Don’t forget about the little guys: documenting diversity in the ocean

Documenting marine species

Species descriptions lay the foundation for so much of biology and are part of the reason that many of us fall in love with the natural world in the first place. As humans, we have a knack for recognizing patterns and an innate curiosity about other animals around us. Civilizations have been fascinated with the diversity of the oceans for millennia, with marine species described and recorded across cultures and societies, from ancient Greeks to native Hawaiians to English naturalists. Today, species descriptions are a science of their own, referred to as the field of taxonomy, and the International Code of Zoological Nomenclature sets the standard of species descriptions and naming. In our oceans, animals have been collected, documented, and described from coral reefs, kelp forests, the icy arctic, the middle of the oceans, and the deep sea with a total of 247, 686 described species at the time of writing.

But what determines how and when a species is discovered? A general principle is that animals that are easily observable are more likely to be documented. For example, animals that are really common, charismatic, or active are perhaps more noticeable to us, and are more likely to have been described already by a fellow curious scientist. In contrast, animals that are dull in color, inactive, or occur in a specific location are less likely to have been discovered or described. However, research by Dr. Craig McClain and fellow colleagues demonstrates that a species being “easily observable” may have changed over time.

 Discoveries become bigger, life becomes smaller

This research, led by Dr. Craig McClain, asks if species descriptions are biased towards larger animals. To do this, they collected data on all named species from the World Register of Marine Species database (WoRMS), including the species habitat, body size, and year of discovery. They ran an analysis to see if the discovery year is related to body size in a predictable manner.

These researchers found that there is indeed a relationship between species’ discovery year and body size, suggesting that smaller animals are more recently discovered than larger animals. The team suggests that technological advancements and historical context may explain these trends. After the invention of the microscope, smaller animals were discovered, and during periods when science wanes, such as war and social unrest, the discovery of small animals tends to pause. These historical factors alone do not describe the pattern fully and suggest that humans have a general bias towards larger animals as well. As an anecdote for the origin of new small species, a whole new phylum (the most general rank of animals), was discovered only in 1995, 100-200 years after many other phyla where named. This phyla in question, Cycliphora, is only 0.5 mm big, lives only in the mouth of lobsters, and contains only three species.

 The impacts of biodiversity are not small

The ocean is the largest habitat on Earth and houses the most biodiversity.  Scientists have already known that the marine species’ documentation lags behind descriptions of terrestrial diversity. In fact, scientists estimate that we are still far from describing all the ocean’s life; at minimum, 37% of species are still left to be discovered (Appellan et al. 2013), but some estimates suggest that 91% of species are undiscovered (Mora et al. 2011).

Having proper estimates of biodiversity is essential to protecting our oceans. Scientists and policymakers alike use the number of species as a metric of the value of an ecosystem as well as an indicator of its health under impacts or damage. Therefore, to protect our oceans, we need to know how many animals there are and how many animals we have left to discover. Our previous estimates of biodiversity loss are based on animals that are well-known and easily discoverable. This research by Dr. McClain and colleagues paints a better picture; the biodiversity of the ocean is likely much vaster than we imagined, and includes many much smaller animals. Further, this research emphasizes the need to inventory the ocean’s biodiversity, including the little guys, before major impacts and biodiversity loss occur globally.

Gabrielle Ellis

I am a  recent PhD grad in Biological Oceanography at the University of Hawaiʻi at Mānoa. I study the community ecology of abyssal animals across space, time, and habitat, and I ask questions often with regard to human impact, specifically deep-sea mining.