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Progress on the taxonomy and systematics of three Indo-Pacific fish genera, Ofer Gon [et al.]

Progress on the taxonomy and systematics of three Indo-Pacific fish genera, Ofer Gon [et al.]

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The exceptional visual solution of the

pearlsides (Sternoptychidae) to optimize

vision in twilight conditions.

Fanny De Busserolles ∗† 1,2 , Fabio Cortesi 1 , Jon Vidar Helvik 3 , Wayne

Davies 4 , Rachel Templin 1 , Robert Sullivan 1 , Craig Michell 2 , Jessica

Mountford 4 , Shaun Collin 4 , Xabier Irigoien 2,5 , Stein Kaartvedt 2,6 ,

Justin Marshall 1


Queensland Brain Institute, The University of Queensland – St Lucia, QLD 4072, Australia

King Abdullah University of Science and Technology – Thuwal, 23955-6900, Saudi Arabia


University of Bergen – Bergen 5020, Norway


University of Western Australia – Crawley, WA 6009, Australia


IKERBASQUE, Basque Foundation for Science; Bilbao – Spain


University of Oslo – Oslo, 0316, Norway


Most vertebrates have a duplex retina comprising two photoreceptor types, rods for dimlight (scotopic) vision, and cones for bright-light (photopic) and color vision. Deep-sea fishes,

however, are only active in dim-light conditions hence, most species have lost their cones in favor

of a simplex retina composed exclusively of rods. While pearlsides, Maurolicus spp., appear to

possess such a pure rod retina, their behavior is at odd with this simplex visual system. Contrary

to other deep-sea fishes, pearlsides are mostly active during dusk and dawn close to the surface,

where light levels are intermediate (twilight or mesopic) and require the use of both rods and

cone photoreceptors. To explore this paradox, we investigated the visual system of two species

of pearlsides, Maurolicus muelleri from the Norwegian fjords and M. mucronatus from the Red

Sea. Using a multidisciplinary approach including transcriptomics, in situ hybridization, in

vitro regeneration, immunohistochemistry, retinal mapping and microscopy, this study shows

that pearlsides have evolved an unconventional visual system to optimize visual performance

in twilight conditions. Their previously categorized all-rod retina is in fact composed almost

exclusively of transmuted cone photoreceptors. In other words, the pearlside does not possess

the usual rods and/or cones, like most animals, but instead possess a third and more efficient

type of photoreceptor that combines properties of both rods and cones. In more details, these

transmuted cells combine the morphological characteristics of a rod photoreceptor with a cone

opsin and a cone phototransduction cascade to form a unique photoreceptor type, a rod-like

cone, specifically tuned to the light conditions of the pearlsides’ habitat (blue-shifted light at

mesopic intensities). Combining properties of both rods and cones into a single cell type instead

of possessing two photoreceptor types that do not function at their full potential under mesopic

conditions, is the most efficient and economical solution to optimize visual performance in these

conditions. This is the first report of photoreceptor transmutation mediating a cone-opsin-based

visual system in teleost fishes. These results challenge the standing paradigm of the vertebrate


Corresponding author: f.debusserolles@uq.edu.au


duplex retina and its evolution, and call for more comprehensive evaluations of visual systems

in general.


F1/ Causes and consequences of

change for macroalgae-associated



Algal herbivory dynamics of fish across

habitats in a shallow tropical seascape

Maria Eggertsen ∗ 1 , Dinorah Chacin 2 , Carolina ˚

akerlund 1 , Christina

Halling 1 , Amelia Buriyo 3 , Charlotte Berkstrăom 1,4,5


Department of Ecology, Environment and Plant Sciences (DEEP) Stockholm University SE-10691

Stockholm, Sweden


College of Marine Science, University of South Florida – 140 7th Avenue South St. Petersburg, FL

33701, United States


Botany Department, University of Dar es Salaam – University of Dar es Salaam P.O. BOX 35060, Dar

es Salaam, Tanzania, Tanzania


Stockholm University (SU) – Stockholm University SE-10691 Stockholm, Sweden


Department of Aquatic Resources, Swedish University of Agricultural Sciences Skolgatan 6, SE-742




Consumer-producer dynamics are important forces in the marine environment, shaping

ecosystems by structuring benthic communities and transferring energy to higher trophic levels.

