Leigh Michael Howarth

• Doctor in Marine Biology
• Research Scientist at Cawthron Institute

Many over-exploited marine ecosystems worldwide have lost their natural populations of large predatory finfish and have become dominated by crustaceans and other invertebrates. Controversially, some of these simplified ecosystems have gone on to support highly successful invertebrate fisheries capable of generating more economic value than the fish...

This study investigated the effects of a newly established, fully protected marine reserve on benthic habitats and two commercially valuable species of scallop in Lamlash Bay, Isle of Arran, United Kingdom. Annual dive surveys from 2010 to 2013 showed the abundance of juvenile scallops to be significantly greater within the marine reserve than outs...

Human activities can elevate coastal levels of dissolved inorganic nitrogen (DIN). As macroalgae readily absorb and accumulate DIN, the elemental (total N and C:N ratio) composition of their tissues is less affected by temporal fluctuations compared to more direct measures of DIN concentration. Additionally, their isotopic (δ15N) composition can re...

The Firth of Clyde, on the west coast of Scotland, was once one of the most productive fishing grounds in Europe. However, successive decades of poor management and overfishing led to a dramatic loss of biodiversity and the collapse of finfish fisheries. In response, concerned local residents on the Isle of Arran, which lies in the middle of the Cl...

Understanding how different drivers shape relationships between abundance and body mass (size spectra) is important for understanding trophic and competitive interactions in food webs and for predicting the effects of human pressures. Here, we sample seabed communities from small polychaetes (<0.001 g) to large fish (>1 kg) in the Celtic Sea and th...

The aquaculture industry can be impacted by mortality events triggered by marine heatwaves, pathogens, and other environmental factors. Aquaculture managers would benefit from advanced warning of mortality events so they can make decisions to maximise production and profitability. To help monitor fish health and performance, finfish farms are often...

The development of offshore aquaculture is globally gaining momentum in response to increasing space constraints in the coastal zone, and because offshore aquaculture has the potential to generate fewer conflicts and reduced environmental impacts. Due to the large size of Canada’s open ocean and proximity to key markets, there is strong potential t...

This paper reviews the impacts of shellfish and finfish aquaculture on eelgrass Zostera marina, the most widely distributed seagrass species in the northern hemisphere. Shellfish aquaculture can have positive, neutral, and negative effects on eelgrass. Positive interactions can be generated by the filtering activity of cultured bivalves, which may...

Climate change is increasing global ocean temperatures and causing reduction in pH and oxygen. Global sea level is also rising at an accelerating rate, increasing the risk of coastal erosion and flooding. Nova Scotia is highly dependent on coastal resources for employment and infrastructure,and climate change is a threat to coastal communities and...

Finfish aquaculture is a source of dissolved nutrients, which can impact water quality in the wider environment. Therefore, the potential effects of dissolved nutrient loading must be considered if management is to transition towards an Ecosystem Approach to Aquaculture. In this study, the dissolved nitrogen dispersion pattern from a rainbow trout...

Some eelgrass beds in Atlantic Canada have receded in recent years due to a multitude of interacting stressors including disease, species invasions, nutrient enrichment, and climate change. There have been concerns that aquaculture may also have the potential to negatively impact eelgrass, given aquaculture is primarily a coastal activity. This rep...

Macroalgae can incorporate the isotopic signature (δ 15 N) of their external environment and be used as 'bioin-dicators' to map and identify between multiple sources of anthropogenic nitrogen. However, evidence suggests that the isotopic signature of their tissues can also be influenced by a range of other factors, which could confound their use as...

Predicting how species will respond to increased environmental temperatures is key to understanding the ecological consequences of global change. The physiological tolerances of a species define its thermal limits, while its thermal affinity is a summary of the environmental temperatures at the localities at which it actually occurs. Experimentally...

Although many studies have investigated the effects of disturbance and environmental drivers on marine ecosystems, comparatively few have studied their interactions. Using fuzzy coded biological traits, we compared the functional composition, diversity and evenness of benthic communities in the English Channel and in the Celtic and Irish Seas acros...

Understanding links between habitat characteristics and foraging efficiency helps predict how environmental changes influence populations of top predators. This study examines whether measurements of prey (clupeids) availability varied over stratification gradients, and determined if any of those measurements coincided with aggregations of foraging...

Global landings of scallops have grown dramatically in recent decades and these fisheries are now among the most lucrative in several countries around the world. Despite this apparent success story, concerns have arisen about the wider ecosystem effects of scallop fisheries. This is particularly the case for the most common type of fisheries that u...

This study investigated the effects of a community-led temperate marine reserve in Lamlash Bay, Firth of Clyde, Scotland, on commercially important populations of European lobster (Homarus gammarus), brown crab (Cancer pagurus), and velvet swimming crabs (Necora puber). Potting surveys conducted over 4 years revealed significantly higher catch per...

Traditionally, marine ecosystems have been described through indices of species composition, diversity and abundance. However, such studies often result in “noisy data”, which is very difficult to interpret and draw any solid conclusions. This is because marine ecosystems are incredibly complex and dynamic. “Size spectra” based approaches have ther...

The king scallop fishery is the fastest growing fishery in the UK and currently the second most valuable. The UK is also home to the largest queen scallop fishery out of all of Europe. However, concerns have been raised about the effects of this recent growth of UK scallop fisheries among scientists and conservation bodies, as well as amongst the p...

Despite the implementation of several precautionary management measures in Scotland, evidence suggests that scallop fisheries based in the Firth of Clyde may not reach long-term sustainability. It is argued that only the establishment of No take Zones (NTZs) can restore the age structure and spawning biomass of scallop stocks. The aim of this study...

This study investigated the effects of a fully protected marine reserve on commercially valuable scallops and benthic habitats in Lamlash Bay, Isle of Arran, United Kingdom. Dive surveys found the abundance of juvenile scallops to be greater within the marine reserve than outside. A novel multivariate approach, based upon neural networks and genera...