Maximum Shell Length Research Articles

Developing a dynamic energy budget model to project potential effects of deep-sea mining plumes on the Atlantic deep-sea mussel, Bathymodiolus azoricus

Due to the consistent lack of Environmental Risk Assessment (ERA) for deep-sea mining scenarios, the potential impacts of this industry on marine ecosystems remain largely unknown. In order to fill this gap, a Dynamic Energy Budget (DEB) model was developed to study the consequences of toxic sediment plumes derived from deep-sea mining on the energy budget of the Atlantic deep-sea mussel, Bathymodiolus azoricus. Model calibration was based on environmental conditions observed at the Menez Gwen (MG) vent field (Mid-Atlantic Ridge- MAR), assuming a B. azoricus lifespan of 10 years and a maximum shell length of 119 mm. Scenario simulations were conducted to mimic the effects of increased concentrations of toxic sediment plumes on mussel filtration rates, the absorption of reduced substrates by their endosymbionts, and the energetic costs associated with metal toxicity. Data were sourced from B. azoricus and, when necessary, from proxy species. One disturbance scenario (EF1) incorporated measured rates and realistic parameters, while the other (EF2) was intentionally designed to encompass cumulative effects and uncertainties, representing a potential worst-case scenario. Both disturbance scenarios were initiated at three different timings (0, 1200 and 2400 days) to accommodate the mining effects at different stages of the mussels' life cycle. Results indicate that B. azoricus is significantly impacted by toxic sediment plumes, particularly during earlier life stages, potentially leading to severe growth impairment and mortality. These results were integrated into a food web model of the MG vent field, revealing that disruptions to the energetic balance of the vent mussel have widespread consequences for the entire ecosystem. Overall, we argue that this numerical framework offers a valuable tool for conducting ERA and Environmental Impact Assessments (EIA) in the context of industrial deep-sea mining.

An Investigation and Invasiveness Analysis of Two Species of Giant African Snail in a Coastal City of Southern China

Investigations and research on the giant African snail (GAS) mainly focus on Achatina fulica. However, in recent years, a more harmful GAS, Achatina immaculata, has been reported. In order to understand the invasive status of A. immaculata in China, we take Shenzhen, a coastal city in Southern China, as an example to carry out an ecological survey on the field populations of the two species of GAS in various districts. We explore the differences in the invasive characteristics of the two species of snails in terms of their dietary intake, cold adaptation and drought resistance. The results indicate that, based on the phylogenetic tree analysis, more than half of the sampled snails exhibit higher similarity to A. immaculata. The number of wild A. immaculata is significantly greater than that of A. fulica, and 70.64% of the 746 GAS are A. immaculata. At the same time, it is also found that the maximum shell length of A. immaculata is 135.83 mm, with an average shell length of 76.00 mm, which is significantly different from the average shell length of A. fulica (56.57 mm, p < 0.01). The food intake assay shows that there is no difference in the food preferences of the two species, but the food demand of A. immaculata is significantly greater than that of A. fulica (2.32 fold, p < 0.01). In the cold adaptation assay, A. immaculata recovers from the cold dormancy state significantly faster than A. fulica (1.92 fold, p < 0.05), and the speed with which A. immaculata enters the dormancy state in the drought environment is significantly slower than that of A. fulica (0.706 fold, p < 0.05). With the characteristics of a large body size, large food intake and strong resistance to cold and drought resistance, A. immaculata has the potential to be dominant in competition with A. fulica in the same ecological niche, and it has become the main invasive species of GAS in Shenzhen.

Growth of Allopeas gracile under starvation: does it comply with von Bertalanffy growth equation?

The growth of the land snails is a primary indicator of the fitness at the individual and population levels. Considering starvation as a limiting factor of growth, the adaptation of the land snail Allopeas gracile (Hutton 1834) (Gastropoda: Subulinidae) was assessed using von Bertanlaffy growth equation. As a starvation treatment, the laboratory reared 0-day old snails were fed at a gap of 1 to 6 days (six levels of starvation treatment) or fed regularly (control). In all instances, the shell length and the biomass (indicators of growth) increased with the time interval complying with the von Bertalanffy growth equation, but the magnitude of maximum shell length, Lmaximum, and the asymptotic length, L∞, decreased, while the growth rate coefficient (k) increased, as the duration of starvation period extended. The k and L∞ were represented as functions of the starvation gap (T) and substituted in classical von Bertalanffy equation, representing a better fit model explaining the growth. The results indicate that the food availability is a crucial factor determining the pace of growth in the land snail A. gracile. As an extension, the present model can be used for the portrayal of the growth of the macroinvertebrates under varying level of starvation.

