Pedro A. Quijón

Predation regulation of sedimentary faunal structure: potential effects of a fishery-induced switch in predators in a Newfoundland sub-Arctic fjord

The collapse of the cod fishery in Newfoundland has coincided with marked increases in abundances of snow crab, pandalid shrimp, and other crustaceans that prey on sedimentary infauna. A 3-year sampling program in Bonne Bay, Newfoundland indicates differences in composition and number of these predators in the two main arms of the fjord that coincide with strong differences in benthic community structure. To test whether predation pressure contributes to the observed patterns in sedimentary fauna, exclusion field experiments with full and partial cages were deployed in both arms at 30-m depth and sampled along with ambient sediments at 0-, 4-, and 8-week periods. Predation significantly influenced species composition, abundance and, in some cases, diversity. The most striking changes included increases in the polychaetes Phöloe tecta and Ophelina cylindricaudata in exclusions relative to controls, and concurrent declines in the polychaete Paradoneis lyra and the cumacean Lamphros fuscata. In laboratory experiments, fresh non-disturbed sediment cores from each experimental area were either protected or exposed to snow crab, the most abundant predator in the bay. A snow crab inclusion experiment was also carried out in the field, using cages similar to those used for exclusions. Despite differences in sedimentary faunas in the two arms, both types of experiments detected a predator effect that was very similar to that documented in exclusion experiments. Thus, despite differences in the scales associated with each type of manipulation, our results suggest that crab predation is a significant structuring force in Newfoundland sedimentary communities. Given the historical changes that have occurred in predator composition as a result of cod over-fishing, we hypothesize that broad-scale community changes may be taking place in North Atlantic benthic ecosystems.

Regional differences in foraging behaviour of invasive green crab (Carcinus maenas) populations in Atlantic Canada

Invasive green crab populations initially established in Canada within the Bay of Fundy, New Brunswick in the 1950s and were present in all five Atlantic provinces by 2007. Genetic evidence suggests that the Atlantic Canadian populations originated from two separate introductions with differences in time of establishment among regions and possible population-level behavioural differences. In this study, we examine intraspecific foraging behaviour among crabs from different populations, and interspecific foraging behaviour between genetically similar crabs and juvenile lobsters. Both sets of foraging experiments involved competition for a limited food source over a 1-h period. In intraspecific match-ups, recent invaders from Newfoundland (NL) were significantly superior foragers than long-established invaders from Nova Scotia (NS) and New Brunswick (NB) populations; however, we found no differences between NL and Prince Edward Island (PE) invaders. Crabs from PE were better competitors than those from NS and NB, but these differences were not significant. Interspecific competition experiments indicated that the feeding behaviour of recent invaders (NL) and genetically similar, but long-established invaders (NS), differed in the presence of juvenile lobsters. Our study documents striking behavioural differences among populations of green crab from a small geographic region, which may reflect a combination of both genetic differences and time since establishment. These differences may result in varying impacts on newly invaded habitats.

Polychaete assemblages of a sub-arctic Newfoundland fjord: habitat, distribution, and identification

This study explores the association of 24 polychaete species with sandy and muddy habitats located in a sub-arctic fjord, and across Atlantic Canada including Labrador, Newfoundland, and the Gulf of St. Lawrence. Key characters used to facilitate species identification are also summarized. Within Bonne Bay, distinctive polychaete assemblages were associated with specific sediment types and polychaete species richness and density were significant both predictors of corresponding total (infaunal) density and species richness. Polychaetes were denser and more diverse in sandy sediments, partly because sandy locales were associated with the outer portion of the bay, and therefore were closer to the more productive and diverse Gulf of St. Lawrence. In general, species that occupied both sediment types were more widely distributed within Bonne Bay and across the region. The biogeography of most species also suggests that the Bonne Bay fauna is transitional between Labrador and Acadian biogeographic provinces.

Light pollution reduces activity, food consumption and growth rates in a sandy beach invertebrate.

