How are manta rays affected by volcanic activity in Hawaii?

Jun 5, 2023 | Manta Rays in Hawaii

Volcano eruptions can have significant effects on surrounding marine life, depending on the intensity and duration of the eruption, as well as the proximity of the volcano to the ocean and the marine ecosystem. In this article, I explore the impact volcanic activity can have on manta rays and other marine life around Hawaii.

Volcanic Activity in Hawaii

The Hawaiian archipelago and the adjacent aquatic habitats have been created over millions of years by volcanic eruptions.

The Big Island of Hawaiii is home to five volcanoes that contribute to its unique landscape and rich biodiversity. Two volcanoes are active (Mauna Loa and Kilauea), two are dormant (Mauna Kea and Hualalai) and one is extinct (Kohala).

The Hawaii Volcano Observatory vigilantly keeps a watchful eye on the volcanoes of Hawaii for any signs of activity or eruption. When a volcano erupts, lava might reach and flow into the ocean and can create new landmasses while also impacting marine life.

In 2018, the Big Island of Hawaii was highly affected by the activity of the Kilauea volcano. I wrote a piece back then (and went live on Facebook) to share how we experienced it (although living on the other side of the island), how it impacted tourism, and most of all, how it directly affected the manta rays (very little, at first sight). Read the full post here!

In November 2022, Mauna Loa erupted for two weeks. Its flow stayed at high elevation and did not reach the ocean, but it made up for more exciting times.

How volcano eruptions affect the ocean ecosystems

The introduction of lava into Hawaiian waters has both short-term and long-term effects on marine ecosystems.

Release of materials into the ocean

The primary way in which volcanic eruptions can impact marine life is through the release of ash, gas, and other materials, directly into the ocean.

These materials cloud the water, reducing the amount of sunlight that penetrates the surface, which can affect the photosynthesis of marine plants and the entire food chain.

The release of gases such as carbon dioxide, sulfur dioxide, and hydrogen sulfide, can create toxic conditions underwater, and harm or even kill marine life.

These materials can physically damage marine organisms: debris can clog the gills of fish (limiting their ability to breathe), as well as damage the skin and other tissues of animals.

Volcanic eruptions can also affect the chemical composition of seawater, which alters acidity and nutrient levels. For instance, volcanic ash can introduce high levels of phosphorus stimulating the growth of algae and other microorganisms. This might lead to harmful algal blooms that prevent coral reefs from forming in the short term.

Ocean water temperature

The high temperature of lava entering the ocean causes thermal stress and damage to coral reefs and marine life. Hot lava can cause the seawater to literally start boiling.

This was the case during the 2018 eruption of Kilauea, with devastating results in areas with limited flow, where fish and sea turtles were often not able to get away in time.

Read the fascinating article on this topic on the Smithsonian website!

Altered Seafloor Topography and New Habitats

As new land starts forming from cooling lava flows, seafloor topography changes dramatically which alters current patterns and affects nutrient distribution.

Over time, however, hardened lava can provide substrate for the formation of new coral reefs, creating new habitats for marine life including reef manta rays.

The National Ocean Service has a lot of information on these topics – search for words like “lava” or “volcano” on their website for more insights!

Recovery of the Underwater Ecosystem

The recovery process for underwater ecosystems after a period of volcanic activity is complex. It depends on several factors including lava flow characteristics, pre-existing ecosystem conditions, and local environmental variables.

Repopulation is key to the recovery process. Over time, different species colonize newly formed habitats, leading to a gradual change in the ecosystem, until a stable state is reached. “Gradual” is of importance here as it takes time for nature to take its course.

Healthy marine ecosystems possess inherent resilience allowing them to recover from disturbances (such as volcanic events) more quickly than degraded systems. Ocean conservation measures are essential for maintaining ecosystem health and helping affected areas recover faster from disruptions.

The Impact of Volcano Activity on Manta Rays in Hawaii

Manta rays can be found throughout the warm tropical waters around Hawaii, and volcanic activity can have both direct and indirect effects on manta ray populations.

During the 2018 eruption of the Kilauea volcano, repercussions could have been much worse for marine life around the Big Island – a swift (cooler) current running along the Western shoreline of the island acted as a buffer to surrounding ecosystems.

Kilauea is an active volcano for over 30 years and any lava flow affects the South-East side of the Big Island. We do not have any information about the manta ray population on this side of the island, but we assume that they don’t come near shallow waters if they can avoid it, and they seem to be able to stay away from affected areas. That is why when I did the video and published the article back in 2018, I was mostly relieved because the manta population along the West side of the island did not seem to be directly hurt or even killed by the volcano activity!

Long-term, however, volcano eruptions cause changes to the manta ray habitats due to lava flows altering underwater landscapes.

But excessive volcano activity can also lead to altered composition of the ocean water, decreased water quality, and reduced visibility due to suspended particles in the water column. This can make it more difficult for manta rays to find food, prompting them to migrate to other feeding grounds.

How we can help

The precise impact of volcanic activity in Hawaii is complex and can varry widely.

However, in many cases, they can have a significant and long-lasting effect on marine ecosystems and the organisms (and even people) that depend on them, like our beloved manta rays.

The main thing we can do to counteract the effects of volcano eruptions on manta rays (and other marine life), is to support ocean conservation so that underwater areas stay healthy and can recover faster when affected by volcanic activity.

Learn more about the gentle giants of the oceans



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