Verification of ageing methods for the burrowing shrimp, Neotrypaea californiensis, using extractable lipofuscin and gastric mill cuticular features

The burrowing shrimp Neotrypaea californiensis is an important ecosystem engineer that inhabits estuaries along the US Pacific Northwest coast. This species plays an important role in the estuarine ecosystem but negatively impacts oyster aquaculture through its burrowing activities. Development of population models for burrowing shrimp management requires more detailed life history information and accurate estimates of age. Ageing studies have been limited for crustaceans because it is generally believed that they do not retain structures with annual deposits commonly used to age other marine organisms, when they moult their exoskeletons. A mesocosm growth experiment and field surveys were combined to compare the performance of two ageing techniques, quantification of autofluorescent lipofuscin and gastric mill ossicular lamellae, for estimating age in N. californiensis. Animals of known age were grown in outdoor mesocosms and sampled regularly to correlate age metrics with body size and true age. Lipofuscin concentration increased with time across multiple cohorts at the rate of 1.430 ± 0.060 ng µg−1 year−1. Lamellae counts also increased with time (4.922 ± 0.337 lamellae year−1). While age estimates based on lipofuscin concentration and lamellae counts generally agreed, carapace size did not correlate to either age metric. Lamellae counts from field collections suggest they are added sequentially with age but the relationship can vary by location. When used together, the application of both techniques may provide robust estimates of crustacean age especially when size-based measurements are imprecise.

Denitrification and Nitrogen Fixation Dynamics in the Area Surrounding an Individual Ghost Shrimp (Neotrypaea californiensis) Burrow System

ABSTRACTBioturbated sediments are thought of as areas of increased denitrification or fixed-nitrogen (N) loss; however, recent studies have suggested that not all N may be lost from these environments, with some N returning to the system via microbial dinitrogen (N2) fixation. We investigated denitrification and N2fixation in an intertidal lagoon (Catalina Harbor, CA), an environment characterized by bioturbation by thalassinidean shrimp (Neotrypaea californiensis). Field studies were combined with detailed measurements of denitrification and N2fixation surrounding a single ghost shrimp burrow system in a narrow aquarium (15 cm by 20 cm by 5 cm). Simultaneous measurements of both activities were performed on samples taken within a 1.5-cm grid for a two-dimensional illustration of their intensity and distribution. These findings were then compared with rate measurements performed on bulk environmental sediment samples collected from the lagoon. Results for the aquarium indicated that both denitrification and N2fixation have a patchy distribution surrounding the burrow, with no clear correlation to each other, sediment depth, or distance from the burrow. Field denitrification rates were, on average, lower in a bioturbated region than in a seemingly nonbioturbated region; however, replicates showed very high variability. A comparison of denitrification field results with previously reported N2fixation rates from the same lagoon showed that in the nonbioturbated region, depth-integrated (10 cm) denitrification rates were higher than integrated N2fixation rates (∼9 to 50 times). In contrast, in the bioturbated sediments, depending on the year and bioturbation intensity, some (∼6.2%) to all of the N lost via denitrification might be accounted for via N2fixation.

Ecological periodic tables for nekton usage of four US Pacific Northwest estuarine habitats

We compared the species composition and abundance of the total nekton community, using the Bray–Curtis similarity coefficient, and mean total nekton, fish and crab species richness, abundance and biomass, and shrimp abundance across four intertidal habitats in a US Pacific Northwest estuary: (i) eelgrass ( Zostera marina ); (ii) burrowing mud shrimp ( Upogebia pugettensis ); (iii) burrowing ghost shrimp ( Neotrypaea californiensis ); and (iv) unvegetated sand. Field sampling was conducted during daytime high tides, and was quantitative, stratified-by-habitat, randomized, and estuary-wide. More than 10 000 nekton specimens belonging to 64 taxa were collected in 454 samples during 10 sampling periods, each approximately one-month-long (from June to November), over 3 years (1998–2000). Non-metric multidimensional scaling analyses revealed annually recurring across-habitat patterns in total nekton Bray–Curtis similarity. Two-way (habitat, year) analyses of variance revealed annually recurring across-habitat patterns on 10 indicators of nekton-habitat quality and preference. Total nekton species richness, abundance, and biomass were, respectively, on average, 8 ×, 25 ×, and 25× greater in eelgrass, 4 ×, 6 ×, and 5× greater in mud shrimp, and 2 ×, 3 ×, and 2× greater in ghost shrimp, than in sand habitat. Our findings validate the ecological relevance of our habitats to nekton, and suggest they can serve as elements in ecological periodic tables of nekton habitat usage.