Population status of the world's largest limpet,Scutellastra mexicana(Mollusca: Patellidae), on María Madre Island, Mexico: Possible last bastion of a species facing global extinction

AbstractScutellastra mexicanais the largest patellid in the world, with records of up to 35.5 cm in length, and is one of the most endangered marine invertebrates from tropical Pacific rocky shores.The decline of this species occurred during the 20thcentury, when fishing cooperatives reported the capture of millions of specimens in less than 2 decades (1970–1980). Since then, the species has continued to be captured illegally to the point that it has practically disappeared.This paper reports the population status ofS. mexicanain María Madre Island (Mexican Pacific Ocean), which was used as a Federal Prison from 1905 until 2019.A total of 2,381 limpets were recorded in four main populations: Guayacama, Borbollones, Punta Halcones and Papelillos. The density was very low: from 0.05 to 0.3 individuals m−2, with an ageing population structure, and no recent recruitment. The size‐frequency distribution of the populations showed that most of the individuals were between 9 and 15 cm. Mean and maximum shell length varied between 10.5 and 19 cm at Papelillos, 13.6 and 20.3 cm at Punta Halcones, 13.7 and 17.6 cm at Borbollones, and 12 and 20 cm at Guayacama.Evidence of illegal extraction was evident in Papelillos since the size of the limpets was significantly the smallest of the four populations studied, and also significantly smaller than those in an adjacent midden.Now that the prison has been closed it is imperative to establish legal measures, to provide extreme protection of María Madre, and to change the current status ofS. mexicanain the Official Mexican Standard (NOM‐059‐ECOL‐2010) from threatened species to in danger of extinction. This may be the last hope for the species.

Population and Reproductive Dynamics of Zebra Mussels (Dreissena polymorpha) in Warm, Low-Latitude North American Waters.

AbstractZebra mussels (Dreissena polymorpha), first reported in Texas during 2009, have infested 28 Texas reservoirs over 11 years. This species has not previously invaded water bodies as warm as those in Texas, where temperatures approach or exceed its previously accepted incipient upper thermal limit of 30 °C, raising the question of how such temperatures impact its population dynamics. Over 3-5 years, monthly collections of mussels, sampling for planktonic mussel veligers, juvenile settlement data, and water quality parameters, were undertaken at Texas lakes Texoma, Ray Roberts, and Belton to estimate mussel shell length growth rates, life spans, reproductive periods, and settlement patterns. Biannual spawning periods occurred at water temperatures of 18 to 28 °C, resulting in distinct spring and fall juvenile settlement cohorts. Growth rates were rapid, with both cohorts attaining mean maximum shell lengths of 20-25 mm within 8-15 months of settlement, compared to European and northeastern US populations that attained similar sizes after 2-4 years. Shortened life spans were demarcated by adult mussel die-offs during summer months of elevated water temperature the year after initial settlement, leading to short-term cyclical fluctuations in population densities. Large-scale mussel die-offs were caused by flooding and hypoxia events. Elevated temperatures appeared to facilitate mussel invasiveness by increasing spawning frequency and elevating growth rates, thus reducing time to maturity and allowing population recovery within 1-2 years after environmentally induced severe population declines.

Dynamic energy budget modeling of Atlantic surfclam, Spisula solidissima, under future ocean acidification and warming

A dynamic energy budget (DEB) model integrating pCO2 was used to describe ocean acidification (OA) effects on Atlantic surfclam, Spisula solidissima, bioenergetics. Effects of elevated pCO2 on ingestion and somatic maintenance costs were simulated, validated, and adapted in the DEB model based upon growth and biological rates acquired during a 12-week laboratory experiment. Temperature and pCO2 were projected for the next 100 years following the intergovernmental panel on climate change representative concentration pathways scenarios (2.6, 6.0, and 8.5) and used as forcing variables to project surfclam growth and reproduction. End-of-century water warming and acidification conditions resulted in simulated faster growth for young surfclams and more energy allocated to reproduction until the beginning of the 22nd century when a reduction in maximum shell length and energy allocated to reproduction was observed for the RCP 8.5 scenario.

