Production and decay of mangrove (Avicennia marina subsp. australasica) detritus and its effects on coastal benthic communities

Temperate mangrove forests have been poorly studied compared to their tropical counterparts, because they constitute just 1.4% of the global mangrove forest area. Research from tropical mangrove forests suggests they are open systems that provide a large array of ecosystem goods and services. For example, tropical mangrove forests frequently support invertebrate communities in adjacent habitats through the production, export, decomposition and uptake of organic matter. However, ecological differences between temperate and tropical mangrove forests means that information collected in tropical regions cannot be readily extrapolated to temperate systems. Therefore, it is unclear how, or if, temperate mangrove forests supply an organic subsidy to estuarine ecosystems. Here I investigate the linkages between mangrove organic matter production and the role that decomposing mangrove detritus (dead, broken down organic matter) plays in structuring estuarine benthic communities. Research was conducted at two sites (encompassing small-scale differences in sediment properties and macrofaunal communities) in Whangamata Harbour, New Zealand. The production of mangrove detritus was quantified by measuring litter production and its decomposition into detritus. A manipulative detritus addition experiment explored the role of exported mangrove detritus in structuring benthic communities of unvegetated intertidal flats. The temperate Whangamata Harbour mangrove forest produced the equivalent of 3.24 - 5.38 t DW ha-1 yr-1 of litter, which is comparable to forests at similar latitudes and overlaps with the lower range of tropical mangrove productivity. The decomposition rates of litter following summer litterfall were dependent upon the type of litter, as well as the burial state. However, hypotheses that tidal position and site would affect litter degradation rates were not supported. Leaf and wood litter that was buried in the sediment decomposed significantly slower (1.3 - 1.4 times slower) than litter on the sediment surface. Leaf litter decomposition was faster (63 days to decay by 50%) than wood and root material (460 and 316 days, respectively). Decay models predicted that wood and root material will take years to breakdown, which has implications for New Zealand mangrove removal plans, where wood and roots often remain in situ (following clearances). Finally, a manipulative detrital addition experiment found that mangrove detritus created subtle changes in the relative abundances of a few dominant taxa, rather than shifts in whole community species composition. Communities responded similarly to the addition of mangrove detritus, with the same dominant taxa responding at both experimental sites. The subtle benthic community responses to the large amount of detritus added suggests that mangrove detritus plays a relatively minor role in shaping communities on temperate intertidal flats. The studies that comprise this thesis have together shown that as a result of different input and decomposition rates of mangrove litter, temperate estuarine benthic communities are probably less reliant on mangrove productivity than tropical communities

Quantifying macrodetritus fluxes from a small temperate estuary

Empirical measurements of estuary-to-coast material fluxes usually exclude the fraction of primary production that is exported as macrodetritus (marine plant litter), potentially leaving a gap in our understanding of the role of estuaries as outwelling systems. To address this gap, we sampled water and suspended material seasonally from the mouth of Pepe Inlet, Tairua Estuary, New Zealand. From samples collected hourly over 24 h, we calculated the lateral tidal fluxes (import, export, net flux) of macrodetritus, particulate and dissolved forms of nitrogen (N) and phosphorus (P). Annually, the inlet was a net exporter of N and P (5145 and 362 kg respectively). However, macrodetritus accounted for 87%). Nevertheless, seasonal pulses in the source and supply of macrodetritus may have consequences for the temporal scales over which this resource subsidy affects receiving ecosystems (e.g. intertidal sandflats). These mensurative investigations are useful to inform estuarine nutrient budgets that quantify the ecosystem services provided by temperate estuaries (e.g. contribution to fisheries food webs)

Coupling marine ecosystem state with environmental management and conservation: A risk-based approach

\ua9 2024 The Author(s)The sustainability of marine ecosystems demands a focus on ecological improvement, necessitating managers and conservationists to consider a range of actions from those that limit stressors to those that actively restore. Deciding the most appropriate action should be informed by environmental context, which includes assessing information on both degradation and recovery potential. Here, we provide an analysis of how the degree of ecological degradation coupled with the stressor regime can inform environmental management and conservation actions (e.g., stressor reductions, adaptive management, assisted recovery/restoration). With this analysis we design a risk framework combining principles that define ecosystem resilience and recovery times with those that characterize stressor regimes (i.e., the number, type, and impact). The combination of these principles defines where an ecosystem is placed along sliding scales of degradation and recovery and likely response to protective and restorative interventions. It is designed to facilitate place-based conversations regarding the risks of different management actions informed by the temporal dynamics of ecosystem degradation and recovery

