Changes in nutritional value of Alaria esculenta during degradation with potential for shellfish production

Background/Question/Methods

Bivalves can consume detritus. However, little is known about spatial and temporal dynamics of detritus ingestion and utilization for growth. In particular, kelp is abundant on Maine coasts and sheds detrital particles while degrading potentially providing a nutritional supplement for nearby farmed shellfish. To detect the ingestion and utilization of detritus, one must understand how kelp changes during degradation. Stable isotopes (δ¹³C, δ¹⁵N) coupled with lipid and fatty acid profiles can be used to track the potential change in nutritional quality through degradation. In order to get a baseline for these isotope and lipid biomarkers, a lab experiment was performed using Alaria esculenta from the same source grown in a controlled environmental pool. Replicate kelp fronds were placed in 1-liter tumble cultures in a bath (10º C) for 5 weeks. Half of the cultures were held in darkness, the other on an 8 hour per day light cycle. The results of this experiment will determine whether stable isotope and lipid signatures of kelp change during degradation and provide a baseline for future studies aimed at detecting uptake of kelp detritus in farmed shellfish. This work may provide insight to optimal farm placement or lead to development of supplemental shellfish feeds.

Results/Conclusions

An unpaired, two-tail T-test with unequal variances showed that at α< 0.05, H_o is rejected showing that the mean δ¹³C of the light treatment is significantly higher than the mean of dark treatment. P-value obtained was 0.014. Therefore, the most significant result discovered so far is that Alaria organic matter composition does change when it degrades, offering a different isotopic δ¹³C signature in food web studies. It is well known that detritus plays an important role in nutrient flow within ecosystems, on average more primary production is processed by detrital pathways than conventional food webs. Since detritus forms from a diverse variety of sources (i.e. terrestrial plants, estuarine marsh grass, macroalgae and phytoplankton) it is important to know the nutritional quality of the primary producers forming the detritus. Detritus is a major food source for bivalves, and the shellfish industry in Maine is continuing to expand. By understanding how the isotopic signatures change during degradation, the most nutritious source of detritus can be tracked through an ecosystem and thus, farm placement can be optimized.