Bivalve Density Research Articles

Efficient and reliable methods for estimating the abundance of keystone coastal macrofauna over large spatial scales.

Coastal bivalves are important ecosystem engineers, and identifying critical habitats can enhance conservation outcomes for threated keystone species as well as determining hotspots for invasive species. As early action is more efficient in both conservation and mitigation of species invasions, efficient and reliable tools for mapping and monitoring species over large scales are essential. We assessed the reliability and efficiency of towed video and quadrat sampling for estimating the abundance of three keystone macrofaunal bivalve species. To assess reliability, we compared the measured density based on each of the two methods to the "true" density estimated by manually surveying an entire transect. We found that both the video and quadrat method caused underestimation of the density of bivalves, but that the amount of underestimation was comparable, and further that both methods took substantially less time than surveying an entire transect manually. The video method underestimated the abundance of Pacific oysters (Magallana gigas), European flat oysters (Ostrea edulis), and blue mussels (Mytilus spp.) by 23%, 24%, and 16%, respectively. The causes of underestimation for the two oyster species were bivalves grouped in clusters, large amounts of small individuals, and generally higher abundances. While Mytilus spp. were underestimated overall, here observer experience was important, with inexperienced observers overestimating and experienced observers underestimating. Our study found both methods to be reliable and efficient for estimating the abundance of three keystone macrofaunal species, suggesting their potential applicability to other sessile or slow-moving species. We propose that these methods, due to their efficiency, can advance scientific knowledge and enhance conservation outcomes by establishing population baselines, assessing trends over time, and identifying and protecting critical habitats.

Density‐dependent influence of ribbed mussels on salt marsh nitrogen pools and processes

Abstract Bivalves are becoming an increasingly popular tool to counteract eutrophication, particularly in vegetated coastal ecosystems where synergistic interactions between bivalves and plants can govern important N sequestration pathways. In turn, new calls to evaluate how bivalve densities modify N pools and processes across multiple scales have surfaced. Ribbed mussels, Geukensia demissa, and their relationship with smooth cordgrass present a classic demonstration of positive bivalve‐plant interactions and offer a useful model for assessing density dependence. We measure porewater ammonium concentrations, N stable isotope signatures in cordgrass tissue, and sediment N fluxes in mussel aggregations and in cordgrass‐only plots across a southeastern U.S. salt marsh. In addition to measuring the effect of mussel presence, we evaluate mussel density dependence through a multiscale approach. At the patch scale, we quantify mussel density effects within their aggregations (individuals m−2) while at a larger landscape scale, we quantify mussel density effects on the cordgrass‐only areas they neighbour (individuals ~30 m−2). Porewater ammonium concentrations were halved in mussel biodeposits relative to sediments in cordgrass‐only areas and negatively related to mussel density within aggregations. Leaf clip ẟ15N signatures were nearly 2‰ higher in cordgrass growing among mussel aggregations and increased with increasing patch mussel density. Microcosm incubations showed that mussels enhanced N2 flux (i.e., nitrogen removal) and DIN flux (i.e., N regeneration) into the water column, where only nitrogen removal increased with increasing patch‐scale mussel density. Across the marsh landscape, mussel coverage drove ammonium accumulation and N2 flux in sediments. Synthesis. Our results suggest that, at the patch scale, mussels stimulate the microbial metabolism of N, the assimilation of this bioavailable N by cordgrass, and nitrogen removal in a positive, density‐dependent manner. Tidal currents redistribute mussel biodeposits from mussel aggregations to surrounding areas, influencing biogeochemical transformations at scales beyond their physical footprint. We emphasize that the N regeneration potential of bivalve populations is a significant metric contributing to their mitigation potential and that bivalve density effects may be non‐linear, vary across patch to ecosystem scales, and have differing implications for the plants with which they interact.

A global synthesis of predation on bivalves.

