Enhanced chlorophyll-a concentration in the wake of Sable Island, eastern Canada, revealed by two decades of satellite observations: a response to grey seal population dynamics?

Elevated surface chlorophyll-a (chl-a) concentration ([chl-a...

Descripción completa

Guardado en:

Detalles Bibliográficos
Autores principales:	E. Devred, A. Hilborn, C. E. den Heyer
Formato:	article
Lenguaje:	EN
Publicado:	Copernicus Publications 2021
Materias:	Ecology QH540-549.5 Life QH501-531 Geology QE1-996.5
Acceso en línea:	https://doaj.org/article/407ceb84fd8b4e84af5937f9228099fa
Etiquetas:	Agregar Etiqueta Sin Etiquetas, Sea el primero en etiquetar este registro!

id	oai:doaj.org-article:407ceb84fd8b4e84af5937f9228099fa
record_format	dspace
institution	DOAJ
collection	DOAJ
language	EN
topic	Ecology QH540-549.5 Life QH501-531 Geology QE1-996.5
spellingShingle	Ecology QH540-549.5 Life QH501-531 Geology QE1-996.5 E. Devred A. Hilborn C. E. den Heyer Enhanced chlorophyll-<i>a</i> concentration in the wake of Sable Island, eastern Canada, revealed by two decades of satellite observations: a response to grey seal population dynamics?
description	<p>Elevated surface chlorophyll-<span class="inline-formula"><i>a</i></span> (chl-<span class="inline-formula"><i>a</i></span>) concentration ([chl-<span class="inline-formula"><i>a</i></span>]), an index of phytoplankton biomass, has been previously observed and documented by remote sensing in the waters to the southwest of Sable Island (SI) on the Scotian Shelf in eastern Canada. Here, we present an analysis of this phenomenon using a 21-year time series of satellite-derived [chl-<span class="inline-formula"><i>a</i></span>], paired with information on the particle backscattering coefficient at 443 <span class="inline-formula">nm</span> (<span class="inline-formula"><i>b</i><sub>bp</sub>(443)</span>, a proxy for particle suspension) and the detritus/gelbstoff absorption coefficient at 443 <span class="inline-formula">nm</span> (<span class="inline-formula"><i>a</i><sub>dg</sub>(443)</span>, a proxy to differentiate water masses and presence of dissolved organic matter) in an attempt to explain some possible mechanisms that lead to the increase in surface biomass in the surroundings of SI. We compared the seasonal cycle, 8 <span class="inline-formula">d</span> climatology and seasonal trends of surface waters near SI to two control regions located both upstream and downstream of the island, away from terrigenous inputs. Application of the self-organising map (SOM) approach to the time series of satellite-derived [chl-<span class="inline-formula"><i>a</i></span>] over the Scotian Shelf revealed the annual spatio-temporal patterns around SI and, in particular, persistently high phytoplankton biomass during winter and spring in the leeward side of SI, a phenomenon that was not observed in the control boxes. In the vicinity of SI, a significant increase in [chl-<span class="inline-formula"><i>a</i></span>] and <span class="inline-formula"><i>a</i><sub>dg</sub>(443)</span> during the winter months occurred at a rate twice that of the ones observed in the control boxes, while no significant trends were found for the other seasons. In addition to the increase in [chl-<span class="inline-formula"><i>a</i></span>] and <span class="inline-formula"><i>a</i><sub>dg</sub>(443)</span> within the plume southwest of SI, the surface area of the plume itself expanded by a factor of 5 over the last 21 years. While the island mass effect (IME) explained the enhanced biomass around SI, we hypothesised that the large increase in [chl-<span class="inline-formula"><i>a</i></span>] over the last 21 years was partly due to an injection of nutrients by the island's grey seal colony, which has increased by 200 % during the same period. This contribution of nutrients from seals may sustain high phytoplankton biomass at a time of year when it is usually low following the fall bloom. A conceptual model was developed to estimate the standing stock of chl-<span class="inline-formula"><i>a</i></span> that can be sustained by the release of nitrogen (N) by seals. Comparison between satellite observations and model simulations showed a good temporal agreement between the increased abundance of seal on SI during the breeding season and the phytoplankton biomass increase during the winter. We found that about 20 % of chl-<span class="inline-formula"><i>a</i></span> standing stock increase over the last 21 years could be due to seal N fertilisation, the remaining being explained by climate forcing and oceanographic processes. Although without in situ measurements for ground truthing, the satellite data analysis provided evidence of the impact of marine mammals on lower trophic levels through a fertilisation mechanism that is coupled with the IME with potential implications for conservation and fisheries.</p>
format	article
author	E. Devred A. Hilborn C. E. den Heyer
author_facet	E. Devred A. Hilborn C. E. den Heyer
author_sort	E. Devred
title	Enhanced chlorophyll-<i>a</i> concentration in the wake of Sable Island, eastern Canada, revealed by two decades of satellite observations: a response to grey seal population dynamics?
title_short	Enhanced chlorophyll-<i>a</i> concentration in the wake of Sable Island, eastern Canada, revealed by two decades of satellite observations: a response to grey seal population dynamics?
title_full	Enhanced chlorophyll-<i>a</i> concentration in the wake of Sable Island, eastern Canada, revealed by two decades of satellite observations: a response to grey seal population dynamics?
title_fullStr	Enhanced chlorophyll-<i>a</i> concentration in the wake of Sable Island, eastern Canada, revealed by two decades of satellite observations: a response to grey seal population dynamics?
