Chester B. Zarnoch

Aquaculture Methods and Early Growth of Juvenile Horseshoe Crabs ( Limulus polyphemus )

Current knowledge of horseshoe crabs (HSC) has been derived, in large part, from field studies. Comprehending the biology and conservation of HSC could be facilitated and augmented by understanding and improving their culture methods. Although many researchers and even lay people are capable of getting animals to the early stages of development, very few are successful in getting them to survive for longer periods of time. The Aquatic Research and Environmental Assessment Center (AREAC) has been successful in rearing HSC in annual cohorts, some for more than 7 years. We have used indoor recirculating aquaculture systems (RAS) containing medium prepared with artificial sea salts. Animals have been given various diets, including both natural and specially formulated feeds. We have traced the earliest developmental stages through juvenile development in animals that were derived from eggs fertilized in the field and laboratory. This chapter will discuss the problems and successes of culturing adult and developing HSC in RAS, methods of fertilization, feed regimes, growth, and survivorship and observations on HSC development from egg to juvenile.

Effect of Eastern Oysters (Crassostrea virginica) and Seasonality on Nitrite Reductase Gene Abundance (nirS, nirK, nrfA) in an Urban Estuary

The influence of oysters on nitrogen (N) cycling has received increased research attention. Previous work focused on fluxes of N solutes and gases, but the effects on microbes responsible for N transformations are unknown. In May 2010, we deployed eastern oysters (Crassostrea virginica) in mesh cages above sand-filled boxes at four sites across a nutrient gradient in Jamaica Bay, New York City. In fall and winter, we used quantitative PCR to measure abundance of 16S rRNA and nitrite reductase genes for denitrification (nirS and nirK) and dissimilatory nitrate reduction to ammonium (nrfA) in sediment. We measured water column nutrients and chlorophyll a, sediment C:N and organic matter (OM), exchangeable ammonium (NH4+), ammonification, nitrification, and denitrification potential (DNP). Oysters did not affect gene abundance in fall, when we predicted that their influence would be strongest, or in winter. However, gene abundance was significantly different among sites and seasons. Factors which explained 16S rRNA, nirS, and nirK gene abundance included sediment OM, water column N, and chlorophyll a, similar to previous research. Abundance of nrfA was lower than that of nir genes and positively related to sediment C:N, suggesting OM lability may drive the balance between nir and nrfA. Finally, nirS and nirK abundance was unrelated to DNP, which is consistent with variable results from the literature. More studies that combine molecular techniques with N transformation rates in the context of oyster reefs are needed. Results will advance models which predict the ecosystem effects of reef conservation and restoration under variable environmental conditions.

Growth Performance of Walleye, Sander vitreus, in Recirculating Aquaculture Systems

Walleye, Sander vitreus, fingerlings were reared in two recirculating aquaculture systems (RAS) to compare growth performance at three stocking densities (11, 24, and 36 kg/m3). There was a negative relationship between increasing stocking density and growth calculated as percent body weight (BW) gain/day, total length (mm) gain/day, specific growth rate (SGR) of weight (%/day), and SGR of total length (%/day). Growth parameters were significantly reduced in the 36 kg/m3 treatment. Results suggest maintaining a tank density between 24 and 36 kg/m3 to achieve economic efficiency when rearing walleye fingerlings in RAS. In a long-term growth trial conducted in a third RAS, fingerlings were raised from 22 g to 180 g over 241 days while being fed 2.5%-7.5% body weight/day and cultured at 22°C. We estimate >810 days in culture would be needed for walleye to reach market size (567 g).

Contributions of freshwater mussels (Unionidae) to nutrient cycling in an urban river: filtration, recycling, storage, and removal

Consumers contribute to nutrient cycling in aquatic ecosystems by nutrient retention in tissues, metabolic transformations and excretion, and promoting microbial processes that remove nutrients (i.e., nitrogen (N) loss via denitrification). Freshwater mussels (Unionidae) form dense assemblages in rivers, and affect nutrient transformations through feeding, biodeposition, and bioturbation. However, the effects of Unionid mussels on N and phosphorus (P) retention are not commonly measured. We quantified rates of filtration, retention, and biodeposition of carbon (C), N, and P for two Unionid species: Lasmigona complanata and Pyganodon grandis. We used continuous-flow cores with 15N tracers to measure denitrification in sediments alone and with a single individual of each species. We conducted measurements in an urban river near Chicago, IL, USA that is a target for Unionid restoration. Both Unionid species showed high rates of P-specific feeding and retention, but low N-specific rates. This was in agreement with high N:P ratio in the water column. Each species significantly increased denitrification relative to sediment alone. 15N tracers suggested direct denitrification of nitrate increased denitrification, although enhanced coupled nitrification–denitrification likely also contributed to denitrification. Finally, denitrification rates with and without mussels were used to estimate the value of N loss under different scenarios for mussel restoration at the river scale. Overall, restored Unionid populations may enhance P retention in soft tissues and shells and N loss via denitrification. Ecosystem managers may find greater support for restoration of Unionid populations with careful calculations of their ecosystem role in nutrient retention and removal.