Predation is a dominant structuring force in ecological communities. In aquatic environments, predation on bivalves has long been an important focal interaction for ecological study because bivalves have central roles as ecosystem engineers, basal components of food webs, and commercial commodities. Studies of bivalves are common, not only because of bivalves' central roles, but also due to the relative ease of studying predatory effects on this taxonomic group. To understand patterns in the interactions of bivalves and their predators we synthesised data from 52 years of peer-reviewed studies on bivalve predation. Using a systematic search, we compiled 1334 studies from 75 countries, comprising 61 bivalve families (N = 2259), dominated by Mytilidae (29% of bivalves), Veneridae (14%), Ostreidae (8%), Unionidae (7%), and Dreissenidae and Tellinidae (6% each). A total of 2036 predators were studied, with crustaceans the most studied predator group (34% of predators), followed by fishes (24%), molluscs (17%), echinoderms (10%) and birds (6%). The majority of studies (86%) were conducted in marine systems, in part driven by the high commercial value of marine bivalves. Studies in freshwater ecosystems were dominated by non-native bivalves and non-native predator species, which probably reflects the important role of biological invasions affecting freshwater biodiversity. In fact, while 81% of the studied marine bivalve species were native, only 50% of the freshwater species were native to the system. In terms of approach, most studies used predation trials, visual analysis of digested contents and exclusion experiments to assess the effects of predation. These studies reflect that many factors influence bivalve predation depending on the species studied, including (i) species traits (e.g. behaviour, morphology, defence mechanisms), (ii) other biotic interactions (e.g. presence of competitors, parasites or diseases), and (iii) environmental context (e.g. temperature, current velocity, beach exposure, habitat complexity). There is a lack of research on the effects of bivalve predation at the population and community and ecosystem levels (only 7% and 0.5% of studies respectively examined impacts at these levels). At the population level, the available studies demonstrate that predation can decrease bivalve density through consumption or the reduction of recruitment. At the community and ecosystem level, predation can trigger effects that cascade through trophic levels or effects that alter the ecological functions bivalves perform. Given the conservation and commercial importance of many bivalve species, studies of predation should be pursued in the context of global change, particularly climate change, acidification and biological invasions.

BIVALVE COMMUNITY STRUCTURE IN THE INTERTIDAL ZONE OF PASUMPAHAN ISLAND PADANG CITY WEST SUMATERA PROVINCE

Bivalvia is a class of the Mollusca phylum. Bivalvia is also known as Pelecypoda and Lamellibrankhiata. Bivalvia occupies an area of the intertidal zone, one of which is in the intertidal zone of Pasumpahan Island. But information about bivalves in the area does not exist. To know/understand information about the density and distribution pattern of bivalves on Pasumpahan Island, this research was conducted in January 2022. The sampling area was in the intertidal zone of Pasumpahan Island. Sampling was carried out at three stations, each station was divided into three transects. Bivalve sampling was carried out using a 1 x 1mm sieve. The movement of bivalves to the gravel substrate is very fast to avoid splashing waves. Bivalves samples were then identified. The density of bivalves in the intertidal zone of Pasumpahan Island ranged from 1.78-3.56 Ind/m2. Station 2 has a higher density of bivalves, namely 3.56 Ind/m2, the calculation of bivalves in the intertidal zone of Pasumpahan Island obtained bivalves distribution pattern data in groups

Evaluating sea cucumbers as extractive species for benthic bioremediation in mussel farms

Filter-feeding mussels blend suspended particles into faeces and pseudo-faeces enhancing organic matter flows between the water column and the bottom, and strengthening benthic-pelagic coupling. Inside operating farms, high bivalve densities in relatively confined areas result in an elevated rate of organic sinking to the seabed, which may cause a localized impact in the immediate surrounding. Deposit-feeding sea cucumbers are potentially optimal candidates to bioremediate mussel organic waste, due to their ability to process organic-enriched sediments impacted by aquaculture waste. However, although the feasibility of this polyculture has been investigated for a few Indo-Pacific species, little is known about Atlanto-Mediterranean species. Hence, for the first time, in the present study, we conducted a comparative investigation on the suitability of different Mediterranean sea cucumber species, to be reared in Integrated Multitrophic Aquaculture (IMTA) with mussels. A pilot-scale experiment was accomplished operating within a mussel farm where two sea cucumbers species, Holothuria tubulosa and Holothuria polii, were caged beneath the long-line mussel farm of Mytilus galloprovincialis. After four months, H. tubulosa showed high survivorship (94%) and positive somatic growth (6.07%); conversely H. polii showed negative growth (− 25.37%), although 92% of specimens survived. Furthermore, sea cucumber growth was size-dependent. In fact, smaller individuals, independently from the species, grew significantly faster than larger ones. These results evidenced a clear difference in the suitability of the two sea cucumber species for IMTA with M. galloprovincialis, probably due to their different trophic ecology (feeding specialization on different microhabitats, i.e. different sediment layers). Specifically, H. tubulosa seems to be an optimal candidate as extractive species both for polycultures production and waste bioremediation in M. galloprovincialis operating farms.

