Lower Trophic Level Production Research Articles

Restoring gradual land-water transitions in a shallow lake improved phytoplankton quantity and quality with cascading effects on zooplankton production

Land-water transition areas play a significant role in the functioning of aquatic ecosystems. However, anthropogenic pressures are posing severe threats on land-water transition areas, which leads to degradation of the ecological integrity of many lakes worldwide. Enhancing habitat complexity and heterogeneity by restoring land-water transition areas in lake systems is deemed a suitable method to restore lakes bottom-up by stimulating lower trophic levels. Stimulating productivity of lower trophic levels (phytoplankton, zooplankton) generates important food sources for declining higher trophic levels (fish, birds). Here, we study ecosystem restoration project Marker Wadden in Lake Markermeer, The Netherlands. This project involved the construction of a 700-ha archipelago of five islands in a degrading shallow lake, aiming to create additional sheltered land-water transition areas to stimulate food web development from its base by improving phytoplankton quantity and quality. We found that phytoplankton quantity (chlorophyll-a concentration) and quality (inversed carbon:nutrient ratio) in the shallow waters inside the Marker Wadden archipelago were significantly improved, likely due to higher nutrient availabilities, while light availability remained sufficient, compared to the surrounding lake. Higher phytoplankton quantity and quality was positively correlated with zooplankton biomass, which was higher inside the archipelago than in the surrounding lake due to improved trophic transfer efficiency between phytoplankton and zooplankton. We conclude that creating new land-water transition areas can be used to increase light and nutrient availabilities and thereby enhancing primary productivity, which in turn can stimulate higher trophic levels in degrading aquatic ecosystems.

Late Holocene centennial to millennial-scale variability in lower trophic level productivity off southern Hokkaido, Japan, and its response to dissolved iron-replete Coastal Oyashio dynamics

AbstractLittle is known about the dynamics of marine food chains spanning primary to higher trophic levels on centennial and longer timescales, especially where the supply of dissolved iron limits primary productivity. To elucidate the long-term dynamics of biological productivity in the Coastal Oyashio (CO), which is a major pathway for transporting dissolved iron into the western North Pacific from winter to spring, we reconstructed the lower trophic level productivity over the last 3000 years in the CO. Our results demonstrate that the concentrations and mass accumulation rates of both Chl-a (chlorophyll a and its derivatives) and biogenic opal used as proxies of primary productivity, and steryl chlorin esters (SCEs) used as that of zooplankton productivity, show a millennial-scale increasing trend and centennial-scale variability beginning ca. AD 400. SCEs were positively correlated with Chl-a, indicating that changes in zooplankton productivity were induced by bottom-up control of primary productivity. The Chl-a and SCEs showed synchronous centennial-scale patterns with a relative abundance of sea-ice-associated diatom species transported by CO, and with a ventilation index in the Okhotsk Sea Intermediate Water. This synchronous pattern indicates that lower trophic-level productivity during the spring bloom responded to the intensity of iron-replete CO.

Plankton monitoring in the Northwest Atlantic: a comparison of zooplankton abundance estimates from vertical net tows and Continuous Plankton Recorder sampling on the Scotian and Newfoundland shelves, 1999–2015

Abstract Assessment of zooplankton abundance, distribution, community composition, and temporal variability is critical to understanding the effects of climate variability and change on lower trophic level production and availability for consumption by larger consumers. Zooplankton sampling is performed across the Canadian continental shelf system by Fisheries and Oceans Canada's Atlantic Zone Monitoring Programme (AZMP). Sampling includes semi-monthly to monthly collection of zooplankton using vertical net tows (VNTs) deployed from near-bottom to surface at stations on the central Scotian Shelf (Stn 2, 150 m depth) and Newfoundland Shelf (Stn 27, 175 m depth), and by Continuous Plankton Recorders (CPRs) in the near-surface layers along routes over the Scotian and Newfoundland shelves (0–10 m depth). Here, we compare abundance metrics for 11 copepod taxa collected using both gear types in both regions between 1999 and 2015. Seasonal cycles of VNT and CPR abundance were similar for near-surface residents. VNT: CPR abundance ratios varied year-round for vertical migrants, as ontogenetic migrants shifted their vertical distribution, and as diel migrants changed their migratory behaviour. For some taxa, differences in annual average VNT: CPR abundance ratios between regions suggest differences in vertical distribution, while for others differences in inter-annual variability for VNT and CPR abundances suggest differences in the dynamics of the near- and sub-surface components of the populations.

