Sea Urchin Abundance Research Articles

Abundance, size and biomass of long-spined sea urchins (Centrostephanus rodgersii) and red sea urchins (Heliocidaris tuberculata) in New South Wales, Australia

Context Detailed demographic information for the commercially harvested long-spined sea urchins (Centrostephanus rodgersii) and red sea urchins (Heliocidaris tuberculata) on nearshore reefs of New South Wales is unavailable. Aims This is the first detailed study of abundances and sizes of these sea urchin species on shallow reefs of New South Wales where the fishery operates. Methods Divers counted sea urchins and measured their sizes in transects in the nearshore mosaic habitat and in extensive barrens habitat at 51 sites along ~800 km of coast. Key results Centrostephanus was found at most sites in both habitats, whereas Heliocidaris was found at lower densities and at fewer sites. Heliocidaris was rare in the far south and in barrens habitat. Centrostephanus was, on average, smaller in barrens habitat than in the nearshore mosaic habitat, and size structures shifted towards smaller individuals from north to south. Conclusions Centrostephanus occurred at higher densities than did Heliocidaris and had a broader distribution along the coast and across the nearshore reefs where the fishery operates. Implications This study provides a historical baseline for these commercially and ecologically important species. The small biomass of Heliocidaris (~3% that of Centrostephanus) and its restricted distribution suggest it is vulnerable to overfishing.

Spatial structure and potential processes linking fish and benthic communities in a protected reef ecosystem in SE Brazil

Top-down and bottom-up processes can mediate the structuring of biological communities. Several studies have provided separate support for those processes in pelagic and benthic compartments of reef systems but studies focusing on whole-reef processes are less common. Here, we sampled 3 ‘reef compartments’ in the Alcatrazes Archipelago in Southeastern Brazil: benthic cover of colonial organisms, solitary organisms, and reef fish (i.e. pelagic) to identify the groups responsible for spatial community structure among reefs. A dynamic mosaic structure best defines the assemblages of each compartment, with substantial changes observed among sites over 2 consecutive years and at 2 depth strata, separated by a sharp thermocline. Changes in benthic cover of colonial organisms are largely due to the extent of the blooming of Sargassum canopies, algal turfs, and the zoanthid Palythoa caribaeorum. Solitary organisms show a consistent monotonic change in the abundance of sea urchins, ascidians, and snails. Fish assemblage structure differed among reefs; however, we observed that large invertivore fish tended to concentrate in warmer water above the thermocline and small fish of different feeding habits were found in deeper and colder water in all reefs. We observed a potential strong link between the reefscape and solitary organisms, with a negative relationship between the abundance of urchins and the cover of Sargassum spp. suggesting top-down control. A second link is indicated by a positive relationship between low-lying cover composed of articulated turf and P. caribaeorum and larger invertivorous fish, suggesting bottom-up control through the provision of favorable foraging grounds.

Taxa-dependent temporal trends in the abundance and size of sea urchins in subtropical eastern Australia.

Subtropical reefs host a dynamic mix of tropical, subtropical, and temperate species that is changing due to shifts in the abundance and distribution of species in response to ocean warming. In these transitional communities, biogeographic affinity is expected to predict changes in species composition, with projected increases of tropical species and declines in cool-affinity temperate species. Understanding population dynamics of species along biogeographic transition zones is critical, especially for habitat engineers such as sea urchins that can facilitate ecosystem shifts through grazing. We investigated the population dynamics of sea urchins on coral-associated subtropical reefs at 7 sites in eastern Australia (28.196° S to 30.95° S) over 9 years (2010-2019), a period impacted by warming and heatwaves. Specifically, we investigated the density and population size structure of taxa with temperate (Centrostephanus rodgersii, Phyllacanthus parvispinus), subtropical (Tripneustes australiae) and tropical (Diadema spp.) affinities. Counter to expectation, biogeographic affinity did not explain shifts in species abundances in this region. Although we expected the abundance of tropical species to increase at their cold range boundaries, tropical Diadema species declined across all sites. The subtropical T. australiae also showed declines, while populations of the temperate C. rodgersii were remarkably stable throughout our study period. Our results show that temporal patterns of sea urchin populations in this region cannot be predicted by bio-geographic affinity alone and contribute critical information about the population dynamics of these important herbivores along this biogeographic transition zone.

