Researchers highlight the role of certain shoreline spiders, particularly long-jawed spiders, in transferring mercury pollution from aquatic areas to terrestrial ecosystems. Mercury comes primarily from industrial pollution and can enter water systems and convert into the toxic form methylmercury. This methylmercury then moves up the aquatic food chain and is consumed by spiders, which in turn are eaten by land animals.
Some shoreline spiders, such as the long-jawed spider pictured here, transfer mercury pollution from river beds to land animals along the food chain. Image Credit: Dr. Ryan Otter, Grand Valley State University
Many spiders sit quietly in their webs, patiently waiting for their prey to arrive. Spiders along lakes and rivers feed on aquatic insects, such as dragonflies. When these insects live in mercury-contaminated waterways, they can pass the metal to spiders that feed on them. Now, reporting in ACS' Environmental Science & Technology Letters, researchers show how some coastal spiders transfer mercury pollution from riverbeds down the food chain to land animals.
Most mercury entering waterways originates from industrial pollution and other human activities, but it can also come from natural resources. Once in the water, microorganisms convert this element into methylmercury, a more toxic form that biomagnifies and increases in organisms higher up the food chain.
Scientists are increasingly recognizing spiders that live on lakeshores and rivers as a potential link between waterway pollution and animals that live primarily on land, such as birds, bats and amphibians. So Sarah Janssen and colleagues wanted to assess whether the tissues of coastal spiders contained mercury from nearby river beds and determine how these animals linked mercury contamination in water bodies and land animals.
The research team collected long-jawed spiders along two tributaries of Lake Superior and sampled sediment, dragonfly larvae and yellow perch from these waterways. Next, the team measured and identified sources of mercury, including direct industrial pollution, precipitation and soil runoff. The team observed that mercury in sediments comes from the same sources as aquatic food chains in wetlands, reservoir shorelines, and urban shorelines. For example, when there were higher levels of industrial mercury in the sediment, there were also higher levels in collected tissue from dragonfly larvae, spiders and yellow perch.
Based on these data, the scientists said the long-jawed spiders could show how mercury pollution is transferred from aquatic environments to terrestrial wildlife. The significance of these findings, the researchers explain, is that spiders living near water provide clues to the sources of mercury pollution in the environment, informing management decisions and providing new tools for monitoring remediation activities.
The researchers also collected and analyzed tissue from two other species of spiders from some sites: fishing spiders and orb-weaver spiders. Comparison of the data showed that the sources of mercury varied among the three taxa. The team attributed this result to differences in feeding strategies. Fishing spiders hunt near water but mostly on land. Coccidioides eat both aquatic and terrestrial insects; however, the long-billed species feed primarily on adult aquatic insects.
The researchers say these results show that while long-jawed spiders can help monitor aquatic pollutants, not all species that live near coasts are accurate sentinels.