Biology Reference
In-Depth Information
rigorous experimental studies have found conflicting results shows that both factors
are important under different circumstances and often interact simultaneously.
The human population is projected to steadily increase, which will result in
further anthropogenic pressure on coastal marine systems. It is likely that nutrient
loading rates and fishing pressure will intensify, despite management efforts. The
impacts of nutrient loading and overfishing will also be exacerbated by other global
changes, such as rising seawater temperatures, sea level rise, and ocean acidifica-
tion. Nutrients in combination with warmer waters may promote more occurrences
of macroalgal blooms, as photosynthesis, growth rates of macroalgae, and recruit-
ment are thought to be positively affected by an interaction of these factors
(Longstaff et al.
2002
; Lotze and Worm
2002
; Bintz et al.
2003
; Tsai et al.
2005
).
Additionally, enhanced CO
2
conditions have been shown to benefit some ephemeral
bloom-forming macroalgal species over other slower growing species (Gordillo
et al.
2001
; Wootton et al.
2008
), while negatively impacting many benthic
invertebrates (Fabry et al.
2008
). Additionally, the increase in invasions by nonna-
tive macroalgal species to new coastal habitats may promote blooms of macroalgae
that are better adapted to changing environmental conditions (Thomsen et al.
2006
).
Cascading effects up or down the food web and, thus, the strength of bottom-up and
top-down controls acting on macroalgal communities will likely be altered due to
these shifts in species composition and environmental change (Fox et al.
2010
).
Management of all aspects (nutrients, fishing, habitat protection, reduction of
CO
2
emissions) is important, and choosing one management practice over another
will not be successful at controlling macroalgal blooms. The management and
removal of nitrogen and phosphorus is necessary as a first step. Wastewater treat-
ment plants and improvements in septic systems have shown significant positive
effects on water quality through the removal of the bulk of nutrients prior to entering
the coast or groundwater. Reduction of fertilizer use and phosphate-free detergents
can also reduce the amount of nutrients entering these systems. Preservation and
restoration of wetlands will help to filter nutrient inputs before they enter rivers and
coastal waters. Additionally, improving hydrodynamics of low-flow systems by
increasing tidal flushing could help to mitigate nutrient effects. Increases in fishing
regulations and protected areas with no take zones may help to increase fish and
invertebrate populations. This will impact food web communities in multiple ways
and will strengthen top-down controls on macroalgal growth.
In many cases, these management practices may not be enough to facilitate
recovery of marine habitats to their natural state prior to disturbances, and much is
still unknown as to how bottom-up and top-down controls will interact with future
global change projections. It is very likely that macroalgal blooms will continue to
become more frequent and severe in coastal systems before conditions improve.
A better understanding of how these controls will interact under predicted future
conditions is critical to develop tools to mitigate these changes.