Within the tropical seascape, herbivorous fish are among the most important consumers, forming

a heterogeneous community which is functionally diverse and often species-specific. Among the

producers, algal communities play a prominent and highly dynamic role as different functional

groups and species of algae sustain different species or life stages of consumers/herbivorous fish.

Grazing pressure distribution across the shallow seascape and the responsible factors for observed patterns are complex processes which have mainly been studied in coral reef habitats

in East Africa. Therefore, we adopt an across-habitat view and investigate grazing pressure on

algal resources in three common habitats; coral reefs, seagrass- and macroalgal beds, by different

functional groups of fish. Grazing pressure was investigated by 1) video-recorded experiments

with tethered macroalgae, 2) recording of bite rates and feeding choice, and 3) inventories of

feeding scars by excavating/scraping parrotfish. Herbivore surveys were performed in all three

shallow-water habitats and fish communities were documented by underwater visual census

(UVC). Herbivorous fish communities differed among habitats, and herbivores from all functional groups (browsers, grazers, scrapers, excavators) were generally most abundant on coral

reefs. Macroalgal consumption was density-dependent, and grazing intensity (bites minute -1)

was highest on coral reefs. Also, food choice was strongly dependent on available resources.

Several herbivorous species within the same functional group was observed to consume algae,

suggesting a high redundancy within reef habitats. Results illustrate how dynamic ecological

processes can be, even over smaller scales (1-10 km) and the importance of including habitat,

functional groups, and densities of both consumers and producers to better understand herbivory

patterns in tropical seascapes.



Edge effects on seaweed- and seagrass

browsing within a tropical seascape

Charlotte Berkstrăom 1,2 , Carolina

akerlund 1 , Maria Eggertsen 1 ,

Dinorah Chacin 3 , Amelia Buriyo 4 , Christina Halling 1



Dept. of Ecology, Environment and Plant Sciences, Stockholm University (DEEP) – Stockholm

University, 106 91 Stockholm, Sweden

Swedish University of Agricultural Sciences (SLU) – Department of Aquatic Resources Skolgatan 6



SWEDEN, Sweden


College of Marine Science [St Petersburg, FL] – University of South Florida, Saint Petersburg,

Florida, USA, United States


Botany Department, University of Dar es Salaam – University Road, Dar es Salaam, Tanzania

With increasing anthropogenic pressure from eutrophication, dredging and CO2-emission,

coastal ecosystems are subjected to habitat loss and fragmentation. Hence the understanding

of seascape- and patch dynamics are urging. Previous studies have focused on how seascape attributes and edge effects influence species abundance and richness in seagrass meadows, and how

species are distributed within and between patches. However, research on the effects of seascape

variables and edge on seaweed patches is lacking. Furthermore, the effect of patch edges on

important ecological functions such as herbivory and predation are non-existent. In the present

study we therefore investigated browsing by fishes along edges and the interior parts of seaweedand seagrass patches through a combination of tethering experiments, browsing estimations and

visual census in Mafia Island, Tanzania. Biomass loss of tethered Sargassum aquifolium was

higher in the centre of seaweed patches than along edges, although no differences were found in

seagrass areas. On the contrary, there were higher number of bites on Thalassodendron ciliatum

shoots along seagrass patch edges compared to the interior parts. The abundance and diversity

of browsing herbivores was higher in seagrass patches than seaweed patches, although there was

no difference between the interior and edge of patches in either habitat. Macrophyte cover (%)

was significantly higher in the middle than along the edges of seaweed areas. However, there

were no differences in mean canopy height. The opposite pattern was found in seagrass patches

where there were no differences in shoot density between interior and edge of seagrass beds but

shoots in the middle were significantly higher than shoots at the edges of seagrass patches. Our

results suggest that both habitat type and seascape characteristics like patch edges can influence important ecological functions such as herbivory. This information is crucial for proper

management, especially with the alarming increase of habitat loss and fragmentation in shallow

coastal areas worldwide.



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Progress on the taxonomy and systematics of three Indo-Pacific fish genera, Ofer Gon [et al.]

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