A test of the provisioning hypothesis of recruitment control in Georges Bank haddock

The haddock (Melanogrammus aeglefinus) stock of the Georges Bank region of the US Northeast Continental Shelf displays a pattern of large, episodic recruitments. Among the hypothesized controlling mechanisms is the idea that recruitment events are related to provisioning of prespawning haddock by the fall bloom the year before. With the occurrence of a recent large recruitment event in 2013, it would be prudent to retest this hypothesis. Fall bloom magnitude was positively correlated (r = 0.645, p = 0.005) with haddock survivor ratio (recruits per spawning biomass), including data from the 2013 recruitment. This relationship identifies a pathway of bottom-up control of a resource species, thus focusing concern over recent changes in lower trophic-level productivity.

Significant Biologically Mediated CO2 Uptake in the Pacific Arctic During the Late Open Water Season

AbstractShifting baselines in the Arctic atmosphere‐sea ice‐ocean system have significant potential to alter biogeochemical cycling and ecosystem dynamics. In particular, the impact of increased open water duration on lower trophic level productivity and biological CO2 sequestration is poorly understood. Using high‐resolution observations of surface seawater dissolved O2/Ar and pCO2 collected in the Pacific Arctic in October 2011 and 2012, we evaluate spatial variability in biological metabolic status (autotrophy vs heterotrophy) as constrained by O2/Ar saturation (∆O2/Ar) as well as the relationship between net biological production and the sea‐air gradient of pCO2 (∆pCO2). We find a robust relationship between ∆pCO2 and ∆O2/Ar (correlation coefficient of −0.74 and −0.61 for 2011 and 2012, respectively), which suggests that biological production in the late open water season is an important determinant of the air‐sea CO2 gradient at a timeframe of maximal ocean uptake for CO2 in this region. Patchiness in biological production as indicated by ∆O2/Ar suggests spatially variable nutrient supply mechanisms supporting late season growth amidst a generally strongly stratified and nutrient‐limited condition.

Biological productivity evaluation at lower trophic levels with intensive Pacific oyster farming of Crassostrea gigas in Hiroshima Bay, Japan

Enclosed seas are suitable for bivalve farming due to high primary production, which provides food sources. The impact of oyster farming on the biological productivity of lower trophic levels was evaluated in Hiroshima Bay. The area-weighted mean primary production in the estuary (northeastern bay; NB) was 1.1 to 2.1 times higher than that of the offshore area (southwestern bay; SB) in all four seasons. In contrast, the area-weighted mean secondary production by net zooplankton in the NB was lower than that of the SB, except in August. The area-weighted mean secondary production by oysters in the NB was 2.2 to 2.8 times higher than that of the SB in all four seasons, and exhibited a similar spatial pattern to that of the primary production. The primary production was more efficiently utilized and transferred to secondary producers in the SB (16.7% on average) than in the NB (9.4% on average). This study provides guidance for oyster farming in Japan.

No correlation between the diversity and productivity of assemblages: evidence from the phytophage and predator assemblages in various cotton agroecosystems.

Biodiversity research has shown that primary productivity increases with plant species number, especially in many experimental grassland systems. Here, we assessed the correlation between productivity and diversity of phytophages and natural enemy assemblages associated with planting date and intercropping in four cotton agroecosystems. Twenty-one pairs of data were used to determine Pearson correlations between species richness, total number of individuals, diversity indices and productivity for each assemblage every five days from 5 June to 15 September 2012. At the same trophic level, the productivity exhibited a significant positive correlation with species richness of the phytophage or predator assemblage. A significant correlation was found between productivity and total number of individuals in most cotton fields. However, no significant correlations were observed between productivity and diversity indices (including indices of energy flow diversity and numerical diversity) in most cotton fields for either the phytophage or the predator assemblages. Species richness of phytophage assemblage and total individual numbers were significantly correlated with primary productivity. Also, species richness of natural enemy assemblage and total number of individuals correlated with phytophage assemblage productivity. A negative but not significant correlation occurred between the indices of numerical diversity and energy flow diversity and lower trophic-level productivity in the cotton-phytophage and phytophage-predator assemblages for most intercropped cotton agroecosystems. Our results clearly showed that there were no correlations between diversity indices and productivity within the same or lower trophic levels within the phytophage and predator assemblages in cotton agroecosystems, and inter-cropped cotton fields had a stronger ability to support the natural enemy assemblage and potentially to reduce phytophages.

