Brittle Stars, Sea Urchins, and Starfish

Posted by on Feb 16, 2017

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The increase of heat-trapping greenhouse gases in Earth’s atmosphere is warming the Antarctic Peninsula at a unprecedented rate. A recent study from Angulo-Preckler et al. in Continental Shelf Research explores whether significant decreases in sea ice and melting glaciers in the waters west of the Antarctic Peninsula favor some species of marine life and harm others. Among the species which call the waters home, the authors of this study focus on echinoderms, an invertebrate phylum that includes starfish, sea urchins and brittle stars.

Accounting for approximately 45 percent of biomass on the ocean floor west of the Antarctic Peninsula, echinoderms live between the intertidal zone and the sea floor. With no heart, brain or eyes, echinoderms use tentacle-like structures with attached suction pads on their appendages to slowly traverse underwater surfaces. As filter-feeders, echinoderms grab their prey with tentacles, consuming it through a mouth located on their underside. Although echinoderms already live in an environmentally challenging location, with water temperatures reaching 0°C and below, melting glaciers are adding an additional level of complexity to their ecosystem.

A seafloor community near King George Island in the South Shetland Islands of Antarctica (Source: Courtesy of Ricardo Sahade/Images not for reuse).

A seafloor community near King George Island in the South Shetland Islands of Antarctica (Source: Courtesy of Ricardo Sahade/Images not for reuse).

For example, on Deception Island, a volcanically-active island in the South Shetland Islands archipelago, physical disturbance from the volcano and glacier retreat are causing alterations to the ecosystem. Deception Island’s volcano last erupted in 1970, yet volcanic ash from that eruption and previous eruptions settled on nearby glaciers. As the glaciers melt, volcanic ash travels from glacial surfaces to the marine waters below.

In turn, mixing marine waters distribute volcanic ash to depths where echinoderms dwell in a process called sedimentation. This impacts the survival of some echinoderms as they are incapable of thriving under high levels of sedimentation. High sedimentation is problematic for certain species because the additional material prevents them from easily inhabiting crevices between rocks and sponges.

Deception Island and Port Foster (Source: Apcbg/Wikimedia Commons).

Deception Island and Port Foster (Source: Apcbg/Wikimedia Commons).

Port Foster, a bay encompassed by Deception Island, is fed by the surrounding melting glaciers. Angulo-Preckler et al. examined eight different locations in the Deception Island bay, at both 5 meters and 15 meters, to determine a relationship between high sedimentation rates and the number of echinoderms. The study found three dominant echinoderms – the brittle star (Ophionotus victoriae), the Antarctic sea urchin (Sterechinus neumayeri) and the Southern Ocean starfish (Odontaster validus) – are coping well to the high sedimentation rates, at the expense of other echinoderms.

The researchers found that the opportunistic brittle star and sea urchin are now dominating areas of Deception Island Bay by replacing other echinoderms, such as the sea cucumber. Where there was once a large variety of species, there are now just three main echinoderms. This reduction in biodiversity has implications for the health of the ecosystem.

Starfish near the South Shetland Islands, Antarctica (Source: Courtesy of Ricardo Sahade/Images not for reuse).

Starfish near the South Shetland Islands, Antarctica (Source: Courtesy of Ricardo Sahade/Images not for reuse).

High ash sedimentation from the volcano and high sedimentation rates due to the retreat of glaciers could decrease biodiversity levels at Port Foster by forcing other species out of their habitat. Since the last eruption, many of the echinoderms that once flourished in the area have now disappeared. As the region continues to warm, research suggests that increasing sedimentation from melting glaciers could continue to impact the communities of the intertidal and benthic zone of western Antarctica.

Ricardo Sahade, an Antarctic ecologist from the National University of Córdoba in Argentina, confirmed to GlacierHub that “coastal ecosystems experiencing glacier retreat can be threatened by increased sedimentation.” More sedimentation and melting glaciers change the composition of echinoderm habitat. Further research will provide fuller details on whether higher sedimentation reduces biodiversity in this marine ecosystem. Even now, it is evident that disturbances from retreating glaciers are changing the Antarctic ecosystem and the habitat it provides.

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