The continued growth of human activity and infrastructure has translated into a widespread increase in light pollution. Natural daylight and moonlight cycles play a fundamental role for many organisms and ecological processes, so an increase in light pollution may have profound effects on communities and ecosystem services. Studies assessing ecological light pollution (ELP) effects on sandy beach organisms have lagged behind the study of other sources of disturbance. Hence, we assessed the influence of this stressor on locomotor activity, foraging behavior, absorption efficiency and growth rate of adults of the talitrid amphipod Orchestoidea tuberculata. In the field, an artificial light system was assembled to assess the local influence of artificial light conditions on the amphipods locomotor activity and use of food patches in comparison to natural (ambient) conditions. Meanwhile in the laboratory, two experimental chambers were set to assess amphipod locomotor activity, consumption rates, absorption efficiency and growth under artificial light in comparison to natural light-dark cycles. Our results indicate that artificial light have significantly adverse effects on the activity patterns and foraging behavior of the amphipods, resulting on reduced consumption and growth rates. Given the steady increase in artificial light pollution here and elsewhere, sandy beach communities could be negatively affected, with unexpected consequences for the whole ecosystem.

Moulting synchrony in green crabs (Carcinus maenas) from Prince Edward Island, Canada

ABSTRACT The growth and spread of non-indigenous green crabs (Carcinus maenas) in Atlantic Canada is of concern to the sustainability of shellfish resources, particularly in areas recently invaded. Commercial green crab fishing has been initiated on Prince Edward Island to help control this species and provide a new resource for inshore fishermen. Developing a soft-shell crab product modelled after the Venetian ‘Moleche’ would provide an economic incentive beyond the existing hard-shell crab bait market. However, answers to questions such as the timing and characteristics of green crab moulting are required. A pilot study conducted in 2014–2015 collected seven groups of crabs and held them in individual compartments for 2–4 weeks to record moulting rates and physical characteristics. We found that a synchronized ‘moulting window’ occurs during July for male crabs. Field experiments in 2015 had an average moulting rate of 34%, with group-specific rates as high as 60%. The same cohort of crabs held in the laboratory had an average moulting rate of 48%, with group-specific rates as high as 75%. We observed a gradual increase in moulting rates from early to mid-July, after which all crabs caught had recently moulted, with evidence of new carapaces on all crabs. In 2015, the moulting window followed a 5°C increase in water temperature. Regarding morphology, the presence of a ‘halo’ on the episternites of the carapace was an indicator that a crab would soon moult. These promising results represent the first step in assessing the feasibility of a soft-shell, green crab industry.

Spatial linkages between decapod planktonic and benthic adult stages in a Newfoundland fjordic system

The relative importance of predatory decapod crustaceans in sedimentary communities depends on the spatial variability in their abundance and composition. At the scale of a fjord, such spatial patterns could be related to sill-mediated larval supply. This study examines larval and adult distributions of abundant predatory decapods at six representative sites in a sub-arctic Newfoundland fjord during three consecutive summers. Adult snow crab (Chionoecetes opilio) and toad crab (Hyas coarctatus, H. araneus) characterized outer areas of the fjord, whereas pandalid shrimp (Pandalus montagui) dominated inner areas, and rock crab (Cancer irroratus) showed only minor spatial differences. Multivariate analysis and nonparametric comparisons of larval abundance and composition suggest that the sill separating inner and outer areas of the fjord results in differences in larval supply that correspond to adult abundances for at least two of the species analyzed here: snow crab and pandalid shrimp. Although larval abundance was not related to adult distribution when all zoeal stages were considered, correspondence between larval and adult patterns emerged when only late stages (zoeae II) were included in the multivariate analyses. Nonparametric comparisons supported these results, indicating significant differences in larval abundance inside and outside the sill for corresponding species and stages. Our results suggest that larval supply may play a critical role in establishing adult spatial patterns at the scale of the entire fjord for some species, but a less relevant role at the finer scale represented by the sites and habitats located at each side of the sill.

Animal–sediment relationships in an Atlantic Canada marine protected area: Richness, composition and abundance in relation to sediment food indicators

Abstract Despite growing concern for biodiversity loss, many coastal areas remain unexplored and their species composition and ecology virtually unknown. This study addressed these issues for intertidal communities of one of the few Atlantic Canada marine protected areas (MPAs). A nested sampling design was used to assess patterns for infauna and indicators of sediment food supply from three main areas of the MPA and from three sites randomly selected within each area. Samples were collected using a 7 cm diameter cylinder (38.5 cm2) inserted 5 cm into the sediment. The data were used to document composition, richness and abundance and to assess their potential relationship with sediment food indicators (organic carbon, total carbon, total N, C : N ratio, and chlorophyll a in the sediment). Twenty-eight taxa, primarily deposit-feeding spionid and capitellid polychaetes as well as venerid clams, were the numerically dominant taxa in most areas and sites. Composition and abundance and the concentration of most sediment food indicators differed significantly among areas. Quadratic regression analyses identified several significant relationships (R 2≥0.54) between food indicators, primarily organic carbon, carbon and nitrogen contents and several faunistic variables. In general, increases in sediment food supply were correlated with an increase and a subsequent decrease in richness and overall abundance, as well as the abundance of polychaetes and deposit feeders. Food indicators clearly contributed to, but were not the only factors driving spatial variation in community structure. Further studies addressing the physical and biological factors structuring sedimentary communities in MPAs and other coastal areas are encouraged.

