How are coastal benthos fed?: How are benthos fed?

Waples, James T.; Bootsma, Harvey A.; Klump, J. Val

doi:10.1002/lol2.10033

To understand whether or how climate change will drive changes in Antarctic marine benthic ecosystems, one must first understand baseline population dynamics of the system. Species abundances may change seasonally, annually, or on decadal scales, for example, or due to rare cataclysmic events unrelated to a changing climate. We used SCUBA to collect foraminiferan protists in Explorers Cove, McMurdo Sound in austral spring in 1986 to 2016. Our research involved the cell biology and molecular evolution of large (>1mm), earlyevolving, agglutinated members of this assemblage, but during the course of this work we also charted changes in their populations from bulk surface sediment collection and semi-quantitative 0.25-m2 to 1-m2 quadrat sampling. We focused on two species of Astrammina, two species of Crithionina, Notodendrodes hyalinosphaira, larger calcareous species (Pyrgo peruviana, Cornuspira sp., Glandulina sp.), as well as Gromia cf. oviformis. During the 1990s, we noted that relative species abundances fluctuated substantially on an inter-annual basis. For example, Astrammina rara was very abundant in 1990 (75.9% of the total assemblage), dipped in 1993 and 1994 (54.9% and 58.7%, respectively), and rebounded in 1998 and 1999 (65% and 67%). By contrast, Astrammina triangularis abundances were low in 1990 (0.3%), peaked in 1993 (18.3%) and declined to 6.5% of the total assemblage in 1998. During the 2000s, we began tracking numericaldensities quantitatively by taking 7.4cm-diameter cores and wet-picking specimens recovered from the top cm of sediment. Similar fluctuations were observed in target species. Most notable was the rapid increase in a “silver saccamminid” species, first recognized at low abundance in 1998. In 2005 there were 412/m2 and since that time their numbers have increased to become the dominant species in the area (186,732/m2 in 2016). Over our study period, we also noted changes in meio- and macrofauna. In particular, we noted a dramatic increase in the numerical density of small epifaunal and infaunal tunicates (360/m2 in 2005 to 11,379 in 2016). We also observed a dramatic, qualitative reduction in the population of the Antarctic scallop Adamussium colbecki along the Explorers Cove ice wall, prompting us to examine the extent of their decrease by re-sampling the six stations reported by Stockton in 1982 using his methods. The results were surprising: The average scallop population had decreased 74%. Similar results were obtained in 2015 and 2016. Although the cause of the reduction remains unknown, we noted new recruits on the seafloor in 2016, indicating initial recovery from this event. Clearly, the Antarctic benthos is anything but static. Standardized, long-term environmental monitoring is necessary to uncover changes attributable to climate change. Explorers cove, with its proximity to McMurdo Station and the Taylor Dry Valley LTER site, is a prime candidate for such an endeavor.

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