Marine communities in the youngest fossil record

Using otoliths to describe changes in the reef fish community in Caribbean reefs

My contributions to this field began when I was a postdoc at the Smithsonian Tropical Research Institute (STRI) in 2017-2018. I have been focusing on reconstructing historical fish communities using otoliths in the sediments. To some extent, this is an extension of my previous studies on the sea bottom otoliths, nevertheless, I have shifted to answer in-depth ecological questions. I have started to apply paleontological data in answering conservational questions with a suite of ecological methods. The goal of the project is to determine how reef fish communities have changed from an ancient environment without human activity (mid-Holocene, as a baseline condition) to a degrading recent environment (modern, disturbed condition), and ultimately, how these can be applied to a larger marine ecosystem.

Very little is known about long-term changes in coral reef fish communities because quantitative historical data are rare and fish remains are considered near absent in reef sediments. The study demonstrates for the first time that unconsolidated reef sediments can yield diverse and abundant otolith assemblages and can be used to explore reef fish community dynamics over time and space. Here, more than 5400 otoliths from 169 modern (<50 years) and mid-Holocene (~7000 years) coral reef samples in Caribbean Panama and the Dominican Republic were extracted. With a specially-built reference collection, I was able to confidently assign over 4400 of the otoliths to one of 56 taxa (35 families). Modern otolith assemblages are significantly different from their mid-Holocene counterparts, probably reflecting changes in the cryptobenthic fish fauna driven by a decline in the structural complexity of coral reefs due to pervasive historical and contemporary human disturbances. 

Our findings that demonstrate otoliths in modern and fossil reef sediments can provide a powerful tool to explore ecological changes in reef fish communities over time and space have a high impact potential in conservation biology. READ THE PAPER 

The next step will be to explore the shifts of ecological functioning  between the mid-Holocene and modern otolith assemblages using size frequency distributions and isotopic signals of dominant taxa. 

Significances of changes in the fish community composition in NW Pacific over the last 2 Ma, with an evaluation of population structure 

Despite the growing awareness about human impact on marine ecosystems and marine fish communities, little is known about how specific fish taxa within a fish community responded to such impact in terms of abundance and taxonomic composition. Such detailed studies require a more comprehensive comparison between fish communities before and after human activities and environmental disturbances, and identifying past baselines without any disturbances is very challenging. In regions around Taiwan and NW Pacific, the local fish community has been modified by intensive fishing activities. Therefore, I hypothesize that the structure of the fish community in the NW Pacific nearshore area has changed over the last 2 Ma. Specifically, I will select the croakers (Sciaenidae) as a study model and hypothesize that their population structure has shifted. The present project will thus reconstruct ancient fish communities by using fossil otoliths from various nearshore Pleistocene deposits, setting a baseline community that is prior to any latest (human) disturbances. The geographical distribution, taxonomic composition, abundance, and diversity indices will be assessed to understand their significance. Based on availability, changes of the population structure of the dominant croaker species will be evaluated by measuring and aging their Pleistocene, archaeological, and Recent otoliths. These otoliths can potentially reveal shifts in size frequency distribution and any changes in size-at-age that might indicate fishing activity at different levels. The goal is to determine how croaker populations have changed from an ancient environment without anthropogenic disturbances to a degrading recent environment, and ultimately, how these can be applied to a larger fish community in the marine ecosystem. 

It is widely considered that fish fossils are rare in Taiwan and adjacent areas, meaning we lack adequate data for understanding the geological history of marine biodiversity in the whole subtropical-tropical Indo-West Pacific. Recently, we have reviewed previous fish fossil records of Taiwan with updated stratigraphic correlation and further investigated potential horizons yielding new materials. 

Our extensive literature reviews indicated that the number of fish body fossils remain scarce, though unstudied specimens gradually accumulate in the museums and private collections. The majority of the fish fossils are in the form of teeth (elasmobranch) and otoliths (teleost), and their high numbers in the marine deposits potentially allow further exploration. Using established examples, we thus recommend studying these isolated fish remains for attaining the spatiotemporal dynamics of fish faunas in the region and, finally, for providing the data necessary for conservational purposes. READ THE PAPER