Nutrient enrichment caused by marine cage culture and its influence on subtropical coral communities in turbid waters

Abstract

The scale and intensity of marine cage culture have increased in the Asian-Pacific region, particularly in oligotrophic waters where coral reef organisms flourish. In this study, the influence of marine cage culture on subtropical coral communities in turbid waters was evaluated by measuring environmental parameters and benthic community compositions at Magongwan in the Penghu Islands, Taiwan. A canonical discriminant analysis of environmental parameters revealed that elevated levels of ammonium, nitrite, and chlorophyll a (chl a) released from the cages were the main pollution indicators that, in addition to sedimentation and turbidity, distinguished Impact Zone 1 (cage-culture zone) from the other 2 zones -Impact Zone 2 (800 m away from the cages) and the reference zone -in these turbid waters. Results of the canonical correlation analysis indicated that the coverage extents of macroalgae, sponges, and zoanthids were strongly correlated with levels of ammonium, nitrite, phosphate, chl a, and dissolved oxygen. Coral communities in Impact Zone 1 were mostly composed of stress-tolerant massive and submassive corals, but were lacking branching Acropora corals. In contrast, coral communities in the other zones, with high habitat complexity and species richness, were dominated by coral species with diverse morphologies, including branching Acropora coral communities. These results suggest that marine cage culture has been causing chronic nutrient enrichment in the surrounding waters at Magongwan, which may have resulted in a deterioration of suitable habitats for coral reef organisms. Nevertheless, intermediate levels of nutrients and particulate organic matter relative to the other zones might have been caused by the adjacent cage culture, resulting in the high coral coverage and diversity in the Impact Zone 2 in particular.

Marine cage culture and the environment: effects on water quality and primary production

“…Phytoplankton communities varied greatly in terms of abundance and species composition around the 3 types of farms and compared to samples from outside the farms, but interestingly the authors found no clear relationship between farm nutrient discharge and phytoplankton biomass. In Taiwan, Huang et al (2011) found chl a levels ranging from 1.5−1.8 µg l at a nearby reference site. Macroalgae fouling on net pens at farm sites was 2−10 times higher than at reference locations, and nutrient concentrations were above eutrophication thresholds.…”

First record of Zoanthus gigantus Reimer & Tsukahara, 2006 (Anthozoa, Hexacorallia) from Indian waters, South Asia

“…There the intertidal area receives effluents from the fish landing harbor and domestic waste. Costa et al (2008) and Huang et al (2011) showed that zoantharian growth were favored in the habitats with nutrient enrichment and with increased concentration of organic matter. Although we did not sample for nutrient load in our study, the occurrence of yet another Zoanthus species from hypertrophic, fecal polluted conditions suggests the resilience capacity of zoantharians, similar to the findings of Hernández-Delgado et al (2008).…”

Distribution pattern and community structure of zoanthids (Zoantharia) along the coast of Saurashtra, Gujarat, India

“…Apart from the abiotic factors, the nutrient concentration also affects the benthic distribution pattern. Huang et al (2011), in a study has concluded growth of zoanthid colonies is favoured by nutrient enrichment and increased organic matter concentration. Similar results have been reported by Costa et al (2008) (2008) which reported dominance of zoanthid colonies under hypertrophic, faecal-polluted conditions.…”