An approach to analyzing environmental drivers to shape spatial variations in body-size structure of biofilm-dwelling protozoa during an annual cycle in marine ecosystems

Abstract. Allometric scaling of body size versus growth rate and mortality has been suggested to be a universal macroecological pattern, as described by the metabolic theory of ecology (MTE). However, whether such scaling generally holds in natural assemblages remains debated. Here, we test the hypothesis that the size-specific growth rate and grazing mortality scale with the body size with an exponent of −1/4 after temperature correction, as MTE predicts. To do so, we couple a dilution experiment with the FlowCAM imaging system to obtain size-specific growth rates and grazing mortality of natural microphytoplankton assemblages in the East China Sea. This novel approach allows us to achieve highly resolved size-specific measurements that would be very difficult to obtain in traditional size-fractionated measurements using filters. Our results do not support the MTE prediction. On average, the size-specific growth rates and grazing mortality scale almost isometrically with body size (with scaling exponent ∼0.1). However, this finding contains high uncertainty, as the size-scaling exponent varies substantially among assemblages. The fact that size-scaling exponent varies among assemblages prompts us to further investigate how the variation of size-specific growth rate and grazing mortality can interact to determine the microphytoplankton size structure, described by normalized biomass size spectrum (NBSS), among assemblages. We test whether the variation of microphytoplankton NBSS slopes is determined by (1) differential grazing mortality of small versus large individuals, (2) differential growth rate of small versus large individuals, or (3) combinations of these scenarios. Our results indicate that the ratio of the grazing mortality of the large size category to that of the small size category best explains the variation of NBSS slopes across environments, suggesting that higher grazing mortality of large microphytoplankton may release the small phytoplankton from grazing, which in turn leads to a steeper NBSS slope. This study contributes to understanding the relative importance of bottom-up versus top-down control in shaping microphytoplankton size structure.

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Resurgence of an apex marine predator and the decline in prey body size

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1910930116 ◽

2019 ◽

Vol 116 (52) ◽

pp. 26682-26689 ◽

Cited By ~ 8

Author(s):

Jan Ohlberger ◽

Daniel E. Schindler ◽

Eric J. Ward ◽

Timothy E. Walsworth ◽

Timothy E. Essington

Keyword(s):

Life History ◽

Body Size ◽

Chinook Salmon ◽

Marine Mammal ◽

Marine Mammals ◽

Size Structure ◽

Economic Value ◽

Killer Whales ◽

Selective Predation ◽

Marine Predator

In light of recent recoveries of marine mammal populations worldwide and heightened concern about their impacts on marine food webs and global fisheries, it has become increasingly important to understand the potential impacts of large marine mammal predators on prey populations and their life-history traits. In coastal waters of the northeast Pacific Ocean, marine mammals have increased in abundance over the past 40 to 50 y, including fish-eating killer whales that feed primarily on Chinook salmon. Chinook salmon, a species of high cultural and economic value, have exhibited marked declines in average size and age throughout most of their North American range. This raises the question of whether size-selective predation by marine mammals is generating these trends in life-history characteristics. Here we show that increased predation since the 1970s, but not fishery selection alone, can explain the changes in age and size structure observed for Chinook salmon populations along the west coast of North America. Simulations suggest that the decline in mean size results from the selective removal of large fish and an evolutionary shift toward faster growth and earlier maturation caused by selection. Our conclusion that intensifying predation by fish-eating killer whales contributes to the continuing decline in Chinook salmon body size points to conflicting management and conservation objectives for these two iconic species.

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Rapid emergence of climate change in environmental drivers of marine ecosystems

Nature Communications ◽

10.1038/ncomms14682 ◽

2017 ◽

Vol 8 (1) ◽

Cited By ~ 101

Author(s):

Stephanie A. Henson ◽

Claudie Beaulieu ◽

Tatiana Ilyina ◽

Jasmin G. John ◽

Matthew Long ◽

...

Keyword(s):

Climate Change ◽

Marine Ecosystems ◽

Environmental Drivers ◽

Rapid Emergence

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Evidence for benthic body size miniaturization in the deep sea

Journal of the Marine Biological Association of the United Kingdom ◽

10.1017/s0025315406014366 ◽

2006 ◽

Vol 86 (6) ◽

pp. 1339-1345 ◽

Cited By ~ 16

Author(s):

Janne I. Kaariainen ◽

Brian J. Bett

Keyword(s):

Body Size ◽

Deep Sea ◽

Size Structure ◽

Size Class ◽

The Body ◽

Significant Shift ◽

Individual Biomass ◽

Wet Weight ◽

Accumulation Curves ◽

Average Individual

The benthic body size miniaturization hypothesis states that deep-sea communities are dominated by organisms of smaller body size, although some field studies have produced contradictory results. Using appropriate sample sets, this study tests this hypothesis by contrasting the benthic communities of the Fladen Ground (North Sea, 150 m) and the Faroe–Shetland Channel (1600 m). Samples were collected for large (500 μm) and small macrofauna (250–355 μm), meiofauna (45 μm) as well as an intermediate sized ‘mesofauna’ (180 μm) to ensure comprehensive coverage of the full meio- and macro-faunal body size-range. The body size structure of the benthos was compared using two methods. The more widely used average individual biomass method involves dividing the total sample biomass by sample abundance. Additionally, body size accumulation curves were constructed by assigning all specimens into a logarithmic size-class and then plotting the cumulative percentage of individuals present in each size-class. The results seem to support the hypothesis that the deep-sea environment is a small organism habitat. Although these findings only represent two locations, the overall body size accumulation curves clearly display a statistically significant shift towards smaller body sizes at the deeper site. The magnitude of the effect is appreciable with median metazoan body size reducing from 14.3 μg wet weight in the Fladen Ground to 3.8 μg wet weight in the Faroe–Shetland Channel. The average individual biomass measurements are shown to be of limited value and can lead to potentially misleading conclusions if the underlying size structure is not analysed in detail.

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