Aquatic vegetation and largemouth bass population responses to water-level variations in Lake Okeechobee, Florida (USA)

Abstract

A five-year study examined the responses of submerged aquatic vegetation (SAV), emergent vegetation, and largemouth bass (Micropterus salmoides) to variations in water level in a large lake in Florida, USA. SAV was assessed using a combined transect survey/spatial mapping approach, emergent vegetation was quantified with aerial photography and GIS, and bass were surveyed by electro-shocking. During the period leading up to this study (1995)(1996)(1997)(1998)(1999), water levels were high in the lake, and the SAV was reduced in spatial extent and biomass, compared to its condition in the early 1990s. Spatial extent of emergent vegetation also was low, and largemouth bass surveys indicated low densities and failure to recruit young fish into the population. This was attributed to the lack of critical vegetative habitat. In spring 2000, the lake was lowered by discharging water from major outlets, and this was followed by a regional drought. Water levels dropped by 1 m, and there was widespread development of Chara lawns in shoreline areas, with coincident increases in water clarity. There was some germination of vascular SAV, but Chara was the extreme dominant, such that structural complexity remained low. There was no substantive improvement in bass recruitment. During 2001, water levels declined further, and emergent plants germinated in exposed areas of the lake bottom. SAV was restricted to sites farther offshore, and continued to be dominated by Chara. There again was no bass response. In 2002, conditions changed when water levels increased to a moderate depth, flooding shoreline habitat to $0.5 m. Vascular SAV increased in biomass and spatial extent, such that the community developed a high structural complexity. At the same time, emergent aquatic plants developed dense stands along the western shoreline. Largemouth bass had a strong recruitment of young fish for the first time in 5 years. Recruitment continued to be successful in 2003, when spatial extent of SAV was somewhat reduced by higher water but total biomass and diversity remained high. These results demonstrate an important effect of inter-annual variation in water depth on the population dynamics of aquatic plants and fish in a subtropical lake.

Monitoring freshwater fish in Florida lakes using electrofishing: Lessons learned

“…Aquatic vegetation in Florida's shallow lakes is often the only structure or habitat available for fish populations (Havens et al 2005) and is one of the few factors impacting fish populations that can be effectively managed. The…”

Zooplankton response to extreme drought in a large subtropical lake

“…In shallow eutrophic lakes a particularly important abiotic factor is water depth, because a change in depth of just one meter may translate into a large relative change in lake volume and substantially increased area that can be colonized by vascular plants and benthic algae (Havens et al, 2004). Increased coverage by plants can have substantial effects on recruitment of fish (Havens et al, 2005), biomass and composition of phytoplankton (Moss et al, 1997) and structure of the zooplankton (Schriver et al, 1995;Stansfield et al, 1997).…”

“…Previous studies documented that in response to the 2 year period (2000)(2001) of lowered water levels in Lake Okeechobee, the spatial extent of submerged aquatic plants increased from less than 150 ha in 1999 to over 15,000 ha in 2000, with a large spatial extent of plants persisting through 2004 (Havens et al, 2005). This response of the plants occurred due to reduced water depths, increased underwater irradiance, and oxidation of a layer of organic detritus in areas that became dry and then re-flooded, which allowed plants to germinate from oospores and seeds in the sediments (Havens, 2003;Havens et al, 2004).…”

Developing water level regulation strategies for macrophytes restoration of a large river-disconnected lake, China

“…However, the degradation of aquatic vegetation has often been explained by increased nutrient loads (Scheffer and Carpenter, 2003;Tracy et al, 2003), and little attention was paid to hydrological alterations such as WLF in lakes (Van Geest et al, 2007). WLF can trigger regime shift between clear and turbid stable states in lakes, as low water level promotes the establishment of macrophytes by increasing light availability (Havens et al, 2005). Water level regulation is also regarded as an effective measure for aquatic vegetation restoration in lakes (Coops et al, 2004;Havens et al, 2004Havens et al, , 2005Li et al, 2008).…”

“…WLF can trigger regime shift between clear and turbid stable states in lakes, as low water level promotes the establishment of macrophytes by increasing light availability (Havens et al, 2005). Water level regulation is also regarded as an effective measure for aquatic vegetation restoration in lakes (Coops et al, 2004;Havens et al, 2004Havens et al, , 2005Li et al, 2008). However, some studies still showed that extremely low or high water level is unfavorable to the growth of aquatic vegetation (Coops et al, 2003;O'Farrell et al, 2011) important to understand such requirements for a successful water level regulation with regard to aquatic vegetation restoration.…”