“… the most delicious fish …”—toward a zooarchaeology of the green sea urchin, Strongylocentrotus droebachiensis, on the coastal Northeast of North America

Recent studies have underlined the importance of shellfish in Ancestral Wabanaki diets. Green sea urchin (Strongylocentrotus droebachiensis) remains are a substantial component of shellfish assemblages from some Ancestral Wabanaki habitation sites and are present in smaller amounts in many other archaeological sites on the coastal Northeast. We summarize extant knowledge of archaeological sea urchin remains in the Quoddy Region of New Brunswick and Maine, part of the traditional homeland of the Peskotomuhkatiyik (the Passamaquoddy people). We position this information in regional historical, ecological, and archaeological contexts. Our results suggest that sea urchins were harvested at specific points in the annual tidal cycle. We also suggest that changes in sea urchin abundance through time could reflect changes in local environments, perhaps partially associated with changing climates.

The behavior of sympatric sea urchin species across an ecosystem state gradient.

In temperate macroalgal forests, sea urchins are considered as a keystone species due to their grazing ability. Given their potential to shape benthic communities, we monitored the habitat use by three sympatric sea urchin species and compared their behaviors in a vegetated habitat (VH) and an adjacent isoyake habitat (IH). We monitored the environmental conditions and sea urchin density along deep and shallow transects of the VH and IH for over a year. The benthic rugosity at both sites were also surveyed. A mark-recapture experiment was conducted on the two most abundant sea urchins, Diadema setosum and Heliocidaris crassispina, to elucidate sea urchin movement patterns and group dynamics. We found that exposure to waves was highest at the VH while the IH was sheltered. The deep IH experienced the least amount of light due to high turbidity. Water temperature patterns were similar across sites. The VH benthic topography was more rugose compared to the smoother and silt-covered IH substate. Peak macroalgal bloom occurred three months earlier in IH, but macroalgae persisted longer at the shallow VH. Among the sympatric sea urchins, H. crassispina was most abundant at the shallow VH and was observed in pits and crevices. The most abundant across IH and in the deep VH was D. setosum, preferring either crevices or free-living, depending on hydrodynamic conditions. The least abundant species was D. savignyi, and most often observed in crevices. Small and medium sea urchins were most often observed at the IH site, whereas larger sea urchins were more likely observed at the VH. The mark-recapture study showed that D. setosum was found to displace further at the IH, and H. crassispina was more sedentary. Additionally, D. setosum was always observed in groups, whereas H. crassispina was always solitary. The behaviors of sympatric urchins, Diadema savignyi, D. setosum and H. crassispina, differed in response to changes in the benthic environment and physical conditions. Sea urchin displacement increased when rugosity and wave action were low. Habitat preference shifted to crevices in seasons with high wave action. In general, the mark-recapture experiment showed that sea urchins displaced further at night.

Abundance and distribution of Echinometra lucunter (Echinodermata, Echinoidea) at a rocky platform on the central coast of Venezuela

ABSTRACT Echinometra lucunter is a common Caribbean sea urchin, which the abundance and distribution were evaluated along a rocky platform at Cepe beach, Venezuela. Two surveys were conducted along transects perpendicular and parallel to the coast, from the shore to the wave breaking zone (WB), using 1m2 quadrat method. In survey-1 the smaller sea urchins (<1.8 cm) occurred in the tide pool zone (TP) and medium and large dominated in the WB. The average density recorded in the WB and TP (140.2 and 272.7 ind/m2 respectively) are among the highest values reported in the Caribbean. The maximum density recorded was 562 ind/m2 in the TP and most of them were juveniles (<1.8 cm). In survey-2 sea urchins (³3.0 cm) density ranged from 1 to 156 ind/m2 and the overall average was 29.6 (± 32.4) ind/m2. The highest density occurred in the platform western sector (average 43.2 ±41.3 ind/m2). In the transects parallel to the coast the sea urchin's abundance gradually decreased from the WB (130 ±12 ind/m2) towards the coast (0.3 ±0.37 ind/m2). In conclusion, the E. lucunter densities recorded on the Cepe beach platform are the highest values reported in the Caribbean.

