Pseudechinus magellanicus is an ecologically important and small sea urchin in coastal and nearshore habitats off southern South America. We provide the first growth assessment for the species using tag (calcein) and recapture procedures in central Patagonia (Argentina). The individual growth rate of P. magellanicus ranged 0.05–1.3 mm year−1. The Brody–Bertalanffy and Richards growth models provided asymptotic maximum diameters of 29.89 and 26.01 mm, respectively. Both models yielded low values for the growth constant (k), with 0.046 (Brody–Bertalanffy) and 0.062 (Richards). Maximum instantaneous growth rate was estimated at 1.36 mm year−1 for the Brody–Bertalanffy model, and 2.69 mm year−1 for the Richards model. Model selection (corrected Akaike information criterion) showed a slight better fit for the Brody–Bertalanffy growth model compared to the Richards model. A significant variability in growth was observed within the studied population, which can be attributed to genetic factors and micro-environmental effects. P. magellanicus displays a combination of slow growth and small body size, with the lowest recorded growth performance index (θ = 3.72) recorded so far in sea urchins. The species has a long lifespan, with the most common adult sizes estimated to range from 15 to 21 years according to the Brody–Bertalanffy model. Due to the broad geographic distribution and occupation of contrasting habitats, further studies are necessary to explore growth of P. magellanicus under different environmental conditions and/or along a bathymetric gradient.

Sea urchins have important effects on marine ecosystems such as rocky shores and coral reefs across the world. However, species diversity and molecular phylogeny of most echinoid taxa are poorly known in Iran. In this study, the phylogenetic relationships of one of the most abundant species of the genus Echinometra in the Persian Gulf were examined. Echinoids were collected from the intertidal zone of Qeshm Island and Lengeh Port on March and December 2017. Morphological criteria based on valid identification keys combined with molecular analysis of a fragment of the mitochondrial cytochrome c oxidase subunit I (COI) protein-coding gene were used to delineate Echinometra species. Our analyses showed that all specimens (N = 15) belong to Echinometra sp. EZ. Tree topologies indicated that our individuals from two sampling sites formed a distinct monophyletic clade with E. sp. EZ, demonstrating high support values. This is the first phylogenetic analysis of E. sp. EZ from Iran.

No-take marine reserves directly promote the recovery of predatory species, which can have negative indirect effects on prey populations in reserves. When harvesting also occurs on prey species there is potential conflict between the direct and indirect effects of protection, and reserves may not have conservation benefits for prey species. For example, sea urchins are fished in many regions, but may decline in reserves due to increased predation rates. To investigate this potential conflict, this paper compares density, size, biomass and reproductive potential of both a harvested and an unharvested urchin species between a long-term reserve and unprotected sites in California. Consistent with density-mediated indirect interactions, densities of the unharvested species were 3.4-times higher at unprotected sites compared to reserve sites. However, for the harvested species, densities were comparable between reserve and unprotected sites. Both species were consistently larger at reserve sites, and the biomass and reproductive potential of the harvested species was 4.8- and 7.0-times higher, respectively, than at unprotected sites. This is likely due to differences in size-selectivity between harvesting and predators, and potential compensatory effects of predators. While the generality of these effects needs to be tested, these results suggest mechanisms whereby reserves can benefit both predator and prey species.

Sedentary consumers play an important role on populations of prey and, hence, their patterns of abundance, distribution and coexistence on shores are important to evaluate their potential influence on ecosystem dynamics. Here, we aimed to describe their spatio-temporal distribution and abundance in relation to wave exposure in the intertidal rocky shores of the south-west Atlantic to provide a basis for further understanding of ecological processes in this system. The abundance and composition of the functional groups of sessile organisms and sedentary consumers were taken by sampling the intertidal of sheltered and moderately exposed shores during a period of one year. The sublittoral fringe of sheltered areas was dominated by macroalgae, while the low midlittoral was dominated by bare rock and barnacles. In contrast, filter-feeding animals prevailed at exposed shores, probably explaining the higher abundance of the predator Stramonita haemastoma at these locations. Limpets were more abundant at the midlittoral zone of all shores while sea urchins were exclusively found at the sublittoral fringe of moderately exposed shores, therefore, adding grazing pressure on these areas. The results showed patterns of coexistence, distribution and abundance of those organisms in this subtropical area, presumably as a result of wave action, competition and prey availability. It also brought insights on the influence of top-down and bottom-up processes in this area.