Carbon-based balanced trophic structure and flows in the offshore Lake Ontario food web before (1987–1991) and after (2001–2005) invasion-induced ecosystem change

Replicate mass-balanced solutions to Ecopath models describing carbon-based trophic structures and flows were developed for the Lake Ontario offshore food web before and after invasion-induced disruption. The food webs link two pathways of energy and matter flow: the grazing chain (phytoplankton–zooplankton-fish) and the microbial loop (bacteria–protozoans) and include 19 species-groups and three detrital groups. Mass-balance was achieved by using constrained optimization techniques to randomly vary initial estimates of biomass and diet composition. After the invasion, production declined for all trophic levels and species-groups except Chinook salmon. The trophic level (TL) increased for smelt, adult sculpin, adult alewife and Chinook salmon. Changes to ecotrophic efficiencies indicate a reduction in phytoplankton grazing, increased predation pressure on Mysis, adult smelt and alewife and decreased predation pressure on protozoans. Specific resource to consumer TTE changed; increasing for protozoans (8.0–11.5%), Mysis (0.6–1.0%), and Chinook salmon (1.0–2.3%) and other salmonines (0.4–0.5%) and decreasing for zooplankton (20.2–15.1%), prey-fish (9.7–8.8%), and benthos (1.7–0.6%). Direct trophic influences of recent invasive species were low. The synchrony of the decline in PP and species-group production indicates strong bottom-up influence. Mass balance required an increase of two to threefold in lower trophic level biomass and production, confirming a previously observed paradoxical deficit in lower trophic level production. Analysis of food web changes suggest hypotheses that may apply to other similar large pelagic systems including, (1) as pelagic primary productivity declines, overgrazing of zooplankton results in an increase in protozoan production and a loss of trophic transfer efficiency, (2) habitat and food web changes increased Mysis predation on Diporeia and contributed to their recent decline, and (3) production of Chinook salmon, the primary piscivore, was uncoupled from pelagic production processes. This study demonstrates the value of food web models to better understand the impact of invasive species and to develop novel hypotheses concerning trophic influences.

Ecosystem dynamics at a productivity gradient: A study of the lower trophic dynamics around the northern atolls in the Hawaiian Archipelago

Application of a lower trophic ecosystem model coupled with an ocean circulation model allows us to derive a time series of estimated plankton biomass for waters around Kure Atoll, Pearl & Hermes Atoll and Midway Islands, over the period 1964–2006. This time series shows considerable interannual and decadal variation in productivity, and changes in recent years that are coherent with observed changes at higher trophic levels. Further the model results show that the change in productivity can be viewed from the perspective that the atolls, at the northern edge of the subtropical gyre, are situated at a strong physical, chemical and biological gradient. The gradient moves north and south seasonally and interannually resulting in changes in lower trophic level productivity around the atolls fixed in position. Variation in biome boundaries or gradients may be a key factor in ecosystem dynamics in many ecosystems located near such boundaries.

Reconsidering diversity–productivity relationships: directness of productivity estimates matters

AbstractDespite extensive research efforts, the controversy over diversity–productivity (D–P) patterns in natural communities still looms large. Recent meta‐analyses suggest that unimodal D–P relationships tend to pre‐dominate in plant studies, while positively linear relationships are more common in animal studies. These patterns, however, are based on studies in which productivity is estimated either directly, based on the biomass or energy of the studied organisms, or indirectly, according to the productivity of lower trophic levels, and various surrogates. Our analysis shows that the distribution of D–P patterns is sensitive to the directness of productivity estimates in animal studies but not in plant studies. Analysis of D–P patterns should be based on direct productivity estimates of the studied organisms, especially in comparative meta‐analyses of communities from multiple trophic levels, where productivity is often affected nonlinearly by indirect factors or when complex feedback interactions are expected between productivity and diversity.

Evaluation of biological productivity of lower trophic levels and carrying capacity of aquaculture areas

Evaluation of biological productivity of lower trophic levels and carrying capacity of aquaculture areas