As Oceans Change, HABs Invade

Global ocean temperatures are currently rising and have been for decades. Scientists are working to discover how this changing climate affects species around the world, from the very large to the very small. This includes phytoplankton, the microscopic marine algae that live in most bodies of water around the globe and produce half the world’s oxygen. But some of these species are toxic, and can cause harm to human and wildlife alike if they are able to grow out of control. Though a number of studies have been undertaken to try and understand more about these harmful algal blooms, much is still unknown about their growth. A group of scientists were interested in how changing ocean temperatures affected the geographic ranges of harmful algal blooms over time in order to better predict blooms in the future.

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Are Harmful Algal Blooms a New Concern For Coral Reefs?

Coral reefs are marine invertebrates that create a diverse ecosystem that supports sea life, fish communities, and humans. Corals have a symbiotic relationship with the algae that grows inside their shell, providing coral food through photosynthesis, and allowing the coral to expand its reef. However, coral reefs are already under pressure from a changing ocean climate, human pollution, overfishing, and development, all which can stress the coral and their algae counterparts. Harmful algal blooms (HABs), a consequence of human derived nutrient pollution, were investigated to determine their impact to coral reef or fish communities. Reef and fish communities at two sites in the Gulf of Oman were surveyed before and after a HAB in 2008. One site saw coral reef abundance reduced from 53% before the bloom, to 6% after, and both sites had a significant decrease in total fish biomass. These results demonstrate that HABs have a negative impact on both coral and fish communities. HABs cloud surface waters, preventing the coral’s algae from photosynthesizing and providing food for corals. Once the HAB dies, it decays and depletes the oxygen along the seafloor, suffocating corals. These changes to corals impact fish, as a struggling coral reef cannot provide food and shelter to attract sea life and fish communities. These impacts are felt by the nearly 30 million people that depend on coral reefs for their livelihood. Nutrient pollution to coastal waters resulting in HABs, along with other stressors, need to be addressed to safeguard coral reef ecosystems for the future.

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