Cesar Cardenas | Instituto Antártico Chileno (original) (raw)

Papers by Cesar Cardenas

Our ongoing studies of the Chilean sponge fauna revealed four new species of Lissodendoryx (Ectyo... more Our ongoing studies of the Chilean sponge fauna revealed four new species of Lissodendoryx (Ectyodoryx) that are described here, including three from the fjord’s region (< 30 m depth, L.(E.) ballena sp. nov., L. (E.) corrugata sp. nov., L. (E.) coloanensis sp. nov.), and one from the deep waters off Diego Ramírez Archipelago (ca. 2000 m, L. (E.) diegoramirezensis sp. nov.). In addition, the type of L. (E.) anacantha was revised and found to bear much larger acanthostyles than originally reported. Our results revealed skeletal architectures quite distinct from that reported from the type species of L. (Ectyodoryx), and not predicted in the current diagnosis of Lissodendoryx, requiring an amended diagnosis. Ectosomal megascleres also set the majority of the new species apart from the type species of L. (Ectyodoryx), which does not have terminally microspined (sub)tylotes. This character is widespread in Lissodendoryx and might be pointing to phylogenetic affinities across the current subgeneric arrangement. Further morphologic characters and alternative phylogenetic scenarios are discussed, including hymedesmiid and myxillid affinities of the species described here

Background: Antarctic marine organisms have evolved a variety of physiological, life-history and ... more Background: Antarctic marine organisms have evolved a variety of physiological, life-history and molecular adaptations that allow them to cope with the extreme conditions in one of the coldest and most temperature-stable marine environments on Earth. The increase in temperature of the Southern Ocean, product of climate change, represents a great challenge for the survival of these organisms. It has been documented that some Antarctic marine invertebrates are not capable of generating a thermal stress response by means of an increase in the synthesis of heat shock proteins, which could be related with their low capacity for acclimatization. In order to understand the role of heat shock proteins as a compensatory response in Antarctic marine species to projected scenarios of increased seawater temperatures, we assessed the expression of the genes Hsp90, Grp78, Hyou1 and Hsc70 in the Antarctic sea urchin Sterechinus neumayeri under three thermal treatments (1 °C, 3 °C and 5 °C), for a period of exposure of 1, 24 and 48 h.

The aim of this work was to carry out a qualitative assessment of the subtidal algal assemblages ... more The aim of this work was to carry out a qualitative assessment of the subtidal algal assemblages occurring at Fildes
and Collins Bays. We conducted subtidal sampling of seaweeds between 1 and 10 m in Collins and Fildes Bay during late
summer 2009. Our results showed that Rhodophyta was the most diverse group (63% of species) followed by Phaeophyceae
(33.3%) and Chlorophyta (3.7%). Differences in species richness and structure of algal assemblages were recorded between
sites. Depth significantly influenced algal assemblages; however there was a significant interaction between site and depth,
suggesting that the effect of depth varied among sites. Observed differences between sites may be explained by differences
in ice-scour disturbance, habitat heterogeneity (availability of refugia) and identity of canopy-forming species.

Polar Biology

Previous studies from other latitudes have demonstrated that depth and spatial heterogeneity, pro... more Previous studies from other latitudes have demonstrated that depth and spatial heterogeneity, produced by surface inclination, can have strong effects on diversity and distribution of sessile assemblages on rocky reefs. Rocky reef communities in the subantarctic Magellan region have been rarely studied, and the factors influencing diversity, distribution and abundance of benthic communities remain poorly understood. Sessile benthic assemblages inhabiting rocky reefs habitats were studied by SCUBA diving at Punta Santa Ana, Magellan Strait from 0 to 30 m water depth. We describe the sessile assemblages assessing the effect of depth, inclination and other environmental factors on species richness and community structure. A total of 37 taxa of invertebrates and 31 taxa of macroalgae were identified based on 280 high-resolution photoquadrats. Species richness and percent coverage varied with depth and inclination. Macroalgae dominated in abundance in the shallows, while bryozoans and ascidians (mound and tree-like forms) increased their coverage with depth. Lithothamnion sp. dominated on vertical and inclined surfaces while sheet-like organism such as bryozoans increased their coverage on overhanging surfaces. Multivariate analyses showed that sessile assemblages at Punta Santa Ana are strongly influenced by the interaction between inclination and depth, which alter the effect of other physical factors such as light and sedimentation. In this regard, our results suggest that sedimentation may play a role structuring benthic assemblages in Punta Santa Ana, especially in deeper zones, where it may replace the structuring effect produced by light in the shallows.

