Expanded consumer niche widths may signal an early response to spatial protection

Abstract

Marine management interventions are increasingly being implemented with the explicit goal of rebuilding ocean ecosystems, but early responses may begin with alterations in ecological interactions preceding detectable changes in population-level characteristics. To establish a baseline from which to monitor the effects of spatial protection on reef fish trophic ecology and track future ecosystem-level changes, we quantified temperate reef fish densities, size, biomass, diets and isotopic signatures at nine sites nested within two fished and one five-year old marine protected area (MPA) on the northwest coast of Canada. We calculated rockfish (Sebastes spp.) community and species-specific niche breadth for fished and protected areas based on δ13C and δ15N values. We found that rockfish community niche width was greater inside the MPA relative to adjacent fished reefs due to an expanded nitrogen range, possibly reflecting early changes in trophic interactions following five years of spatial protection. Our data also demonstrated that the MPA had a positive effect on the δ15N signature of rockfish (i.e., trophic position), but the effect of rockfish length on its own was not well-supported. In addition, we found a positive interaction between rockfish length and δ15N signature, such that δ15N signatures of rockfish caught within the MPA increased more rapidly with body size than those caught in fished areas. Differences in rockfish size structure and biomass among fished and unfished areas were not clearly evident. Species of rockfish and lingcod varied in trophic and size responses, indicating that life-history traits play an important role in predicting MPA effects. These results may suggest early changes in trophic behavior of slow-growing rockfish due to predation risk by faster growing higher trophic level predators such as lingcod inside MPAs established on temperate reefs. Consequently, spatial protection may restore both the trophic and behavioral roles of previously fished consumers earlier and in measurable ways sooner than observable changes in abundance and size.

Evaluation of the Residency of Black Rockfish (Sebastes schlegelii) in Artificial Reef Areas Based on Stable Carbon Isotopes

“…Second, developing tailored spatial-specific fishing strategies that account for both residency and potential sources of black rockfish contributes significantly to local fishery sustainability. Owing to the limited space and food availability in the reef areas, a high assemblage of individuals can lead to intraspecific competition for refuge and food resources [59,60]. By considering the diverse potential sources of black rockfish, implementing a spatial-specific fishing strategy with distinct quotas can help alleviate intraspecific competition within the reef area and foster a sustainable level of exploitation in coastal regions [61].…”

Protecting our coast for everyone's future: Indigenous and scientific knowledge support marine spatial protections proposed by Central Coast First Nations in Pacific Canada

“…Long‐term research in California indicates that spatial protections can help rebuild the densities and body sizes of rockfish and of lingcod ( Ophiodon elongatus : a co‐occurring, highly mobile, fished species) (Caselle et al, 2015; Keller et al, 2019; Starr et al, 2015; Thompson et al, 2017). Also, research within the NSB points to differences between protected and fished areas in the trophic structure of rockfishes and lingcod (Olson et al, 2019). MPA benefits for rockfish, however, may require many years to accrue and the required time may vary between species and locations (McGreer et al, 2020; Starr et al, 2015).…”

Growth parameter k and location affect body size responses to spatial protection by exploited rockfishes

“…For some species, however, declines in size and age structure have continued and their biomass remains depressed and references within). RCAs can help reverse these trends, yet prior studies in British Columbia, conducted only 5-7 years after RCA implementation, found no evidence of larger or more abundant rockfishes inside protected sites (Haggarty, Shurin & Yamanaka, 2016;Olson, Trebilco & Salomon, 2019). As time since RCA implementation progresses, size and biomass increases are more likely to be detected (Starr et al, 2015;Keller et al, 2019), particularly for shorter-lived species with greater k values (Kaplan et al, 2019).…”