Is the threatened land crab Cardisoma guanhumi conquering human-dominated systems?

Land use changes are heralded as a major driver of biodiversity loss. However, recent findings show that cities, perhaps the most radical habitat transformation, sustain increasing numbers of threatened species. This emerging trend has been mostly chronicled for vertebrates from landlocked cities, although loss of biodiversity and rates or urbanization are higher in coastal marine systems. To advance our understanding on how threatened species may conquer human-dominated systems, we studied the threatened edible crab Cardisoma guanhumi and assessed how it is proliferating in croplands and urban systems at different spatial scales and whether populations show consequences of long-term exploitation. We gathered the data on crab populations covering the whole distribution range, including three countries reporting this as a threatened species. The abundance, distribution, and size structure of crab populations among different land uses at local scales were compared and published data for populations thriving in different habitats throughout their distribution range were compiled. We found that at local scale this species is able to thrive in natural and human-disturbed habitats, where food sources are heavily altered. At larger scales, the species showed no differences in abundance and size structure among natural and anthropogenic habitats. In areas near the southern distribution edge, crab populations were more abundant and composed of larger animals in urban areas and croplands than those in natural habitats, suggesting that human-disturbed systems are stepping stones to extend the geographic range. However, we found a long-term reduction in maximum body size, exacerbated by land use changes, that likely reflects exploitation regimes consistently targeting larger crabs. Despite its status as a threatened species, the long history of human exploitation combined with livestock farming practices may explain the proliferation of this crab in human-dominated systems, which emphasize the need to consider conservation in human-dominated systems.

A bioengineer in the city -the Darwinian fitness of fiddler crabs inhabiting plastic pollution hotspots.

Mangrove forests have been widely recognized as effective traps for plastic litter, which tends to accumulate in landward areas. In mangrove forests surrounding cities, plastic litter may increase up to two orders of magnitude. Therefore, crabs that process sediments for feeding and burrowing in landward areas are likely to be impacted by marine litter and other disturbances. As counterintuitive as it may seem, crabs are developing dense populations in urban mangroves from different countries, suggesting parallel adaptive processes related to the availability of anthropogenic food sources. To better understand this, we compared the loads of macroplastics within and between mangroves along an urban-rural-wild forest gradient in the Urabá Gulf, Colombian Caribbean. We then assessed if there is directional selection on crab phenotypes likely associated with human-provided food sources in urbanized forests. Finally, we evaluated the hypothesis that crabs in urban areas exhibit increased fecundity and survival - components of the Darwinian fitness - of female crabs in urban (versus wild) populations through three spawning seasons. Crabs in urban areas were larger (males), showed a healthier body condition (both sexes), and females had a larger reproductive lifespan than crabs in wild areas, strongly suggesting responses to the availability of predictable anthropogenic food subsidies in urban forests. Despite this, higher female fecundity was observed only during a spawning season. However, this short-lived increase in fecundity was offset by reduced survival among female crabs in urban forests, likely due to increased predation by birds, which appear to be emerging as dominant consumers in urban mangroves.

Inhabiting the technosphere: The encroachment of anthropogenic marine litter in Neotropical mangrove forests and its use as habitat by macrobenthic biota.

Coastal urbanization is leading to the accumulation of anthropogenic litter. Understanding the distribution and habitat use of litter by marine biota is important to predict how organisms will respond to anthropogenic changes. We assessed the density, distribution and composition of surface macro-litter (SML) in mangrove forests in Buenaventura (Colombia) and analysed how these microhabitats are used by marine biota. SML density ranged from 2 to 314 g m-2 (0.22 to 35.5 items m-2), implying that mangrove forests surrounding Buenaventura city are among the most polluted coastal areas in the World. Biological assemblages colonizing SML differed according to position on the forest and litter type. The encroachment of SML in mangrove forest enables a seemingly transient colonization of resident and immigrant biota from intertidal rocky shores and subtidal hard bottoms. The successful colonization of SML poses questions regarding the potential for plastics or their leaching chemicals to transfer through food webs.

Macrobenthic communities in a shallow normoxia to hypoxia gradient in the Humboldt upwelling ecosystem.