The 330 kDa fibrillar glycoprotein hyalin is a well known component of the sea urchin embryo extracellular hyaline layer. Only recently, the main component of hyalin, the hyalin repeat domain, has been identified in organisms as widely divergent as bacteria and humans using the GenBank database and therefore its possible function has garnered a great deal of interest. In the sea urchin, hyalin serves as an adhesive substrate in the developing embryo and we have recently shown that exogenously added purified hyalin from Strongylocentrotus purpuratus embryos blocks a model cellular interaction in these embryos, archenteron elongation/attachment to the blastocoel roof. It is important to demonstrate the generality of this result by observing if hyalin from one species of sea urchin blocks archenteron elongation/attachment in another species. Here we show in three repeated experiments, with 30 replicate samples for each condition, that the same concentration of S. purpuratus hyalin (57 μg/ml) that blocked the interaction in living S. purpuratus embryos blocked the same interaction in living Lytechinus pictus embryos. These results correspond with the known crossreactivity of antibody against S. purpuratus hyalin with L. pictus hyalin. We propose that hyalin–hyalin receptor binding may mediate this adhesive interaction. The use of a microplate assay that allows precise quantification of developmental effects should help facilitate identification of the function of hyalin in organisms as divergent as bacteria and humans.

An important principle of environmental science is that changes in single components of systems are likely to have consequences elsewhere in the same systems. In the sea, food web data are one of the few foundations for predicting such indirect effects, whether of fishery exploitation or following recovery in marine protected areas (MPAs). We review the available literature on one type of indirect interaction in benthic marine ecosystems, namely trophic cascades, which involve three or more trophic levels connected by predation. Because many indirect effects have been revealed through fishery exploitation, in some cases we include humans as trophic levels. Our purpose is to establish how widespread cascades might be, and infer how likely they are to affect the properties of communities following the implementation of MPAs or intensive resource exploitation. We review 39 documented cascades (eight of which include humans as a trophic level) from 21 locations around the world; all but two of the cascades are from shallow systems underlain by hard substrata (kelp forests, rocky subtidal, coral reefs and rocky intertidal). We argue that these systems are well represented because they are accessible and also amenable to the type of work that is necessary. Nineteen examples come from the central-eastern and north-eastern Pacific, while no well-substantiated benthic cascades have been reported from the NE, CE or SW Atlantic, the Southern Oceans, E Indian Ocean or NW Pacific. The absence of examples from those zones is probably due to lack of study. Sea urchins are very prominent in the subtidal examples, and gastropods, especially limpets, in the intertidal examples; we suggest that this may reflect their predation by fewer specialist predators than is the case with fishes, but also their conspicuousness to investigators. The variation in ecological resolution amongst studies, and in intensity of study amongst systems and regions, indicates that more cascades will likely be identified in due course. Broadening the concept of cascades to include pathogenic interactions would immediately increase the number of examples. The existing evidence is that cascade effects are to be expected when hard-substratum systems are subject to artisanal resource exploitation, but that the particular problems of macroalgal overgrowth on Caribbean reefs and the expansion of coralline barrens in the Mediterranean rocky-sublittoral will not be readily reversed in MPAs, probably because factors other than predation-based cascades have contributed to them in the first place. More cascade effects are likely to be found in the soft-substratum systems that are crucial to so many large-scale fisheries, when opportunities such as those of MPAs and fishing gradients become available for study of such systems, and the search is widened to less conspicuous focal organisms such as polychaetes and crustaceans.