Population dynamics of Anadara antiquata of East Coast of Aceh, Indonesia

Abstract. Azmi F, Mawardi AL, Sinaga S, Nurdin MS, Febri SP, Haser TF. 2021. Population dynamics of Anadara antiquata of East Coast of Aceh, Indonesia. Biodiversitas 23: 436-442. Small-scale fishery effects are often overlooked by fishery and environmental managers. This study aimed to assess the impact of traditional cockle fishery on its population in the northeastern coast of Sumatra, Indonesia. The study took place from January 2018 to December 2018. Samples were obtained from Ujung Perling in Aceh Timur Regency, which is the only fishing ground exploited at present. Parameters estimated in this study include growth, mortalities, and exploitation levels. Analysis revealed that the average length was 50.03 mm, with the maximum shell length captured is 78 mm. Von Bertalanffy K-coefficient is 2.3 with a lifespan that can reach 3 years. Natural mortality is 2.27 year-1, while fishing mortality is 6.74 year-1. The exploitation rate in this study is 0.75. Growth parameters indicate that Ujung Perling is a suitable habitat for the cockle to grow, but mortalities and exploitation parameters suggest overexploitation is taking place in the area. To keep the population at a safe level, exploitation needs to be lessened to 33% from the current level.

Assessing Evolutionary Significant Units (ESU) of the Endangered Freshwater Pearl Mussel (Margaritifera margaritifera) in Southeast Norway on the Basis of Genetic Analysis.

A total of 312 specimens of freshwater pearl mussel (Margaritifera margaritifera) were sampled from 11 populations, located in four different river systems in Southeast Norway, and analyzed for 11 simple sequence repeat (SSR) (microsatellite) markers. All study populations have landlocked brown trout (Salmo trutta) as the only possible host. Several populations had experienced recruitment failure, probably due to low pH (about 6.0) and calcium concentration. STRUCTURE clustering analysis revealed two genetic clusters, of which one cluster occurred mainly in the western river systems, and totally dominated in one population (Fallselva (A-FAL)) that had higher genetic diversity than the others. Cluster 2 completely dominated in the populations of the eastern river systems, and all of them had low genetic diversity. Bottleneck events were indicated in all populations and the inbreeding coefficient FIS was significant in all populations, except for the southernmost population (Sørkedalselva (B-SØR)), which was the only population with genotypes in Hardy–Weinberg equilibrium. FIS were especially high in the populations of the eastern river systems, and maximum shell length was negatively correlated to FIS. If artificially breeding and stocking should become necessary for future preservation, it should be based on single populations; alternatively, the eastern populations should be based on cross-breeding of populations within the cluster to increase their genetic diversity.

Evaluating the role of predatory fish controlling the invasion of the Asian golden mussel Limnoperna fortunei in a subtropical river

Abstract The invasive Asian golden mussel Limnoperna fortunei is continuously expanding through South America, altering aquatic ecosystem structure and functioning. While several native fish species predate on this mussel, these interactions, and their consequences for the food web, have not been studied in depth. We combine a survey of the fish assemblage trophic structure using gut contents and stable isotope analysis with an in situ exclusion experiment in order to: (a) determine the main fish species predating on L. fortunei; (b) estimate the contribution of L. fortunei to the biomass of fish assemblage; and (c) evaluate the role of fish on the density and maximum shell length of L. fortunei in the lower Uruguay River (the Río de La Plata Basin). We found that about one third of fish species in the assemblage (28 out of 81 species) consumed L. fortunei, which was an important food item (>10% of the dietary volume and >30% of frequency of occurrence) for 11 fish species. Stable isotope mixing models consistently suggested that >14% of the total biomass of the fish assemblage was derived directly from carbon derived from L. fortunei tissues. In addition, the exclusion experiment demonstrated that fish predation reduces the mussel density by c. 70% and the mussel maximum shell length by c. 40%. Synthesis and applications. Our research suggests a top‐down effect of fish on the invasive Asian golden mussel's abundance. This work highlights the need to preserve the native fish communities, particularly in South America, where many vulnerable migratory fish are of key relevance as Limnoperna fortunei consumers. In the light of these findings, actions such as implementing efficient fish passage technologies in the actual (and projected) dams of the Uruguay River basin and elsewhere become essential to avoid local extinctions of these natural invasion controls upstream of the dams.

