Body size and trophic level increase with latitude, and decrease in the deep-sea and Antarctica, for marine fish species

Abstract

The functional traits of species depend both on species’ evolutionary characteristics and their local environmental conditions and opportunities. The temperature-size rule (TSR), gill-oxygen limitation theory (GOLT), and temperature constraint hypothesis (TCH) have been proposed to explain the gradients of body size and trophic level of marine species. However, how functional traits vary both with latitude and depth have not been quantified at a global scale for any marine taxon. We compared the latitudinal gradients of trophic level and maximum body size of 5,619 marine fish from modelled species ranges, based on (1) three body size ranges, <30, 30–100, and >100 cm, and (2) four trophic levels, <2.20, 2.20–2.80, 2.81–3.70, >3.70. These were parsed into 5° latitudinal intervals in four depth zones: whole water column, 0–200, 201–1,000, and 1,001–6,000 m. We described the relationship between latitudinal gradients of functional traits and salinity, sea surface and near seabed temperatures, and dissolved oxygen. We found mean body sizes and mean trophic levels of marine fish were smaller and lower in the warmer latitudes, and larger and higher respectively in the high latitudes except for the Southern Ocean (Antarctica). Fish species with trophic levels ≤2.80 were dominant in warmer and absent in colder environments. We attribute these differences in body size and trophic level between polar regions to the greater environmental heterogeneity of the Arctic compared to Antarctica. We suggest that fish species’ mean maximum body size declined with depth because of decreased dissolved oxygen. These results support the TSR, GOLT and TCH hypotheses respectively. Thus, at the global scale, temperature and oxygen are primary factors affecting marine fishes’ biogeography and biological traits.

Numbers of fish species, higher taxa, and phylogenetic similarity decrease with latitude and depth, and deep-sea assemblages are unique

“…Thus, the species richness of the Arctic is higher than of the Antarctic and Southern Ocean fish fauna ( Fig. 1 , Lin & Costello, 2023 ).…”

“…This allowed notothenioids to live and evolve in this cold environment ( McGonigal & Woodworth, 2002 ; Duhamel et al, 2014 ). In contrast to this stability of the Southern Ocean developing an endemic fauna, the Arctic Ocean is an extension of the Pacific and Atlantic Ocean, and is a more environmentally variable environment ( Lin & Costello, 2023 ). Thus, the species richness of the Arctic is higher than of the Antarctic and Southern Ocean fish fauna ( Fig.…”

A Comprehensive Review of Climatic Threats and Adaptation of Marine Biodiversity

“…In another study, Lin et al [39] found that the number of fish species with higher taxon and phylogenetic similarity decreases with latitude and ocean depth because of climate change. Lin and Costello [40] also found that fish body size and trophic level increase with latitude because of climate change, likely because of changes in temperature and oxygen levels. On the other hand, Manes et al [41] noted that the projected increase in temperature could lead to the extinction of endemic marine and island species.…”

Widespread Coral Bleaching and Mass Mortality of Reef-Building Corals in Southern Mexican Pacific Reefs Due to 2023 El Niño Warming

“…Omnivores (low-trophiclevel omnivores) who consume plant matter and other prey (e.g., sponges, isopods, and amphipods) have a level ranging from 2.20 to 2.80, while omnivores (high-trophic-level omnivores) with a preference for animals but feed on diverse prey (e.g., algae, bivalves, isopods, and fish larvae) have a value of 2.81-3.70. Piscivores and carnivores, with a preference for large decapods, cephalopods, and fish (carnivores), have a value above 3.70 [27,28].…”