Struktur Komunitas Bivalvia pada Ekosistem Lamun di Pantai Tukak Kabupaten Bangka Selatan

Bivalves are one of the aquatic biotas that have important economic value and have a fairly high nutritional content role in the waters. The high ecomonic value of bivalves can lead to over exploitation, resulting in reduced productivity and impact on the sustainability of bivalves in seagrass ecosystems. Bivalves are a class of mollusk phylum associated with seagrass ecosystem and have an important role in water. Based on this, it is necessary to conduct recearch related to the structure of the bivalves community in seagrass ecosystems. This research was conducted in Mei 2021 at Tukak Beach South Bangka Regency. Seagrass data were collected using a 50x50 cm² quadrant transect and a distance of 50 m and a distance between transects of 5 m, while bivalves data were taken according to the seagrass transect. Data retrieval is divided into 3 stations, where each station consisting of 3 sub-stations. Where each stasion consists of sub stations. The results obtained 4 species of seagrass and 10 spescies of bivalves from families. Bivalves density value of 8,67-30,67 ind/m². diversity index 1,88-2,33, uniformity index 0,73-0,85, and dominance index 0,29-0,35. Based on principal component analysis (PCA) it was found that the density of bivalves was positively correlated with pH, brightneess, and DO. While the results of the correlation factorial analysis (CA) that there were 3 groups that had a close relationship between the density of seagrass and the density and the bivalves.

Application of eDNA for monitoring freshwater bivalve Nodularia nipponensis and its glochidium larvae

AbstractHabitat loss, the introduction of invasive species, and climate change due to human activity have threatened many freshwater unionid bivalves worldwide. Unionid bivalves represent important members of freshwater ecosystems, providing bitterling fish with spawning grounds and contributing to water clarification via the filtration of suspended solids. This study examined an environmental DNA (eDNA) approach for monitoring the unionid bivalve Nodularia nipponensis in a lake environment. We developed oligonucleotide primers for the specific detection of mitochondrial DNA from N. nipponensis and evaluated the decay and release rates of eDNA in a laboratory tank experiment under two bivalve densities (49 and 164 individuals m−2) selected to ensure sufficient eDNA yields. The eDNA release rate was weakly and positively correlated with bivalve density but strongly and positively correlated with inorganic nitrogen and phosphorus excretion from the bivalve. In a eutrophic lake, Lake Hachiro, 67% of the samples (16 out of 24) collected from June to July yielded detectable amounts of eDNA and were not detected at all in May and August (0 out of 20). This difference was probably due to the release of N. nipponensis glochidium larvae. During these months, unionid glochidia adhered to bundles of polyvinylidene chloride fibers placed on the lake bottom for 8 h, confirmed by microscopic inspection. We successfully obtained N. nipponensis eDNA from all bundles examined over the months, demonstrating the efficacy of bundle capture in quantifying unionid bivalve eDNA. Our eDNA‐based technique with specific oligonucleotide primers and fiber bundles may be a promising tool for monitoring N. nipponensis in freshwater environments. Fiber bundles are useful for tracing eDNA derived from glochidium larvae, even at low unionid bivalve densities, which may be conducive to conservation efforts.

DENSITY AND DISTRIBUTION PATTERN OF BIVALVES IN WATERS OF MALANG RAPAT VILLAGE, GUNUNG KIJANG DISTRICT, BINTAN REGENCY

The purpose of this study was to determine the density, diversity, uniformity, dominance and distribution pattern of bivalves in the waters of Malang Rapat Village. This research uses purposive sampling method. Determination of the sampling point based on the consideration of activities in the waters of Malang Rapat Village. Sampling using a quadrant transect method measuring 1x1 meter. The results showed that the highest species density was Gafrarium pectinatum with a value of 63,333 ind/ha, and the lowest species was Pinctada radiata with a value of 1,111 ind/ha. The species diversity index obtained values in the range of 0.54-0.76 and the category of each station is low. The uniformity index is obtained with a value in the range of 0.56-0.76 and categories at stations I and III are medium, stations II and IV are high. The dominance index obtained values in the range of 0.22-0.42 and the category at each station are low, the dominant species was G. pectinatum with a value of 0.38. The distribution pattern of bivalves in the sea of Malang Rapat Village at stations I and 3 obtained values of 2.43 and 3.05 with clustered categories, while at stations II and IV obtained values of 0.07 and 0.48 with the same or uniform categories.

