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Bloodsworth K.H.,University of New England at Biddeford | Tilburg C.E.,University of New England at Biddeford | Yund P.O.,University of New England at Biddeford | Yund P.O.,Downeast Institute for Applied Marine Research and Education
Estuaries and Coasts | Year: 2015

Larvae of most coastal marine invertebrates develop through a series of pelagic stages in the inner shelf regions where they are subject to strong velocity fields, including buoyancy-driven flows from river plumes. Taxon-specific larval behavior can interact with flow fields to determine dispersal trajectories. In this study, we examined the hydrodynamic features of the Saco River plume (in the southwestern Gulf of Maine) from July to August and explored how larval behavior may alter the distribution of mytilid (i.e., Mytilus and Modiolus) bivalve larvae and three genera of brachyuran (Carcinus, Hemigrapsus, and Cancer) crab larvae in and around that plume. Hydrographic surveys (via conductivity-temperature-depth casts) and larval sampling (via plankton tows) were conducted to assess temporal and spatial variation in the horizontal and vertical distribution of larvae. The horizontal extent of the Saco River plume varied little during our study and was governed by both inertial and rotational effects. Late stage mytilid larvae were relatively homogeneously distributed in and out of the plume, while the distribution of brachyuran larvae varied among different locations, species, and larval stages. We conclude that mytilid larvae entered the plume through physical entrainment and/or upward swimming processes and could tolerate salinities associated with the plume (<25). By contrast, brachyuran larvae avoided the plume via downward swimming to avoid osmotic stress, or had perished prior to sampling. © 2015, Coastal and Estuarine Research Federation. Source


Beal B.F.,University of Maine at Machias | Protopopescu G.C.,Downeast Institute for Applied Marine Research and Education
Journal of Shellfish Research | Year: 2012

Historically, stock enhancement programs for American lobster, Homarus americanus, have a common theme: production and release of large numbers of stage IV or stage V individuals. However, these animals are difficult to mark, highly mobile when released on the bottom, and susceptible to a wide array of predators, and their claws have yet to develop bilateral asymmetry. Many of these attributes make it difficult to test the efficacy of hatch-and-release efforts. It is possible to hold postlarval lobsters individually in the laboratory or hatchery and provide food regularly for several months to release older, larger individuals (as with enhancement efforts in Europe with Homarus gammarus). However, the costs to do so compared with the value of commercial-size animals makes this practice cost prohibitive. Attempts to reduce costs of rearing early postlarvae to larger sizes in ocean-based nursery cages in eastern Maine for periods of longer than 1 y have resulted in variable survival (in general, <50%) and slow growth (doubling in carapace length (CL) from 4.28.9 mm). A series of field trials (2004 to 2010) examined methods to improve survival rates and enhance growth with the goal of producing animals large enough to apply a physical tag that can be seen easily by fishers and scientists interested in testing directly the efficacy of enhancement efforts. The effect of flow rates into and out of various types of containers (350 mL and 440 mL) holding individual, cultured stage IV lobsters was examined experimentally during a 309-day period from August 2004 to July 2005 in off-bottom, ocean-based nursery cages deployed in shallow (12 m) water near Great Wass Island, Beals, ME. Mean survival rate varied directly with flow as animals in containers with the greatest exchange of seawater demonstrated survival rates of ca. 90% compared with ca. 30% in containers allowing lower flow rates. Sediment deposition in the low-flow rate containers tended to be high, and was associated with significantly lower mean lobster survival. In a separate field trial in shallow water from August 2009 to October 2010 (419 days), lobster growth in submerged wooden trays was assessed using 5 different container sizes that ranged from 0.020.26 m 2 (ca. 1.521 L). Growth was best described by a sigmoidal function, with a strong linear component over container sizes between 0.02 m 2 and 0.13 m 2 (ca. 1.510 L), and no significant difference observed in mean CL of lobsters in the largest 2 container sizes. Final mean CL and mass (23.9 ± 1.4 mm and 10.7 ± 2.1 g, respectively, ±95% CI) of animals in the 2 largest containers was 57.4% and 349% greater, respectively, than animals in the smallest containers. Rearing cultured individuals of H. americanus to large sizes in ocean-based nursery cages may provide managers of stock enhancement programs with a more viable assessment tool than those used traditionally. Source


Grant
Agency: NSF | Branch: Standard Grant | Program: | Phase: | Award Amount: 175.92K | Year: 2012

Intellectual Merit
This project will test whether the southern range boundary of a northern blue mussel, Mytilus trossulus, is determined by limitations on the dispersal of larvae, or the physiological tolerance of larvae and/or juveniles. Mytilus trossulus and its sister species, M. edulis, co-occur throughout the Canadian maritime provinces and the northern Gulf of Maine. While the abundance of M. trossulus decreases abruptly south of the Canadian border, M. edulis ranges south to North Carolina. Work to date has demonstrated that: 1) Adult M. trossulus in northeastern Maine inhabit coastal sites, islands, and man-made structures that are within the colder water of the Eastern Maine Coastal Current (EMCC). 2) Drifters released in the EMCC rarely enter nearshore waters to the south, suggesting that across-shelf transport is extremely limited. 3) Larvae of the two species may differ slightly in thermal tolerance, and some evidence suggests that tolerance may also be affected by nutritional status. 4) Mytilus trossulus juveniles transplanted within the northeastern Maine region, but outside of the EMCC, have high survivorship, while transplants further to the southwest suffer high mortality. In combination, these results suggest that larval transport sets the proximate range boundary within northeastern Maine (on a scale of 10 km), but thermal tolerance would ultimately limit the distribution on a larger spatial scale (200 km).

