Subhronil Mondal

Bio: Subhronil Mondal is an academic researcher from University of Calcutta. The author has contributed to research in topics: Coastal erosion & Predation. The author has an hindex of 10, co-authored 33 publications receiving 251 citations. Previous affiliations of Subhronil Mondal include University of South Florida & Indian Institute of Science.

Gastropod drilling predation in the upper jurassic of kutch, india

Abstract: Gastropod drillholes on prey shells provide an opportunity to test the importance of predation in an evolutionary context. Although records of drilling predation are widespread across the Phanerozoic, the temporal distribution and relative importance of this mode of predation is still controversial. Further, some studies indicate a decline of drilling predation in the Mesozoic but other studies do not. In this study, we present a new dataset of gastropod drilling predation on Kimmeridgian and Tithonian bivalves of Kutch, India. Our study suggests that drilling was one of the prevailing modes of predation in the Upper Jurassic of Kutch with strongly variable intensities, ranging from 2% in the Kimmeridgian Seebachia to 26% in the Tithonian Pinna. A significant, albeit small, increase in drilling intensity from the Kimmeridgian to the Tithonian assemblages is associated with a change in relative sea-level and depositional environment. The morphology of drillholes and recent discovery of body fossils from the same stratigraphic units suggest naticid gastropods as the most likely drillers. A literature survey, along with previously collected specimen from the Jurassic of Kutch, reveals a more complex history of drilling predation than previously assumed.

Sediment characterization and dispersal analysis along a part of the meso- to microtidal coast: a case study from the east coast of India

Abstract: Sediment trend analysis with temporal and spatial variations is appropriate to understand the sediment remobilization, temporal accretion-erosion sites, and change in the sea levels due to climate change and/or hydrodynamic modifications which will enhance our knowledge towards dynamic coastal resilience. Moreover, the complex processes like accretion-erosion are controlled by sediment motion and coastal erosion, and restoration measures applied will be inappropriate without a proper assessment of sediment trends. To understand this dynamic nature of grain size distribution and redistributions, a novel approach of studying spatial trends in grain size associated with net sediment transport directions of the beach sediments has been/was carried out along an arcuate (Bakkhali coast) and a straight beach (Talsari coast) region of east coast of India. Different statistical parameters like mean, sorting, skewness, and kurtosis for measuring grain size distributions were used for this purpose. Our results indicate from grain size distributions that dunes are spatially homogeneous and beach sediments characters are distinctly different, which are also supported by the multivariate principal component analysis (PCA). However, in individual locations, significant amount of mixing between dune and beach sediments is evident showing varied degree of homogenization in both beaches. Sediment transport pathways obtained on the basis of the trend analysis show that in the arcuate Bakkhali beach, transport trends are convergent with trends from eastern and western part converges towards south, while in the straight Talsari beach, sediment movement is directed towards the north east along the entire coastline. The study finds its universal application as the complex processes like accretion-erosion are controlled by sediment motion and coastal erosion and restoration measures applied will be inappropriate without a proper assessment of sediment trends.