The bivalves Amarilladesma mactroides and Donax hanleyanus as bioindicators of the impact of vehicles on Cassino Beach, southern Brazil.

Sandy beaches are the main recreational ecosystems of the world, enabling high ecological impacts, especially on the benthic macrofauna, which inhabit the sandy matrix and have a low capacity of locomotion. Cassino Beach, located in southern Brazil, has intense vehicle traffic during the summer, so the purpose of this study was to evaluate the impact of vehicles on the key species Amarilladesma mactroides and Donax hanleyanus. For this purpose, samplings were performed in three sectors of this beach (High Impact, Moderate Impact and Control) during six periods of the year. The results showed lower densities of both bivalves in the High Impact sector than in to the other sectors in all periods, except in first summer sampling, and a predominance of recruits throughout the study. Thus, it suggests that the two species were influenced by the intense vehicle traffic, especially in the most impacted sector. In this way, we conclude that these bivalves could be used as good indicators of pulse disturbance by vehicle traffic on this beach and the results can support in management plans regarding the use of Cassino Beach, considering ecological aspects of this ecosystem in addition to economic and cultural demands.

Using Freshwater Bivalves (Corbicula Fluminea) to Alleviate Harmful Effects of Small-Sized Crucian Carp (Carassius Carassius) on Growth of Submerged Macrophytes during Lake Restoration by Biomanipulation

Increased recruitment of small-sized fish following biomanipulation by reducing the biomass of plankti-benthivorous fish, not least in (sub)tropical lakes, may deteriorate water quality and thereby potentially hamper the recovery of submerged macrophytes. Filter-feeding bivalves remove suspended particles from the water and may, thereby, somewhat or fully counteract this negative effect of the increasing abundance of small-sized fish. So far, only few studies have investigated the interactive effects of fish and bivalves on water clarity and macrophyte growth. We conducted a 2 × 2 factorial designed outdoor mesocosm experiment with two densities of small crucian carp Carassius carassius (low 10 g m−2 and high 40 g m−2) and two densities of bivalves Corbicula fluminea (low 204 g m−2 and high 816 g m−2). We found significant interactive effect of fish and bivalves on the growth of the macrophyte Vallisneria natans. In the low density bivalve regime, the relative growth rates, root mass, root:shoot ratio and number of tubers were 30.3%, 30.8%, 21.6% and 27.8% lower in the high than in the low density fish treatments, while the decrease was less pronounced in the high density bivalve regime: 1.2%, 8.7%, 2.1% and 13.3%, respectively. Thus, bivalves reduced the negative effects of fish, not least when bivalve density was high. The weaker effects of small fish on plants in the high- than in the low-density C. fluminea regime can be attributed to lower total suspended solids (TSS) and Chl a in the first week of the experiment. Better light conditions further stimulated the growth of benthic algae, potentially increasing the removal of nutrients from the water and reducing fish-driven resuspension of the sediment. In addition, high densities of C. fluminea also enriched the sediment total nitrogen (TN) and total phosphorus (TP) content, favouring plant growth as indicated by an increase in leaf tissue TN and TP contents. Our results demonstrate that filter-feeding bivalves can alleviate harmful effects of small fish by prolonging a clear-water state that facilitates submerged macrophyte growth. Addition of the bivalve C. fluminea can be a promising tool for the restoration of submerged macrophytes in shallow eutrophic lakes, in particular lakes containing small, rapidly reproducing fish that due to their small sizes are not capable of controlling the bivalves.