Identifying "vital attributes" for assessing disturbance-recovery potential of seafloor communities

Despite a long history of disturbance–recovery research, we still lack a generalizable understanding of the attributes that drive community recovery potential in seafloor ecosystems. Marine soft‐sediment ecosystems encompass a range of heterogeneity from simple low‐diversity habitats with limited biogenic structure, to species‐rich systems with complex biogenic habitat structure. These differences in biological heterogeneity are a product of natural conditions and disturbance regimes. To search for unifying attributes, we explore whether a set of simple traits can characterize community disturbance–recovery potential using seafloor patch‐disturbance experiments conducted in two different soft‐sediment landscapes. The two landscapes represent two ends of a spectrum of landscape biotic heterogeneity in order to consider multi‐scale disturbance–recovery processes. We consider traits at different levels of biological organization, from the biological traits of individual species, to the traits of species at the landscape scale associated with their occurrence across the landscape and their ability to be dominant. We show that in a biotically heterogeneous landscape (Kawau Bay, New Zealand), seafloor community recovery is stochastic, there is high species turnover, and the landscape‐scale traits are good predictors of recovery. In contrast, in a biotically homogeneous landscape (Baltic Sea), the options for recovery are constrained, the recovery pathway is thus more deterministic and the scale of recovery traits important for determining recovery switches to the individual species biological traits within the disturbed patch. Our results imply that these simple, yet sophisticated, traits can be effectively used to characterize community recovery potential and highlight the role of landscapes in providing resilience to patch‐scale disturbances.Peer reviewe

Can large taonga bivalves speed up recovery in degraded estuaries?

THE QUESTION: Will there introduction of adult, long-lived bivalves with differing functional traits speed up recovery of degraded soft sediment habitats in estuaries? RESULTS: Average bivalve survival after one year was 18% in + tuangi plot sand 59% in + hanikura plots. Sediment oxygen consumption (SOC) after one month was enhanced by 116% in treatments containing tuangi compared to control treatments. After one year those were similar to ambient levels, still showed higher SOC than control plots

Old Tools, New Ways of Using Them: Harnessing Expert Opinions to Plan for Surprise in Marine Socio-Ecological Systems

Copyright © 2019 Gladstone-Gallagher, Hope, Bulmer, Clark, Stephenson, Mangan, Rullens, Siwicka, Thomas, Pilditch, Savage and Thrush. With globally accelerating rates of environmental disturbance, coastal marine ecosystems are increasingly prone to non-linear regime shifts that result in a loss of ecosystem function and services. A lack of early-detection methods, and an over reliance on limits-based approaches means that these tipping points manifest as surprises. Consequently, marine ecosystems are notoriously difficult to manage, and scientists, managers, and policy makers are paralyzed in a spiral of ecosystem degradation. This paralysis is caused by the inherent need to quantify the risk and uncertainty that surrounds every decision. While progress toward forecasting tipping points is ongoing and important, an interim approach is desperately needed to enable scientists to make recommendations that are credible and defensible in the face of deep uncertainty. We discuss how current tools for developing risk assessments and scenario planning, coupled with expert opinions, can be adapted to bridge gaps in quantitative data, enabling scientists and managers to prepare for many plausible futures. We argue that these tools are currently underutilized in a marine cumulative effects context but offer a way to inform decisions in the interim while predictive models and early warning signals remain imperfect. This approach will require redefining the way we think about managing for ecological surprise to include actions that not only limit drivers of tipping points but increase socio-ecological resilience to yield satisfactory outcomes under multiple possible futures that are inherently uncertain

Social-ecological connections across land, water, and sea demand a reprioritization of environmental management

Despite many sectors of society striving for sustainability in environmental management, humans often fail to identify and act on the connections and processes responsible for social-ecological tipping points. Part of the problem is the fracturing of environmental management and social-ecological research into ecosystem domains (land, freshwater, and sea), each with different scales and resolution of data acquisition and distinct management approaches. We present a perspective on the social-ecological connections across ecosystem domains that emphasize the need for management reprioritization to effectively connect these domains. We identify critical nexus points related to the drivers of tipping points, scales of governance, and the spatial and temporal dimensions of social-ecological processes. We combine real-world examples and a simple dynamic model to illustrate the implications of slow management responses to environmental impacts that traverse ecosystem domains. We end with guidance on management and research opportunities that arise from this cross-domain lens to foster greater opportunity to achieve environmental and sustainability goals.Peer reviewe