Underwater science methods for marine environmental monitoring

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Professor Rob Dunbar of Stanford University gives us an in depth look in to the science techniques being used to monitor environmental conditions in the British Indian Ocean Territory (BIOT).

The current Bertarelli Foundation-funded conservation science expedition aboard the Grampian Frontier has deployed 35 environmental monitoring instruments at 11 sites within the Chagos archipelago.

Instruments are monitoring dissolved oxygen levels, salinity, ocean temperatures and light levels as well as water flow, tides, and coral reef boundary layer dynamics. At three sites, the team deployed a modified BEAMS (benthic ecosystem and acidification monitoring system) array for periods ranging from 1.5 to 3 days.

The BEAMS methods provides accurate measurements of primary production rates and calcification on coral reefs. In turn, this allows us to assess reef health using some important but hard to acquire information.

When deployed over longer periods (the science plan for next field season) we can estimate whether a reef system is laying down skeleton or losing density through dissolution. We can also assess the extent to which BIOT reefs are exporting versus retaining food – one key step in determining linkages between island and reefs systems and the pelagic food webs.

Middle Brothers BEAMS units put in place, BIOT
BEAMS unit set up on Middle Brother reef in BIOT

This photo of the BEAMS deployed at Middle Brother Island shows its various components. Water is alternately pumped from 20 cm and 70 cm above the reef substrate and flows through sensors that very precisely record temperature, salinity, pressure and pH. We also monitor photosynthetically active light levels and measure current velocities in 3 directions within 1 cm thick layers throughout the lower half of the water column.

This system allows us to determine gradients in oxygen and pH above the reef and to convert these gradients to rates of production and dissolution over timescales of minutes using the flow data. Coral reefs have evolved over millions of years to become hotspots of biochemical processing in shallow water – a system fueled by sunlight, carbon dioxide, nutrients, and carbonate salts dissolved in the water.

The BEAMS system is providing the first quantitative understanding of how efficiently this processing is occurring on reefs recovering from recent bleaching events. Although we haven’t completed at the necessary calculations we’ve examined the raw data sets and know that all instrumentation operated as expected.

For more updates from this and future expeditions follow us on Twitter @BIOTScience

This work was kindly funded by the Bertarelli Foundation as part of the Bertarelli Programme in Marine Science.

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