Algal cover and sea urchin spatial distribution at Madeira Island (NE Atlantic)

AbstractIn this contribution, we propose fishery driven predator release as the cause for the largest grazing event ever observed in the NE Atlantic. Based on the evolving appreciation of limits to population connectivity, published and previously unpublished data, we discuss whether overfishing caused a grazer bloom of the sea urchin (Strongylocentrotus droebachiensis) resulting in overgrazing of more than 2000 km2 kelp (Laminaria hyperborea) forest along Norwegian and Russian coasts during the 1970 s. We show that coastal fisheries likely depleted predatory coastal fish stocks through modernization of fishing methods and fleet. These fish were important predators on urchins and the reduction coincided with the urchin bloom. From this circumstantial evidence, we hypothesize that coastal predatory fish were important in regulating sea urchins, and that a local population dynamics perspective is necessary in management of coastal ecosystems.

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Temporal sequence and spatial distribution of early events of fertilization in single sea urchin eggs.

The Journal of Cell Biology ◽

10.1083/jcb.99.5.1647 ◽

1984 ◽

Vol 99 (5) ◽

pp. 1647-1654 ◽

Cited By ~ 119

Author(s):

A Eisen ◽

D P Kiehart ◽

S J Wieland ◽

G T Reynolds

Keyword(s):

Spatial Distribution ◽

Sea Urchin ◽

Pyridine Nucleotide ◽

Membrane Depolarization ◽

Temporal Sequence ◽

Cortical Granule ◽

Free Calcium ◽

Sea Urchin Eggs ◽

Cortical Granule Exocytosis ◽

Cytoplasmic Free Calcium

Measurements and observations of five early events of fertilization, singly and in pairs, from single sea urchin eggs have revealed the precise temporal sequence and spatial distribution of these events. In the Arbacia punctulata egg, a wave of surface contraction occurs coincident with membrane depolarization (t = 0). These two earliest events are followed by the onset of a rapid, propagated increase in cytoplasmic-free calcium at approximately 23 s as measured by calcium-aequorin luminescence. The luminescence reaches its peak value by 40 s after the membrane depolarization. The luminescence remains uniformly elevated for some time before its decay over several minutes. The onset of an increase in the pyridine nucleotide (NAD(P)H) fluorescence follows the membrane depolarization at approximately 51 s. The fertilization membrane begins its elevation in a wave-like fashion coincidentally with the increase in NAD(P)H fluorescence. Similar results are observed in the Lytechinus variegatus egg. The results suggest that while the increase in cytoplasmic-free calcium may be important for many changes occurring in the egg, the elevated-free calcium is not directly responsible for the propagated wave of cortical granule exocytosis.

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Spatial and temporal characterization of the exposure of island-associated cetacean populations to whale-watching in Madeira Island (NE Atlantic)

Regional Studies in Marine Science ◽

10.1016/j.rsma.2021.102084 ◽

2021 ◽

pp. 102084

Author(s):

Annalisa Sambolino ◽

Filipe Alves ◽

Marc Fernandez ◽

Anja Badenas Krakauer ◽

Rita Ferreira ◽

...

Keyword(s):

Ne Atlantic ◽

Whale Watching ◽

Madeira Island

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Interplay of deep-marine sedimentary processes with seafloor morphology offshore Madeira Island (Central NE-Atlantic)

Marine Geology ◽

10.1016/j.margeo.2021.106675 ◽

2021 ◽

pp. 106675

Author(s):

C. Roque ◽

F.J. Hernández-Molina ◽

P. Madureira ◽

R. Quartau ◽

V. Magalhães ◽

...

Keyword(s):

Ne Atlantic ◽

Sedimentary Processes ◽

Seafloor Morphology ◽

Madeira Island

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Disease Outbreak in a Keystone Grazer Population Brings Hope to the Recovery of Macroalgal Forests in a Barren Dominated Island

Frontiers in Marine Science ◽

10.3389/fmars.2021.645578 ◽

2021 ◽

Vol 8 ◽

Author(s):

Francesca Gizzi ◽

João Gama Monteiro ◽

Rodrigo Silva ◽

Susanne Schäfer ◽

Nuno Castro ◽

...

Keyword(s):

Sea Urchin ◽

Alternative Stable States ◽

Disease Outbreak ◽

Coralline Algae ◽

Spatial And Temporal Variation ◽

Stable States ◽

Benthic Assemblages ◽

Madeira Island ◽

Mortality Event ◽

Barren Grounds

Macroalgal forests play a key role in shallow temperate rocky reefs worldwide, supporting communities with high productivity and providing several ecosystem services. Sea urchin grazing has been increasingly influencing spatial and temporal variation in algae distributions and it has become the main cause for the loss of these habitats in many coastal areas, causing a phase shift from macroalgae habitats to barren grounds. The low productive barrens often establish as alternative stable states and only a major reduction in sea urchin density can trigger the recovery of macroalgal forests. The present study aims to assess if the 2018 disease outbreak, responsible for a strong reduction in the sea urchin Diadema africanum densities in Madeira Island, was able to trigger a reverse shift from barren grounds into macroalgae-dominated state. By assessing the diversity and abundance of benthic sessile organisms, macroinvertebrates and fishes before, during and after that particular mass mortality event, we evaluate changes in benthic assemblages and relate them to variations in grazer and herbivore densities. Our results revealed a clear shift from barren state to a macroalgae habitat, with barrens characterized by bare substrate, sessile invertebrate and Crustose Coralline Algae (CCA) disappearing after the mortality event. Overall variations in benthic assemblages was best explained by four taxa (among grazers and herbivores species). However, it was the 2018 demise of D. africanum and its density reduction that most contributed to the reverse shift from a long stable barren state to a richer benthic assemblage with higher abundance of macroalgae. Despite this recent increase in macroalgae dominated habitats, their stability and persistence in Madeira Island is fragile, since it was triggered by an unpredictable disease outbreak and depends on how D. africanum populations will recover. With no control mechanisms, local urchin populations can easily reach the tipping point needed to promote a new shift into barren states. New conservation measures and active restoration are likely required to maintain and promote the local stability of macroalgal forests.

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