Sea urchins in the intertidal zone on Karanrang Island, Pangkep Regency; Density, abundance, community structure, and distribution patterns

Sea urchins were ecologically and economically important biota, but scientific information on sea urchins is still very minimal and there is no ongoing monitoring. The purpose of this study was to determine the density, abundance, community structure, and distribution patterns of sea urchins in the intertidal zone of Karanrang Island, Pangkep Regency. The research in June-July 2022 was carried out at high and low tide using three transects measuring 1 x 1 m consisting of four plots measuring 50 x 50 cm. Determination of stations based on information from local residents to get observation stations based on tidal conditions. The results showed that three species of sea urchins from two families were found, namely Diadema setosum, Echinothrix calamaris, and Tripneustes gratilla. The species of D. setosum was found to be very abundant (97.3-97.6%) and tended to be more abundant during high tide than during low tide. The index of diversity and uniformity of porcupine species is low (H' = 0.130-0.142 and E = 0.118-0.129). The species dominance index was in the range of 0.946-0.953 indicating high dominance of D. setosum. Spatially, D. setosum had a uniform distribution pattern, whereas E. calamaris and T. gratilla were distributed in clusters. Further spatial and temporal research is needed to comprehensively determinant the conditions of the sea urchin population on Karanrang Island, Pangkep Regency.

Effect of Season and Increased Temperature on Survival, Roe Enhancement, and Reproductive Cycle of the Green Sea Urchin (Strongylocentrotus droebachiensis) Collected from Four Relatively Close Sites in Northern Norway

A series of three trials were conducted in the North of Norway at different times of the year. The trials consisted of harvesting sea urchins from four sites, situated within 5 km of each other and then holding them in land-based enhancement facilities. They were held at ambient seawater temperatures as well as ambient plus 3.0°C. Samples were taken from the wild at the time of collection and at the end of the enhancement period as well as from the enhanced sea urchins from each site. Results showed that utilising the sea urchins from a variety of sites, even from areas where there is an abundance of sea urchins (sea urchin barrens) and the Gonad Index (GI) is almost always low, is viable in terms of the final, post roe enhancement GI. The results of the study indicate that differences in initial and final GI and the increase in GI between the sites, despite the relatively close proximity, show site selection is most likely not as important as ease of harvesting and sea urchin availability and the positive environmental impact from removal of sea urchins and these are the factors that harvesting strategies should focus on. The study has shown that it is possible to have a relatively consistent roe enhancement from S. droebachiensis from the North of Norway regardless of seasonality (time of year), site selection, and initial GI. Relatively small changes (up to 3°C) in the seawater temperature appear to have a slightly negative impact on enhancement efforts. However, this may vary when larger differences in temperature are experienced.

ASSOCIATION BETWEEN ECHINOID AND SEAGRASS COMMUNITY IN DERAWAN ISLAND WATERS

Sea urchins a biota that is often associated with seagrasses were often found in seagrass beds. The objectives of this research were to discover the condition of sea urchins and seagrass, such as diversity, uniformity, dominance in sea urchins, density, and cover on seagrass, and related to variables in this research. This research was conducted on Derawan Island. The research method that was used is a 5m x 5m (sea urchin) quadrate and 0.5m x 0.5m (seagrass) placed intentionally on 2 stations with a total of 30 quadrats. The results found 3 species of sea urchins and 4 species of seagrass. At station 1 abundance of sea urchins is 2.94 individual/m2 whereas at station 2 is 0,28 individual/m2. At station 1 seagrass density 117,33 shoot/m2 whereas station 2 is 120,13 shoot/m2. Seagrass cover at station 1 is 58,75% and at station 2 is 60,28%. The dominant sea urchin species is Diadema setosum with the following diversity values H'=0,36, E=0,3, and C=0.81. There was no significant difference between variables at each station except temperature (0.020&lt;0.05) and DO (0.027&lt;0.05). Variables that were correlated with sea urchins in the seagrass ecosystem are nitrate, salinity, phosphate, temperature, and pH. The association with seagrasses in Derawan Island is positive.

