Benthic polychaetes as good indicators of anthropogenic impact

201-211 Seven stations were sampled within the Mormugao harbour area for benthos and environmental variables from September 2003 to July 2004. A total of 71 polychaete taxa were identified from the area. Polychaete abundance, biomass and species number was highest during post monsoon, mainly due to new recruitment. Pre monsoon is the most stable period for community development when, the fauna was dominated by opportunistic deposit feeding polychaete species. Average abundance ranged from 652-4096 ind m-2 reported at channel and harbour station respectively. Harbour station was dominated by P. pinnata, Magelona sp., Tharyx sp. and Cossura sp. Univariate and multivariate analyses showed clear demarcation of outer harbour, inner harbour and channel stations. Correlation of physico-chemical and biotic parameters did not show a significant correlation. Dominance of opportunistic deposit feeding species and low polychaete diversity in the inner harbour indicate negative impact of harbour activities on the species composition. </smarttagtype

Report of ciliate-bryozoan-crustacean hyperepibiosis on crab (Decapoda Brachyura) from west coast of India, Arabian Sea

Chatterjee, Tapas, Dovgal, Igor, Vieira, Leandro M., Dutta, Arpita, Nanajkar, Mandar (2020): Report of ciliate-bryozoan-crustacean hyperepibiosis on crab (Decapoda Brachyura) from west coast of India, Arabian Sea. Zootaxa 4890 (3): 347-360, DOI: https://doi.org/10.11646/zootaxa.4890.3.

Oxygen minimum seafloor ecological (mal) functioning

Although organic matter (OM) settling on the seafloor is generally rapidly recycled, a key ecological process, large scale burial events manifest itself in the marine sedimentary record as organic carbon (Corg)-rich layers. Presently, this prevails under certain oceanic settings such as the oxygen minimum zones (OMZ) where OM accumulates in underlying sediments. A basic question that remains is as to what extent this Corg accumulation reflects ecological “malfunctioning” or a shunting of ecological processes? Experimenting with eastern Arabian Sea OMZ sediment we found no evidence that Corg accumulation here is not due to trophic satiation or to low tolerance of biota to severe oxygen depletion. However, we found direct evidence that suggests that the OMZ sediment Corg has very low bioavailability that probably impairs biological transformation. In the first set of experiments, the impact of oxygenation on the benthic ecological functioning was examined by following the fate of fresh, highly degradable OM (13C-labelled diatoms) in intact sediment cores incubated for 7 days under normoxic versus suboxic bottom water conditions. Tracer organic matter assimilation (by bacteria and fauna) and respiration was evident and similar under both treatments and demonstrates that the benthic response was not hindered by severe oxygen depletion. Furthermore, relatively low biomass standing stock of fauna and bacteria, in spite of sediment high Corg content, together with this clear uptake of fresh tracer OM suggest that the benthic community was not food saturated. In a second set of experiments, the bioavailability of in situ OMZ organic matter was determined directly through CO2 production rate measurements in bottle sediment–water slurry incubations. In sharp contrast to fresh tracer algal carbon which had a half-life 0.07 years, the OMZ surficial sediment OM half-life was ~ 67 years already in very early diagenesis. Clearly, a distinct difference in functioning and indicates that a large fraction of OMZ sediment organic matter is evidently excluded from immediate first-hand biotic transformation but on its own represents a link between the “fast (biological)” and the “slow (geological)” carbon cycle along the continuum of OM recycling. Furthermore, while this rapid shift out of the “fast” biological cycle may be common or characteristic of large scale OM accumulation events, a comparison with an ancient Corg-deposit suggest that the trigger mechanisms may not be uniform.