Life history traits of the exotic freshwater snail Melanoides tuberculata Müller, 1774 (Gastropoda, Thiaridae), and its sensitivity to common stressors in freshwaters

Abstract: Aim In the present study has analyzed several aspects of the life history traits of Melanoides tuberculata, an exotic species, under laboratory conditions, and its response to some stressors has also been applied. Methods Sensitivity to two toxic substances was tested. The mollusks were collected and cultured in the laboratory under controlled conditions of temperature of 25 ± 1 °C and ad libitum food regime. Growth rates and biomass were experimentally obtained and the individual growth curve obtained. Results The experiment lasted 287 days and the maximum shell lengths registered was 11.67 mm. The growth curve indicated a rate of 3.98 year-1 and a maximum theoretical length of 10.61 mm. The mean post-embrionary development time until first reproduction was 275 days and the size of the primipara was 10.13 mm. An accelerated growth of juveniles was observed with fast increase in the shell length until sexual maturity, but growth rate decreased afterwards as more energy was devoted to reproduction. Under the combination of 25 °C and fed on alternate days, M. tuberculata had a slow growth and a long-life expectancy under laboratory conditions. The tolerance of this mollusk to temperature as a stressor ranged between 16 °C and 37 °C, being the optimum temperature situated between 29 °C and 34 °C. The LC(I)50-24h for reference substances were: 0.70 g L-1 for KCl and 9.05 g L-1 for NaCl. Conclusion Based on these results, we can conclude that M. tuberculata is a species tolerant to temperature and salinity, what partially explains to accordance to its wide and rapid dispersion throughout tropical waters.

Recruitment of the limpetPatella ulyssiponensisand its relationship with crustose coralline algae: patterns of juvenile distribution and larval settlement

AbstractRecruitment of the limpetPatella ulyssiponensiswas investigated in relation to the presence of living crustose coralline algae (CCA) in rocky-shore habitats. Juvenile limpets (≤10 mm maximum shell length) were counted in CCA-present and CCA-absent habitats, on three shores in SW Portugal during summer 2007 and winter 2009. Furthermore, the settling response of laboratory-reared larvae ofP. ulyssiponensisto CCA-covered substratum, and bare-rock, was examined. Across the intertidal zone, we found a clear association between the distribution and abundance of juveniles and the presence of CCA. Although the presence of CCA was not an absolute requisite for juvenile occurrence, null juvenile densities were mostly recorded in CCA-absent areas. The highest juvenile densities (maximum of 64 individuals in 15 × 15 cm) were consistently found in CCA-dominated habitats, namely steep wave-exposed areas at low-shore and rock-pools. The hypothesis of CCA-enhanced settlement was not supported, as settlement intensities of laboratory-reared larvae were similar between chips of rock encrusted by CCA and chips of bare-rock. From the overall number of settlers onto CCA-encrusted rock chips, 51% were found in tiny pits lacking CCA. This was the first study of the settlement patterns of larvae of the genusPatellausing naturally occurring rocky substrata. These results are preliminary and should be confirmed with choice-experiments and improved monitoring of the position of settlers. We suggest that CCA plays a role in the recruitment ofP. ulyssiponensis, potentially promoting survivorship of early benthic stages, but possibly not enhancing settlement.

