Biodiversity and Biogeography of Amphipod Crustaceans

Abstract

This dissertation presents aspects of the taxonomy, biodiversity, and biogeography of amphipod crustaceans and is an attempt to address the significant knowledge gaps in the absence of global assessments of the diversity and biogeography of amphipods and put a regional-scale study in Indonesia into a global context. This thesis first assessed trends in species descriptions across all, benthic, pelagic, marine, freshwater, and subterranean amphipods. The prediction of the number of amphipod species remaining to be described, the taxonomic effort indicators, the number of single and multiple authorship species, and the authors’ publication lifetime and productivity were analysed. A total of 9,980 species, 1,664 genera, 444 subfamilies, and 221 families were described over the past 250 years. Of these, almost 20% of species have been discovered within the last decade, including 18 fossil records for amphipods. There are more authors describing species and decreasing rate of species being described in relation to the number of active authors in a year, which implies a greater taxonomic effort and that it might be harder to find new amphipod species, respectively. There was no evidence of any change in papers per author per year or publication lifetimes of authors over time that might have biased apparent efforts. A statistical model predicted that about 6,000 species remained to be described by the 21st century. This indicates that about one-third of amphipods remain to be discovered, which is similar to the proportion for other taxa. To study the global biogeography of marine amphipod crustaceans, I determined the regions of endemicity and latitudinal gradients for three measures of diversity (alpha, gamma, and beta diversity). The analysis of the spatial patterns of richness and endemicity, based on over 400,000 distribution records of 4,876 amphipod species, identified 12 regions of endemicity that were similar to the global biogeography of other marine taxa. The latitudinal patterns of richness (alpha, gamma, and ES50) and species turnover were at least bimodal, as found for other marine taxa. That most records of species occurrence and greater alpha and gamma richness were in mid-latitudes reflected sampling bias. Both ES50 and beta diversity had a similar richness in the tropics, mid-latitudes, and on the Antarctic shelf around 70° S. To reduce the gap of knowledge on amphipod crustaceans in Indonesia, eight different sites in the Wallacea region and adjacent seas were sampled using two sampling methods amongst three substrata. One new amphipod species, Victoriopisa bantenensis was described. It is possible that there are several more species that are new to science and should be described in the future. The geographic distribution of 147 benthic amphipod crustaceans in Indonesian waters were analysed using cluster analysis and neural network analysis to assess the existence of Wallace’s Line as a biogeographic boundary for species dispersal. Five groups of benthic amphipod crustaceans were found. These groups showed no resemblance to Wallace’s faunal division but did show relationships with sampling methods, depth, and substrata. There was only one biogeographic region detected by neural network analysis that matched with the global amphipod regions and marine biogeographic realms defined for all marine taxa. Therefore, this study found no evidence of a biogeographic boundary for amphipods, concurring with the majority of marine studies that the Indo-West Pacific is one biogeographic region extending into the Indian and Pacific oceans. In conclusion, this thesis expands the number of known amphipods from Indonesian seas with a description of species new to science and first records of eight genera and seven families for the country. It highlights that there does not appear to be a dispersal barrier along Wallace’s Line in Indonesia for either marine or terrestrial taxa. Moreover, it suggests that amphipod species discovery is in a productive era and that amphipods do not appear so dispersal limited as may be expected by their lacking a planktonic life-stage. This thesis also gives insight into the intense fish predation in the tropics that limiting amphipod abundance as one hypothesis for low amphipod species richness in the equator.