title_full_unstemmed	Enhanced chlorophyll-<i>a</i> concentration in the wake of Sable Island, eastern Canada, revealed by two decades of satellite observations: a response to grey seal population dynamics?
title_sort	enhanced chlorophyll-<i>a</i> concentration in the wake of sable island, eastern canada, revealed by two decades of satellite observations: a response to grey seal population dynamics?
publisher	Copernicus Publications
publishDate	2021
url	https://doaj.org/article/407ceb84fd8b4e84af5937f9228099fa
work_keys_str_mv	AT edevred enhancedchlorophylliaiconcentrationinthewakeofsableislandeasterncanadarevealedbytwodecadesofsatelliteobservationsaresponsetogreysealpopulationdynamics AT ahilborn enhancedchlorophylliaiconcentrationinthewakeofsableislandeasterncanadarevealedbytwodecadesofsatelliteobservationsaresponsetogreysealpopulationdynamics AT cedenheyer enhancedchlorophylliaiconcentrationinthewakeofsableislandeasterncanadarevealedbytwodecadesofsatelliteobservationsaresponsetogreysealpopulationdynamics
_version_	1718406677762408448
spelling	oai:doaj.org-article:407ceb84fd8b4e84af5937f9228099fa2021-11-30T08:55:13ZEnhanced chlorophyll-<i>a</i> concentration in the wake of Sable Island, eastern Canada, revealed by two decades of satellite observations: a response to grey seal population dynamics?10.5194/bg-18-6115-20211726-41701726-4189https://doaj.org/article/407ceb84fd8b4e84af5937f9228099fa2021-11-01T00:00:00Zhttps://bg.copernicus.org/articles/18/6115/2021/bg-18-6115-2021.pdfhttps://doaj.org/toc/1726-4170https://doaj.org/toc/1726-4189<p>Elevated surface chlorophyll-<span class="inline-formula"><i>a</i></span> (chl-<span class="inline-formula"><i>a</i></span>) concentration ([chl-<span class="inline-formula"><i>a</i></span>]), an index of phytoplankton biomass, has been previously observed and documented by remote sensing in the waters to the southwest of Sable Island (SI) on the Scotian Shelf in eastern Canada. Here, we present an analysis of this phenomenon using a 21-year time series of satellite-derived [chl-<span class="inline-formula"><i>a</i></span>], paired with information on the particle backscattering coefficient at 443 <span class="inline-formula">nm</span> (<span class="inline-formula"><i>b</i><sub>bp</sub>(443)</span>, a proxy for particle suspension) and the detritus/gelbstoff absorption coefficient at 443 <span class="inline-formula">nm</span> (<span class="inline-formula"><i>a</i><sub>dg</sub>(443)</span>, a proxy to differentiate water masses and presence of dissolved organic matter) in an attempt to explain some possible mechanisms that lead to the increase in surface biomass in the surroundings of SI. We compared the seasonal cycle, 8 <span class="inline-formula">d</span> climatology and seasonal trends of surface waters near SI to two control regions located both upstream and downstream of the island, away from terrigenous inputs. Application of the self-organising map (SOM) approach to the time series of satellite-derived [chl-<span class="inline-formula"><i>a</i></span>] over the Scotian Shelf revealed the annual spatio-temporal patterns around SI and, in particular, persistently high phytoplankton biomass during winter and spring in the leeward side of SI, a phenomenon that was not observed in the control boxes. In the vicinity of SI, a significant increase in [chl-<span class="inline-formula"><i>a</i></span>] and <span class="inline-formula"><i>a</i><sub>dg</sub>(443)</span> during the winter months occurred at a rate twice that of the ones observed in the control boxes, while no significant trends were found for the other seasons. In addition to the increase in [chl-<span class="inline-formula"><i>a</i></span>] and <span class="inline-formula"><i>a</i><sub>dg</sub>(443)</span> within the plume southwest of SI, the surface area of the plume itself expanded by a factor of 5 over the last 21 years. While the island mass effect (IME) explained the enhanced biomass around SI, we hypothesised that the large increase in [chl-<span class="inline-formula"><i>a</i></span>] over the last 21 years was partly due to an injection of nutrients by the island's grey seal colony, which has increased by 200 % during the same period. This contribution of nutrients from seals may sustain high phytoplankton biomass at a time of year when it is usually low following the fall bloom. A conceptual model was developed to estimate the standing stock of chl-<span class="inline-formula"><i>a</i></span> that can be sustained by the release of nitrogen (N) by seals. Comparison between satellite observations and model simulations showed a good temporal agreement between the increased abundance of seal on SI during the breeding season and the phytoplankton biomass increase during the winter. We found that about 20 % of chl-<span class="inline-formula"><i>a</i></span> standing stock increase over the last 21 years could be due to seal N fertilisation, the remaining being explained by climate forcing and oceanographic processes. Although without in situ measurements for ground truthing, the satellite data analysis provided evidence of the impact of marine mammals on lower trophic levels through a fertilisation mechanism that is coupled with the IME with potential implications for conservation and fisheries.</p>E. DevredA. HilbornC. E. den HeyerCopernicus PublicationsarticleEcologyQH540-549.5LifeQH501-531GeologyQE1-996.5ENBiogeosciences, Vol 18, Pp 6115-6132 (2021)

Enhanced chlorophyll-<i>a</i> concentration in the wake of Sable Island, eastern Canada, revealed by two decades of satellite observations: a response to grey seal population dynamics?

Ejemplares similares