Distribution and growth of bivalve molluscs Serripes groenlandicus (Mohr) and Macoma calcarea (Gmelin) in the Pechora Sea

We studied distribution and growth of Serripes groenlandicus and Macoma calcarea in the southeastern part of the Pechora Sea. The hypothesis was tested that trends in the site-to-site variability of population characteristics of these two bivalve species were driven by their feeding types (suspension-feeder and deposit-feeder, respectively). However, such a trend was found only in the abundance distribution of these species and site-to-site variability in growth rates of S. groenlandicus. M. calcarea density on silty sediments was almost twice as high as on sandy sediments, while Serripes biomass was almost 1.5 times higher on sandy sediments than on silty sediments. The slowest-growing Serripes were found at the deepest stations and in habitats with the largest content of fine fractions (silt) in sediments. Differences in the growth of S. groenlandicus could reflect variability of feeding conditions of this suspension-feeder (e.g., hydrodynamic conditions). Thus, the growth rate of S. groenlandicus was sensitive to environmental conditions, which means it can be used as an indicator of their changes. In general, S. groenlandicus in the Pechora Sea is very slow-growing compared to other areas (maximum life span and shell length are 28 years and 70 mm, respectively). Their growth rate was closest to that in Arctic-influenced locations. On the contrary, the maximum life span and shell length of M. calcarea in the Pechora Sea (15 years and 30 mm, respectively) were similar to those in other parts of the distribution area. No significant differences were found in the group growth of M. calcarea from different studied localities.

Length frequency and morphometric analysis of the non-indigenous red-rimmed melania (Melanoides tuberculata) populations in Slovakia

The red-rimmed melania Melanoides tuberculata (O. F. Muller) has been used in the aquarist trade and biocontrol programs, leading to its emergence outside its native range. Two populations of the red-rimmed melania occur in Slovakia. We investigated the morphometric features of mentioned populations and made a comparison. These two populations differ significantly in investigated features. Mean shell length of red-rimmed melania individuals from the Opatovce nad Nitrou was 14.7 mm, while the mean shell length of specimens from Piesťany was 24.4 mm (p < 10−6). Mean shell width, aperture length, and aperture width for specimens from the Opatovce nad Nitrou was 4.4 mm, 4.1 mm, and 2.3 mm, respectively. Mean shell width, aperture length, and aperture width of Piesťany specimens was 7.5 mm (p < 10−6), 7.1 mm (p < 10−6), and 3.8 mm (p < 10−6), respectively. The maximum shell length of specimens from the Opatovce nad Nitrou site was 22–23 mm, while shell length of specimens from Piesťany reached 32–33 mm. Regression analysis of the shell length and shell width, aperture length and aperture width, indicate equivalent relationship of the shell patterns for the two populations. Population structure analysis provided first inside of their population status, identifying a proliferating population at the Opatovce nad Nitrou site, while only adult individuals were observed at the site in Piesťany. The red-rimmed malania is a good candidate for possible biological invasions in thermal waters of temperate zone.

Patterns of the vertical distribution limits of the limpet Patella depressa on the Portuguese coast

