Anthropogenic disturbance homogenizes seagrass fish communities

Abstract

Anthropogenic activities have led to the biotic homogenization of many ecological communities, yet in coastal systems this phenomenon remains understudied. In particular, activities that locally affect marine habitat-forming foundation species may perturb habitat and promote species with generalist, opportunistic traits, in turn affecting spatial patterns of biodiversity. Here, we quantified fish diversity in seagrass communities across 89 sites spanning 6° latitude along the Pacific coast of Canada, to test the hypothesis that anthropogenic disturbances homogenize (i.e., lower beta-diversity) assemblages within coastal ecosystems. We test for patterns of biotic homogenization at sites within different anthropogenic disturbance categories (low, medium, and high) at two spatial scales (within and across regions) using both abundance- and incidence-based beta-diversity metrics. Our models provide clear evidence that fish communities in high anthropogenic disturbance seagrass areas are homogenized relative to those in low disturbance areas. These results were consistent across within-region comparisons using abundance- and incidence-based measures of beta-diversity, and in across-region comparisons using incidence-based measures. Physical and biotic characteristics of seagrass meadows also influenced fish beta-diversity. Biotic habitat characteristics including seagrass biomass and shoot density were more differentiated among high disturbance sites, potentially indicative of a perturbed environment. Indicator species and trait analyses revealed fishes associated with low disturbance sites had characteristics including stenotopy, lower swimming ability, and egg guarding behavior. Our study is the first to show biotic homogenization of fishes across seagrass meadows within areas of relatively high human impact. These results support the importance of targeting conservation efforts in low anthropogenic disturbance areas across land- and seascapes, as well as managing anthropogenic impacts in high activity areas.

Trait sensitivities to seagrass fragmentation across spatial scales shape benthic community structure

“…Differential responses of fauna to fragmentation across scales based on species traits suggest that habitat fragmentation may alter community structure by shifting selective pressures on species traits during multiple community assembly stages. Similarly, a recent analysis of seagrass fish communities along the Pacific coast of Canada found distinct shifts in trait composition associated with human disturbance (Iacarella et al, ). Thus, we argue that multi‐scale, trait‐based approaches provide much future promise in continued efforts to disentangle the complex and interacting ways by which humans are altering biodiversity across systems.…”

“…Differential responses of fauna to fragmentation across scales based on species traits suggest that habitat fragmentation may alter community structure by shifting selective pressures on species traits during multiple community assembly stages. Similarly, a recent analysis of seagrass fish communities along the Pacific coast of Canada found distinct shifts in trait composition associated with human disturbance (Iacarella et al, 2018).…”

Nearshore seascape connectivity enhances seagrass meadow nursery function

“…In British Columbia, anthropogenic disturbances are degrading seagrass habitats, in which rockfish species may be particularly sensitive (Iacarella et al. ). To counter these trends, our findings support the inclusion of a mosaic of nearshore habitats in protection zones where preserving and/or elevating nursery function is a primary goal of coastal conservation or management.…”

Change in the dominance structure of two marine‐fish assemblages over three decades

“…Many of these (Baudron et al ., ; Dutz et al ., ; Engelhard et al ., ) report marked changes over the past few years. Recently, however, attention has turned to the dynamics of entire marine assemblages (Greenwood & Maitland, ), with investigators increasingly recognizing the need to quantify spatial and temporal change in biodiversity (Iacarella et al ., ; Jung & Houde, ; Magurran et al ., ; Morley et al ., ). Shifts in species richness (Daan, ; Hiddink & ter Hofstede, ; ter Hofstede et al ., ) and size (Bell et al ., ) have been reported, but as biodiversity is a multifaceted concept (Magurran, ), there is still much to be learnt about the nature of biodiversity change in assemblages of wild fish.…”