GLOBAL - Many coral reef fisheries have seen a decline in catches as reefs become increasingly more degraded. Concerns surrounding the negative impacts of growing seaweed farming on coral reef health has been raised across the world. New research however suggests that in some situations, seaweed farms could bolster catches of coral reef herbivorous fish – and potentially the coral reefs themselves.
Many developing nations are faced with increasing population growth, and social inequity with high rates of poverty. These same areas are where the majority of the world’s coral reefs can be found, providing both food and revenue for a vast number of people. Unfortunately reefs are becoming increasingly degraded, with subsequent declining catches having implications for those who previously relied upon them for food and livelihoods.
In many parts of these same regions, seaweed farming is becoming an increasingly important source of revenue for people living along the coast, particularly those in China and across Southeast Asia, which combined contribute just under 99% of the global farmed seaweed production. Much of this production goes towards making carrageenan – a thickening agent commonly found in a host of everyday products like toothpaste and even beer.
Comparing seaweed production and FAO reported catches of rabbitfish – a commercially valuable family of herbivorous fish, James Hehre, a PhD student based at The University of Western Australia (UWA), and Professor Jessica Meeuwig (also at UWA) found that in Southeast Asia, seaweed farming production is positively correlated with rabbitfish catch.
What is more, whilst catch of coral reef fish in general is showing a decline, rabbitfish catches have been increasing. When the researchers looked at Africa and the Western Pacific however, they failed to find the same pattern. The reason for this discrepancy may lie in the differing production rates.
Seaweed farming in Southeast Asia has a long history and relatively steady pattern of growth, with key areas becoming the centre of high levels of production. Conversely, seaweed farming in Africa and the Western Pacific is of a much smaller scale, and has more sporadic patterns of growth than seen in Southeast Asia for a variety of reasons.
The exact mechanism behind the growth in rabbitfish catch is not completely clear. It could be that the seaweed farms are providing extra food for rabbitfish, boosting their growth, or that the farms are replacing food that has been removed during their very creation (often areas are cleared prior to farm establishment). Another possibility is that rabbitfish are concentrating in and around seaweed farms, making them much easier to catch.
The researchers also postulate that any increases in rabbitfish could important for coral reefs at risk of being smothered by algae which can take over degraded reefs. With more rabbitfish grazing on algae growing on reefs, the risk of reefs being smothered by excess algal growth could be reduced.
Whether this is actually happening or not, however, requires further research. Nevertheless, the potential for seaweed farms to improve fishery catches of these commercially important fishes could prove vital in maintaining livelihoods in communities dependent on marine resources.