Development of Aquaculture Methods to Enhance Horseshoe Crab Populations: An Example from Delaware Bay, U.S.A.

The New Jersey Aquaculture Innovation Center (AIC) at Rutgers University has instituted a program to enhance the population of the American horseshoe crab Limulus polyphemus in the Delaware Bay Estuary (DBE) by using aquaculture at the earliest stages in its life history, when losses are greatest and production costs are minimal. Located on the Cape May Canal, the AIC pumps provide both raw and treated (sand-filtered, UV-sterilized) DBE water throughout the facility. Eggs of L. polyphemus were collected from local, sub-optimal nesting beaches impacted by coastal development and rising sea level, and hatched in jars normally used for trout eggs. A hatching system was built that uses recirculating treated seawater and a header tank to provide constant, independently controllable flow through 12 jars. An experiment performed using the hatching system tested the effects of egg stocking density and seawater flow rates on hatching success. The results showed highest hatching success at high egg densities with low flow rates. Hatchlings were reared in downweller silos in a raceway tank with flow-through, raw seawater. Half of the hatchlings were allowed to feed on organic matter in the incoming raw seawater while the others were given a supplement of Artemia nauplii. Statistically, there was no difference in growth or development between the treatments. After 10 weeks, most hatchlings were at the 3rd instar stage. This suggests that aquaculture of the early stages of L. polyphemus, utilizing natural estuarine DBE water, maximizes the impact to the future population by protecting eggs and early instars, the most vulnerable life stages, at minimal cost.

Nitrogen regulation by natural systems in “unnatural” landscapes: denitrification in ultra-urban coastal ecosystems

ABSTRACT Dense cities represent biogeochemical hot spots along the shoreline, concentrating fixed nitrogen that is subsequently discharged into adjacent coastal receiving waters. Thus, the ecosystem services provided by natural systems in highly urban environments can play a particularly important role in the global nitrogen cycle. In this paper, we review the recent literature on nitrogen regulation by temperate coastal ecosystems, with a focus on how the distinct physical and biogeochemical features of the urban landscape can affect the provision of this ecosystem service. We use Jamaica Bay, an ultra-urbanized coastal lagoon in the United States of America, as a demonstrative case study. Based on simple areal and tidal-based calculations, the natural systems of Jamaica Bay remove ~ 24% of the reactive nitrogen discharged by wastewater treatment plants. However, this estimate does not represent the dynamic nature of urban nitrogen cycling represented in the recent literature and highlights key research needs and opportunities. Our review reveals that ecosystem-facilitated denitrification may be significant in even the most densely urbanized coastal landscapes, but critical uncertainties currently limit incorporation of this ecosystem service in environmental management.

Eelgrass meadows, Zostera marina (L.), facilitate the ecosystem service of nitrogen removal during simulated nutrient pulses in Shinnecock Bay, New York, USA

Seagrass meadows are important sites of nitrogen (N) transformations in estuaries, however, the role of N loading in driving relative rates of N fixation and denitrification in seagrass habitats is unclear. The current study quantified N fluxes in eelgrass meadows (Zostera marina (L.)) and nearby unvegetated sand in trials representing in situ and N enriched conditions. Net N2 fluxes were low or negative under in situ conditions in both eelgrass and sand. Under N enriched conditions, denitrification was higher than N-fixation, and denitrification in eelgrass was significantly higher than sand. Denitrification of water column NO3- was more significant than coupled nitrification-denitrification in the eelgrass. Denitrification was likely supported by greater organic carbon and N within the eelgrass sediment compared to sand. Eelgrass meadows in Shinnecock Bay may facilitate the ecosystem service of N removal and retention during short-term nutrient pulses that can originate from groundwater discharge and stormwater runoff.

Ecology of Jamaica Bay: History, Status, and Resilience

Coastal estuaries are renowned for their ecological diversity and abundance (e.g., Beck et al., 2003; Bertness, 2006). The same qualities that attract a variety of species draw people to settle on their shores and even build cities. Over time, these biologically rich environments can either be overwhelmed by human activities or relieved if people take proactive steps to conserve and restore estuaries and their watersheds, making them more resilient to environmental and human-induced change. These are challenges we address in this chapter reviewing the history, current status of, and prospects for resilience of Jamaica Bay’s ecology.

Oysters in an Eastern Estuary

Photo 1. Eastern oysters (Crassostrea virginica) were deployed at three densities in mesh cages suspended above sand-filled boxes at four sites in Jamaica Bay, New York City. Controls consisted of boxes with empty cages attached. (A) All boxes (N = 20 per site) were attached to a trot line between two cinderblocks, and deployed subtidally. Boxes were collected bimonthly by hand and walked to the shore. (B) We counted oyster mortality, replaced dead individuals, and sampled sediment for carbon and nitrogen dynamics