Hungry for the Fruit of the Sea: Missing Shrimp

Glass shrimp ('opae) have been present in the fishpond since I started working here. These little shrimp, which typically measure < 3 cm in length, are important nutrient shunts because they consume microalgae and detritus, grow rapidly, and are a food source for fish and invertebrates. Glass 'opae are so small that you have to dissect a lot of them in order to get enough tissue for a single stable isotope sample, and dissection requires a tiny scalpel and many hours at the microscope. In the fishpond, you can see them grazing in the shallows, and when we used dip nets or seines in the past, the nets came up covered in tiny shrimp-- so many that obtaining the 50-100 shrimp needed for a complete muscle tissue sample was not a difficult task. This past weekend, there were barely any. We used seines and dip nets at four sites across the pond, and the most shrimp we got at a single site was...twelve. This may be a result of heavy rains (salinity patterns in the water can change species distributions), or other changes in water quality. There may also be some seasonality (=change over the seasons) in shrimp populations in the pond. Seasonality in the abundance of certain species in the pond will surely affect the diets of fish and invertebrates, so it's something I'll need to investigate more in my field work.