Diversity and Mollusca Distribution Patterns (Gastropoda and Bivalvia) In the North of Poncan Gadang Island, Sibolga City North Sumatera Province

This research was conducted in July-August 2019 in the northern part of the Poncan Gadang Island Sibolga, North Sumatra Province. This study discusses the distribution and distribution patterns of molluscs (gastropods and bivalves) which contain species, density, and species discussed in the northern part of Poncan Gadang Island, North Sumatra Province. The method used is a survey method, where the research location is divided into 5 observation stations and each station consists of 1 transect and each transect consists of 4 maps. The results showed that the type of gastropods found in the study site consisted of 11 species belonging to 6 families. Gastropod species that are commonly found are Littorina littorea. While the type of bivalves that were found at the study site consisted of 9 species belonging to 6 families, and the bivalves species that were found were Anadara granosa. Highest density at station III in the river mouth. Various index (H ') of gastropods and bivalves in all research stations are included in the medium category. Distribution Patterns both gastropods and bivalves are distributed in groups. The index value of approved gastropod and bivalve types (Ss) can be requested types which are found to be quite the same. The substrate at the study site was approved by the sand substrate. The density of both gastropods and bivalves were not significantly different between stations.

Sediment stability: can we disentangle the effect of bioturbating species on sediment erodibility from their impact on sediment roughness?

Benthic organisms, in particular bioturbators, can influence erosion processes either by affecting sediment roughness through their mere presence and/or activities, or by modulating sediment characteristics (e.g., silt content, granulometry), thus altering its erodibility. To date, it was not possible to distinguish the influence of bioturbating species on sediment roughness from their impact on sediment erodibility. Consequently, uncertainties remain regarding the role played by benthic species on sediment dynamics. In this study, we used a canal flume which allows to record the bed shear stress at the surface of a non-cohesive sediment (4% of mud) during erosion experiments, thus allowing to disentangle the influence of bioturbators, here the common cockle Cerastoderma edule, on the two erosion mechanisms. In order to assess the influence of bioturbators on sediment stability in different environmental situations, we additionally tested for the effects of three factors, i.e. bivalve density, availability of suspended food (i.e. phytoplankton presence) and microphytobenthos (MPB) occurrence, which may modulate the behavior of cockles. We observed that cockles promote the erosion of the sediment surficial layer by increasing its roughness as a consequence of their sediment reworking activity and/or presence at the sediment surface (emerging shell). In contrast, we calculated similar critical bed shear stress for erosion with and without bivalves suggesting that cockles have a minor influence on the erodibility of non-cohesive substrates with a low silt content. The destabilizing effect of cockles increased with the bivalve density whereas it was attenuated by the presence of phytoplankton. We hypothesize that the magnitude of cockles' bioturbation activity was lower when a high proportion of suspended food is available. High concentrations of suspended food may also have enhanced the filtration and biodeposition rates of cockles, thus rapidly leading to the ‘muddification’ of the sediment bed and consequently counteracting with the own destabilizing effect of the bivalves. Finally, the sole presence of MPB did not significantly affect the resuspension dynamics of non-cohesive sediments with a low proportion of mud.

Steam and Flame Applications as Novel Methods of Population Control for Invasive Asian Clam (Corbicula fluminea) and Zebra Mussel (Dreissena polymorpha)

Control strategies for established populations of invasive alien species can be costly and complex endeavours, which are frequently unsuccessful. Therefore, rapid-reaction techniques that are capable of maximising efficacy whilst minimising environmental damage are urgently required. The Asian clam (Corbicula fluminea Müller, 1774), and the zebra mussel (Dreissena polymorpha Pallas, 1771), are invaders capable of adversely affecting the functioning and biodiversity of freshwater ecosystems. Despite efforts to implement substantial population-control measures, both species continue to spread and persist within freshwater environments. As bivalve beds often become exposed during low-water conditions, this study examined the efficacy of steam-spray (≥100 °C, 350 kPa) and open-flame burn treatments (~1000 °C) to kill exposed individuals. Direct steam exposure lasting for 5 min caused 100% mortality of C. fluminea buried at a depth of 3 cm. Further, combined rake and thermal shock treatments, whereby the substrate is disturbed between each application of either a steam or open flame, caused 100% mortality of C. fluminea specimens residing within a 4-cm deep substrate patch, following three consecutive treatment applications. However, deeper 8-cm patches and water-saturated substrate reduced maximum bivalve species mortality rates to 77% and 70%, respectively. Finally, 100% of D. polymorpha specimens were killed following exposure to steam and open-flame treatments lasting for 30 s and 5 s, respectively. Overall, our results confirm the efficacy of thermal shock treatments as a potential tool for substantial control of low-water-exposed bivalves. Although promising, our results require validation through upscaling to field application, with consideration of other substrate types, increased substrate depth, greater bivalve densities, non-target and long-term treatment effects.

