How much do the methods we use matter when monitoring the tiny critters that call the beach home?
Sandy beaches can look like deserts, but they are not. Many resident species, such as semiterrestrial crustaceans (talitrid amphipods: sand-hoppers and beach-hoppers), burrowing isopods, scavenging insects and even beach-specialized spiders spend their whole lives there, and each beach is likely hosting it's own populations, perfectly tuned to local events (it's a matter of survival!) like seasons, tides, and the arrival of wrack (like seaweed). So how do we get information about the little critters that call a beach home? By collecting them of course! But what’s the best way to do this? We find that both common methods give us the same answer, and so can be compared when monitoring beach biodiversity.
Walking around and hoping to find tiny beach inhabitants is not the best option. To study biodiversity on beaches there are typically only two collection methods available: placing little traps, or sieving the sand. Both methods are being used with same aim: getting biodiversity data (in this case, how many species, and how many individuals per species are at a given place). But they are quite different methods. Traps imply that the animals are walking around the surface, and sand sieving implies that the animals are burrowing in the sand. Will these methods tell us the same things at the end of the study?
To answer the question, we tried both methods on five beaches in NSW and found that trapping and sieving work equally well in providing biodiversity estimates.This was nice, as it’s not always possible to use both methods. For example, on beaches with coarse sand the sieve will not separate the animals from the substrate, and on beaches with lots of people, pitfall traps may end up smashed or taken away. So there were, and there will be more, results based on the two different methods. But because they are comparable, we can compare the results. This is, again, based on survival skills of the little citters: most of them are active at night time, walking around, and spend the hottest part of the day burrowed in the sand.
We also found that every single beach had a unique fauna. Some species were found only on some beaches and not on others. So, even though the worldwide picture is important, the local dimension matters too. And losing little pieces of biodiversity such as the ones hosted by single beaches, means that we may never get that piece of life back again.
A particular group of animals, the talitrids, told us something more. They are distributed worldwide, as a consequence of very successful adaptations to life on beaches and are realtively well-studied. During this study we discovered a large difference between two groups of talitrids, those inhabiting cast wrack (beach-hoppers), and in those inhabiting sand (sand-hoppers). We could not find any sand-hoppers in places with lots of humans trampling the sand, while beach-hoppers were more evenly found across the beaches of NSW, as long as wrack was present. So when sampling, be aware that not all hoppers are the same, and if considered as a general group, you may get back very confusing ideas about what's going on!
If this seems complicated ... it is! But life is complicated, and it's all needed to keep things in a dynamic equilibrium and get a nice, healthy beach. Continuous monitoring on beaches allows us to detect risky conditions and act in a timely manner. Feel free to choose your collection method: they are both easy and give back valuable information.
Dr Lucia Fanini
Hellenic Centre for Marine Research, Institute of Marine Biology, Biotechnology and Aquaculture (IMBBC)
Dr Jim K. Lowry
Senior Fellow, AMRI
Fanini, L., & Lowry, J. K. (2016). Comparing methods used in estimating biodiversity on sandy beaches: Pitfall vs. quadrat sampling. Ecological Indicators, 60, 358-366.