Recovery of marine animal populations and ecosystems

Abstract

Many marine populations and ecosystems have experienced strong historical depletions, yet reports of recoveries are increasing. Here, we review the growing research on marine recoveries to reveal how common recovery is, its magnitude, timescale and major drivers. Overall, 10-50% of depleted populations and ecosystems show some recovery, but rarely to former levels of abundance. In addition, recovery can take many decades for long-lived species and complex ecosystems. Major drivers of recovery include the reduction of human impacts, especially exploitation, habitat loss and pollution, combined with favorable life-history and environmental conditions. Awareness, legal protection and enforcement of management plans are also crucial. Learning from historical recovery successes and failures is essential for implementing realistic conservation goals and promising management strategies.A new focus on recovery An increasing number of studies have reported strong declines in marine animal populations and the degradation of ocean ecosystems over past decades and centuries around the world [1][2][3][4][5][6][7], leading to a widespread perception of empty oceans and polluted waters. Yet, throughout history, humans have responded to declining resource abundance and ecosystem degradation by implementing management and conservation measures. Some of these have been successful and resulted in recovery, whereas others have failed [3,8,9].Therefore, an important question to science and management is: how common is recovery among depleted populations and degraded ecosystems in the ocean? Today, many marine mammal, bird, reptile and fish populations are at low abundance, and several species are endangered or extinct on regional or global scales [5,[10][11][12]. However, despite long periods of intense human impacts, most marine species persist and some populations do show signs of recovery [3,8,9]. Similarly, many coastal habitats, including wetlands, seagrass beds, mangrove and kelp forests, and oyster and coral reefs, have been severely reduced or degraded [2][3][4]6], yet partial recovery has been achieved in some regions in response to protection and pollution controls [3,13]. Restoration attempts at an ecosystem level have often been followed by the return and recovery of former species assemblages and ecosystem functions [13][14][15][16][17], but some ecosystems have remained in an altered state [18]. Such successes could serve as important guides for efforts to prevent further biodiversity loss and enhance future recoveries.Despite a growing number of case studies on the recovery of specific populations or ecosystems, an overview of the general patterns and drivers of marine recoveries over historical timescales is lacking. A recent review on the recovery of damaged ecosystems found that many terrestrial and marine ecosystems can recover on timescales of a few years to a few decades after major perturbations [19]. However, most case studies in the review, especially among marine and brackish examples, included small, short-...

Response of seafloor ecosystems to abrupt global climate change

“…The gradual nature of this recovery is not considered to be an artifact of sediment bioturbation, because bioturbation is limited to <20 cm of sediment. The recovery of seafloor diversity in response to the oxygenation reversal in the Younger Dryas is an order of magnitude longer than known rates of recovery for seafloor biodiversity after disturbance (42). This evidence expands previous expectations for rates of biological recovery by an order of magnitude, from <100 y to >1,000 y, and reveals long-term consequences of climate-driven successional changes in ocean ecosystems.…”

Drivers and hotspots of extinction risk in marine mammals

“…So, together, these two variables index the speed of life history and are the primary determinants of r max , the maximum or intrinsic rate of population increase and the capacity for species to recover from reduced populations after threats have been removed. Rate of population increase after depletion is important to marine conservation (29)(30)(31). For example, baleen whales have fast life histories for their body size, and several species, including humpbacks and gray whales (Megaptera novaeangliae and Eschrichtius robustus), have shown strong recoveries following the international ban on commercial whaling (4,30).…”

“…Rate of population increase after depletion is important to marine conservation (29)(30)(31). For example, baleen whales have fast life histories for their body size, and several species, including humpbacks and gray whales (Megaptera novaeangliae and Eschrichtius robustus), have shown strong recoveries following the international ban on commercial whaling (4,30). Other taxa, including sea otters (Enhydra lutris) and northern elephant seals (Mirounga angustirostris), have increased exponentially after protection (30).…”

“…For example, baleen whales have fast life histories for their body size, and several species, including humpbacks and gray whales (Megaptera novaeangliae and Eschrichtius robustus), have shown strong recoveries following the international ban on commercial whaling (4,30). Other taxa, including sea otters (Enhydra lutris) and northern elephant seals (Mirounga angustirostris), have increased exponentially after protection (30). The latter had been reduced to 20-30 individuals by 1900, and despite very low genetic diversity, elephant seals increased at an estimated 8.3% per year to a population of ∼170,000 today (23,32).…”

Biology in the Anthropocene: Challenges and insights from young fossil records

“…Compared with short-term assessments, metaanalysis using (geo)historical baselines reveals a lower frequency (10-50%) and magnitude of recovery, especially in species abundance and ecosystem structure, and finds that recoveries often require decades or more and attention to multiple stressors (ref. 106; and see Ranking Multiple Stressors below). This hard truth-even for marine systems, which are arguably less altered by human pressures than terrestrial systems (30)-needs to spur collaborative analyses and action, not discouragement or denial.…”