A.V. Raman

Oxygen, ecology, and the Cambrian radiation of animals

The Proterozoic-Cambrian transition records the appearance of essentially all animal body plans (phyla), yet to date no single hypothesis adequately explains both the timing of the event and the evident increase in diversity and disparity. Ecological triggers focused on escalatory predator–prey “arms races” can explain the evolutionary pattern but not its timing, whereas environmental triggers, particularly ocean/atmosphere oxygenation, do the reverse. Using modern oxygen minimum zones as an analog for Proterozoic oceans, we explore the effect of low oxygen levels on the feeding ecology of polychaetes, the dominant macrofaunal animals in deep-sea sediments. Here we show that low oxygen is clearly linked to low proportions of carnivores in a community and low diversity of carnivorous taxa, whereas higher oxygen levels support more complex food webs. The recognition of a physiological control on carnivory therefore links environmental triggers and ecological drivers, providing an integrated explanation for both the pattern and timing of Cambrian animal radiation.

Isotopic composition (C & N) of the suspended particles and N uptake by phytoplankton in a shallow tropical coastal lagoon

ABSTRACT The spatial distribution of the C/N ratios and variations in δ13C and δ15N of suspended particulate matter were used to characterise their source in Asia’s largest brackish water lagoon, Chilika, India. In addition, the significance of re-mineralised nutrients in the primary productivity of the shallow lagoon was also determined through quantification of the subsurface nitrogen uptake conditions at two relatively stable locations in the lagoon. The results indicated that the influence of terrestrial organic matter was the maximum in the northern sector and was relatively limited at the central and southern part of the lagoon. In situ 15N uptake experiments (daytime) under biogeochemically stable conditions revealed that the N uptake by phytoplankton ranged between 0.24 and 1.01 mM m−3 h−1 during pre-monsoon and post-monsoon seasons. New production and regenerated production in the shallow lagoon was also estimated by calculating f-ratios (ratio of nitrate assimilation by phytoplankton to total nitrogenous nutrient assimilation, have been estimated), which varied from 0.52 in the post-monsoon to 0.38 in the pre-monsoon. Lowering of the f-ratio from post- to pre-monsoon indicated a dominance of mineralisation over the new production.

New host record of pea crab Arcotheres purpureus (Alcock, 1900) (Crustacea: Decapoda: Pinnotheridae) with first description of male

BackgroundArcotheres purpureus, a species of pea crab has been reported from the Red Sea, Maldives and Andaman Sea with no description of the male. According to existing literature the single host for this species is Ostrea.MethodsThe specimens examined were obtained from the dredge hauls.ResultsIn the present study we report Arcotheres purpureus for the first time from the coastal waters of mainland India. The specimens have been observed within the mantle cavity of a venerid bivalve Protapes gallus a new host record for this species. A description of the male specimen is also communicated herein for the first time.ConclusionsBivalve fisheries is an alternative livelihood option for the fishermen of this region. In this context the manifestation of Arcotheres purpureus, from a commercially viable species of bivalve such as Protapes gallus as well as its incidence in waters of mainland, India is a cause for concern necessitating further investigations.