Jyothibabu R, Jagadeesan L, Lallu K R
CSIR-National Institute of Oceanography, Regional Centre, Kochi, 682018, India.
Environ Monit Assess. 2015 Oct;188(10):559. doi: 10.1007/s10661-016-5572-0. Epub 2016 Sep 10.
Dead copepods (carcasses) are widespread in aquatic systems, but their scientific quantification is rare due to the difficulty in discriminating them from live ones. In this paper, we hypothesized that due to large spatial and temporal changes in hydrography in the Cochin backwaters, the percentage of copepod carcasses in the system could also change significantly on a spatial and temporal scale. In order to understand this aspect, we quantified the live and dead copepods in the Cochin backwaters under different hydrographical settings based on live and mortal staining technique. The most prominent temporal hydrographical feature during the study period was the large decline in salinity across the system, which was more pronounced downstream (15-20 units) and was caused by the large freshwater influx associated with the southwest monsoon. During the entire sampling period, copepod carcasses were pervasive all over the study area with large spatial and temporal variations in their percentage contribution (2.5-35.8 %) to the total community abundance. During all sampling, carcasses concentrated more in the downstream region, with maximum turbidity (16.5-35.8 %), than in the upstream region (2.5-14.5 %). The percentage of carcasses was the highest during the onset of the southwest monsoon (av. 23.64 ± 8.09 %), followed by the pre-southwest monsoon (av. 13.59 ± 6.72 %) and southwest monsoon (av. 8.75 ± 4.14 %). During the onset of the southwest monsoon, copepod carcasses in the downstream were contributed by ∼80 % high saline and ∼15 % low saline species, indicating a salinity shock-induced mortality. On the other hand, the cumulative effect of the long residence time of the Cochin backwaters and high partial predation rate of carnivores contributed to the high abundance of carcasses during the pre-monsoon.
死亡的桡足类动物（尸体）在水生系统中广泛存在，但由于难以将它们与活体区分开来，对其进行科学量化的研究很少。在本文中，我们假设由于科钦潟湖水文特征在空间和时间上的巨大变化，该系统中桡足类动物尸体的百分比在空间和时间尺度上也可能发生显著变化。为了了解这一方面，我们基于活体和死亡染色技术，对科钦潟湖不同水文条件下的活体和死亡桡足类动物进行了量化。研究期间最显著的时间水文特征是整个系统盐度大幅下降，下游更为明显（15 - 20个单位），这是由西南季风带来的大量淡水流入造成的。在整个采样期间，桡足类动物尸体遍布整个研究区域，其在总群落丰度中的百分比贡献存在很大的空间和时间变化（2.5 - 35.8%）。在所有采样中，尸体在下游区域的浓度更高，浊度最大（16.5 - 35.8%），高于上游区域（2.5 - 14.5%）。尸体百分比在西南季风开始时最高（平均23.64 ± 8.09%），其次是西南季风前（平均13.59 ± 6.72%）和西南季风期间（平均8.75 ± 4.14%）。在西南季风开始时，下游的桡足类动物尸体约80%由高盐度物种贡献，约15%由低盐度物种贡献，表明盐度冲击导致了死亡。另一方面，科钦潟湖较长的停留时间和食肉动物较高的部分捕食率的累积效应导致了季风前尸体的高丰度。