Research note a note on edge drilling predation by naticid gastropods

Abstract: Edge drilling is a strategy used by some gastropod predators when feeding on bivalve or brachiopod prey in which the borehole is positioned at the valve margin. This strategy can potentially reduce drilling times by a factor of two to three as compared with wall drilling (i.e. drilling near the thicker centre of the valve), the typical default drilling behaviour (Dietl & Herbert, 2005). Dietl, Herbert & Vermeij (2004) showed that, at least for muricid predators, edge drilling is expressed more frequently when drillers are exposed to intense competition risk. They speculated that the reduction in drilling time achieved by edge-drilling snails may be advantageous, allowing a predator to achieve either a higher net energy gain per unit time or reduced exposure to their own predators. There are few reports of edge-drilling behaviour by species of the gastropod family Naticidae, however, and the extent of its use across the family has never been investigated systematically, either in field studies or in experimental settings. A review of the literature on drilling studies indicates that gastropods of the family Naticidae employ multiple modes of predation when attacking bivalve prey (Table 1; Vermeij, 1980; Ansell & Morton, 1985, 1987). Drilling is most prevalent, but other methods include feeding through the open gape of bivalves that cannot tightly shut their valves (Edwards, 1974) or suffocating prey by enveloping them within the foot (Vermeij, 1980; Hutchings & Herbert, 2013; Visaggi, Dietl & Kelley, 2013). Wall drills are the most common type of drilling employed, particularly by naticid species outside the tropics (Kitchell et al., 1986; Ansell & Morton, 1987). Wall drills are typically placed near the umbonal region of the shell (Kelley & Hansen, 2003 and references therein; Morton, 2008) or directly over the centre of the valve (Cata, 1992; Kingsley-Smith, Richardson, & Seed, 2003). The first confirmed observations of edge drilling by naticids were made in an experimental study of Polinices tumidus in Guam, where edge drilling was used against soft-bottom bivalves, with frequencies ranging from 50 to 100%, depending on the prey species (Vermeij, 1980; see also Ansell & Morton, 1985, 1987). Although edge drilling in the laboratory is potentially a behavioural artefact, edge-drilling traces attributed to various naticids have also been reported in field samples collected from localities in and around Guam (Vermeij, 1980) and Hong Kong (Taylor, 1980; Ansell & Morton, 1985). Examples of edge drilling by naticids are mostly restricted to Pacific species of the genus Polinices, as defined by Torigoe & Inaba (2011), the sole exception being Morton & Knapp’s (2004) report of edge drilling by the western Atlantic Naticarius canrena, which was based on field samples from the Florida Keys. However, no direct observations of edge drilling by N. canrena were made by Morton & Knapp (2004) in their limited experimental trials; other confirmed edge drillers co-occurred at their field sites (e.g. muricids Chicoreus dilectus and Phyllonotus pomum: Dietl, Herbert & Vermeij, 2004; Dietl & Herbert, 2005; Stramonita rustica: G.S. Herbert, unpublished) and could account for the edge-drilled bivalves found in their field samples. Therefore, there are no confirmed examples of edge drilling naticids in the Atlantic. Here, we report the first laboratory studies of the predatory behaviours of Polinices lacteus, which include the first direct observation of edge drilling by an Atlantic naticid. Our results are limited in scope due to the opportunistic nature of our collections and the small number of naticid individuals available. Dead shells of P. lacteus are not uncommon throughout the Florida Keys, but live animals are nocturnal and difficult to find. Five specimens of P. lacteus were collected at night from Ohio Key, Florida, in March 2011. Predators were housed separately in recirculating seawater aquaria (50 26 30 cm, salinity: 34+ 2, temperature: 22+28C) with well-sorted siliciclastic sand as a substrate and were offered three Chione elevata prey at a time, replenished ad libitum. Prey ranged in length from 16.0 to 30.1 mm (mean prey shell length: 22.8+2.6 mm). Chione elevata was chosen as the prey as it is one of the most common bivalves in habitats where P. lacteus is found and is frequently drilled with ‘naticid-like’ bevelled holes over the umbo, valve centre and valve margins. Aquaria were monitored daily. Observations included checking for dead prey and whether or not the drillers were feeding. Over the 4-month trial, all predators were active, but three eventually died of unknown causes without feeding. Only two of the snails, with shell lengths of 22.8 and 24.8 mm, drilled and consumed prey. Every attack by these two predators resulted in an edge drill located at the valve margins, with semicircular, countersunk traces on both valves (Fig. 1). Predation success frequencies—as measured by presence of a complete drill hole and dead, consumed prey—were 60% (3 of 5 prey successfully consumed) and 92% (12 of 13 prey successfully consumed), respectively, for these two snails. Edge drilling occurred over the entire range of prey sizes offered. Experiments with other species of Polinices have found that edge-drilling behaviour may be a response to shell traits of the prey (Ansell & Morton, 1985) rather than the threat of

Large-scale spatial biostratinomic patterns along the Eastern Indian coasts: Identification of a generalized siliciclastic beach taphofacies applicable in analogues (paleo)environments