Event Abstract Back to Event Patterns of the vertical distribution limits of the limpet Patella depressa on the Portuguese coast Daniela Nobre1*, Maria I. Seabra1 and Teresa Cruz1, 2 1 Centro de Ciências do Mar e do Ambiente (MARE), Portugal 2 Departamento de Biologia, Escola de Ciências e Tecnologia, Universidade de Évora, Portugal The limpet Patella depressa is a keystone species in the rocky shores of the Northeast Atlantic. Vertical distribution limits may vary spatially and temporally due to different physical and biological factors. The spatial variation on the intertidal limits of the distribution of P. depressa, as well as on the abundance of this species, was studied during the winter of 2012, in three shores (two in the north - Moledo and Gelfa - and one in the southwest - Oliveirinha - coast of Portugal). In each shore, three transects across the vertical intertidal gradient were considered; within each transect, we measured the shore height at the lower and the upper limits of P. depressa distribution (defined by the position of the last individual found in the lower and upper extremes along the transect), as well as the horizontal extension (the distance along the rock surface) between those two limits. Densities of two size classes (<2 cm and > 2 cm of maximum shell length – MSL) of limpets in 0.25 m2 were assessed in the area of the species’ greatest abundance within the same transects (n = 6 replicates). Spatial variation of the in situ temperature at the lower and the upper limits of distribution was also analyzed by deploying limpet-biomimetic sensors at both limits in all shores and transects, recording semi-continuous temperature every 15 minutes. Furthermore, the temporal variation on the shore height of the vertical distribution limits was studied in Oliveirinha in two dates (March and July 2014) along seven to ten transects, by comparing the marked locations of each limit (the position of the last individual found in the lower and upper extremes along each transect) between dates. Overall, the height of the lower limit did not vary among shores, whereas the upper limit was, on average, one meter lower in Oliveirinha compared to Moledo and Gelfa. Total abundance was four times higher in the shores of the north coast, although the density of larger limpets (> 2 cm MSL) was twenty times higher in Oliveirinha. In all shores, temperature was more variable on the upper limits than on the lower limits, and the daily minimum temperature at both limits was consistently lower in Oliveirinha when comparing with the northern shores. Regarding temporal variation in Oliveirinha, although the average height of both lower and upper limits did not differ between dates, we found significant differences between dates in the relative direction of the change in individual positions marked for each limit, with a consistent decrease of both limits in July relatively to March. Keywords: Patella depressa, vertical distribution, temperature, abundance, limpets Conference: IMMR'18 | International Meeting on Marine Research 2018, Peniche, Portugal, 5 Jul - 6 Jul, 2018. Presentation Type: Poster Presentation Topic: Biodiversity, Conservation and Coastal Management Citation: Nobre D, Seabra MI and Cruz T (2019). Patterns of the vertical distribution limits of the limpet Patella depressa on the Portuguese coast. Front. Mar. Sci. Conference Abstract: IMMR'18 | International Meeting on Marine Research 2018. doi: 10.3389/conf.FMARS.2018.06.00051 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 27 Apr 2018; Published Online: 07 Jan 2019. * Correspondence: Ms. Daniela Nobre, Centro de Ciências do Mar e do Ambiente (MARE), Lisbon, Portugal, daniela.nobre.silva@hotmail.com Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Daniela Nobre Maria I Seabra Teresa Cruz Google Daniela Nobre Maria I Seabra Teresa Cruz Google Scholar Daniela Nobre Maria I Seabra Teresa Cruz PubMed Daniela Nobre Maria I Seabra Teresa Cruz Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

The demographics and morphometries of biogenic reefs: important considerations in conservation management

Modiolus modiolus L. (horse mussel) reefs are a priority marine habitat of high conservation value that is currently listed as endangered and/or threatened across its European distribution. Population structure, density or shell morphology may influence the biodiversity of a reef, either directly or indirectly. Thus, such metrics are important considerations for successful conservation management of these biodiversity hotspots. Population structure, shell morphology and growth rates were examined in M. modiolus reefs across the UK range of the habitat to examine differences between key populations, including those near the Lleyn Peninsula in Wales (southern range), off Port Appin in Western Scotland (mid-range) and in Scapa Flow in the Orkney Isles, Scotland (northern range). Additionally, the influence of physical conditions (temperature and tidal flow) to growth rate and predicted maximum shell length for each population was examined. Growth rates were determined using acetate peels of sectioned shells. Lower juvenile abundance was observed in Scapa Flow. Small, narrow-shaped shells were found to be characteristic of North Lleyn mussels, and larger, globular-shaped shells were characteristic of mussels in Scapa Flow and off Port Appin. Mussels in Scapa Flow were slower growing, yet reached a longer asymptotic length (L∞) than mussels of Port Appin and North Lleyn. Growth curves from sites within this study were analysed with other published data. A trend of higher L∞ at higher latitudes and at lower flow rates was observed. Variations in growth and age are discussed in relation to flow regimes, connectivity to other reefs, density and latitude.

Ingestion rates and grazing impact of the brackwater mussel Brachidontes virgiliae in Lake St Lucia, iSimangaliso Wetland Park, South Africa

Bivalves feed on a combination of phytoplankton and zooplankton and have the potential to impact considerably the planktonic biomass, especially when they occur in high densities, such as in oyster and mussel beds. The brackwater mussel Brachidontes virgiliae is numerically dominant during wet phases within Africa’s largest estuarine lake, St Lucia, in the iSimangaliso Wetland Park on the east coast of South Africa. The ingestion rates and potential grazing impact of this small mussel (maximum shell length = 2.5 cm) were estimated for both the wet and dry seasons using an in situ gut fluorescence technique. Ingestion rates were higher during the wet season (5.78 µg pigment ind.−1 d−1) than during the dry season (4.44 µg pigment ind.−1 d−1). This might be explained by the increased water temperature and food availability during the wet season. Because of the patchy distribution of mussel populations, there could be higher localised grazing impact near mussel aggregations. Results showed a potential grazing impact of up to 20 times the available phytoplankton biomass at specific sites. These high grazing impacts have the potential to deplete phytoplankton stocks in the lake, especially during wet phases in the northern reaches, where mussel densities are highest. This needs to be factored into ecological models of Lake St Lucia, because the system might function differently during increased flood events.