Revisiting recent history: records of occurrence and expansion of the European green crab across Prince Edward Island, Atlantic Canada

BackgroundLate in the 1990s, the non-indigenous European green crab (Carcinus maenas) colonized the shorelines of eastern Prince Edward Island, in Atlantic Canada. Due to concerns of further spread into productive shellfish habitats, an annual survey was conducted between 2000 and 2013 to detect a potential range expansion of this species. We compiled and analyzed that data and document green crab expansion using records of annual occurrence and relative density.MethodsSurveys were conducted during the fall season of each year by deploying baited traps at 29 sites along the island’s two main shorelines (north and south shores). These sites were selected based on areas deemed more likely to be invaded by the green crab. Raw data per site and date was transformed to catch per unit effort (CPUE) to estimate relative abundances.ResultsPopulations of this species showed an uneven westward expansion along the north and south shores. Expansion rates changed among years but, overall, crab abundance was higher and changes in abundance were faster along the south shore than the north shore of the island. The westward expansion continues until this day.ConclusionsBased on the information compiled we hypothesize that the dissimilarity in range expansion rate was related to the availability of suitable habitat to sustain large green crab populations along the south shore. We also discuss implications of this expansion for commercial shellfish and native coastal communities.

Living on a trophic subsidy: Algal quality drives an upper-shore herbivore’s consumption, preference and absorption but not growth rates

The transfer of seaweeds from subtidal bottoms to nearby intertidal rocky shores is a common but often overlooked phenomenon. Freshly detached seaweeds often represent critical trophic subsidies for herbivores living in upper-shore rocky intertidal areas, such as the marine snail Diloma nigerrima. This species relies on three species of seaweeds for food and displays feeding strategies to deal with a resource that is scarce and at times unpredictable. This study focused on the nutritional quality of freshly detached algae (Durvillaea antarctica, Lessonia spicata and Lessonia trabeculata) and measured Diloma nigerrima’s algal consumption rates in trials with and without choice. Absorption efficiency and growth of individual snails fed on each alga were also measured. Durvillaea antarctica had the highest nutritional quality and was the most consumed algae in both single and multiple-choice trials. Absorption efficiency was also highest for D. antarctica but growth rates of snails fed with this species were similar to those fed with the other algae. Combined, these results suggest that D. nigerrima has the ability to discriminate among seaweeds based on their nutritional quality. A potential increase in oxygen uptake when D. nigerrima is consuming the preferred food item is also proposed as a plausible hypothesis to explain the mismatch between snails’ preference and growth rate. These results aim to guide further studies on trophic subsidies and their role in coastal systems.

Diagnostic morphological characteristics of laboratory-reared Cancer oregonensis (Brachyura: Cancridae) with recommendations for identifying cancrid zoeae in the Salish Sea

Abstract Cancrid larvae are among the most abundant decapods in the meroplankton in the Northeast Pacific; however, their study remains problematic because of difficulty discriminating among larvae of sympatric congeners. We addressed this issue by providing morphological characteristics from laboratory-reared Cancer oregonensis zoeae that can be used to distinguish this species from published descriptions of zoeae of other species of Cancer found in the Salish Sea (C. magister, C. productus, C. gracilis, C. antennarius). The angle of lateral exospines projecting from the furca of the telson and the length of the exospines relative to the length of the furcal branches of C. oregonensis are smaller in comparison to all stages of C. magister and C. productus. The setal formula on the inner margin of the telson furca and the number of setae on the exopod of the second maxilliped also vary between certain stages of C. oregonensis, C. magister and C. productus. The carapace length of C. oregonensis becomes noticeably longer than that of C. antennarius and C. gracilis as zoeal stages progress. The ratio of the length of the posterolateral spines projecting from the third and fourth abdominal somite to the length of the subsequent abdominal somite is greater in C. oregonensis than in C. antennarius and C. gracilis, and may be especially useful for identification when size differences are less apparent at early stages. We also observed stage duration and mortality of zoeae reared at ~13°C, which were consistent with previous estimates reported for laboratory-reared cancrid larvae.