variation in heat coma temperatures in Littorina species (Mollusca: Gastropoda)

Upper critical thermal limits were measured as heat coma temperatures in Littorina species (Mollusca: Gastropoda) from sites around the British Isles. Thermal tolerance was found to be stable within a population but extensive variation occurred between populations and species. The majority of species examined displayed heat coma values of around 30°C and did not show a positive correlation with shore height. The highest capacity for thermal tolerance was found along the coast of South Wales, while the lowest was found on the south-west coast of Ireland and on the east coast of Scotland.

Intraspecific burrow plasticity of an intertidal population of Callianassa filholi (Crustacea: Decapoda: Thalassinidea) in relation to environmental conditions

Burrow morphology and intraspecific burrow plasticity in relation to environmental conditions were examined for an intertidal population of Callianassa filholi Milne‐Edwards, 1878 in southeastern New Zealand. Multivariate analysis of burrow features revealed no significant differences in burrow morphology between seasons. However, dissimilarities between burrows from different seasons could be identified and included differences in lateral extent, total length, and volume of burrows. These size parameters each showed low values in winter, coinciding with low seawater temperature and high organic content of the sediment. There was no significant relationship between any of the three size parameters and sediment grain size or shore height of the burrow, but lateral extent and total length of the burrow were significantly related to organic content of the sediment, decreasing with increasing organic content. Furthermore, there was a significant positive relationship between seawater temperature and total length of the burrow. Data from the present study imply that intraspecific variation in burrow morphology for callianassids is dependent on environmental variables, which has consequences for the construction of useful burrow models.

The intertidal distribution of two algal symbionts hosted by Anthopleura xanthogrammica (Brandt 1835).

This paper quantifies the spatial distribution of zooxanthellae (ZX) and zoochlorellae (ZC), two algal symbionts common to the temperate anemone, Anthopleura xanthogrammica, in relation to shore height. Anemones in tidepools and crevices had varying algal proportions: >0.90 ZC (green anemones), 0.10 to 0.90 ZX (mixed), and >0.90 ZX (brown). Brown anemones are primarily found in the high intertidal and the upper region of tidepools. Mixed anemones are most common at intermediate shore heights and green anemones are exclusive to the low shore and at increasing depth in tidepools. Microhabitat was also important to algal proportion, as anemones in crevices had greater proportions of ZC than anemones in tidepools at the same shore height. In a reciprocal transplant experiment, A. xanthogrammica were moved between high and low shallow tidepools. All anemones moved from a low to a high tidepool exhibited a shift from ZC to ZX populations, while the anemones transplanted from high to low tidepools maintained ZX dominance. This is the first documentation that field algal populations can shift from ZC to ZX in Anthopleura. The field survey and transplant study results support the hypothesis that the relative abundance of ZX and ZC in A. xanthogrammica is influenced by the environmental gradient associated with shore height and microhabitat.

Stormwater Contamination of Urban Estuaries. 2. Testing a Predictive Model of the Build-Up of Heavy Metals in Sediments

We describe the results of a sampling program to test a simple, management-oriented, predictive model of the build-up of contaminants (Cu, Pb, and Zn) in sediments in sheltered estuaries. The model, described in detail in a companion paper, is generally applicable to these environments but its development and testing is described for two urban estuaries in Auckland, New Zealand. There was good agreement between observed concentrations of metals and those predicted by the model. The model predicted larger concentrations within a defined settling zone at the upper end of the estuary than outside this zone, and such a difference was detected for lead and zinc. Differences in concentrations of metals were detected among locations several hundreds of meters apart, with increasing concentrations from downstream to upstream locations. These patterns were apparent above smaller scale variation among and within sites 10s of meters apart within each location. This small-scale variation did not conform to any obvious patterns. For example, there were no clear patterns in the metals distributions in sediments among different shore heights. Patterns of contaminants distributions found in the present study may be generalized to similar urban estuaries in other parts of the world through their correspondence to those derived from the model, which is based on general assumptions and principles.