Reproduction, growth and size of a burrowing intertidal clam exposed to varying environmental conditions in estuaries

Bivalves in estuaries are exposed to many environmental variables but little is known about how such variables, including reduced salinity, affect reproduction and growth in burrowing clams. These were measured in the New Zealand little-neck clams, Austrovenus stutchburyi, from one urban and three rural estuaries with different contaminant inputs. Two shellfish sites were selected within each estuary reflecting high- and low-salinity exposure. Reproductive activity was seasonal and similar amongst the estuarine systems. The gravimetric condition index (CI) of the clams decreased significantly on exposure to low-salinity regimes. The gonad index increased significantly with CI and per cent glycogen in the foot tissue. At most sites, shell length increased significantly with the age of the clam, and maximum shell length and growth was reduced in clams exposed to the low-salinity regime. Reproductive indices of the clams did not correlate with sediment characteristics or sediment trace metal pollution index. It was concluded that salinity was the main factor affecting shellfish condition and that seasonal CI measurements could be a good indicator of growth and reproductive success. This knowledge is useful for the future management of this and other similar shellfish species.

Fishing and bottom water temperature as drivers of change in maximum shell length in Atlantic surfclams (Spisula solidissima)

Maximum shell length of Atlantic surfclams (Spisula solidissima) on the Middle Atlantic Bight (MAB) continental shelf, obtained from federal fishery survey data from 1982-present, has decreased by 15–20 mm. Two potential causes of this decreasing trend, fishery removal of large animals and stress due to warming bottom temperatures, were investigated using an individual-based model for post-settlement surfclams and a fifty-year hindcast of bottom water temperatures on the MAB. Simulations showed that fishing and/or warming bottom water temperature can cause decreases in maximum surfclam shell length (body size) equivalent to those observed in the fished stock. Independently, either localized fishing rates of 20% or sustained bottom temperatures that are 2 °C warmer than average conditions generate the observed decrease in maximum shell length. However, these independent conditions represent extremes and are not sustained in the MAB. The combined effects of fishing and warmer temperatures can generate simulated length decreases that are similar to observed decreases. Interannual variability in bottom water temperatures can also generate fluctuations in simulated shell length of up to 20 mm over a period of 10–15 years. If the change in maximum size is not genotypic, simulations also suggest that shell size composition of surfclam populations can recover if conditions change; however, that recovery could take a decade to become evident.

High density of Tridacna crocea in exposed massive corals proximate the Ranger Station of Tubbataha Reefs Natural Park, Cagayancillo, Palawan, Philippines

