- NEWSDAY.CO.TT - A la Une - Hier 13:40

Our coral clocks

The sun, moon and stars have provided us with the means to mark seasons, a system we call time. Dr Anjani Ganase considers the rhythm of biological clocks in the ocean. Telling time is basic and integral to all life on earth. All biological functions of growth, reproduction, regulation, movement are predicated on the planet’s orbit around the sun and the spin of the earth about its axis by which we track time. For us humans, we’ve studied and documented day/ night cycles, lunar and seasonal cycles that see corresponding changes in temperature, weather and other environmental or biological cues (sandflies at dusk) that influence food availability, survival of offspring, health and anything essential for survival. At sea, telling time is tied to navigation and exploration, as we track the movements and positions of the sun, stars and the moon across the sky. Tidal changes are observed for fishing, and even coastal defence. Our time tracking skills improved and we developed tools such as sun dials and clocks, to global positioning systems (GPS) that function on atomic clocks (very accurate clocks that rely on the oscillation of atoms) located in satellites. The consistency of these cycles, daily, monthly, seasonally, and over decades, exert strong influence over our evolution as humans and extended to the evolution of our societies, ancient and modern. It is therefore no wonder that any abrupt changes or anomalies in the environment over relatively short periods – solar eclipses, sea-level rise, volcanic eruptions, earthquakes – would be noted in significant recorded history. Time also provides markers for mass mortality or cultural shifts. Below the surface In the ocean, organisms living in the photic zone – which is the surface layer of water that is exposed to sunlight – also utilise light and have dominant circadian clocks to govern their everyday activities. This light layer penetrates only to 200 metres and the remaining majority of the ocean down to 6,000 metres sits in complete darkness. However, given the strong influence of tides that can change water conditions, scientists have also observed an additional clock referred to as the circatidal cycles, where organisms have evolved 12.4-hour cycles to be able to respond to tidal changes that influence the ocean chemistry and physical conditions, such as temperature, Ph, salinity, and nutrients. [caption id="attachment_1162865" align="alignnone" width="1024"] Tide pools of Culloden where marine organisms such as molluscs have learned to exposure during low tide. - Photo by Anjani Ganase[/caption] Associated with the tidal cycles, lunar cycles greatly influence intensity of tidal changes, which may bring with it even more food or nutrient mixing, or alternatively permit marine organisms to identify calmer phases better suited for foraging, migrating or even mating. Corals are among those communities that are responsive to both seasonal and tidal changes. Occurring along tropical coasts around the planet, they rely on relatively small changes in light, water temperature and currents to identify their seasons. Coral reproduction occurs during the calmer months when there is less wave action and fewer storm activities, between May and September. Coral spawning which is the process by which corals release sperm and eggs into the water column, benefit from calm conditions to maximise fertilisation on the water’s surface. The seasonal timing is critical, for successful reproduction, however, more precise timing is needed for these creatures that lack mobility and language to facilitate spawning synchrony. It is desirable that all the corals of the same species in the same area will spawn at the same time for successful cross fertilisation. This specific rhythm is based on the lunar cycle, and coral species spawn during a fixed window in the nights following the full moon, when the moon is the brightest in the sky. During the window, species will then spawn at a particular time after sunset; some coral species would spawn within one hour, while other species might spawn over four hours. [caption id="attachment_1162863" align="alignnone" width="1024"] Tide pool of Rocky Point. - Photo by Anjani Ganase[/caption] In Tobago, we know that the boulder brain coral, for example, spawns between five to eight days after the full moon. And we know that they will spawn between 30 minutes to two hours after sunset. Most of this species will spawn on the seventh night after the full moon. The timing is so particular and exact that we have been able to predict and use these timings to conduct coral breeding from the gametes released. There is one species in the Caribbean that spawns during daylight hours, one hour before sunset. It is the grooved brain coral. Their time-keeping is obviously critical for survival and evolution. Other marine critters on reefs and in shallow waters use similar cues for timing activities. Sharks are known to hunt during the dusk and dawn hours where light is low, to successfully stalk prey. Migrating marine mammals base their migratory patterns on their reproductive cycles, navigating to warmer waters to raise their young. Beyond the light How does the deep ocean mark time without the significant environmental cue such as light? [caption id="attachment_1162864" align="alignnone" width="1024"] A dense bed of hydrothermal mussels covers the slope of Northwest Eifuku volcano. - Photo courtesy NOAA Office of Ocean Exploration[/caption] This is the largest ecosystem in the ocean – on the planet – that sits below 1,000 metres, making up 66 per cent of the ocean. A zone without light has made scientists question what environmental cues influence time telling in the deep ocean and do these timings in the dark ocean match the circadian sunlit cycles? Traditionally, it was thought that the biological cycles would be absent or completely independent of the photic zone, however, there are a few studies to show otherwise. One study looked at the timings of gene expressions for a mussel species ( Bathymodiolus azoricus) present on a hydro thermal vents found at 1,688 metres depth at the Mid-Atlantic Ridge. Turns out that some of the mussels’ biology and physiological functions were linked to internal tidal cycles, which marked temperature changes and currents. When this species was exposed to light cycles in the lab, they responded by displaying daily (light/ dark) cycles, indicating that the mussels were responsive to day/night cycles even though they occur in the deep ocean. In the Pacific, studies at other hydrothermal vents found that internal cycles also influenced community populations and mussel growth. However, there is still so much more to be understood about the deep ocean clocks of the many marine creatures that reside permanently in the dark. It seems clear that universal cycles – sun, moon, stars – determine the rhythms of all life on our planet. Over time, as we explore the deep ocean, we learn how creatures far away from the light tell time and season.   The post Our coral clocks appeared first on Trinidad and Tobago Newsday.