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) and Hormomya mutabilis (Gould), formed vertically contiguous mussel beds in the upper-middle and lower zones, respectively. At low tide in April, the snail density increased with decreasing shore height and was greatest at the middle level of the H. mutabilis bed. Then, the density decreased towards the lower littoral fringe. Newly settled juveniles smaller than 2 mm in shell height appeared abundantly in late summer and autumn within algal turf on the lower shore. As snails grew larger than 2 mm, they appeared within the gaps of the H. mutabilis bed and the S. virgatus bed. They increased in size monotonically towards the next summer, but rate of growth in shell height tended to be great in autumn and small in winter. Seasonal change in the density of snails found within the gaps of the mussel beds was remarkable during a three year period, increasing from autumn to winter and then decreasing towards next summer. Reproduction occurred in summer, and adult snails disappeared by September. It is thus suggested that this species has a one year lifespan and shows a habitat shift from algal turf to the gaps of the mussel beds with growth.

Factors influencing sediment turnover by the burrowing ghost shrimp Callianassa filholi (Decapoda: Thalassinidea)

Bioturbation by the burrowing thalassinidean shrimp Callianassa filholi (Milne-Edwards 1878) was studied at an intertidal sandflat in Otago Harbour, south-eastern New Zealand, over a period of 12 months. The amount of sediment expelled from shrimp burrows was measured each month (by direct entrapment over 24 h) and inhabiting shrimp were subsequently captured from the burrows. Rate of sediment expulsion was significantly related to seawater temperature, shore height of burrow and time, whilst the amount of sediment expelled from individual burrows was positively related to size of inhabiting shrimp but independent of sex. Annual sediment turnover for C. filholi was estimated at 96 kg (dry) m−2 year−1 which accounted for the variability imposed by monthly changes in seawater temperature and the spatial and temporal dynamics of the shrimp population. The results demonstrate the need to take account of physical and biological factors when constructing sediment turnover estimates for callianassid shrimps, and inferring their bioturbatory significance.

Settlement and post-settlement interactions between Semibalanus balanoides (L.) (Crustacea: Cirripedia) and three species of fucoid canopy algae

Manipulative field experiments carried out on sheltered rocky shores investigated settlement and post-settlement interactions between Semibalanus balanoides and three species of fucoid canopy algae, Fucus spiralis L., Ascophyllum nodosum (L.) Le Jolis and Fucus serratus L. All three species had a negative effect on settlement and early recruitment of S. balanoides, densities being significantly lower on settlement tiles beneath the canopy compared to cleared areas. Investigation of the mechanism by which settlement and recruitment were inhibited showed the importance of sweeping of algal fronds at all three shore heights. In addition, we found that the F. serratus canopy inhibited settlement not only by its sweeping action but also by limiting the access of cyprids to the substratum. Detailed examination of the sweeping effect in F. serratus showed that newly settled cyprids transplanted beneath a canopy suffered extremely high mortality (between 82 and 97%) over just one high water period. Mortality was significantly reduced for individuals that had settled within a matrix of adults. Metamorphosis of cyprids to spat conferred no additional resistance to sweeping-induced mortality but resistance increased in 6 day old spat. Mortality in S. balanoides after the end of the settlement season was monitored for three months in experimental treatments and controls. Mortality rates were significantly lower under the canopy than in cleared areas in both the F. spiralis and Ascophyllum zones. The overall influence of each canopy species on the development of barnacle populations on sheltered shores is discussed.