Journal of the Marine Biological Association of the United Kingdom, 2015

Experimental removals of the dominant canopy-forming kelp Ecklonia radiata were conducted at two ... more Experimental removals of the dominant canopy-forming kelp Ecklonia radiata were conducted at two sites on rocky walls in New Zealand and monitored for approximately 1.5 years. We hypothesized that the removal of the E. radiata canopy would affect the structure of subcanopy assemblages, such that there would be a reduction in sponge species richness and abundance. Furthermore, we investigated the biological and physical (predictor) variables that best explained variability in sponge assemblages after canopy removal. Canopy removal led to a community dominated by turf algae, which corresponded with a decrease in sponge abundance and richness. Our results suggest that the Ecklonia canopy may positively influence the presence of sponge species such as Crella incrustans; we propose that the canopy may allow its coexistence with turf algae underneath the canopy by altering the light regime and other environmental factors, which may be detrimental for some species. Our results highlight how any loss of canopy-forming species might have negative effects on sponge assemblages, which could affect the energy flow and the overall biodiversity found in these habitats.

Sponges are an important component of temperate subtidal marine ecosystems, with a range of impor... more Sponges are an important component of temperate subtidal marine ecosystems, with a range of important functional roles and extensive symbiotic relationships with microorganisms. However, much remains unknown about their relationships with these symbiotic microorganisms, and specifically, the role that these symbionts play in sponge physiology, feeding and adaptation to local environmental conditions. Changes in environmental factors may alter relationships between sponges and their symbionts, which could conceivably influence the abundance and distribution patterns of some temperate sponge species. Here, we analyzed the effect of transplantation of sponges between different habitats to test the effect of changes in environmental conditions on the stability of the bacterial communities in specimens of Tethya bergquistae and Ecionemia alata, based on pyrosequencing of amplified 16S rRNA genes. Bacterial communities differed markedly between the two host species. While some morphological changes were observed in transplanted sponges, transplantation had little overall effect on sponge-associated bacterial communities at either phylum or 97%-OTU level. Our results show the importance of host species and also the stability of sponge-associated bacterial communities under environmental variation.

The parasitic bopyrid isopod Pseudione tuberculata Richardson, 1904 infests the branchial chamber... more The parasitic bopyrid isopod Pseudione
tuberculata Richardson, 1904 infests the branchial chamber of
species of the family Lithodidae found along the southern tip
of South America. It was previously known only as a parasite
of Neolithodes off the Chonos Archipelago, Chile, as well as
Paralomis granulosa (Jacquinot, 1847) and Lithodes santolla
(Molina, 1782) from shallow waters of the Beagle Channel,
Argentina. This is the first time the parasite is documented in
Chile at the Magellan Strait, located about 640 km north of the
Beagle Channel, infesting mainly on juveniles of L. santolla
(23.0 to 51.6 mm CL in females and from 24.0 to 48.7 mm in
males). Prevalence of the parasite in crabs was 27.9% in females
and 21.4% in males. Prevalence was higher than those reported
in other Chilean crustaceans parasitized by other Pseudione
species. Each king crab carried a single pair of P. tuberculata
within the branchial chamber on the left side of the carapace.
High rates of parasitism of P. tuberculata on juvenile king crabs
in this area could occur in shallow water inhabited by
Macrocystis pyrifera kelp due to the plant’s effect on the local
hydrodynamic conditions, reducing flow and damping waves,
providing habitats for several organisms. It is concluded that
P. tuberculata infesting L. santolla at the Magellan strait
responds in a similar way when compared with prevalence
values from previous studies developed at the Beagle Channel,
Argentina, where it has been reported infesting P. granulosa
and L. santolla.

