Abstract:The ecotoxicological effects of oil spill from the grounded vessel MV River Princess on the intertidal benthic organisms of Sinquerim -Candolim beach at Goa were investigated. An intertidal expanse of 1km on either side of the grounded vessel was selected to evaluate the concentration of Total Petroleum Hydrocarbon (TPH) in the sediment and its effects on the composition, abundance and diversity of micro-, meio-and macrobenthos. TPH in the intertidal sediment ranged from 7.8 to 89 µg g -1 (mean35.44 ± 26.35 SD). Microbenthos comprised of microalgae, protozoans and juvenile forms of meiobenthos. Apart from juvenile nematodes, which were abundant, Coscinodiscus spp, Navicula spp, and Nitzschia spp. representing microalgae were also observed in microbenthic samples. Meiobenthos was represented by 13 taxa and their total density ranged between 92-1057 no. 10cm -2 . Maximum meiobenthic abundance of 1057 no.10cm -2 was observed at Sinquerim. Nematodes were the dominant meiobenthic taxa followed by turbellarians and harpacticoid copepods. The macrobenthoc was numerically dominated by polychaetes, followed by crustaceans whereas bivalve molluscs were less represented. There was substantial increase in the petroleum concentration in the beach sediment compared to the previously reported values and highest TPH (89µg.g -1 sediment) values were in the vicinity of the grounded vessel. The polychaete/amphipod ratio and cumulative and partial dominance abundance-biomass curves showed significant negative impact of TPH on macrofauna. The benthic community structure also showed measurable changes, as there was significant decrease (60%) in the number of species. Given that the microalgal counts were low in sediment, it is assumed that the intertidal meiofauna was possibly using oildegrading bacteria as alternate food source. In conclusion, the results reported here suggest that the grounded ore carrier is not only detrimental to the beach community, that may take longer time for recovery, but also affect the beach morphology which may have long-term impact on local fishery.

The deep-sea is well known for high benthic biodiversity despite being a low-food environment. However, most deep-sea organisms are very small in size as an adaptation to food limitation. Macrofauna are generally considered to be organisms larger than 0.5 mm and smaller than 3 cm. However, the smaller body size in the deep sea has led to the use of mesh sizes ranging between 0.25 and 0.5 mm to collect macrofauna, 0.3 and 0.5 mm being the most commonly used mesh sizes for deep-sea sampling. In this study, we tested the effectiveness of sieves of two different mesh sizes (0.3 and 0.5 mm) in assessing macrofaunal diversity, density and biomass. A total of 66 species were obtained with the smaller mesh, while the larger mesh retained only 40 macrofaunal species. Thus, use of larger mesh resulted in the loss of 39% species over the smaller mesh (p00.0001). However, both sieves yielded high densities of organisms, high species diversity and steep rarefaction curves for nematodes and polychaetes. Using the larger mesh resulted in a significant loss in biomass of 90% and 78% for polychaetes and nematodes, respectively. Vertically in the sediment, faunal density was sampled more effectively with the smaller mesh sieve. Our results show a significant reduction in the number of species, organism density, and biomass of macrofauna with use of a 0.5 mm mesh rather than a 0.3 mm mesh and that a sieve of lower mesh size is more suitable for evaluation of deep-sea macrofauna.

Colonization of deep-sea (5000-5500-m depths) metazoan meiofaunal assemblage (in terms of abundance and community structure) were investigated in the Central Indian Ocean Basin (CIOB), immediately after and also 44 months after a benthic disturbance experiment. The abundance of nematodes, which are normally dominating the deep-sea meiofauna, was reduced (by 50%; p<0.001) in post-disturbance. The density of meiofauna was generally low during the monitoring phase and varied moderately inside and outside the test area Bringing up nutrients from sub-surface and depositing this organically rich material on the sediment surface, could have acted as a stimulating factor for meiofaunal recovery as most of the meiofauna feed on bacteria and dead organic material (DOM). This experimental study suggests that whereas on one hand commercial mining of the deep-sea mineral resources may affect deep-sea benthic communities immediately after the impact, on other hand, availability of food material due to turn over (similar to plowing) of sediments may help recolonisation at temporal scale.