Vertical Changes in Density, Size Structure and Shell Shape of the Bivalve Lasaea Undulata Within Intertidal Mussel Beds

Vertical changes in density, size structure and shell shape of Lasaea undulata (Bivalvia: Galeommatoidea) inhabiting intertidal mussel beds were studied at Wakayama Prefecture, Japan. At the study site, where two mytilids Septifer virgatus and Hormomya mutabilis formed vertically contiguous mussel beds, Lasaea density decreased downshore within the S. virgatus bed of the upper and mid zones. Few individuals were found within the H. mutabilis bed of the lower zone. Multiple linear regression analysis revealed that shore height was the only factor which showed a significant, positive correlation with density. Size structure differed between the upper and lower parts of the S. virgatus bed, suggesting that reproductive periods or growth rates of L. undulata differed with shore height. Prodissoconch length and shell shape were also different among shore heights. Number, size and shell shape of juveniles brooded within parents indicated that this species releases its young as non-planktotrophic, crawl-away juveniles. There was no significant difference in density of recruits between artificial mussel clumps of S. virgatus and H. mutabilis within enclosure cages, and no specific association was detected between L. undulata and either of the two mussel species.

The relationship between the distribution of genetically distinct inbred lines and upper lethal temperature in Lasaea rubra

Lasaea rubra is an inbreeding bivalve species, living at most heights on rocky shores. Freshly collected animals from different shore heights showed significantly different upper median lethal temperatures (MLTs), with upper shore animals having higher MLTs than lower shore specimens. Experiments with animals acclimated for at least one month to a single temperature (15°C) demonstrated that these differences in upper MLT were unaffected by thermal acclimation. Electrophoretic investigation showed that the differences in thermal response had a genetic basis. Homogeneous populations of the high-water inbred line (‘Inbred line A’) had a higher MLT than homogeneous populations of ‘Inbred line C’ which was found on the middle and lower shore. No differences were detected between the MLTs of separate populations of Inbred lines A or C. A third inbred line (‘Inbred line B’) was found on the middle shore, but no homogeneous populations were found. However, indirect evidence suggests that Inbred line B has a thermal response intermediate between those of Inbred lines A and C. Study of populations made up of mixtures of inbred lines confirmed the relationship between upper MLTs and genetic composition of the population.

Phosphate uptake by intertidal algae in relation to zonation and season

The removal of phosphate from ambient seawater by whole plants of five species of fucoid algae, collected from the east coast of N. Ireland in 1988 and 1989, was followed over 6-h periods. A transient uptake pattern was observed forPelvetia canaliculata (L.) Dcne. et Thuret,Fucus spiralis L.,F. vesiculosus L. andF. serratus L., consisting of an initial period of high uptake, followed by a phase of zero uptake and then a period at an intermediate rate.Ascophyllum nodosum (L.) Le Jolis had a constant slow rate of uptake over 6 h. The initial uptake rate ofF. spiralis was significantly greater than that of any other species. Phosphate uptake over a 2-h period was measured at concentrations ranging from that of ambient seawater to 25µg-at. l−1 for whole plants ofF. spiralis andF. serratus, using a large scale batch method. A small scale batch method was used for whole plants ofP. canaliculata and sections of the other four species investigated. Uptake abilities of the algae at low concentrations of phosphate were compared using the parameterV 1 (the uptake rate at 1µg-at. l−1) and at high concentrations usingV max, the maximum uptake rate. These kinetic parameters of uptake were calculated using a method that avoids bias and permits statistical evaluation of the results. The fucoid algae studied could be divided into two distinct groups on the basis of their abilities to take up phosphate from seawater.P. canaliculata andA. nodosum had low values ofV 1 in winter, which were also correlated with their positions on the shore and did not vary between winter and summer. TheFucus species had higher values ofV 1 in winter, which were also correlated with their positions on the shore. In summer, however,V 1-values for these species decreased and no longer correlated with their shore heights. TheV max-value forF. spiralis was higher in winter than in summer but was signifcantly greater than that of any other species at all times of year. The ecological significance ofV max is discussed in relation to nutrient limitation and the possible occurrence of patches of high nutrient concentration in the intertidal environment.