Reference Genome of the California Sheephead, Semicossyphus pulcher (Labridae, Perciformes), A Keystone Fish Predator in Kelp Forest Ecosystems.

Keystone species are known to play a critical role in kelp forest health, including the well-known killer whales, sea otter, sea urchin, kelp trophic cascade in the Aleutian Islands, Alaska, USA. In California, a major player in the regulation of sea urchin abundance, and in turn, the health of kelp forests ecosystems, is a large wrasse, the California Sheephead, Semicossyphus pulcher. We present a reference genome for this ecologically important species that will serve as a key resource for future conservation research of California's inshore marine environment utilizing genomic tools to address changes in life-history traits, dispersal, range shifts, and ecological interactions among members of the kelp forest ecological assemblages. Our genome assembly of S. pulcher has a total length of 0.794 Gb, which is similar to many other marine fishes. The assembly is largely contiguous (N50 = 31.9 Mb) and nearly complete (BUSCO single-copy core gene content = 98.1%). Within the context of the California Conservation Genomics Project (CCGP), the genome of S. pulcher will be used as an important reference resource for ongoing whole genome resequencing efforts of the species.

Sea Urchen (Echinoidea) Diversity in the Coastal Area at Mawasangka District, Central Buton Regency

Sea urchins are marine invertebrates that are grouped in the Echinoidea class and Echinodermataphylum. Mawasangka is a district that has a large coastal area with a fairly good seagrass and coral reef ecosystem that plays an important role in the life cycle process of marine organisms, for instant as a habitat and food source for sea urchins. However, until now, information about the diversity of sea urchins in the coastal areas in Mawasangka District has not been reported. Thus, this research is very important. This research began with a location survey, field observation, and sampling. Supporting data such as temperature, pH, brightness, depth and salinity were also measured. The results showed that the number of species in 3 research locations in the coastal area of Mawasangka District was 5 species, consisting of 3 species from the genus Diadema, namely Diadema cytosum, Diadema antillarium, and Diadema savignyi, and 2 species from the Echinotrix genus, namely Echinothrix calamaris and Echinothrix diadema. The highest number of species diversity was found on the Pasi Kobungi beach. This happened because the habitat and environmental conditions at Pasi Kobungi Beach were very compatible for 5 species found. The species with the greatest abundance was sea urchins from the species of Diadema cytosum. It was found out that the coral reef substrate and seagrass in three research locations were important habitats for the growth of Diadema setosum and were easy to adapt to the environment. Due to the abundance of sea urchins from the Diadema cytosum species as well as many benefits of it for the environment, it can be concluded that the condition of the coastal area of Mawasangka District is still classified as healthy and well preserved.

Sea urchin harvest inside marine protected areas: an opportunity to investigate the effects of exploitation where trophic upgrading is achieved.

BackgroundMarine protected areas (MPAs) usually have both positive effects of protection for the fisheries’ target species and indirect negative effects for sea urchins. Moreover, often in MPAs sea urchin human harvest is restricted, but allowed. This study is aimed at estimating the effect of human harvest of the sea urchin Paracentrotus lividus within MPAs, where fish exploitation is restricted and its density is already controlled by a higher natural predation risk. The prediction we formulated was that the lowest densities of commercial sea urchins would be found where human harvest is allowed and where the harvest is restricted, compared to where the harvest is forbidden.MethodsAt this aim, a collaborative database gained across five MPAs in Sardinia (Western Mediterranean, Italy) and areas outside was gathered collecting sea urchin abundance and size data in a total of 106 sites at different degrees of sea urchin exploitation: no, restricted and unrestricted harvest sites (NH, RH and UH, respectively). Furthermore, as estimates made in past monitoring efforts (since 2005) were available for 75 of the sampled sites, for each of the different levels of exploitation, the rate of variation in the total sea urchin density was also estimated.ResultsResults have highlighted that the lowest sea urchin total and commercial density was found in RH sites, likely for the cumulative effects of human harvest and natural predation. The overall rate of change in sea urchin density over time indicates that only NH conditions promoted the increase of sea urchin abundance and that current local management of the MPAs has driven towards an important regression of populations, by allowing the harvest. Overall, results suggest that complex mechanisms, including synergistic effects between natural biotic interactions and human pressures, may occur on sea urchin populations and the assessment of MPA effects on P. lividus populations would be crucial to guide management decisions on regulating harvest permits. Overall, the need to ban sea urchin harvest in the MPAs to avoid extreme reductions is encouraged, as inside the MPAs sea urchin populations are likely under natural predation pressures for the trophic upgrading.

