How Sea Floor Ecosystems Are Damaged By, And Recover From, Abrupt Climate Change

A new study by Sarah Moffitt, Tessa Hill, Peter Roopnarine, and James Kennett (Response of seafloor ecosystems to abrubt global climate change) gets a handle on the effects of relatively rapid warming and associated Oxygen loss in the sea on invertebrate communities. The study looked at a recent warming event (the end of the last glacial) in order to understand the present warming event, which is the result of human-caused greenhouse gas pollution.

Here is what is unique about the study. A 30 foot deep core representing the time period from 3,400 to 16,100 year ago, was raised from a site in the pacific, and the researchers tried to identify and characterize all of the complex invertebrate remains in the core. That is not usually how it is done. Typically a limited number of species, and usually microscopic surface invertebrates (Foraminifera) only, are identified and counted. There are good reasons it is done that way. But the new study looks instead at non-single-celled invertebrates (i.e., clams and such) typically found at the bottom, not top, of the water column. This study identified over 5,400 fossils and trace fossils from Mollusca, Echinodermata, Arthropoda, and Annelida (clams, worms, etc.).

Complex invertebrates are important because of their high degree of connectivity in an ecosystem. In the sea, a clam, crab, or sea cucumber may be the canary in the proverbial coal mine. Study co-author Peter Roopnarine says, “The complexity and diversity of a community depends on how much energy is available. To truly understand the health of an ecosystem and the food webs within, we have to look at the simple and small as well as the complex. In this case, marine invertebrates give us a better understanding of the health of ecosystems as a whole.”

The most important finding of the study is this: the marine ecosystem sampled by this core underwent dramatic changes, including local extinctions, and took up to something like 1,000 years to recover from that. The amount of change in bottom ecosystems under these conditions was previously not well known, and the recovery rate was previously assumed to be much shorter, on the order of a century.

From the abstract of the paper:

Anthropogenic climate change is predicted to decrease oceanic oxygen (O2) concentrations, with potentially significant effects on marine ecosystems. Geologically recent episodes of abrupt climatic warming provide opportunities to assess the effects of changing oxygenation on marine communities. Thus far, this knowledge has been largely restricted to investigations using Foraminifera, with little being known about ecosystem-scale responses to abrupt, climate-forced deoxygenation. We here present high-resolution records based on the first comprehensive quantitative analysis, to our knowledge, of changes in marine metazoans … in response to the global warming associated with the last glacial to interglacial episode. The molluscan archive is dominated by extremophile taxa, including those containing endosymbiotic sulfur-oxidizing bacteria (Lucinoma aequizonatum) and those that graze on filamentous sulfur-oxidizing benthic bacterial mats (Alia permodesta). This record … demonstrates that seafloor invertebrate communities are subject to major turnover in response to relatively minor inferred changes in oxygenation (>1.5 to <0.5 mL·L−1 [O2]) associated with abrupt (<100 y) warming of the eastern Pacific. The biotic turnover and recovery events within the record expand known rates of marine biological recovery by an order of magnitude, from <100 to >1,000 y, and illustrate the crucial role of climate and oceanographic change in driving long-term successional changes in ocean ecosystems.

Lead author Sarah Moffitt, of the UC Davis Bodega Marine Laboratory and Coastal and Marine Sciences Institute notes, “In this study, we used the past to forecast the future. Tracing changes in marine biodiversity during historical episodes of warming and cooling tells us what might happen in years to come. We don’t want to hear that ecosystems need thousands of years to recover from disruption, but it’s critical that we understand the global need to combat modern climate impacts.”

There is a video:

Caption from the figure at the top of the post: Fig. 1. Core MV0811–15JC’s (SBB; 418 m water depth; 9.2 m core length; 34.37°N, 120.13°W) oxygen isotopic, foraminiferal, and metazoan deglacial record of the latest Quaternary. Timescale (ka) is in thousands of years before present, and major climatic events include the Last Glacial Maximum (LGM), the Bølling and Allerød (B/A), the Younger Dryas (YD), and the Holocene. (A) GISP2 ice core δ18O values (46). (B) Planktonic Foraminifera Globigerina bulloides δ18O values for core MV0811–15JC, which reflects both deglacial temperature changes in Eastern Pacific surface waters and changes in global ice volume. (C) Benthic foraminiferal density (individuals/cm3). (D) Relative frequency (%) of benthic Foraminifera with faunal oxygen-tolerance categories including oxic–mildly hypoxic (>1.5 mL·L−1 O2; N. labradorica, Quinqueloculina spp., Pyrgo spp.), intermediate hypoxia (1.5–0.5 mL·L−1 O2; Epistominella spp., Bolivina spp., Uvigerina spp.), and severe hypoxia (<0.5 mL·L−1 O2; N. stella, B. tumida) (19). (E) Log mollusc density (individuals/cm3). (F) Ophiuroids (brittle star) presence (presence = 1, absence = 0, 5-cm moving average). (G) Ostracod valve density (circles, valves/cm3) and 5-cm moving average.