HUBUNGAN KEPADATAN BIVALVIA DENGAN PARAMETER LINGKUNGAN DI PESISIR TANJUNG PURA KABUPATEN BANGKA TENGAH

The destructive fishing feared will give a negative impact on the survival of this organism. This study aims to analyze the density of bivalves, distribution patterns, and to analyze the relationship of bivalves with environmental parameters in Tanjung Pura village. This research was conducted in March 2019. The systematic random system method was used for collecting data of bivalves. The collecting Data retrieval divided into five research stasions. The results obtained 6 types of bivalves from 3 families and the total is 115 individuals. The highest bivalve density is 4.56 ind / m², and the lowest bivalves are located at station 2,1.56 ind / m², The pattern of bivalve distribution in the Coastal of Tanjung Pura Village is grouping. The results of principal component analysis (PCA) showed that Anadara granosa species was positively correlated with TSS r = 0.890, Dosinia contusa, Anomalocardia squamosa, Mererix meretrix, Placamen isabellina, and Tellinella spengleri were positively correlated with currents r = 0.933.

Paleoecology and paleobiogeography of the Cenomanian-Turonian bivalves from the Southern Galala Plateau (Eastern Desert, Egypt)

Fifty-three bivalve species from the Cenomanian-Turonian strata in the Southern Galala Plateau (Eastern Desert, Egypt) were used to identify major factors controlling their regional and global distribution. Non–metric multidimensional scaling (NMDS) indicated that rock type is a major factor controlling the bivalve distribution, while other biotic parameters such as life habit and mobility level have a minor role. Although the diversity and density of bivalves have a punctuated pattern, a general trend of increasing diversity from the Cenomanian onward was observed. In contrast to the Cenomanian, mobile and infaunal species have dominated the Turonian in a low-energy deeper marine environment with an oligotrophic regime. The lower diversity, the rarity of infaunal taxa, in addition to abundant authigenic minerals (glauconite/pyrite) and oyster bivalves in the Cenomanian point to a high-stress environment, where dysoxia at (or just below) the sediment/water interface may exclude the infaunal taxa. Analysis of the geographic distribution of the identified taxa indicates no significant difference between the Middle East and other mega-provinces. The planktotrophic larval development mode of most bivalve taxa (e.g., oysters and heterodonts) and the opening of seaways associated with the global Cenomnian/Turonian flooding may have resulted on wider geographic dispersion and mixing of faunal communities among the different provinces.

Biofouling development in marine fish farm influenced by net colour, immersion period and environmental conditions

Biofouling poses low productivity and high maintenance in aquaculture. This study simulated the nets of fish cages to investigate biofouling composition and development as influenced by net colour, immersion period and environmental conditions. Yellow and green net panels were immersed for 60 days and sampled at 7, 15, 30, 45 and 60 days. Results revealed that biofouling composition was dominated by Bryozoan Bugula sp. (31%–38% cover), tanaids Tanaidae (64–146 individuals.100 cm-2) and nematodes Linhomoeidae and Oncholaimidae (142–189 individuals.100 cm-2). Biofouling development was observed in succession patterns of harpacticoid–nematode–amphipod–tanaid in yellow nets and amphipod–nematode in green nets. Water velocity within the cages significantly and positively influenced the total cover, biomass and the densities of amphipods, bivalves, polychaetes, fish eggs and bryozoans. Polychaetes, gastropods, fish eggs and macroalgae were present in green nets and absent in yellow nets at 7 days. Uniformity of biofouling assemblage in both net colours was observed beyond 7 days which may be largely explained by brown biofilm formation. The result of the study revealed the dynamics of biofouling in a marine fish farm and provides vital information for developing strategies in biofouling management to lessen its impacts.

