Spiders at the Shore: Mercury Transfer through the Web of Contamination

Researchers have underscored the crucial role played by specific shoreline spiders, particularly the long-jawed spiders, in the transference of mercury contamination from aquatic environments to terrestrial ecosystems. Mercury, predominantly originating from industrial pollution, infiltrates water systems and undergoes conversion into its hazardous form, methylmercury. This methylmercury then ascends the aquatic food chain and is ingested by spiders, which are subsequently preyed upon by land animals. These spiders, often found calmly ensconced in their webs, patiently await their prey. Arachnids residing along lakes and rivers typically consume aquatic insects like dragonflies. When these insects inhabit mercury-contaminated water bodies, they can transfer the metal to the spiders that feed on them. Now, researchers reporting in ACS’ Environmental Science & Technology Letters have elucidated how certain shoreline spiders can facilitate the movement of mercury contamination from riverbeds up the food chain to affect land animals.

**Mercury’s Origins and Transfer**
The majority of mercury entering waterways originates from industrial pollution and various human activities, although natural sources can also contribute. Once in the water, microbes transform the element into methylmercury, a more toxic form that accumulates in organisms further up the food chain.

Scientists have increasingly recognized that spiders inhabiting lakeshores and riverbanks could serve as a critical link between waterway contamination and terrestrial animals, such as birds, bats, and amphibians, that primarily prey on insects. Thus, Sarah Janssen and her colleagues sought to assess whether shoreline spiders’ tissues contained mercury from nearby riverbeds and to determine how these creatures could facilitate the connection between mercury pollution in water and its impact on land animals.

**Research Findings**
The research team collected long-jawed spiders from two tributaries near Lake Superior and sampled sediments, dragonfly larvae, and yellow perch fish from these aquatic environments. Subsequently, the team conducted measurements and identified various sources of mercury, including direct industrial contamination, precipitation, and runoff from the soil. The researchers observed that the origins of mercury in the sediments corresponded with those up the aquatic food chain in wetlands, reservoir shorelines, and urban shorelines. For instance, when sediment contained a higher proportion of industrial mercury, so did the collected dragonfly larvae, spider, and yellow perch tissues.

Based on these findings, the scientists posit that long-jawed spiders could serve as indicators of how mercury pollution traverses from aquatic settings to terrestrial wildlife. The implication of these discoveries is that spiders residing near water bodies offer insights into the sources of mercury contamination in the environment, thereby informing management decisions and providing a novel tool for monitoring and remediation activities.

**Species Variations and Contamination**
The researchers also gathered and analyzed tissues from two other types of arachnids found in some locations: fishing spiders and orb-weaver spiders. A comparison of the data revealed variations in mercury sources among these three taxa. The team attributes these differences to variations in feeding strategies: fishing spiders predominantly hunt near water but primarily on land, orb-weavers consume both aquatic and terrestrial insects, whereas the long-jawed species feed most heavily on adult aquatic insects.

According to the researchers, these results suggest that while long-jawed spiders can aid in monitoring aquatic contaminants, not every species residing near the shore serves as an accurate sentinel.

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