Home » Oceanic Manta Rays create food security

Oceanic Manta Rays create food security

by simon

Physical drivers such as wind and currents determine the likelihood of marine vertebrate distribution but the consequence is better food security for people. This process is illustrated by the case of Oceanic Manta Ray abundance in Raja Ampat.

Sighting frequencies of oceanic manta rays. Bars represent total number of sightings. The line represents the El Niño–Southern Oscillation index, indicating that Autumn 2015 / Spring 2016 were during an El Niño as the Mean MEI El Niño Index (MEI) was >0. Photo by Simon Mustoe.

During El Niño, the Indonesian Through Flow strengthens. What the authors of the above paper didn’t realise is that 2015 was also a positive IOD year. This will have massively increased the intensity of upwelling along the continental shelf margins south of the island of Misool. As a result, the paper shows that manta ray abundance increased by several hundred-fold. (During the positive IOD in 2019, manta rays were also very abundant off Jerief in Raja Ampat, based on my own personal observations).  

Coral reefs are non-mobile and micro-organisms such as algae and plankton can become significant sources of pollution if they emerge in large-enough quantities. If El Niño and positive IOD years increase in frequency, aggregations of marine vertebrates such as manta rays, become critical to ecosystem stability–that’s another way of saying “resilience”.  

Because marine vertebrates are mobile, they respond by changing their distribution. The increase in manta rays is a response to increased nutrients and without them, die-off of plankton and algae, would result in increased surplus nutrient landing on coral reefs. Increased nutrient loads result in decreased coral diversity and reduced overall fish biomass, leading to reduced food security for local people.  

So this is one clear example of how biodiversity works and how animals are the critical mechanism in ocean-coupled climate and food-security processes.

Conservation of manta rays needs to be part of Indonesia’s food security strategy. 

Beale, C., et al., Population dynamics of oceanic manta rays (Mobula birostris) in the Raja Ampat Archipelago, West Papua, Indonesia, and the impacts of the El Niño–Southern Oscillation on their movement ecology. Diversity and Distributions, 2019.

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