Abundance and Distribution Patterns of Sea Urchins (Echinoidea) at Lakey Beach, Hu'u District, Dompu Regency

Sea urchins are marine biota that have many benefits for life, so there is a need for information about the existence of sea urchins. The existence of sea urchins in marine ecosystems has a significant influence on the ecological balance, one of which is for coral reefs, because sea urchins are one of the control of macroalgae populations. The purpose of this study was to determine the species abundance, diversity index, dominance index and distribution pattern of sea urchins (Echinoidea) at Lakey Beach, Hu'u District, Dompu Regency. This type of research is descriptive exploratory using purposive sampling method (chosen method) in determining the three research stations. The data obtained were analyzed using the species formula, the Shanon Wienner diversity index, the Simpson dominance index, and the Morisita index. The results showed that the highest species on the Lakey Coast were Echinometra mathei with values of 0.60 Ind/m² and Echinometra viridis with values of 0.45 Ind/m². The diversity index of sea urchins at Lakey Beach is included in the moderate criteria with a species diversity index value of H'=1.03. The sea urchin dominance index in Lakey Beach is included in the low criteria with a species dominance index of 0.42. The distribution pattern of sea urchins on Lakey Beach includes two criteria, namely flocking and uniform. Types of sea urchins that belong to a grouped distribution pattern are Echinometra mathei and Echinometra viridis. While the types of sea urchins that have a uniform distribution pattern are Diadema setosum, Echinotrix calamaris (brown striped spines), Mespilia globulus, and Tripneustus gratilia. This research can be used as a reference and source of information to see the condition of the ecosystem in Lakey Beach, Hu'u District, Dompu Regency. So that the community and can preserve marine life such as sea urchins (Echinoidea) so that their lives can be maintained.

Correlation between Coral Reef Condition and the Diversity and Abundance of Fishes and Sea Urchins on an East African Coral Reef

Coral reefs are one of the most diverse marine ecosystems, providing numerous ecosystem services. This present study investigated the relationship between coral reef condition and the diversity and abundance of fishes, on a heavily fished East African coral reef at Gazi Bay, Kenya. Underwater visual censuses were conducted on thirty 50 × 5 m belt transects to assess the abundance and diversity of fishes. In parallel, a 25-m length of each of the same transects was recorded with photo-quadrats to assess coral community structure and benthic characteristics. For statistical analyses, multi-model inference based on the Akaike Information Criterion was used to evaluate the support for potential predictor variables of coral reef and fish diversity. We found that coral genus richness was negatively correlated with the abundance of macroalgae, whereas coral cover was positively correlated with both the abundance of herbivorous invertebrates (sea urchins) and with fish family richness. Similarly, fish family richness appeared mainly correlated with coral cover and invertebrate abundance, although no correlates of fish abundance could be identified. Coral and fish diversity were very low, but it appears that, contrary to some locations on the same coast, sea urchin abundance was not high enough to be having a negative influence on coral and fish assemblages. Due to increasing threats to coral reefs, it is important to understand the relationship among the components of the coral reef ecosystem on overfished reefs such as that at Gazi Bay.

Recurrent large‐scale sea urchin mass mortality and the establishment of a long‐lasting alternative macroalgae‐dominated community state

