Increasing LAGOON AND OCEAN TEMPERATUREs
The health of our lagoon and coastal ocean is jeopardized by increasing ocean heat content. However, it’s not too late to prepare and reduce the impacts.
One Change Can Affect Many Systems
When we talk about climate change, we usually focus on air temperatures. However, 90% of the heat trapped by greenhouse gases since the 1950s is stored in the oceans (IPCC, 2019; Dalhlman and Lindsey, 2020 ).
Many impacts caused by changes in climate can co-vary, that is, one physical or biological change can cause changes in other systems in difficult-to-predict ways. For example, the increased heat content of our estuarine and ocean waters has effects in almost all of the categories below.
The geophysical sciences that underlie changes in our climate are complex but well-explained in resources such as USGCRP (2018), NOAA (2020), and NASA (2020). For the Indian River Lagoon, these issues are summarized in the IRL Climate Ready Estuaries Report. Please see these and the citations below and on other pages for decades of findings, primarily from the growing geophysics, biology, and economics literatures.
Algal Blooms and Fish Kills
Hotter water can mean both less available oxygen in the water for fishes and faster growth of algae in estuarine and ocean waters, a powerful combination if concerned about algal blooms and fish kills (e.g., Gobler et al,. 2017). Increases in ocean heat and fertilizer runoff contribute to harmful blooms of both algae and cyanobacteria (called blue-green algae, but actually photosynthetic bacteria) that can have widespread impacts (Paerl et al., 2016). These issues are summarized from various science and management perspectives in documents on the IRL NEP website, including the IRL’s Comprehensive Conservation Management Plan (NEP, 2019).
Increased runoff of nitrogen and phosphorus from heavily fertilized lawns with more stormwater events in warmer waters can increase the growth rates of harmful algae (e.g., Paerl et al., 2016; Nazari-Sharabian et al., 2018). Resulting harmful algal blooms can cause fish kills, impact marine mammals, and create other short- and long-term impact cascades on coastal waters and their organisms (e.g., IRL CCMP, 2019; Fire et al. 2020).
Source: D.B. Snyder
Seagrasses are underwater flowering plants with complex biological and physical relationships to their environment (Steward et al., 2005, Steward et al., 2006; Lee et al., 2007). Many major questions can vary by region and are being investigated. Seagrasses in the IRL have declined dramatically since 1999 due to multiple factors including fertilizer and sediment runoff, reduced light penetration from algal blooms and sediment resuspension, and sewage and septic nutrient loading (e.g., IRL CCMP, 2019). These and other features can effect patterns of seasonal occurrence of seagrasses and should influence resource assessment and management decisions (e.g., Metz et al. 2020). Major scientific reviews of seagrasses in terms of climate change (e.g., Short et al. 2016), include the following points.
- Hotter estuarine waters affect seagrass growth and reproduction, and can change geographic distributions in complex manners. The temperature range for tropical and subtropical seagrasses is 73- 90°.
- Increasing ocean temperatures will increase the chances of algal blooms and can result in less light reaching seagrasses.
- Higher temperatures increase extreme weather events which can degrade seagrasses by increasing the frequency and volume of stormwater runoff from surrounding roads and lands, further increasing turbidity and decreasing light penetration.
- Changes in salinity associated with more extreme weather, especially reductions in salinity, can change the species compositions and densities of coastal seagrasses.
Temperature stresses are most obvious at the edges of species ranges and can affect the reproductive output of seagrasses. Seagrass growth can be accelerated as well. These are examples of co-occurring biological processes that may be affected in beneficial or detrimental manners, depending on the system and scale being considered.
Complex effects on the health of mangrove forests can occur from ocean heating which also can co-vary with issues including sea level rise, extreme rain and wind events, increased ultraviolet B exposure, and other factors (e.g., Ward et al. 2016; Jennerjahn et al. 2017).
- Growth rates of mangrove species can accelerate with increased temperatures. There is also evidence that mangroves can be more susceptible to diseases in the presence of increased temperatures.
- Mangroves are showing shifts in distribution towards the poles in both hemispheres, with impacts on pre-existing vegetation communities (e.g. salt marshes).
- Extreme weather events will stress and shape mangrove forests through direct physical and hydrological impacts.
- Large mangrove forests can be efficient at removing carbon from the atmosphere (sequestration) for their own biological processes.
Source: C. Savoia
Source: J. Wasserman
Comparisons among Aquatic Plants
Submerged plants, such as seagrasses and algae, can be affected by temperature increases and changes in water clarity. Emergent plant communities (salt marshes and mangroves) may be more susceptible to hydrological alterations related to extreme weather (e.g., Short et al., 2016).
Warming air and water contribute to extreme weather events, putting additional stress on coastal plants through direct physical damage and turbidity, reducing photosynthetic growth. Both gains and losses to aquatic plants will result from climate change (Short et al., 2016; USGCRP, 2018), with potential growth increases among stress events, with co-occurring negative physiological consequences from changes in temperature, salinity, and other drivers (e.g., Ward et al., 2016).
Corals are animals that build calcium carbonate skeletons with photosynthetic algae that live in their tissues. The corals and algae need each other. Of course, coral reefs have very high ecological and economic values.
- Coral bleaching occurs when hotter water causes the coral to release the algae partners and turn white. The coral animals do not always die from initial bleaching events but they can or will die with multiple bleaching events (e.g., Carpenter et al., 2008; NOAA Coral Reef Program, 2020).
- Diseases that damage or kill corals can also be amplified by increasing ocean temperatures (Randall and van Woesik, 2015; Mera and Bourne, 2018).
Throughout the U.S. and Florida, diverse fishery species and their prey can show physiological and behavioral responses to increased heating of ocean and coastal waters. The bullets below reflect several of many emerging issues involving coastal fisheries and climate change (e.g., Lorenzen et al., 2017; SAFMC, 2017; Selden and Pinsky, 2019; Asch et al., 2019).
- There is evidence for latitudinal shifts to the north and south in several of Florida’s Atlantic fishery species including black sea bass, Atlantic croaker, bluefish, and others.
- Rapid ocean heating may confound physiological and behavioral features of marine fish reproduction, affecting spawning activities and egg production in some species over time.
- Observations of commercial and recreational fishers include: a) the fouling of hooks by algae may be more common , and b) some highly-sought species are showing differing patterns of distribution across the shelf.
- Multi-million dollar economic and socio-cultural resources can be involved. Fishery management agencies throughout the U.S. have created climate change working groups of scientists and fishers to identify, monitor, and predict changes in fisheries due to increasing ocean and atmospheric heat, and other factors.