Cascading Trophic Impacts of Reduced Biomass in the Ross Sea, Antarctica: Just the Tip of the Iceberg?

Abstract

A significant reduction in phytoplankton biomass in the Ross Sea was reported in the austral summer of 2000-2001, a possible consequence of a disruption in sea-ice retreat due to the presence of an immense iceberg, B15 (1) (Fig. 1). Our observations in McMurdo Sound suggest temporally and trophically cascading impacts of that depression in productivity. Reduced phytoplankton stocks clearly affected the pteropod Limacina helicina (Phipps, 1774) (Gastropoda: Mollusca), an abundant primary consumer in the region (2, 3), as indicated by depressed metabolic rates in 2000-2001. The following season, for the first time on record, L. helicina was absent from McMurdo Sound. Many important predators, including whales and fishes, rely heavily on L. helicina for food (3, 4). However, most obviously impacted by its absence was Clione antarctica (Smith, 1902), an abundant pteropod mollusc (Gastropoda) that feeds exclusively on L. helicina (5). Metabolic rates of C. antarctica were depressed by 50% in 2001-2002. Both L. helicina and C. antarctica are important components of polar ecosystems and may be good indicators of overall ecosystem "health" in McMurdo Sound and perhaps in the Ross Sea. In this last austral summer, 2002-2003, sea-ice extent was much higher and phytoplankton stocks were dramatically lower than any reported previously, effects possibly associated with El Niño conditions, and we hypothesize that pteropods and their consumers may be further impacted. In the Southern Ocean, phytoplankton production is linked strongly to the seasonal oscillations in the extent of the sea ice (6, 7) and survival of higher trophic levels is

Environmental extremes versus ecological extremes: impact of a massive iceberg on the population dynamics of a high-level Antarctic marine predator

“…Previous studies of this well-known iceberg event reported dramatic effects on lower-level taxa [25,27] and on two local populations of emperor penguins [29], but the potential impact on the population of Weddell seals was unknown. Our goal was to evaluate whether this event would (i) exceed the acclimation capacity of the species and (ii) be a threat for the population at a mid-term time scale.…”

Temperature compensation of aerobic capacity and performance in the Antarctic pteropod,Clione antarctica, compared to its northern congener,C. limacina

“…Clione spp. from both hemispheres are known to have high lipid content, which may help maintain a neutral buoyancy (Phleger et al, 1997) but also facilitates extended fasting periods (up to 260days) when their exclusive prey are absent (Böer et al, 2005;Böer et al, 2006;Seibel and Dierssen, 2003). Following the incubation period, wings were dissected and preserved as described above.…”

“…An asterisk indicates statistical difference between the two species in the 5-HT experiment. (B)Whole-animal rates normalized to a common body mass using significant scaling relationships measured for each species (data from Seibel and Dierssen, 2003;Seibel et al, 2007). Error bars represent the range of values calculated using the standard error for the slope of the scaling relationships.…”

The global distribution of pteropods and their contribution to carbonate and carbon biomass in the modern ocean

“…lived for more than 2 yr and, although small in number, these individuals may be vital for future recruitment. Strong seasonality increases the vulnerability of early life-stages of pteropods that rely on pulses of production to thrive (Bernard and Froneman, 2009;Seibel and Dierssen, 2003). An overlap of generations gives populations greater stability in temporally variable environments.…”