In this study, we describe for the first time the composition of epibiotic protozoan communities ... more In this study, we describe for the first time the
composition of epibiotic protozoan communities on juvenile
southern king crabs Lithodes santolla. Basibionts were
collected in subantarctic bays near Santa Ana Point
(Magellan Strait, Chile). Seven epibiotic protozoan ciliates
were found: Ephelota gemmipara, Ephelota gigantea,
Podophrya fixa, Acineta tuberosa, Zoothamnium duplicatum,
Chilodochona quennerstedti and Gymnodinioides sp.
The mean number of epibionts per crab was 99 (maximum
897). Both Ephelota species were the most abundant and
most widely distributed epibionts on the crab examined.
The lengths of basibionts were correlated with the number
of epibionts, indicating a relationship between the age of
the crab and the state of epibiosis. Epibionts differed in
their distribution patterns along the anteroposterior axis of
the crab. Less abundant species tended to occupy sites that
are not colonized by the predominant Ephelota species.
Maxillipeds and pereiopods were most densely colonized
by epibionts. The behaviours of epibionts and basibionts
related to epibiosis are discussed. The recent studies about
invasive lithodids in Antarctic areas enhance the interest
for the epibiotic communities colonizing these crustaceans,
which can illustrate changes in biodiversity and state of
these environments.

Experimental removals of the dominant canopy-forming kelp Ecklonia radiata were conducted at two ... more Experimental removals of the dominant canopy-forming kelp Ecklonia radiata were conducted at two sites on rocky walls
in New Zealand and monitored for approximately 1.5 years. We hypothesized that the removal of the E. radiata canopy
would affect the structure of subcanopy assemblages, such that there would be a reduction in sponge species richness and
abundance. Furthermore, we investigated the biological and physical (predictor) variables that best explained variability in
sponge assemblages after canopy removal. Canopy removal led to a community dominated by turf algae, which corresponded
with a decrease in sponge abundance and richness. Our results suggest that the Ecklonia canopy may positively
influence the presence of sponge species such as Crella incrustans; we propose that the canopy may allow its coexistence
with turf algae underneath the canopy by altering the light regime and other environmental factors, which may be detrimental
for some species. Our results highlight how any loss of canopy-forming species might have negative effects on
sponge assemblages, which could affect the energy flow and the overall biodiversity found in these habitats.

Sponges are important for maintaining ecosystem function and integrity of marine and freshwater ... more Sponges are important for maintaining ecosystem function and integrity of marine and freshwater
benthic communitiesworldwide. Despite this, there has been no assessment of their current global conservation
status. We assessed their status, accounting for the distribution of research effort; patterns of temporal variation
in sponge populations and assemblages; the number of sponges on threatened species lists; and the impact
of environmental pressures. Sponge research effort has been variable; marine sponges in the northeastern
Atlantic and Mediterranean and freshwater sponges in Europe and North America have received the most
attention. Although sponge abundance has increased in some locations since 1990, these were typically on
coral reefs, in response to declines in other benthic organisms, and restricted to a few species. Few data
were available on temporal trends in freshwater sponge abundance. Despite over 8500 described sponge
species, only 20 are on threatened species lists, and all are marine species from the northeastern Atlantic
and Mediterranean. Of the 202 studies identified, the effects of temperature, suspended sediment, substratum
loss, and microbial pathogens have been studied the most intensively for marine sponges, although responses
appear to be variable. There were 20 studies examining environmental impacts on freshwater sponges, and
most of these were on temperature and heavy metal contamination. We found that most sponges do not
appear to be threatened globally. However, little information is available for most species and more data are
needed on the impacts of anthropogenic-related pressures. This is a critical information gap in understanding
sponge conservation status.

