Abstract
Studies on marine benthic diatoms in environments contaminated by metals are scarce. The typical structure of benthic diatom assemblages (species richness, diversity, dominance, dominant taxa) from undisturbed environments may be used as reference for contrasting with contaminated environments in order to observe how said assemblages respond to such disturbance. Thus, the Ho that the structure of benthic diatom associations and morphology of their frustules under contamination by metals would be normal, as in unpolluted environments was tested. To do this, concentrations of 24 metals were surveyed in a coastal zone impacted by mining residues, and the structure of benthic local diatom assemblages was described. Metal concentrations measurements for 15 metals surpassed the normal values of the upper earth cortex, seven were under the low range effect, and three (Cd, Cu, Zn) surpassed the medium range effect values. At a control site no element concentration was above the reference values for low range effect (LRE) or medium range effect (MRE) standards. There, diatom species richness (S) was high, particularly on seaweeds; where, 397 diatom taxa were recorded. In contrast, at the contaminated area 217 diatom taxa were recorded, but diversity (H’) ranged from 2.4 to 4.3. Relative high frequencies of deformed diatom valves mainly of Achnanthes spp. were recorded in contaminated sediments. In general, diatom taxocenoses presented a typical structure for non-contaminated environments. However, scarceness of specimens, lower S, and frequency of deformed valves suggest responses to metal contamination. For marine environments, the latter values corresponding to A. longipes may be considered a reliable reference to the response of benthic diatoms to metal contamination.
Highlights
Marine environments are subject to different types of pollution due to anthropic activities, either due to input of excess organic matter or metals, that affect the habitat and biota
The values for six of these metals surpass the low range effect (LRE), and three are higher than the medium range effect (MRE) in SR, i.e., Zn (4755, 740.5 mg kg−1), Cd (42.31 mg kg−1) and Cu (3193 mg kg−1) surpassing the established limits (Cd = 9.6, Zn = 410, Cu = 270 mg kg−1), and implying that 50% of the biota may be affected by their presence at these concentration levels
In the SR port, Ni reached a concentration of 401 mg kg−1, which is over the MRE (51.6 mg kg−1) limit, while all the other sampling stations had values below 0.5 mg kg−1
Summary
Marine environments are subject to different types of pollution due to anthropic activities, either due to input of excess organic matter or metals, that affect the habitat and biota. This has led to the search for taxa that may serve as bio-indicators of the various types of pollution. Those taxa having benthic habits, short reproductive cycles, and that are sensible or tolerant to contaminants are preferred In this way, indicator species of polychaetes have been identified, e.g., Capitella capitata for organic matter pollution, and Nereis diversicolor for high concentration of metals [1,2]. A. minutissima and Brachysira vitrea have been recorded as dominant species under the influence of Zn, Cd and Fe, which reflects their opportunistic strategies and tolerance to Zn and Cd [5], but deformed valves with distorted axial areas of Fragilaria cf. tenera, Fragilaria capucina var. rumpens and Eunotia sp. are frequent in continental environments [6]
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