AbstractRelationships between sea urchins and noncrustose macroalgae are typically nonlinear, and an abrupt phase shift from a barren to a macroalgae‐dominated state and vice versa happens when the sea urchin abundance exceeds a critical threshold. Here, we have used two mass mortality events as a natural experiment to study progressive changes and dynamics between these stable states. In 2009–2010 and 2018, two mass mortalities decimated the populations of the sea urchin Diadema africanum in the Canary Islands (Eastern Subtropical Atlantic). In these islands, this sea urchin is a key‐herbivore controlling the growth of macroalgae, and sea urchin barrens have persisted for more 60 yr. Mass mortality events differed in intensity both in space and time, and two phase shifts from sea urchin barrens to macroalgal beds were detected in both when sea urchin density declined below a critical threshold of 4 indv. · m−2. The first mass mortality was greater in La Palma Island, consequently in this island a long‐lasting alternative state dominated by noncrustose macroalgae has been established. Subsequently, a recurrent mass mortality also favored the transition from the sea urchin barrens to noncrustose macroalgal beds in Tenerife Island. After mass mortalities, D. africanum populations were reduced by 94–98% in both islands. No signs of recovery of these populations have been identified after phase shifts; ecosystem feedbacks may be the cause of the low population density of D. africanum.

Intertidal estimates of sea urchin abundance reveal congruence in spatial structure for a guild of consumers.

We hypothesized congruence in the spatial structure of abundance data sampled across multiple scales for an ecological guild of consumers that exploit similar nutritional and habitat resources. We tested this hypothesis on the spatial organization of abundance of an herbivorous guild of sea urchins. We also examined whether the amount of local along‐shore rocky habitat can explain the observed spatial patterns of abundance. Standardized estimates of abundance of four intertidal sea urchins—Diadema cf. savignyi, Echinometra mathaei, Parechinus angulosus, and Stomopneustes variolaris—were determined by six observers at 105 sites across 2,850 km of coast of South Africa. For each species and observer, wavelet analysis was used on abundance estimates, after controlling for potential biases, to examine their spatial structure. The relationship between local sea urchin abundance and the amount of upstream and downstream rocky habitat, as defined by the prevailing ocean current, was also investigated. All species exhibited robust structure at scales of 75–220 km, despite variability among observers. Less robust structure in the abundances of three species was detected at larger scales of 430–898 km. Abundance estimates of sympatric populations of two species (D. cf. savignyi and E. mathaei) were positively correlated with the amount of rocky habitat upstream of the site, suggesting that upstream populations act as larval sources across a wide range of scales. No relationship between abundance and habitat size was found for P. angulosus or S. variolaris. Within the range of scales examined, we found robust congruence in spatial structure in abundance at the lower, but not the larger, range of scales for all four species. The relationship between abundance and upstream habitat availability in two species suggests that larval supply from upstream populations was probably the mechanism linking habitat size and abundance.

The abundance and distribution patterns of sea urchins in Botubarani waters, Tomini Bay, Indonesia

This study aims to determine the abundance and distribution patterns of sea urchins in Botubarani Waters, Kabila Bone District, Bone Bolango Regency. This research was conducted from July to August 2020. A total of three research stations were established, namely West Tamboa, Central Tamboa and East Tamboa. The abundance of sea urchins was calculated using a quadrant transect measuring 1 × 1 m, which was laid 25 m perpendicular to the coastline using a line transect. Sea urchin species found were identified in situ and the distribution pattern of sea urchins was calculated using the morista dispersion index. The results showed that there were 5 types of sea urchins in Botubarani Beach, namely Echinometra mathaei, Diadema setosum, Echinotrix calamaris, Echinotrix diadema and Tripneustes gratilla. The sea urchin type Echinometra mathaei is the species with the highest abundance in all research stations, namely 25 ind./m2 at Tamboa Barat station, 9 ind./m2 at Tamboa Tengah station and 7 ind./m2 at Tamboa Timur station. The distribution patterns of sea urchins found in Botubarani waters include clusters for Echinometra mathaei and uniform patterns for sea urchins Diadema setosum, Echinotrix calamaris, Echinotrix diadema and Tripneustes gratilla. ANOVA analysis results show that there is no significant difference between sea urchin abundance and water quality parameters in all research stations. This indicates that there is no difference in environmental conditions at the three sampling locations.