Macroborer presence on corals increases with nutrient input and promotes parrotfish bioerosion

Bioerosion by reef-dwelling organisms influences net carbonate budgets on reefs worldwide. External bioeroders, such as parrotfish and sea urchins, and internal bioeroders, including sponges and lithophagid bivalves, are major contributors to bioerosion on reefs. Despite their importance, few studies have examined how environmental (e.g., nutrients) or biological drivers (e.g., the actions of other bioeroders) may influence bioeroder dynamics on reefs. For example, internal bioeroders could promote external bioerosion by weakening the coral skeletal matrix. Our study investigated: (1) whether nutrient supply influences the dynamics between internal and external bioeroders and (2) how the presence of a boring bivalve, Lithophaga spp., influences parrotfish bioerosion on massive Porites corals. We hypothesized that nutrient supply would be positively correlated with Lithophaga densities on massive Porites colonies, and that as bivalve density increased, the frequency and intensity of parrotfish bioerosion would increase. To test these hypotheses, we analyzed six time points over a 10-yr period from a time series of benthic images and nitrogen content of a dominant macroalga from the fringing reefs around Moorea, French Polynesia. We found Lithophaga densities were positively correlated with nitrogen availability. Further, massive Porites that are more infested with Lithophaga had both a higher probability of being bitten by parrotfish and a higher density of bite scars from parrotfishes. Our findings indicate that increasing nutrient availability may strengthen the relationship between internal and external bioeroders, suggesting that colonies at more eutrophic sites may experience higher bioerosion rates.

Driving forces that structure sublittoral macrobenthic communities in sandy beaches along environmental gradients

Sandy beaches are very dynamic and changeable environments that present a wide variety of life forms, and, in some areas, high productivity. In the Gulf of Valencia (Western Mediterranean Sea, Spain) these areas have endured an economically important shellfishery of clams (Donax trunculus and Chamelea gallina). In the Mediterranean, a sea with a notable oligotrophic character, rivers are particularly important because of the contributions of fresh water that carry nutrients and organic matter to coastal ecosystems. Consequently, close to the mouths of the rivers, it is possible to investigate the functions of physical, chemical and biological gradients on the macrofauna structuring of sandy beach communities. The objective of this study was to determine the response of sublittoral benthic communities to environmental variables in microtidal intermediate sandy beaches of the south of the Gulf of Valencia. Samples of benthic macrofauna, water and sediment were collected at 5 stations located in the sublittoral zone at different distances to freshwater sources, each one sampled at five depths, in three sampling campaigns. In general, the physicochemical and nutritional variables of water showed a spatial variation alongshore, and only a few variables (dissolved inorganic nitrogen, suspended solids and salinity) also had an across-shore variation. This variability was due to the different freshwater contributions. The sediment variables (mean grain size and organic matter) presented clear patterns related to depth. With respect to the macrofauna, positive relationships with depth were observed for the total density, density of bivalves, polychaetes, crustaceans and C. gallina, while D. trunculus showed the opposite pattern. The proximity to freshwater sources, favoured a greater abundance of organisms. Regarding temporal variation, two very different phytoplanktonic compositions between winter and summer could be distinguished, while, for the macrofauna, differences in abundance were observed with maximum values in summer. The influence of freshwater discharges on the phytoplankton primary production will have an influence on the abundance of macrobenthic fauna, but after a time lag. By means of CCA analyses, it was found that the communities of benthic macrofauna were strongly influenced by physical factors such as mean grain size, as well as the nutritional variables (organic matter in sediment and microalgae in the water column) and the distance to the freshwater discharges. The identification of these variables is crucial in order to develop an adequate coastal management, paying special attention to the anthropogenic activities that may be modifying the environment and, therefore will affect the biocoenoses.

