Aspects of Polychaete Habitat Preferences in the Intertidal and Subtidal Zones of Bonny River, Nigeria

Abstract

Shoreline Intertidal and Midchannel–subtidal polychaete assemblages of the Bonny River in Nigeria were studied during the months of July, August, September and October 2013 to represent the wet season and December 2013, January 2014, February to March 2014 to represent the dry season. The study showed evidence of Polychaete differences in the species associations that occurred in the intertidal and subtidal habitats along stations on the Bonny River. The cluster analysis from a presence-absence model revealed two groups of Specialists and one group of Generalists. Within the Generalist category, the abundance model revealed three (3) sub-Generalist associations that indicated habitat preferences within stations. The study determined the presence of a generalist-specialist continuum between habitats from Bonny to Iwofe along the Bonny River. Based on the incidence model (presence-absence), the generalist-specialist associations coexisted in a non-linear pattern of habitat-preference between stations. Habitat preference among the Polychaete species was highest for Generalists only at Bonny station (58%). They coexisted with Specialists at Opudakiri (18%), Okrika (15%), Isaka (3%) and Iwofe (6%). For the Specialists, habitat preference between the intertidal and subtidal was interspersed between stations without a discernible pattern at Bonny (33%:13%), Opudakiri (38%:41%), Okrika (13%:21%), Isaka (16%:10%) and Iwofe (9%:0%). Altogether, fine differences in habitat preference were shown for the twenty-eight (28) Generalists. Only two species of Generalists, namely Glycera tridactyla, and Notomastus aberans, had the highest distribution on the basis of their occurrence at five (5) of the intertidal and subtidal stations at Bonny, Opudakiri, Okrika, Isaka and Iwofe. Similar fine-tuned differences were inferred from preferences shown by the Specialists at the intertidal locations between stations. Three species, namely Neanthes sp., Nephthys assimilis and Sigambra tentaculata emerged as those with the highest overall distribution among the intertidal specialists having occurred in five stations from Bonny to Iwofe stations. In contrast, there was no wide overall habitat preference shown by any of the Polychaete species among the midchannel subtidal specialists. Only one species, Sabillides sp., had narrow occupancy in two stations at the mouth of Bonny River, namely Bonny and Opudakiri. As a result, the lines of evidence show that three ecologically relevant findings are plausible. Firstly the wide distribution of few specialists and generalist show they are neither transitional nor opportunistic. Secondly they indicate ecological fitness in inhabiting either the intertidal or subtidal irrespective of episodic changes to the sediment. Thirdly it is plausible that as in some Polychaete and Fish associations they provide biotic cues that may affect behavioral attributes of recruitment for transitional and opportunistic species. Future research priorities by ecologists can use the observed indicator associations and their resource requirements, to interpret changes in habitat preference as Polychaetes respond to man-made and natural environmental changes.