Depth-related plasticity in the diet composition of Pseudechinus magellanicus (Echinoidea, Temnopleuridae) in nearshore environments off central Patagonia, Argentina

Pseudechinus magellanicus is one of the most abundant sea urchins in southern South America, but many aspects of its feeding ecology in nearshore environments remain unknown. Here, we aimed to analyze the variability of the diet composition along a coastal depth gradient from intertidal tidepools to upper circalittoral zones and examine the relation between seaweed availability and the diet composition at intertidal tidepools. A total of 118 food items, including seaweeds and animal components, were identified. The diet composition showed a large variation between the different coastal habitats present along the depth gradient studied. In tidepools, articulate coralline seaweeds (Corallina spp.), mussel shell fragments and small crustaceans were frequent in the gut contents, suggesting that this species behaves like a general omnivore but can also act as a mussel bioeroder when consuming epizoic algae and microeuendolithic organisms. In intertidal tidepools, the species showed a negative preference toward typical species of late successional stages such as Dictyota dichotoma, Adenocystis utricularis, Codium fragile and Chondria macrocarpa. Sea urchins from kelp forests showed higher dietary diversity than those from intertidal and deeper subtidal habitats, but with prevalence of kelps. At upper circalittoral soft bottoms, diverse detrital items as benthic diatoms, cyanobacteria and drifted algae were observed in gut contents, usually associated with fine sediments, indicating that P. magellanicus captures drifted algae and behaves like a biofilm feeder. This trophic plasticity may allow this species to occupy contrasting habitats and may also contribute to explain its wide distribution in southern South America.

Urchin Searchin’: Red urchins and drift kelp found at 284 m in the mesophotic zone

Red sea urchins (Mesocentrotus franciscanus) are kelp-associated ecosystem engineers found in rocky habitats throughout the North Pacific from Baja California, Mexico, to Japan. Red sea urchins depend on kelp detritus, herein ‘drift’, for nutrition; in open coast locations (e.g., California) sea urchin abundance declines precipitously with depth outside the kelp forest owing to a lack of drift and habitat. In the Salish Sea, a region of the Northeast Pacific characterized by steep, glacier-carved rocky reefs, red sea urchins have been reported to 125 m depth. Considering the natural history of this species, we predicted red sea urchins could be found deeper than 125 m in areas with hard substrate and abundant drift. We paired submersible and scuba transects to search for deep red sea urchins and quantified availability of drift to sea urchins from the mesophotic (290 m) to macrophyte zones (90% of rocky shorelines in the Northeast Pacific from Baja California to Alaska, suggesting a major portion of the red sea urchin’s habitat, and natural history, remains to be explored.

Fjordic Lagoons of the Barents Sea as Models for Study of the Dynamics of Coastal Communities with Alien Red King Crab (Paralithodes camtschaticus, Decapoda, Lithodidae)

Benthic communities of the semi-isolated deep fjordic Linjalampi and Sisajarvi lagoons in the apex part of Ambarnaya Bay, Varanger fjord, Barents Sea, are affected by the limited water exchange and wave action in combination with other abiotic and biotic factors. Among the biotic factors, the presence of a numerous group of red king crab (Paralithodes camtschaticus) that naturalized in the southern part of the Barents Sea in the second half of the 20th century may play a particularly important role. The median density of juvenile and adult crabs in the lagoons (42.5–52 specimens/1000 m2 in most years of observation) is comparable to their density in the neighboring open parts of the Varanger fjord. A narrow and shallow strait connecting the lagoons with the sea may restrict crab migrations between these habitats. Thus, adult crabs are present in the lagoons in the seasons when they migrate from the coast to greater depths in their usual habitats. The food chains starting from phytoplankton and macrophytes to benthic predators, red king crabs, spider crabs (Hyas araneus), and hermit crabs (Pagurus pubescens) have been studied using stable isotope analysis. The trophic level of adult king crabs in the lagoons (2.88) is lower than that of both spider crabs (3.16–3.42) and those king crabs that occur in the open part of the coastal area (3.44). This indicates differences in the feeding habits of crabs in the lagoons and in the open coastal waters. The food chain kelp–sea urchins–red king crabs typical for the coastal zone in the Barents Sea is not expressed in the food web of the lagoons. The low abundance and distribution patterns of sea urchins may be due to their consumption by red king crabs over a long period. Although fjordic Linjalampi and Sisajarvi lagoons are full marine water bodies, they are similar to continental lakes in some characteristics. In particular, the conditions in the lagoons make them convenient models for the study of the long-term dynamics of communities and ecosystems.