Abstract: Studies on biostratinomy of modern molluscs are biogeographically (mostly from the Americas and Europe) and environmentally (mostly from subtropical and temperate carbonate settings) restricted, documenting local variation, while large-scale spatio-environmental patterns from the siliciclastic settings are less understood. Here, 8670 dead bivalve specimens were collected from several sandy, sandy-rock mixed, and sandy-clay mixed beach, and beaches associated with tidal flat and sea-grass habitat. Sampling stations were located along a stretch of about 2500 km covering several ecoregions along the eastern Indian coast, a large-scale, biogeographic pattern in biostratinomy is studied. Each shell was assigned seven grades based on shell damages intensities in reference to seven biostratinomic attributes (shell completeness, surface bioerosion, secondary rounding, abrasion, ligament loss, and external and internal wear); the summation of these values indicate the Total Taphonomic Grade (TTG) of individual specimens. Our results suggest, TTG values do not vary systematically with ecological factors (e.g., body size and shape, shell microstructure, etc.), although environmental (e.g., substrate and energy conditions) factors could play some role (e.g., high energy sandy beaches have higher TTG values); no large-scale biogeographic gradient is observed. Based on the characteristics of damage profiles, a siliciclastic beach taphofacies, common in all locations, is proposed: abrasion is the main damage type, whereas, shell fragmentation or biotic damages are negligible. Based on these, a biostratinomic pathway of shells is inferred: after death, shells are immediately locally transported to the beach, reducing exposure time for biotic damages; on beaches, constant swash and backwash cause external and internal abrasion. These taphofacies and biostratinomic pathway models can be used to identify the biostratinomic conditions of analogous modern and fossil assemblages.

The Miocene: The Future of the Past

Abstract: The Miocene epoch (23.03–5.33 Ma) was a time interval of global warmth, relative to today. Continental configurations and mountain topography transitioned towards modern conditions, and many flora and fauna evolved into the same taxa that exist today. Miocene climate was dynamic: long periods of early and late glaciation bracketed a ∼2 Myr greenhouse interval – the Miocene Climatic Optimum (MCO). Floras, faunas, ice sheets, precipitation, pCO2, and ocean and atmospheric circulation mostly (but not ubiquitously) covaried with these large changes in climate. With higher temperatures and moderately higher pCO2 (∼400–600 ppm), the MCO has been suggested as a particularly appropriate analogue for future climate scenarios, and for assessing the predictive accuracy of numerical climate models – the same models that are used to simulate future climate. Yet, Miocene conditions have proved difficult to reconcile with models. This implies either missing positive feedbacks in the models, a lack of knowledge of past climate forcings, or the need for re‐interpretation of proxies, which might mitigate the model‐data discrepancy. Our understanding of Miocene climatic, biogeochemical, and oceanic changes on broad spatial and temporal scales is still developing. New records documenting the physical, chemical, and biotic aspects of the Earth system are emerging, and together provide a more comprehensive understanding of this important time interval. Here we review the state‐of‐the‐art in Miocene climate, ocean circulation, biogeochemical cycling, ice sheet dynamics, and biotic adaptation research as inferred through proxy observations and modelling studies.

Shaping the Latitudinal Diversity Gradient: New Perspectives from a Synthesis of Paleobiology and Biogeography.

Abstract: An impediment to understanding the origin and dynamics of the latitudinal diversity gradient (LDG)-the most pervasive large-scale biotic pattern on Earth-has been the tendency to focus narrowly on a single causal factor when a more synthetic, integrative approach is needed. Using marine bivalves as a model system and drawing on other systems where possible, we review paleobiologic and biogeographic support for two supposedly opposing views, that the LDG is shaped primarily by (a) local environmental factors that determine the number of species and higher taxa at a given latitude (in situ hypotheses) or (b) the entry of lineages arising elsewhere into a focal region (spatial dynamics hypotheses). Support for in situ hypotheses includes the fit of present-day diversity trends in many clades to such environmental factors as temperature and the correlation of extinction intensities in Pliocene bivalve faunas with net regional temperature changes. Support for spatial dynamics hypotheses includes the age-frequency distribution of bivalve genera across latitudes, which is consistent with an out-of-the-tropics dynamic, as are the higher species diversities in temperate southeastern Australia and southeastern Japan than in the tropical Caribbean. Thus, both in situ and spatial dynamics processes must shape the bivalve LDG and are likely to operate in other groups as well. The relative strengths of the two processes may differ among groups showing similar LDGs, but dissecting their effects will require improved methods of integrating fossil data with molecular phylogenies. We highlight several potential research directions and argue that many of the most dramatic biotic patterns, past and present, are likely to have been generated by diverse, mutually reinforcing drivers.