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Long-term ecological time series provide a unique perspective on the emergent properties of ecosystems. In aquatic systems, phytoplankton form the base of the food web and their biomass, measured as the concentration of the photosynthetic pigment chlorophylla(chla), is an indicator of ecosystem quality. We analyzed temporal trends in chlafrom the Long-Term Plankton Time Series in Narragansett Bay, Rhode Island, USA, a temperate estuary experiencing long-term warming and changing anthropogenic nutrient inputs. Dynamic linear models were used to impute and model environmental variables (1959 to 2019) and chlaconcentrations (1968 to 2019). A long-term chladecrease was observed with an average decline in the cumulative annual chlaconcentration of 49% and a marked decline of 57% in winter-spring bloom magnitude. The long-term decline in chlaconcentration was directly and indirectly associated with multiple environmental factors that are impacted by climate change (e.g., warming temperatures, water column stratification, reduced nutrient concentrations) indicating the importance of accounting for regional climate change effects in ecosystem-based management. Analysis of seasonal phenology revealed that the winter–spring bloom occurred earlier, at a rate of 4.9 ± 2.8 d decade−1. Finally, the high degree of temporal variation in phytoplankton biomass observed in Narragansett Bay appears common among estuaries, coasts, and open oceans. The commonality among these marine ecosystems highlights the need to maintain a robust set of phytoplankton time series in the coming decades to improve signal-to-noise ratios and identify trends in these highly variable environments.
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EVALUATING SPECIES-SPECIFIC NAUPLIAR RECRUITMENT DURING THE WINTER-TO-SPRING TRANSITION IN THE NORTHERN GULF OF ALASKA USING MOLECULAR TOOLS
The Gulf of Alaska is a highly seasonal environment that is characterized by an order-of-magnitude increase in copepod biomass in the photic zone between winter and spring. Copepod recruitment processes, including the location and timing of naupliar production, responsible for the transition from low-biomass winter conditions to the highly productive spring are not well characterized. The recruitment patterns of copepod nauplii were examined in Resurrection Bay, Alaska using biweekly sampling between January and March with zooplankton collected from three depth strata. Nauplii were identified using DNA metabarcoding and species-specific naupliar phenologies were contextualized with environmental data and copepodite and adult copepod population data. This study revealed that nauplii were abundant throughout the winter and were comprised of a diverse assemblage of species. The community composition changed over the course of the season, with different copepod species exhibiting three distinct naupliar phenologies. These include species with nauplii that were 1) present during the winter and absent during the spring, 2) absent during the winter and present during the spring, and 3) present during both winter and spring. Several closely related species were split across groups, revealing temporal niche partitioning of reproduction and naupliar phenologies. For most species in the third group, the presence of nauplii during the winter occurred despite the absence of ovigerous females. While ovigerous females may have been missed or the nauplii could have been sourced from reproductive populations outside of Resurrection Bay, it is also possible that some copepods overwinter as nauplii. Prior to the spring phytoplankton bloom, a moderate increase in chlorophyll α concentrations occurred during March, coinciding with a period of female maturation, an increase in naupliar abundances, and the appearance of later developmental stages. These observations suggest smaller increases in chlorophyll prior to the large spring bloom may be critically important to recruitment of copepod nauplii, their survival, and their growth.
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- Award ID(s):
- 2222376
- PAR ID:
- 10533490
- Publisher / Repository:
- UNIVERSITY OF HAWAIʻI AT MĀNOA
- Date Published:
- Subject(s) / Keyword(s):
- Nauplii copepod Gulf of Alaska DNA metabarcoding phenology
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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