This research project is designed to test this pair of hypotheses via a combination of field and lab experiments. Satellite drifters equipped with temperature loggers deployed in and out of the EMCC during the season of M. trossulus larval dispersal (mid-June to mid-August) will be used to quantify the physical flow fields and temperature regimes during larval dispersal. Drogues will allow us to assess whether larvae at different depths may experience different flow fields. Data from hydrographic surveys, combined with regular spatial and temporal sampling of mussel larvae and new settlers, will be used to assess possible associations between larval and post-settlement stages and different water masses. The physiological tolerance of new settlers will be assayed via transplants to sites in and out of the EMCC. Finally, laboratory growth and survival experiments will assay larval performance in different thermal and feeding regimes. The investigators will use molecular markers to identify the morphologically indistinguishable larvae and settlers of these sibling species.

Broader Impacts

This project will provide training for one MS and one PhD student, and several undergraduates. The PIs are at institutions that emphasize undergraduate and graduate research, and our project will provide numerous student opportunities for field and laboratory research in oceanography and benthic ecology. Such research opportunities are likely to attract a number of students who would otherwise pursue careers in biomedical research. The Gulf of Maine is home to a thriving Mytilis edulis aquaculture industry, and M. trossulus is a commercially inferior species - growers are concerned about its possible spread. Hence a better understanding of the factors determining the range boundary of this species will help growers avoid M. trossulus spat. Results will be disseminated to enhance communication with the Maine aquaculture community. All of the fieldwork will be conducted in a region of Maine facing great educational challenges; teachers from area schools will be recruited to assist with summer field and laboratory work.


Grant
Agency: NSF | Branch: Standard Grant | Program: | Phase: BIOLOGICAL OCEANOGRAPHY | Award Amount: 355.92K | Year: 2015

Rocky intertidal habitats in the Gulf of Maine (GoM) provide a model system to examine the structure and dynamics of natural communities. Throughout the Gulf of Maine, the same species are often found in these habitats but community structure, dynamics and productivity differ markedly among 3 distinct regions (southern, central and northern GoM). Past influential work, conducted primarily in the southern and central GoM, focused on the local processes driving intertidal community structure but produced very different conceptual models of how these communities are structured. This project examines whether regional differences in rocky shore community processes are driven by differences in recruitment that are shaped by regional variation in temperature and food availability and nearshore coastal oceanography. This project will improve the understanding of how large-scale environmental forces interact with local processes to control the distribution of species and the structure and dynamics of these communities. Understanding the interaction between processes operating at different scales is fundamentally important to developing more reliable models that can be used to predict community dynamics. In addition, data resulting from this project will have important implications for regional dynamics in commercially important species and for ecosystem and fisheries management within the GoM. Students and postdoctoral researchers will be supported and trained as part of this interdisciplinary project.

The overarching hypothesis of this project is that regional differences in community-level processes are driven by very different patterns of population connectivity and recruitment in a few key species and that these differences are ultimately caused by regional variation in temperature and food availability and mediated by physical larval transport processes. Hence, the project will test the following hypotheses with manipulative field experiments, field sampling, connectivity estimates, and integrative modeling: 1) Locally-dispersing species dominate dynamics in regions with a net export of planktonic larvae (Northern GoM), while species with planktonic larvae dominate the dynamics in regions with high settlement and extensive connectivity among populations (Southern GoM). 2) Settlement density of species with planktonic larvae increases from northern to southern regions in accord with regional variation in food availability. 3) Population connectivity varies greatly among regions, with regions differing in the degree to which they are self-seeded or serve as larval sources vs. sinks; self-seeding leads to relatively localized population dynamics in the middle portion of the GoM. 4) Patterns of population connectivity are driven by physical transport processes and can be represented by coupling basic larval behavior models with circulation models. At 18 different sites in the GoM across ~ 600 km, surveys will evaluate variation in recruitment, food availability and secondary productivity and experiments will assess community processes in wave-exposed and sheltered habitats. The project will use hydrographic, current profile, and larval vertical distribution surveys to collect data for coupled larval/circulation models. Population connectivity will be both modeled and empirically evaluated (for one species) using elemental fingerprinting. A spatially explicit metacommunity model will integrate across all project components and test the relative importance of regional and local processes in controlling community organization and dynamics.


Protopopescu G.C.,University of Maine at Machias | Protopopescu G.C.,Downeast Institute for Applied Marine Research and Education | Beal B.F.,University of Maine at Machias | Beal B.F.,Downeast Institute for Applied Marine Research and Education
Journal of Shellfish Research | Year: 2015

A critical aspect of blue mussel (Mytilus edulis L.) aquaculture is industry dependence on a highly variable supply of wild seed. The objective of this study was to investigate responses of cultured pediveligers of blue mussels to different types of rope collectors. The study consisted of two trials in which competent larvae (approximately 5,000 per experimental tank-400 L) were exposed to rope collectors (polyethylene and polypropylene) exhibiting diverse structural features such as long loops, short loops, long filaments, short filaments, and smooth (Trial I-four rope types; Trial II-five rope types). In Trial I, rope segments (3 cm long) were placed at two different levels in four culture tanks (top and bottom of water column). In Trial II, segments were placed in the middle of the water column in six culture tanks. After 5 days, rope collectors were removed from experimental tanks and the number of settled larvae on each segment was counted. Rope collectors with the highest structural complexity/greatest surface area (long loops) elicited the strongest settlement response (highest densities) of mussel larvae, whereas those with the lowest complexity/least surface area (smooth) elicited the weakest response. Position within tank (top versus bottom; Trial I) had no significant effect on settlement density. Hatchery-reared mussel seed could be a reliable alternative to wild seed, and ropes with complex features should be used as larval collectors as they enhance settlement density which, in turn, could reduce production costs. Source

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