An official website of the United States government
Abstract Islands in oligotrophic oceans act as local sources of nutrients. These nutrients originate from land and from deep oceanic nutrients introduced to the photic zone by tides, currents, and internal waves interacting with island bathymetry. These processes create the island mass effect (IME), in which increased chlorophylla(Chla) is found near islands compared to oceanic waters. The IME has been described via satellite observations, but the effects on phytoplankton community structure are not well documented. From 2013 to 2020, chlorophyll, nutrient, and picoplankton samples were collected from multiple depths on quarterly cruises at two sites south of O'ahu, Hawai'i.Prochlorococcus,Synechococcus, picoeukaryotes, and heterotrophic bacteria were enumerated using flow cytometry. We compared nearshore results to Sta. ALOHA, 100 km from O'ahu. Consistent with the expected IME, Chlaconcentrations were significantly enhanced at both nearshore sites compared to Sta. ALOHA.Prochlorococcusconcentrations increased with greater distance from shore, particularly below 50 m; mixed layer concentrations ofSynechococcusand picoeukaryotes significantly decreased with greater distance from shore, as did concentrations of nitrate and phosphate below the mixed layer. Heterotrophic bacteria concentrations did not show a spatial trend. Carbon‐based biomass estimates of the picoplankton population indicated that the IME‐associated Chlaincreases near the island are likely driven by larger phytoplankton classes. This study describes the IME‐associated shift in the picophytoplankton community distribution, which has implications for nutrient cycling, food web dynamics and fisheries in oligotrophic island ecosystems, and adds to the understanding of spatial heterogeneity in carbon fixation in the ocean.
more »
« less
Bacterioplankton communities reveal horizontal and vertical influence of an Island Mass Effect
Summary Coral reefs are highly productive ecosystems with distinct biogeochemistry and biology nestled within unproductive oligotrophic gyres. Coral reef islands have often been associated with a nearshore enhancement in phytoplankton, a phenomenon known as the Island Mass Effect (IME). Despite being documented more than 60 years ago, much remains unknown about the extent and drivers of IMEs. Here we utilized 16S rRNA gene metabarcoding as a biological tracer to elucidate horizontal and vertical influence of an IME around the islands of Mo′orea and Tahiti, French Polynesia. We show that those nearshore oceanic stations with elevated chlorophyllaincluded bacterioplankton found in high abundance in the reef environment, suggesting advection of reef water is the source of altered nearshore biogeochemistry. We also observed communities in the nearshore deep chlorophyll maximum (DCM) with enhanced abundances of upper euphotic bacterioplankton that correlated with intrusions of low‐density, O2rich water, suggesting island influence extends into the DCM.
more »
« less
- PAR ID:
- 10444445
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Environmental Microbiology
- Volume:
- 24
- Issue:
- 9
- ISSN:
- 1462-2912
- Format(s):
- Medium: X Size: p. 4193-4208
- Size(s):
- p. 4193-4208
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract Corals have complex symbiotic associations that can be influenced by the environment. We compare symbiotic dinoflagellate (family: Symbiodiniaceae) associations and the microbiome of five scleractinian coral species from three different reef habitats in Palau, Micronesia. Although pH and temperature corresponded with specific host‐Symbiodiniaceae associations common to the nearshore and offshore habitats, bacterial community dissimilarity analyses indicated minimal influence of these factors on microbial community membership for the coralsCoelastrea aspera,Psammocora digitata, andPachyseris rugosa. However, coral colonies sampled close to human development exhibited greater differences in microbial community diversity compared to the nearshore habitat for the coral speciesCoelastrea aspera,Montipora foliosa, andPocillopora acuta, and the offshore habitat forCoelastrea aspera, while also showing less consistency in Symbiodiniaceae associations. These findings indicate the influence that habitat location has on the bacterial and Symbiodiniaceae communities comprising the coral holobiont and provide important considerations for the conservation of coral reef communities, especially for island nations with increasing human populations and development.more » « less
-
Abstract Although parasites are ubiquitous in marine ecosystems, predicting the abundance of parasites present within marine ecosystems has proven challenging due to the unknown effects of multiple interacting environmental gradients and stressors. Furthermore, parasites often are considered as a uniform group within ecosystems despite their significant diversity.We aim to determine the potential importance of multiple predictors of parasite abundance in coral reef ecosystems, including reef area, island area, human population density, chlorophyll‐a, host diversity, coral cover, host abundance and island isolation.Using a model selection approach within a database of more than 1,200 individual fish hosts and their parasites from 11 islands within the Pacific Line Islands archipelago, we reveal that geographic gradients, including island area and island isolation, emerged as the best predictors of parasite abundance.Life history moderated the relationship; parasites with complex life cycles increased in abundance with increasing island isolation, while parasites with direct life cycles decreased with increasing isolation. Direct life cycle parasites increased in abundance with increasing island area, although complex life cycle parasite abundance was not associated with island area.This novel analysis of a unique dataset indicates that parasite abundance in marine systems cannot be predicted precisely without accounting for the independent and interactive effects of each parasite's life history and environmental conditions.more » « less
-
Abstract Coral bleaching is a well-documented and increasingly widespread phenomenon in reefs across the globe, yet there has been relatively little research on the implications for reef water column microbiology and biogeochemistry. A mesocosm heating experiment and bottle incubation compared how unbleached and bleached corals alter dissolved organic matter (DOM) exudation in response to thermal stress and subsequent effects on microbial growth and community structure in the water column. Thermal stress of healthy corals tripled DOM flux relative to ambient corals. DOM exudates from stressed corals (heated and/or previously bleached) were compositionally distinct from healthy corals and significantly increased growth of bacterioplankton, enriching copiotrophs and putative pathogens. Together these results demonstrate how the impacts of both short-term thermal stress and long-term bleaching may extend into the water column, with altered coral DOM exudation driving microbial feedbacks that influence how coral reefs respond to and recover from mass bleaching events.more » « less
-
Caroselli, Erik (Ed.)The North Atlantic Oscillation (NAO) has been hypothesized to drive interannual variability in Bermudan coral extension rates and reef-scale calcification through the provisioning of nutritional pulses associated with negative NAO winters. However, the direct influence of the NAO on Bermudan coral calcification rates remains to be determined and may vary between species and reef sites owing to implicit differences in coral life history strategies and environmental gradients across the Bermuda reef platform. In this study, we investigated the connection between negative NAO winters and Bermudan Diploria labyrinthiformis , Pseudodiploria strigosa , and Orbicella franksi coral calcification rates across rim reef, lagoon, and nearshore reef sites. Linear mixed effects modeling detected an inverse correlation between D . labyrinthiformis calcification rates and the winter NAO index, with higher rates associated with increasingly negative NAO winters. Conversely, there were no detectable correlations between P . strigosa or O . franksi calcification rates and the winter NAO index suggesting that coral calcification responses associated with negative NAO winters could be species-specific. The correlation between coral calcification rates and winter NAO index was significantly more negative at the outer rim of the reef (Hog Reef) compared to a nearshore reef site (Whalebone Bay), possibly indicating differential influence of the NAO as a function of the distance from the reef edge. Furthermore, a negative calcification anomaly was observed in 100% of D . labyrinthiformis cores in association with the 1988 coral bleaching event with a subsequent positive calcification anomaly in 1989 indicating a post-bleaching recovery in calcification rates. These results highlight the importance of assessing variable interannual coral calcification responses between species and across inshore-offshore gradients to interannual atmospheric modes such as the NAO, thermal stress events, and potential interactions between ocean warming and availability of coral nutrition to improve projections for future coral calcification rates under climate change.more » « less