Cadmium contamination, accumulation and some effects of this metal in mussels from a polluted marine environment

Results are presented for the effect of two variables on cadmium uptake in the common blue mussel, namely shore height and distance from the point of source of cadmium contamination. A significant increase in cadmium concentration with distance downshore was demonstrated. A cadmium pollution gradient was detected over short horizontal distances away from the source of contamination. Calculation of flesh condition factors for the populations sampled suggested that condition was not affected by the high cadmium levels detected. Investigations to determine the rate of uptake of cadmium in transplanted mussels indicated: (i) that young animals should be used in accumulation experiments because they grow more quickly and, therefore, respond more rapidly to their environment; and (ii) transplanted animals should be given a minimum of 30 days to regain condition and resume growth following the stress effects due to relocation. Attempts to correlate shell thickness with cadmium concentration were inconclusive. The study confirmed that Mytilus edulis is an excellent bioindicator of local pollution be cadmium.

Production and energy flow in relation to age and shore level in the bivalve Choromytilus meridionalis (Kr.)

Annual production ( P ) in terms of growth ( P 2 ) and reproduction ( P r ) was calculated for individual Choromytilus meridionalis of various shell lengths. Peak growth production occurred at approximately 60 mm ( P 2 =5·6 kJ individual −1 year −1 ). Reproductive output increased with increasing size once sexual maturity was attained and rose from 5·2 kJ year −1 in a 20-mm mussel to 51·4 kJ year −1 in a 100-mm individual, representing 61–97% of total production. Population production was calculated for each of three successive years (Y 0 -Y 2 ) at four shore levels (sublittoral, LWS, Midshore and Topshore) following spat settlement in the lower shore areas. Production was greatest in the sublittoral and at LWS and declined with increasing shore height. Maximum production took place in Y 1 , when the mussels were fully mature and P r represented 80% of production. Production in Y 2 decreased as a result of slowing growth rates, particularly at higher shore levels, and a decline in density throughout the population. Maximum population production was 100×10 3 kJ m −2 year −1 (sublittoral in Y 1 ), when the mussels grew from 26 to 38 mm and the P: ratio was 5·1 Population respiration at the various shore levels was calculated taking into account aerial respiration during exposure at low tide. Respiration averaged 66% of assimilation, where A=P g +P r +R . Population energy flow was highest in the lower sampling stations, the maximum assimilation at LWS being 211×10 3 kJ m −2 year −1 . Energy budgets were calculated for mussels in the sublittoral and Topshore areas. Approximately 90% of the energy filtered from seawater per annum was released to other consumers in the form of gamete output, faeces and pseudofaeces production and through mortality of mussels.

Aerial exposure and energy input in the bivalve Choromytilus meridionalis (Kr.)

The effects of aerial exposure on growth, filtration, and assimilation were examined in Choromytilus meridionalis (Kr.) from Bailey's Cottage, False Bay, South Africa. The maximum height at which these mussels occur on the shore corresponds to 50% aerial exposure. Growth rates declined with increasing shore height. The relationships between flesh and shell dry weight and shell length were not significantly different in littoral and sublittoral mussels. Littoral mussels did not show enhanced filtration rates or assimilation efficiencies relative to continually submerged individuals. Thus, littoral mussels experience a decline in ingestion ration which is directly correlated with increasing shore height. Under conditions of limited food availability littoral organisms frequently employ conservative mechanisms to limit energy expenditure. In C. meridionalis this is evidenced by limitation of the growth rate. Energy conservation may also be facilitated by quiescence and reduced respiratory cost during exposure. This requires investigation.

Diversity of Shallow-Water Gastropod Communities on Temperate and Tropical Beaches

Prosobranch gastropod assemblages on a tropical (Costa Rica) and a temperate (Washington) rocky shore were compared to evaluate how composition changes when there is a five-fold difference in regional species lists. Typical tropical beach quadrats (1-4 m2) contained no more species than did ones from the temperate beach; therefore, on the whole, tropical species are distributed more patchily than temperate ones. However, some shore habitats are more diverse than others at each latitude and temperate species are distributed as patchily as tropical ones when equally diverse habitats are compared. Locally, diversity varies with habitat structure (shore height and substrate). However, structure-diversity relationships are different at the two latitudes: High-shore habitats support more species in the temperate community, low-shore cobble habitats support many more in the tropical community, and low-shore rock habitats are equally diverse at both latitudes. Individuals are probably distributed among these habi...