Although the frequency and magnitude of sedimentation often varies across coastal landscapes cre... more Although the frequency and magnitude of sedimentation often varies across coastal landscapes creating patches with different mean sediment loads, duration of sedimentation and rates of sediment resuspension, few studies have documented the emergent effects of spatio-temporal variability in sedimentation. Here, we conducted two laboratory experiments to evaluate such effects on the establishment of Macrocystis pyrifera and Undaria pinnatifida spores. In the first experiment, spore establishment was significantly affected by sediment load (the effective dose required for a 40 % reduction in establishment ranged between 16 and 60 mg sediment l−1) and sediment regime (relative sedimentation occurring before spore settlement, ~3 times more sediment was required for 20 % reduction in spore establishment when sedimentation occurred after spore settlement). The second experiment demonstrated that the effects of sediment depended on sediment load (spore establishment was 2–4 times greater when sediment load was 200 mg l−1 relative to 400 mg l−1), variability in sedimentation (spore establishment was 1.36 times greater with variable than fixed sediment loads), repeated pulses of sedimentation (pulsed sedimentation decreased spore establishment by 59–91 % relative to a single sedimentation event) and timing of sedimentation relative to spore settlement (sedimentation before spore settlement decreased establishment by 51–95 % relative to sedimentation after spore settlement). These results have important implications for ecologists and resource managers attempting to predict the consequences of sedimentation, suggesting that it is not only important to consider sediment load, but also fine-scale temporal variability in sedimentation relative to key life-history events of the impacted organisms.

Although sea urchins play a central role in determining the structure and functioning of macroalg... more Although sea urchins play a central role in determining the structure and functioning of macroalgal communities in many parts of the world, past research in southern Chile has failed to identify strong effects of urchin grazing, despite the prevalence of coralline-dominated communities and abundant urchins, which indicate a likely structuring role for urchins. Here, we conducted experimental removals of the most common urchin, the green sea urchin Arbacia dufresnii, on a single bedrock wall in the Magellan Strait, Chile. We monitored the responses of invertebrate and macroalgal communities relative to a control wall 6 times over 64 wk. The structure of macroalgal communities on each wall remained similar until more than 40 wk after urchin removal, at which time the community structure diverged, with significantly more macroalgae present on the urchin removal wall. These changes coincided with the onset of early summer and were likely driven by greater settlement, recruitment and growth of algae in the absence of urchins. After 64 wk, the abundance of chitons, bryozoans, mussels and the small bivalve Hiatella solida was also significantly greater on the urchin removal wall. Herbivory by A. dufresnii on these high latitude rocky reefs appears to have a potential structuring effect on benthic assemblages, although further replicated field experiments are required to document where and when these effects may occur.

Sponges are important components of temperate rocky reefs whose abundance and diversity are influ... more Sponges are important components of temperate rocky reefs whose abundance and diversity are influenced by a range of biological and physical factors. In high light environments, sponges are generally less abundant and are often restricted to shaded microhabitats. However, this generalisation stems primarily from research conducted in the northern hemisphere, with comparatively little information from the southern hemisphere. The aim of the present study was to examine correlations between sponge abundance and assemblage composition and between algal abundance and environmental variables. We measured the distribution patterns of sponges relative to macroalgal abundance, physical factors (including depth, surface inclination, turbidity, rugosity and temperature) and the abundance of other phyletic groups at multiple sites in New Zealand. A negative correlation was found between sponge abundance and algal abundance, with surface inclination strongly correlating with the distribution patterns of both groups. Our results support the generalisation from previous studies in the northern hemisphere that sponge and algal abundance are negatively correlated.

Polar Biology

Journal of the Marine Biological Association of the United Kingdom, 2015

Experimental removals of the dominant canopy-forming kelp Ecklonia radiata were conducted at two ... more Experimental removals of the dominant canopy-forming kelp Ecklonia radiata were conducted at two sites on rocky walls
in New Zealand and monitored for approximately 1.5 years. We hypothesized that the removal of the E. radiata canopy
would affect the structure of subcanopy assemblages, such that there would be a reduction in sponge species richness and
abundance. Furthermore, we investigated the biological and physical (predictor) variables that best explained variability in
sponge assemblages after canopy removal. Canopy removal led to a community dominated by turf algae, which corresponded
with a decrease in sponge abundance and richness. Our results suggest that the Ecklonia canopy may positively
influence the presence of sponge species such as Crella incrustans; we propose that the canopy may allow its coexistence
with turf algae underneath the canopy by altering the light regime and other environmental factors, which may be detrimental
for some species. Our results highlight how any loss of canopy-forming species might have negative effects on
sponge assemblages, which could affect the energy flow and the overall biodiversity found in these habitats.