GLOBAL PHYSICAL CONTROLS ON ESTUARINE HABITAT ABUNDANCE DURING SEA LEVEL CHANGE WITH IMPLICATIONS FOR RICHNESS AND DIVERSIFICATION OF MARGINAL MARINE FAUNAS

How geological processes shape origination of new biological lineages is of common interest in paleontology and neontology. Specifically, how sea-level change has promoted speciation and extinction has been long-studied within paleontology to differing conclusions. Only recently was this question addressed using DNA techniques and GIS modeling of estuarine habitat as a function of sea-level change. The study found that narrow continental margins produced more differentiated fish populations as these populations were isolated in fewer, smaller habitats than those inhabiting wide margins. This finding was consistent with population genetic principles but was in opposition to paleontological literature that suggested eustatic regressions over Earth’s history have caused extinctions.

To test these relationships globally, we modeled estuarine habitat abundance as a function of sea-level change from LGM (~20 ka, 120–140 mbsl) to present day along the unglaciated coastlines of North America, South America, Africa, India, Australia, and the Japanese Archipelago. We tested which tectonic, sediment, and oceanographic properties best predict habitat abundance and analyzed the relationship between habitat size and present-day distributions of 1,781 fish species. We found an 82% reduction in habitat area at lowstand relative to today and this change was larger on wide (>75 km) margins than narrow (<25 km) margins. Margin width was the foremost predictor of habitat abundance; fore-arc settings were significantly narrower and hosted less habitat than passive margins, effectively linking tectonic setting with estuarine habitat abundance. Species richness was negatively correlated with habitat area, which violates the canonical species-area relationship, but which can be explained if narrow margins generate new species (through physical isolation) or retain species over deep geologic time. Because narrow margins have less estuarine habitat at highstand and lowstand, narrow-margin isolation may operate continuously, even over the lifespan of the margins themselves. These findings with previous molecular work suggest narrow margins can promote diversification of estuarine species. More work is needed to refine this relationship and link these processes to the deep-time paleontological record.