Environmental Drivers of Species Community Dynamics over 37 Years in Pamlico Sound, North Carolina: A Multivariate Approach

Abstract

Coastal ecosystems are subject to a number of anthropogenic pressures, including fisheries impacts, climate change, and habitat loss. Understanding how estuaries are changing on the system level in the face of dynamic pressures, anthropogenic and natural, is crucial for managers and stakeholders. To illustrate the strength of both species abundances and abiotic pressures on aquatic species community structure, multivariate techniques (nonmetric multidimensional scaling or NMDS) were employed on the largest lagoonal estuary in North America, the Albemarle-Pamlico Estuarine System. The primary dataset was from a fisheries-independent trawl survey by the North Carolina Division of Marine Fisheries spanning from 1987 to 2025. To provide additional context to the community dynamics, a suite of other indices investigated species temperature preferences, habitat specialization, and taxon-level changes over time. Results from the NMDS and cluster analyses indicated that June and September sampling seasons represent distinct assemblages, and that the estuary experienced rapid restructuring around the year 2000, in addition to several other minor community reorganizations. The regime shift detected was defined by dominance of new species and groups including pinfish (Lagodon rhomboides), southern kingfish (Menticirrhus americanus), two penaeid shrimp species, and batoid rays. In contrast, other species such as blue crab (Callinectes sapidus) and hogchoker (Trinectes maculatus) represented the “historic” year grouping (1987-2000) based on higher abundances at the beginning of the time series. Of the two most dominant species, spot (Leiostomus xanthurus) increased their abundance while Atlantic croaker (Micropogonias undulatus) catch per unit effort (CPUE) remained stable, while system-wide CPUE nearly doubled between the start of the time series and the end. A change of phase in the Atlantic Multidecadal Oscillation correlated most with species abundances over time, and water temperature also characterizes the changes in the biotic community well. Species that responded positively to these factors included pelagic species, which are increasing in relative abundance, and elasmobranchs, which have overtaken invertebrates in average biomass per haul. Higher average temperature preferences in the annual communities was observed through increases in the Community Temperature Index, especially for the fall season. Biodiversity is increasing mainly due to an influx of novel species that increased richness, because species evenness continues to decrease in a system that has been consistently dominated by less than ten species. This work illustrates the need to view and manage biological systems from an assemblage-scale perspective. It also highlights ongoing community shifts that could indicate a lack of stationarity in the system, which is contrary to most assumptions used by fisheries managers. Both global climate forcing and localized species interactions may be factors in driving these changes. Finally, this research contributes to a growing body of work, previously dominated by single-species studies or work limited to relatively few species, that Pamlico Sound is experiencing significant decadal-scale change.