Density-dependent growth of bivalves dominating the intertidal zone of Banc d’Arguin, Mauritania: importance of feeding mode, habitat and season

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 610:51-63 (2019) - DOI: https://doi.org/10.3354/meps12851 Density-dependent growth of bivalves dominating the intertidal zone of Banc d’Arguin, Mauritania: importance of feeding mode, habitat and season Matthijs van der Geest1,2,*, Jorge A. C. van der Lely1, Jan A. van Gils1, Theunis Piersma1,3, Tamar Lok1 1NIOZ Royal Netherlands Institute for Sea Research, Department of Coastal Systems, and Utrecht University, PO Box 59, 1790 AB Den Burg, Texel, The Netherlands 2MARBEC Centre for Marine Biodiversity, Exploitation and Conservation, UMR 9190, IRD-IFREMER-CNRS-UM, Université de Montpellier, 34095 Montpellier cedex 5, France 3Conservation Ecology Group, Groningen Institute for Evolutionary Life Sciences (GELIFES), University of Groningen, PO Box 11103, 9700 CC Groningen, The Netherlands *Corresponding author: matt.vandergeest@gmail.com ABSTRACT: Accurate predictions of population dynamics require an understanding of the ways by which environmental conditions and species-specific traits affect the magnitude of density dependence. Here, we evaluated the potential impact of season and habitat (characterized by sediment grain size and seagrass biomass) on the magnitude of density dependence in shell growth of 3 infaunal bivalve species dominating the tropical intertidal benthic communities of Banc d’Arguin, Mauritania. Two of our focal species were filter feeders (Senilia senilis and Pelecyora isocardia) and one was a facultative mixotroph (Loripes orbiculatus), mainly relying on organic carbon provided by sulphide-oxidizing endosymbiotic gill-bacteria (i.e. chemosymbiotic). Distinguishing 2 seasons, winter and summer, we manipulated local bivalve densities across habitats (from bare sandy sediments to seagrass-covered mud). In situ growth of individually tagged and relocated clams was measured and compared with those of tagged clams that were allocated to adjacent sites where local bivalve densities were doubled. Growth was negatively density-dependent in both winter and summer in P. isocardia and L. orbiculatus, the 2 species that mainly inhabit seagrass sediments, but not in S. senilis, usually found in bare sediments. As reproduction and survival rates are generally size-dependent in bivalves, our results suggest that in our tropical study system, the bivalve community of seagrass-covered sediments is more strongly regulated than that of adjacent bare sediments, regardless of species-specific feeding mode or season. We suggest that ecosystem engineering by seagrasses enhances environmental stability, which allows bivalve populations within tropical seagrass beds to stay close to carrying capacity. KEY WORDS: Carrying capacity · Chemosymbiosis · Density dependence · Environmental heterogeneity · Feeding guild · Seagrass · Soft-sediment habitat Full text in pdf format Supplementary material PreviousNextCite this article as: van der Geest M, van der Lely JAC, van Gils JA, Piersma T, Lok T (2019) Density-dependent growth of bivalves dominating the intertidal zone of Banc d’Arguin, Mauritania: importance of feeding mode, habitat and season. Mar Ecol Prog Ser 610:51-63. https://doi.org/10.3354/meps12851 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 610. Online publication date: February 01, 2019 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2019 Inter-Research.

Cross-site comparisons of Gulf Sturgeon prey assemblages throughout the northern Gulf of Mexico reveal regional differences

Gulf Sturgeon, Acipenser oxyrinchus desotoi, is listed as threatened, with critical habitat designated throughout the northern Gulf of Mexico (GOM) to protect, in part, areas where feeding occurs. Because not all critical habitat appears to provide equivalent foraging value, reliably identifying areas of relatively high vs. low prey density coupled with appropriate sediment composition may provide important management considerations. Examination of existing benthic datasets (1980-2006) across the Gulf Sturgeon’s range revealed potential prey assemblages differed geographically, with a dominance of amphipods on the northwest coast of Florida, lower overall potential prey densities in the north-central GOM, and relatively high gastropod and bivalve densities in Louisiana. Within sites, high prey densities frequently occurred where high Gulf Sturgeon activity levels previously were identified in telemetry studies, suggesting the historical benthic data sets provide information relevant to foraging habitat. Gulf Sturgeon prey assemblages were correlated with physical parameters at 11 of 14 sites examined and physical parameters included in these correlations differed between eastern and western regions. Gulf Sturgeon prey assemblages were typically correlated with depth and % sand where sand content was high, such as the eastern portion of the sturgeon’s range, as well as parts of both Mississippi Sound and Chandeleur Sound. In contrast, depth, % TOC, and DO were associated with prey assemblages in areas with low sand content in Louisiana and Alabama. These regional results indicate that management approaches on spatial scales smaller than the northern GOM should be considered.