In 2017, two OceanCubes were deployed in the near-shore waters of Panama - one located in the nutrient-rich, upwelling waters of the Tropical Eastern Pacific (TEP), and the other in the warm, high-salinity Tropical Western Atlantic (TWA). Only 80 km apart, these two marine realms have dramatically different coral reef systems and near-shore marine environments. The TEP supports a great diversity and abundance of marine life due to upwelling, which makes it cooler and richer in nutrients than most tropical waters. The TWA hosts a suitable environment for abundant coral, but with episodic warming events causing bleaching of certain coral species. The presence of two oceans so close together provides a unique comparative framework for the study of coral reefs ecosystems and how they respond differently to environmental change.
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The four years of operation of PLUTO, which was located 2 km off shore from LJL between 2006 and 2010, has provided an unprecedented long-term, high-frequency data record on the relative roles and impact of offshore ocean forcing (tides, upwelling of nutrient-rich, cool, salty deep water, large scale currents), surface forcing (winds, insolation, and precipitation - evaporation), and terrestrial runoff of nutrients and particulates on plankton and fish community structure, red tide formation, and coral bleaching in a relatively undisturbed tropical region (Gallager et al. 2008). Regional dynamics at the PLUTO observatory result in a combination of high net heat flux, while minimal wind mixing resulting in a warm (> 27°C) surface layer and very sharp thermocline at a depth of about 30m. However, high pressure atmospheric conditions in the Caribbean during the winter months promote strong westerly wind jets which cross the Isthmus where topological features are low. On the western side of the Isthmus, offshore winds drive the surface layer across shelf thereby reducing sea level and inducing a shoaling of the thermocline and upwelling along the coast of cool, nutrient rich, and high CO2 water from depth. Several studies have documented upwelling in the Gulf of Panama, but the Gulf of Chiriqui is thought to be protected from offshore winds and therefore not affected by upwelling. Where upwelling of cool, nutrient rich water does occur, primary and secondary biological production and the local pelagic fisheries flourish. This intense seasonality is modulated at decadal scale by the Pacific Decadal Oscillation, and on a scale of years by ENSO, which can either temper (El Nino) or augment (La Nina) upwelling onto the shelf. Based on observations from PLUTO over a 3.5 year period, it is now clear that in addition to intense seasonal thermal fluctuations, internal tides and internal waves impact the coastal ocean and benthic communities by elevating the thermocline and inducing mixing of >30°C water with <15°C water that is also rich in nutrients and extremely low in oxygen. The frequency and duration of these oscillations impact pelagic and demersal fish community structure by providing additional foraging space and habitat for some species, but greatly constraining others to a limited temporal window in which to forage. This may result in dynamically changing communities consisting of pools of individuals representing a wide variety of ecotones, and, therefore, may be very sensitive to low frequency changes in their environment. Thus, although the environment is highly dynamic it also may be very fragile.