The crocus clam Tridacna crocea, one of the seven known giant clam species in the Philippines (Poutiers 1998), is widely distributed in the IndoPacific Region but is possibly extinct in Guam and Northern Mariana Islands (IUCN 2014). In the Philippines, the exploitation of all giant clam species is prohibited under Fisheries Administrative Order No. 208, series of 2001 (DA 2001). However, illegal exploitation of giant clams in many parts of the country has greatly reduced natural stock populations (Gomez and MingoaLicuanan 2006; Gonzales et al. 2014; Picardal and Dolorosa 2014), and only in marine protected areas such as Tubbataha Reefs Natural Park (TRNP) where high densities (100-220 ind.100 m-2) of T. crocea (Calumpong and Cadiz 1993; Ozoa 1995; Dolorosa and Schoppe 2005) have been reported. Methods to quantify the abundance of this species involved the use of either belt transect with 1 x 1 m quadrat placed every 10 m or 2 x 100 m belt transect. No data are so far available on the density of T. crocea embedded in coral rocks exposed at low tide. To quantify the abundance of T. crocea in massive corals with heads exposed at low tide, some exposed corals near the vicinity of the Ranger Station of TRNP were randomly sampled in June 2010. The area of coral heads was measured by using a quadrat and then by measuring the shell lengths of T. crocea with calipers (Figure 1). Among the ten coral heads surveyed (area =40.75 m2), a total of 236 T. crocea was noted. The densities of T. crocea ranged from 200-2,200 ind.100 m-2 with an average (±sd) of 767 (±559) ind.100 m-2 (Table 1). The sizes of T. crocea varied between 10-135 mm with an average (±sd) shell length of 67.67 (±32.26) mm (Figure 2). Tridacna crocea can attain 150 mm maximum shell length but commonly 110 mm (Poutiers 1998). There is no available literature on the size at which T. crocea becomes sexually mature, however, if T. crocea begins to reproduce after attaining nearly 40% (60 mm) of its maximum shell length (150 mm) as recorded for Tridacna maxima by Jameson (1976), then at least more than half (57%) are sexually mature. About 14% of samples were very small (10-29 mm) and such may indicate a self seeding reef. These high densities of T. crocea could be due to the manner of survey which only accounted for the coral heads exposed at low tides. In 2009, a survey involving 40 transects (20 x 2 m) in the surrounding reefs within the Ranger Station of TRNP recorded an average density of 39.25 ind.100 m-2 (range: 3.13-126.25 ind.100 m-2 (Dolorosa unpublished data). Previous densities obtained along the transect lines at intertidal (13 ind.100-2m) and 5 m deep (3 ind. 100-2 m) areas of the park (Dolorosa and Schoppe 2005) were lower than the present data. Lower densities (31 ind.100-2 m) were also recorded using transect surveys in Apulit Island, Taytay, Palawan (Gonzales et al. 2014) and many other areas of the Philippines (see bin Othman et al. 2010). Much lower were the densities in Seribu Island (2.80 ind. 100 m-2) and Manado Waters, Indonesia (0.85 ind. 100 m-2) (Yusuf et al.2009), and in intertidal (0.037 ind. 100 m-2) and subtidal (0.027 ind. 100 m-2) reefs of Singapore (Neo and Todd 2012). Giant clams are important component of the reef ecosystems. Their ecological roles have recently been reviewed and quantified which include their capacity to promote a balanced reef ecosystem (Neo et al. 2015). Any reef restoration project should therefore at least include the revival of giant clam populations. The current higher abundance of T. crocea within the Ranger Station of TRNP therefore requires effective protection, as the park represents an important natural genetic bank and seed source for clamdepleted reefs within its vicinity and other reefs in the Sulu Sea.

Variations of 210Po activity in mussel (Perna viridis) of Samut Sakhon and its contribution to dose assessment

The activities of 210Po and its effective dose in green mussel (Perna viridis) collected from a mussel farming area in Samut Sakhon province during the period of 20122013 are presented. Several parameters including maximum shell length and the physiological performance of mussels using condition index and physical properties of seawater (pH, salinity, conductivity, TDS, DO and cation-anion elements) were measured. Each individual mussel was measured for its maximum shell length which was adopted as size class. The activity concentration of 210Po was determined spectroscopically through its 5.30 MeV alpha particle emission, using 209Po as an internal tracer. The 210Po activity concentration in mussels was found to vary between 1.044 and 6.951 Bq/kg wet weight. The 210Po concentration was higher in smaller-sized (≤35 mm) and lower in larger ones (40-70 mm). This confirmed that larger mussels have lower 210Po activities on a weight basis. The 210Po body burden (activity per mussel) ranged from 1.035 to 17.183 mBq. Contrary to the 210Po concentrations, results of the body burden revealed the lower activities in smaller-sized mussels (≤35 mm) and the higher in larger-sized ones (40-70 mm). The type of fluctuations observed with 210Po concentrations were interpreted as a seasonal effect. Total annual effective 210Po dose due to mussel consumption was calculated to be in the range of 3.081 to 16.401 pSv. Based on the international guideline, the average dose calculated due to 210Po in mussels of Samut Sakhon would not pose any significant radiological impact on human health and the mussels are considered to be safe for consumption.