Hypoxia is one of the most important stressors affecting the health conditions of coastal ecosystems. In highly productive ecosystems such as the Humboldt Current ecosystem, the oxygen minimum zone is an important abiotic factor modulating the structure of benthic communities over the continental shelf. Herein, we study soft-bottom macrobenthic communities along a depth gradient-at 10, 20, 30 and 50 m-for two years to understand how hypoxia affects the structure of shallow communities at two sites in Mejillones Bay (23°S) in northern Chile. We test the hypothesis that, during months with shallow hypoxic zones, community structure will be much more dissimilar, thereby depicting a clear structural gradient with depth and correlated abiotic variables (e.g. organic matter, temperature and salinity). Likewise, during conditions of deeper hypoxic zones, communities will be similar among habitats as they could develop structure via succession in conditions with less stress. Throughout the sampling period (October 2015 to October 2017), the water column was hypoxic (from 2 to 0.5ml/l O2) most of the time, reaching shallow depths of 20 to 10 m. Only one episode of oxygenation was detected in June 2016, where normoxia (>2ml/l O2) reached down to 50 m. The structure of the communities depicted a clear pattern of increasing dissimilarity from shallow normoxic and deep hypoxic habitat. This pattern was persistent throughout time despite the occurrence of an oxygenation episode. Contrasting species abundance and biomass distribution explained the gradient in structure, arguably reflecting variable levels of hypoxia adaptation, i.e. few polychaetes such as Magelona physilia and Paraprionospio pinnata were only located in low oxygen habitats. The multivariable dispersion of community composition as a proxy of beta diversity decreased significantly with depth, suggesting loss of community structure and variability when transitioning from normoxic to hypoxic conditions. Our results show the presence of semi-permanent shallow hypoxia at Mejillones Bay, constraining diverse and more variable communities at a very shallow depth (10-20 m). These results must be considered in the context of the current decline of dissolved oxygen in most oceans and coastal regions and their impact on seabed biota.

Floating nurseries? Scyphozoan jellyfish, their food and their rich symbiotic fauna in a tropical estuary.

BACKGROUND: The anthropogenic modification of trophic pathways is seemingly prompting the increase of jellyfish populations at the expense of planktivorous fishes. However, gross generalizations are often made because the most basic aspects of trophic ecology and the diverse interactions of jellyfish with fishes remain poorly described. Here we inquire on the dynamics of food consumption of the medusoid stage of the scyphozoan jellyfish Stomolophus meleagris and characterize the traits and diversity of its symbiotic community. METHODS: S. meleagris and their associated fauna were sampled in surface waters between November 2015 and April 2017 in Málaga Bay, an estuarine system at the Colombian Pacific. Stomach contents of medusae were examined and changes in prey composition and abundance over time analysed using a multivariate approach. The associated fauna was identified and the relationship between the size of medusae and the size those organisms tested using least-square fitting procedures. RESULTS: The presence of S. meleagris medusa in surface waters was seasonal. The gut contents analysis revealed that algae, copepods and fish early life stages were the more abundant items, and PERMANOVA analysis showed that the diet differed within the seasons (P(perm) = 0.001) but not between seasons (P(perm) = 0.134). The majority of the collected medusae (50.4%) were associated with individuals of 11 symbiotic species, 95.3% of them fishes, 3.1% crustaceans and 1.6% molluscs. Therefore, this study reports 10 previously unknown associations. The bell diameter of S. meleagris was positively related to the body sizes of their symbionts. However, a stronger fit was observed when the size relationship between S. meleagris and the fish Hemicaranx zelotes was modelled. DISCUSSION: The occurrence of S. meleagris was highly seasonal, and the observed patterns of mean body size through the seasons suggested the arrival of adult medusae to the estuary from adjacent waters. The diet of S. meleagris in the study area showed differences with previous reports, chiefly because of the abundance of algae that are seemingly ingested but not digested. The low number of zooplanktonic items in gut contents suggest the contribution of alternative food sources not easily identifiable. The observed changes in the composition of food in the guts probably reflect seasonal changes in the availability of prey items. The regular pattern in the distribution of symbionts among medusae (a single symbiont per host) and the positive host-symbiont size relationship reflects antagonistic intraspecific and interspecific behaviour of the symbiont. This strongly suggest that medusa represent an "economically defendable resource" that potentially increases the survival and recruitment of the symbionts to the adult population. We argue that, if this outcome of the symbiotic association can be proven, scyphozoan jellyfish can be regarded as floating nurseries.

