104. Ecological effect of multiple stressors on a tropical coral reef

Sambhaji Mote, Kalyan De*, Rahul Nagesh, Liju Thomas, Vishal Patil, Afreen Hussain & Baban S. Ingole

1 CSIR-National Institute of Oceanography, Dona Paula, Goa-403004, India

Background
Climate change along with anthropogenic stressors (fishing, sedimentation, nutrient load) are exacerbatingly impacting corals by altering the physico-chemical mechanism (recruitment, calcification, growth, bleaching, competition and survival) and also promoting structural community shifting towards algae and sponge.

Methods
To determine the impact of multiple stressors on reef community, we monitored live coral coverage, bleaching, algal growth (turf and macro algae), coverage and growth rate of coral boring sponge Cliona orientalis in a near shore shallow (3-8m) reef in the Malvan Marine Sanctuary, Arabian Sea. Surveys were conducted at four locations in the reef by SCUBA diving during November 2014 to December 2015. Permanent photo quadrate (5mx5m) with tagging sponge infested coral colonies to measure coral-sponge growth rate and 50m Line Intercept transects were used to determine the benthic community structure. Suspended particulate matter, nutrient, pH, salinity and temperature were measured following standard methods.

Findings
PH ranged from 8.03 to 8.18 in premonsoon and 7.96 to 8.13 during postmonsoon season. Average temperature ranged between 23.330C to 31.470C. Average SPM value ranged from 23.01 mg/l to 22.80 mg/l during the study period. Bleaching severity was increased from 15% in November 2014 to 80% during December, 2015, causing coral mortality and increased growth algae and sponge infestation. Settlement of filamentous algae on the bleached coral colonies was higher compared to non-bleached colonies. Boring sponge C. orientalis were usually invading on the surface live corals and area coverage varied between 0.94% to 11.08% among transects. Porites spp.. Favites melicerum, Turbinaria mesenterina were more susceptible to C. orientalis.

Conclusions
Considering our observations, we suggest that multiple stressors may have resulted in an increase in the abundance and coverage of boring sponge such as Cliona orientalis and turf algae. This could be an important indicator of future phase shift in reef community structure largely from species succession.