Community structure of periphytic diatoms in early-stage marine biofilms in a mariculture-impacted area

Abstract

Periphytic diatoms constitute a major part of complex unicellular aggregations called marine biofilm or periphyton, of which little is known about in tropical marine environments. The early-stage community structure of periphytic diatom genera on two artificial substrates – glass slide and polycarbonate sheets was characterized. These artificial substrates were placed underwater for 6 d and examined on Days 1, 3, and 6 in four sites around Santiago Island, Bolinao, Pangasinan, Philippines, with different relative distances from the intensive milkfish mariculture area. Correlations of diatom community structures in these sites with physico-chemical factors were investigated. The five most abundant diatom genera – namely, Cylindrotheca, Nitzschia, Navicula, Amphora, and Pleurosigma – exhibited a weak correlation with nutrients. Less abundant genera Pseudonitzschia, Haslea, Bacillaria, Thalassionema, Rhizosolenia, Eucampia, Diploneis, Asterionellopsis, Chaetoceros, Bacteriastrum, Licmophora, Skeletonema, Lioloma, Thalassiosira, and Thalassiothrix showed a positive correlation with nutrients. Among sites, the highest benthic diatom cell densities (4.6 × 105 cells cm−2) after 6 d was found in Lucero. Generic richness and diversity varied among sites, with the highest diversity (H’ = 1.58) on Day 1 in Tomasa, the site nearest to the mariculture area, whereas the highest richness (D = 2.17–3.26) for all days and diversity (H’ = 1.38–1.52) for Days 3 and 6 were recorded in Silaqui, the most distal site. Generally, the highest diversity and richness were found on Day 1, which then decreased on succeeding days in all sites. The lack of a clear patternin community structure among sites relative to the proximity of these sites to the mariculture area may in part be attributed to the presence of other nutrient sources. Results of the study provide baseline information on the variability of periphytic diatom community structure in a mariculture-impacted area, and insights on how benthic diatoms may be used in monitoring the impacts of nutrient pollution.