Breaking out of the comfort zone: El Niño-Southern Oscillation as a driver of trophic flows in a benthic consumer of the Humboldt Current ecosystem.

The trophic flow of a species is considered a characteristic trait reflecting its trophic position and function in the ecosystem and its interaction with the environment. However, climate patterns are changing and we ignore how patterns of trophic flow are being affected. In the Humboldt Current ecosystem, arguably one of the most productive marine systems, El Niño-Southern Oscillation is the main source of interannual and longer-term variability. To assess the effect of this variability on trophic flow we built a 16-year series of mass-specific somatic production rate (P/B) of the Peruvian scallop (Argopecten purpuratus), a species belonging to a former tropical fauna that thrived in this cold ecosystem. A strong increase of the P/B ratio of this species was observed during nutrient-poor, warmer water conditions typical of El Niño, owing to the massive recruitment of fast-growing juvenile scallops. Trophic ecology theory predicts that when primary production is nutrient limited, the trophic flow of organisms occupying low trophic levels should be constrained (bottom-up control). For former tropical fauna thriving in cold, productive upwelling coastal zones, a short time of low food conditions but warm waters during El Niño could be sufficient to waken their ancestral biological features and display massive proliferations.

The elusive life cycle of scyphozoan jellyfish--metagenesis revisited.

Massive proliferations of scyphozoan jellyfish considerably affect human industries and irreversibly change food webs. Efforts to understand the role of jellyfish in marine ecosystems are based on a life cycle model described 200 years ago. According to this paradigm the pelagic medusae is considered seasonal and alternates with the benthic polyp stage from which it derives. However, we provide evidence that a) the occurrence of several species of medusae is not restricted to a season in the year, they overwinter, b) polyp- and medusa generations are neither temporally nor spatially separated, and c) "metagenesis" which is defined as the alternation between sexual and asexual generations does not always occur. Hence we recommend additions to the current model and argue that the scyphozoan life cycle should be considered multi-modal, rather than metagenetic. The implications of these findings for jellyfish proliferations, including possible consequences and associated environmental drivers, are discussed.

Regulatory factors and structure of a component population of the spionid Polydora bioccipitalis infesting the surf clam Mesodesma donacium.

Spionidae, particularly polydorids, are common polychaete parasites of edible mollusks around the world. However, our understanding of the regulatory factors and population structure of these parasites is scant. In this study involving Polydora bioccipitalis and the surf clam Mesodesma donacium we evaluated (1) the environmental correlates of the prevalence and mean intensity of the infestation, (2) the relationship between the number of egg capsules and juvenile and adult parasites and the time elapsed since infestation, and (3) the spatial patterns of juveniles and adults within the host. Environmental factors showed no significant correlations with prevalence and mean intensity, suggesting that these factors do not act directly as regulators. Rather, storm surges seemingly induced clam stranding, which in turn affected both the prevalence and intensity of the infestation. The numbers of juveniles and egg capsules in blisters were significantly related to the time since infestation, suggesting mechanisms of use and expansion of the space within the host. Juvenile worms showed an aggregated distribution that was probably related to the episodic nature of infestation events, whereas adults exhibited uniform distributions that probably reflect territorial behavior and reproductive strategies.

Long-term parasitic association between the boring polychaete Polydora bioccipitalis and Mesodesma donacium.

