There is currently an increase in heat waves in the oceans, which has brought on many negative effects on the marine ecosystems of the Caribbean.
There are many ways that heat waves may affect ecosystems, especially those that are more sensitive to temperature changes, such as coral reef systems. The heat waves seriously endanger the biodiversity, the beauty and the numerous ecosystem services that the coral reefs have to offer.
These ocean heat waves take place due to the increase in sea temperature. They are characterized by periods in which the sea temperature exceeds “normal” values observed of a certain time period, which is why they are characterized as extreme heat events.
Reef seascape of the Mexican Caribbean. Source: Mario Chow.
Heat stress is one of the main causes of coral bleaching. This phenomenon occurs when corals lose the symbiotic organisms that provide much of their energy.
Bleaching can cause mass mortality and leave the corals, the main builders of this ecosystem, at high risk and more vulnerable to disease.
Left, brain coral affected by the disease of coral tissue loss. Source: Israel Muñiz Castillo. Right, coral seascape dominated by the coral Agaricia teunifolia with severe bleaching. Source: Andrea Rivera-Sosa
In recent years, these bleaching events have become increasingly frequent due to constant exposer to extreme heat waves in the oceans.
In the case of the Caribbean coral reefs, many extreme heat stress events have taken place since 1985, out of which the years 1998, 2005, 2010-2011 and 2014-2017 were especially harsh. During these events more than 30% of the coral reefs of the region ran a risk of bleaching, as these reefs were exposed to very high heat stress.
It should be noted that in the Caribbean there is a trend of increasing exposure to heat stress, being particularly more frequent from 2003 on. This could also be the reason for negative chronic effects on corals and other marine organisms of the region, provoking a lower reproduction and growth
Percentage of the coral reef area of the Caribbean at risk of bleaching and the mortality rate depending on the exposure to heat stress. Source: I., Muñiz Castillo, A. I., Rivera-Sosa, A., Chollett, I., Eakin, C. M., Andrade-Gómez, L., McField, M., & Arias-González, J. E. (2019). Three decades of heat stress exposure in Caribbean coral reefs: a new regional delineation to enhance conservation. Scientific Reports. http://doi.org/10.1038/s41598-019-47307-0″
In addition to this constant chronic impact, in the last two years (2019 and 2020) a high exposure of ocean heat has been observed in the coral reefs, especially in some regions such as the Mesoamerican Reef System (MBRS).
Exposition to accumulated heat stress using the Degree Heating Week indicator (DHW)
Source: development Israel Muñiz Castillo.
Methods of Detection
There are various technological tools that allow for the identification of these ocean heat events, from satellites that offer images of the earth’s surface as well as different physical aspects, such as the sea-surface temperature which is a fundamental indicator of these events. However, there are also some tools such as devices or thermometers that can be put in the marine ecosystems at different depths and hence give us the temperature variation with greater precision.
The most obvious way to reduce the impact caused by extreme heat waves is to attack anthropogenic climate change, raising awareness of better consumption habits and putting forward plans to reduce greenhouse gas emissions.
What-more, it is very important to have tools that allow us to predict these phenomena and their potential impact on marine ecosystems, so the creation of regional or global early warning systems may greatly help to establish monitoring, conservation and rehabilitation.