Polydora and related genera are common pests for molluscs. Establishing differences between native species and recent invaders provides the basis for understanding the effect of parasites and has implications for resource management. P. biocipitalis has been reported as a recently introduced species to the Chilean-Peruvian coast, raising concerns about its threat to native bivalve species. In contrast, studies on the infestation of P. bioccipitalis on the surf clam Mesodesma donacium, one of the most important species for shellfisheries, suggest a long-term parasitic relationship. The present study analyses infested (i.e. blistered) fossil shells of M. donacium deposited during the Holocene and Middle Pleistocene epochs and critically reviews evidence supporting the hypothesis of the recent introduction of P. bioccipitalis to the Chilean-Peruvian coast. The blistering pattern seen on fossil and recent shells can be considered species-specific for the infestation of M. donacium by P. bioccipitalis. No evidence was actually found on vectors, introduction pathways or distribution range to support the status of P. bioccipitalis as an introduced species. On the contrary, our findings point to a long-term association, at least for several hundred thousand years, between M. donacium and P. bioccipitalis.

Dinamica poblacional de Donax dentifer (Veneroida: Donacidae) en Bahia Malaga, Pacifico colombiano durante el fenomeno El Nino 1997/1998 / Population dynamics of Donax dentifer (Veneroida: Donacidae) in Bay of Bahía Málaga, Colombian Pacific

Donax dentifer is a dominant member of the sandy beach communities of the Colombian Pacific coast. A population of this bivalve was monthly sampled in Playa Chucheros at the Bay of Málaga, Colombian Pacific, between August 1997 and July 1998, during the "El Niño 1997/1998" phenomenon. Quantitative samples were taken in perpendicular and parallel to the coastal line transects to determine the population density and a length-frequency distribution. Qualitative samples were taken to study the reproduction and monthly length weight relationship. Sea surface temperature, dissolved oxygen, salinity and pH in the water was monthly registered in the sampling station. Additionally, a tagging-recapture experiment was performed to growth estimations. Results indicate a continuous reproduction cycle with two annual spawning seasons in December and March...

[Population dynamics of Donax dentifer (Veneroida: Donacidae) in Bay of Bahía Málaga, Colombian Pacific during the "El Niño" 1997/1998]. / Dinámica poblacional de Donax dentifer (Veneroida: Donacidae) en Bahía Málaga, Pacífico colombiano durante el fenómeno "El Niño" 1997/1998.

Donax dentifer is a dominant member of the sandy beach communities of the Colombian Pacific coast. A population of this bivalve was monthly sampled in Playa Chucheros at the Bay of Málaga, Colombian Pacific, between August 1997 and July 1998, during the "El Niño 1997/1998" phenomenon. Quantitative samples were taken in perpendicular and parallel to the coastal line transects to determine the population density and a length-frequency distribution. Qualitative samples were taken to study the reproduction and monthly length weight relationship. Sea surface temperature, dissolved oxygen, salinity and pH in the water was monthly registered in the sampling station. Additionally, a tagging-recapture experiment was performed to growth estimations. Results indicate a continuous reproduction cycle with two annual spawning seasons in December and March. The growth parameters of the non-oscillating von Bertalanffy growth function were K = 0.62 yr-1 and L infinity = 29.3 mm. Mortality (Z) was higher (2.65 yr-1) for small individuals (between 2 mm and 5 mm) while a lower Z value (1.71 yr-1) were obtained for larger ones (between 19 mm and 25 mm). An annual mean biomass value of B = 1.229 g ash-free dry weight m-2 and an annual somatic production of Psom = 1.215 g ash-free dry weight m-2 were estimated, which correspond to a Psom/B value of 0.988. Population density increased in November and April, but any population density pattern related with "El Niño" was evident. Low body weight during November-December seems to show a relation between reproductive cycle in D. dentifer and El Niño 97/98 event. The fluctuation in dissolved oxygen show a high correlation with parameters of the reproductive cycle, which could be related to assimilation process and body weight cycle. Growth in D. dentifer in the Colombian Pacific coast was faster than other Donax species, as can be expected for tropical bivalves mollusks in comparison whit high latitude bivalves. The mortality pattern suggest that the population was selectively affected by El Niño 97/98, due to smaller individuals are living in the lowest areas of the beach, where they are exposed to abnormal seawater conditions for a longer time. Individual and population production was higher for medium-size animals than each for small-size ones, which were the most abundant in the population.